Merge remote-tracking branch 'origin/main' into bp/openExr

# Conflicts:
#	src/ImageSharp/Configuration.cs

.github/CONTRIBUTING.md

@@ -28,7 +28,7 @@
 
 #### **Running tests and Debugging**
 
-* Expected test output is pulled in as a submodule from the [ImageSharp.Tests.Images repository](https://github.com/SixLabors/Imagesharp.Tests.Images/tree/master/ReferenceOutput). To succesfully run tests, make sure that you have updated the submodules!
+* Expected test output is pulled in as a submodule from the [ImageSharp.Tests.Images repository](https://github.com/SixLabors/Imagesharp.Tests.Images/tree/main/ReferenceOutput). To succesfully run tests, make sure that you have updated the submodules!
 * Debugging (running tests in Debug mode) is only supported on .NET Core 2.1+, because of JIT Code Generation bugs like [dotnet/coreclr#16443](https://github.com/dotnet/coreclr/issues/16443) or [dotnet/coreclr#20657](https://github.com/dotnet/coreclr/issues/20657)
 
 #### **Do you have questions about consuming the library or the source code?**

.github/ISSUE_TEMPLATE/commercial-bug-report.md

@@ -1,33 +0,0 @@
----
-name: "Commercial License : Bug Report"
-about: |
-  Create a report to help us improve the project. For Commercial License holders only.
-  Please contact help@sixlabors.com for issues requiring private support. 
-labels: commercial, needs triage
-
----
-
-
-### Prerequisites
-
-- [ ] I have written a descriptive issue title
-- [ ] I have verified that I am running the latest version of ImageSharp
-- [ ] I have verified if the problem exist in both `DEBUG` and `RELEASE` mode
-- [ ] I have searched [open](https://github.com/SixLabors/ImageSharp/issues) and [closed](https://github.com/SixLabors/ImageSharp/issues?q=is%3Aissue+is%3Aclosed) issues to ensure it has not already been reported
-
-### Description
-<!-- A description of the bug or feature -->
-
-### Steps to Reproduce
-<!-- List of steps, sample code, failing test or link to a project that reproduces the behavior -->
-
-### System Configuration
-<!-- Tell us about the environment where you are experiencing the bug -->
-
-- ImageSharp version:
-- Other ImageSharp packages and versions:
-- Environment (Operating system, version and so on):
-- .NET Framework version:
-- Additional information:
-
-<!-- Thanks for reporting the issue to ImageSharp! -->

.github/ISSUE_TEMPLATE/commercial-bug-report.yml

@@ -0,0 +1,42 @@
+name: "Commercial License : Bug Report"
+description: |
+  Create a report to help us improve the project. For Commercial License holders only.
+  Please contact help@sixlabors.com for issues requiring private support.
+labels: ["commercial", "needs triage"]
+body:
+- type: input
+  attributes:
+    label: ImageSharp version
+  validations:
+    required: true
+- type: input
+  attributes:
+    label: Other ImageSharp packages and versions
+  validations:
+    required: true
+- type: input
+  attributes:
+    label: Environment (Operating system, version and so on)
+  validations:
+    required: true
+- type: input
+  attributes:
+    label: .NET Framework version
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Description
+    description: A description of the bug
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Steps to Reproduce
+    description: List of steps, sample code, failing test or link to a project that reproduces the behavior. Make sure you place a stack trace inside a code (```) block to avoid linking unrelated issues.
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Images
+    description: Please upload images that can be used to reproduce issues in the area below. If the file type is not supported the file can be zipped and then uploaded instead.

.github/ISSUE_TEMPLATE/oss-bug-report.md

@@ -1,30 +0,0 @@
----
-name: "OSS : Bug Report"
-about: Create a report to help us improve the project. OSS Issues are not guaranteed to be triaged.
-labels: needs triage
-
----
-
-### Prerequisites
-
-- [ ] I have written a descriptive issue title
-- [ ] I have verified that I am running the latest version of ImageSharp
-- [ ] I have verified if the problem exist in both `DEBUG` and `RELEASE` mode
-- [ ] I have searched [open](https://github.com/SixLabors/ImageSharp/issues) and [closed](https://github.com/SixLabors/ImageSharp/issues?q=is%3Aissue+is%3Aclosed) issues to ensure it has not already been reported
-
-### Description
-<!-- A description of the bug or feature -->
-
-### Steps to Reproduce
-<!-- List of steps, sample code, failing test or link to a project that reproduces the behavior -->
-
-### System Configuration
-<!-- Tell us about the environment where you are experiencing the bug -->
-
-- ImageSharp version:
-- Other ImageSharp packages and versions:
-- Environment (Operating system, version and so on):
-- .NET Framework version:
-- Additional information:
-
-<!-- Thanks for reporting the issue to ImageSharp! -->

.github/ISSUE_TEMPLATE/oss-bug-report.yml

@@ -0,0 +1,40 @@
+name: "OSS : Bug Report"
+description: Create a report to help us improve the project. OSS Issues are not guaranteed to be triaged.
+labels: ["needs triage"]
+body:
+- type: input
+  attributes:
+    label: ImageSharp version
+  validations:
+    required: true
+- type: input
+  attributes:
+    label: Other ImageSharp packages and versions
+  validations:
+    required: true
+- type: input
+  attributes:
+    label: Environment (Operating system, version and so on)
+  validations:
+    required: true
+- type: input
+  attributes:
+    label: .NET Framework version
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Description
+    description: A description of the bug
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Steps to Reproduce
+    description: List of steps, sample code, failing test or link to a project that reproduces the behavior. Make sure you place a stack trace inside a code (```) block to avoid linking unrelated issues.
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Images
+    description: Please upload images that can be used to reproduce issues in the area below. If the file type is not supported the file can be zipped and then uploaded instead.

.github/workflows/build-and-test.yml

@@ -1,202 +1,198 @@
 name: Build
 
 on:
-   push:
-       branches:
-           - master
-       tags:
-           - "v*"
-   pull_request:
-       branches:
-          - master
+  push:
+    branches:
+      - main
+    tags:
+      - "v*"
+  pull_request:
+    branches:
+      - main
 jobs:
-    Build:
-        strategy:
-            matrix:
-                options:
-                    - os: ubuntu-latest
-                      framework: net6.0
-                      sdk: 6.0.x
-                      sdk-preview: true
-                      runtime: -x64
-                      codecov: false
-                    - os: macos-latest
-                      framework: net6.0
-                      sdk: 6.0.x
-                      sdk-preview: true
-                      runtime: -x64
-                      codecov: false
-                    - os: windows-latest
-                      framework: net6.0
-                      sdk: 6.0.x
-                      sdk-preview: true
-                      runtime: -x64
-                      codecov: false
-                    - os: ubuntu-latest
-                      framework: net5.0
-                      runtime: -x64
-                      codecov: false
-                    - os: macos-latest
-                      framework: net5.0
-                      runtime: -x64
-                      codecov: false
-                    - os: windows-latest
-                      framework: net5.0
-                      runtime: -x64
-                      codecov: false
-                    - os: ubuntu-latest
-                      framework: netcoreapp3.1
-                      runtime: -x64
-                      codecov: true
-                    - os: macos-latest
-                      framework: netcoreapp3.1
-                      runtime: -x64
-                      codecov: false
-                    - os: windows-latest
-                      framework: netcoreapp3.1
-                      runtime: -x64
-                      codecov: false
-                    - os: windows-latest
-                      framework: netcoreapp2.1
-                      runtime: -x64
-                      codecov: false
-                    - os: windows-latest
-                      framework: net472
-                      runtime: -x64
-                      codecov: false
-                    - os: windows-latest
-                      framework: net472
-                      runtime: -x86
-                      codecov: false
-
-        runs-on: ${{matrix.options.os}}
-
-        steps:
-            - name: Git Config
-              shell: bash
-              run: |
-                  git config --global core.autocrlf false
-                  git config --global core.longpaths true
-
-            - name: Git Checkout
-              uses: actions/checkout@v2
-              with:
-                fetch-depth: 0
-                submodules: recursive
-            
-            # See https://github.com/actions/checkout/issues/165#issuecomment-657673315
-            - name: Git Create LFS FileList
-              run: git lfs ls-files -l | cut -d' ' -f1 | sort > .lfs-assets-id
-
-            - name: Git Setup LFS Cache
-              uses: actions/cache@v2
-              id: lfs-cache
-              with:
-                path: .git/lfs
-                key: ${{ runner.os }}-lfs-${{ hashFiles('.lfs-assets-id') }}-v1
-
-            - name: Git Pull LFS
-              run: git lfs pull
-
-            - name: NuGet Install
-              uses: NuGet/setup-nuget@v1
-
-            - name: NuGet Setup Cache
-              uses: actions/cache@v2
-              id: nuget-cache
-              with:
-                  path: ~/.nuget
-                  key: ${{ runner.os }}-nuget-${{ hashFiles('**/*.csproj', '**/*.props', '**/*.targets') }}
-                  restore-keys: ${{ runner.os }}-nuget-
-
-            - name: DotNet Setup Preview
-              if: ${{ matrix.options.sdk-preview == true }}
-              uses: actions/setup-dotnet@v1
-              with:
-                dotnet-version: ${{ matrix.options.sdk }}
-                include-prerelease: true
-
-            - name: DotNet Build
-              if: ${{ matrix.options.sdk-preview != true }}
-              shell: pwsh
-              run: ./ci-build.ps1 "${{matrix.options.framework}}"
-              env:
-                SIXLABORS_TESTING: True
-
-            - name: DotNet Build Preview
-              if: ${{ matrix.options.sdk-preview == true }}
-              shell: pwsh
-              run: ./ci-build.ps1 "${{matrix.options.framework}}"
-              env:
-                SIXLABORS_TESTING_PREVIEW: True
-
-            - name: DotNet Test
-              if: ${{ matrix.options.sdk-preview != true }}
-              shell: pwsh
-              run: ./ci-test.ps1 "${{matrix.options.os}}" "${{matrix.options.framework}}" "${{matrix.options.runtime}}" "${{matrix.options.codecov}}"
-              env:
-                SIXLABORS_TESTING: True
-                XUNIT_PATH: .\tests\ImageSharp.Tests # Required for xunit
-
-            - name: DotNet Test Preview
-              if: ${{ matrix.options.sdk-preview == true }}
-              shell: pwsh
-              run: ./ci-test.ps1 "${{matrix.options.os}}" "${{matrix.options.framework}}" "${{matrix.options.runtime}}" "${{matrix.options.codecov}}"
-              env:
-                SIXLABORS_TESTING_PREVIEW: True
-                XUNIT_PATH: .\tests\ImageSharp.Tests # Required for xunit
-
-            - name: Export Failed Output
-              uses: actions/upload-artifact@v2
-              if: failure()
-              with:
-                name: actual_output_${{ runner.os }}_${{ matrix.options.framework }}${{ matrix.options.runtime }}.zip
-                path: tests/Images/ActualOutput/
-
-            - name: Codecov Update
-              uses: codecov/codecov-action@v1
-              if: matrix.options.codecov == true && startsWith(github.repository, 'SixLabors')
-              with:
-                flags: unittests
-
-    Publish:
-        needs: [Build]
-
-        runs-on: ubuntu-latest
-
-        if: (github.event_name == 'push')
-
-        steps:
-            - name: Git Config
-              shell: bash
-              run: |
-                  git config --global core.autocrlf false
-                  git config --global core.longpaths true
-
-            - name: Git Checkout
-              uses: actions/checkout@v2
-              with:
-                fetch-depth: 0
-                submodules: recursive
-
-            - name: NuGet Install
-              uses: NuGet/setup-nuget@v1
-
-            - name: NuGet Setup Cache
-              uses: actions/cache@v2
-              id: nuget-cache
-              with:
-                  path: ~/.nuget
-                  key: ${{ runner.os }}-nuget-${{ hashFiles('**/*.csproj', '**/*.props', '**/*.targets') }}
-                  restore-keys: ${{ runner.os }}-nuget-
-
-            - name: DotNet Pack
-              shell: pwsh
-              run: ./ci-pack.ps1
-
-            - name: MyGet Publish
-              shell: pwsh
-              run: |
-                  dotnet nuget push .\artifacts\*.nupkg -k ${{secrets.MYGET_TOKEN}} -s https://www.myget.org/F/sixlabors/api/v2/package
-                  dotnet nuget push .\artifacts\*.snupkg -k ${{secrets.MYGET_TOKEN}} -s https://www.myget.org/F/sixlabors/api/v3/index.json
-              # TODO: If github.ref starts with 'refs/tags' then it was tag push and we can optionally push out package to nuget.org
+  Build:
+    strategy:
+      matrix:
+        options:
+          - os: ubuntu-latest
+            framework: net6.0
+            sdk: 6.0.x
+            sdk-preview: true
+            runtime: -x64
+            codecov: false
+          - os: macos-latest
+            framework: net6.0
+            sdk: 6.0.x
+            sdk-preview: true
+            runtime: -x64
+            codecov: false
+          - os: windows-latest
+            framework: net6.0
+            sdk: 6.0.x
+            sdk-preview: true
+            runtime: -x64
+            codecov: false
+          - os: ubuntu-latest
+            framework: net5.0
+            runtime: -x64
+            codecov: false
+          - os: macos-latest
+            framework: net5.0
+            runtime: -x64
+            codecov: false
+          - os: windows-latest
+            framework: net5.0
+            runtime: -x64
+            codecov: false
+          - os: ubuntu-latest
+            framework: netcoreapp3.1
+            runtime: -x64
+            codecov: false
+          - os: macos-latest
+            framework: netcoreapp3.1
+            runtime: -x64
+            codecov: false
+          - os: windows-latest
+            framework: netcoreapp3.1
+            runtime: -x64
+            codecov: false
+          - os: windows-latest
+            framework: netcoreapp2.1
+            runtime: -x64
+            codecov: false
+          - os: windows-latest
+            framework: net472
+            runtime: -x64
+            codecov: false
+          - os: windows-latest
+            framework: net472
+            runtime: -x86
+            codecov: false
+
+    runs-on: ${{matrix.options.os}}
+
+    steps:
+      - name: Git Config
+        shell: bash
+        run: |
+          git config --global core.autocrlf false
+          git config --global core.longpaths true
+
+      - name: Git Checkout
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+          submodules: recursive
+
+      # See https://github.com/actions/checkout/issues/165#issuecomment-657673315
+      - name: Git Create LFS FileList
+        run: git lfs ls-files -l | cut -d' ' -f1 | sort > .lfs-assets-id
+
+      - name: Git Setup LFS Cache
+        uses: actions/cache@v2
+        id: lfs-cache
+        with:
+          path: .git/lfs
+          key: ${{ runner.os }}-lfs-${{ hashFiles('.lfs-assets-id') }}-v1
+
+      - name: Git Pull LFS
+        run: git lfs pull
+
+      - name: NuGet Install
+        uses: NuGet/setup-nuget@v1
+
+      - name: NuGet Setup Cache
+        uses: actions/cache@v2
+        id: nuget-cache
+        with:
+          path: ~/.nuget
+          key: ${{ runner.os }}-nuget-${{ hashFiles('**/*.csproj', '**/*.props', '**/*.targets') }}
+          restore-keys: ${{ runner.os }}-nuget-
+
+      - name: DotNet Setup
+        uses: actions/setup-dotnet@v1
+        with:
+          dotnet-version: |
+            6.0.x
+            5.0.x
+            3.1.x
+            2.1.x
+
+      - name: DotNet Build
+        if: ${{ matrix.options.sdk-preview != true }}
+        shell: pwsh
+        run: ./ci-build.ps1 "${{matrix.options.framework}}"
+        env:
+          SIXLABORS_TESTING: True
+
+      - name: DotNet Build Preview
+        if: ${{ matrix.options.sdk-preview == true }}
+        shell: pwsh
+        run: ./ci-build.ps1 "${{matrix.options.framework}}"
+        env:
+          SIXLABORS_TESTING_PREVIEW: True
+
+      - name: DotNet Test
+        if: ${{ matrix.options.sdk-preview != true }}
+        shell: pwsh
+        run: ./ci-test.ps1 "${{matrix.options.os}}" "${{matrix.options.framework}}" "${{matrix.options.runtime}}" "${{matrix.options.codecov}}"
+        env:
+          SIXLABORS_TESTING: True
+          XUNIT_PATH: .\tests\ImageSharp.Tests # Required for xunit
+
+      - name: DotNet Test Preview
+        if: ${{ matrix.options.sdk-preview == true }}
+        shell: pwsh
+        run: ./ci-test.ps1 "${{matrix.options.os}}" "${{matrix.options.framework}}" "${{matrix.options.runtime}}" "${{matrix.options.codecov}}"
+        env:
+          SIXLABORS_TESTING_PREVIEW: True
+          XUNIT_PATH: .\tests\ImageSharp.Tests # Required for xunit
+
+      - name: Export Failed Output
+        uses: actions/upload-artifact@v2
+        if: failure()
+        with:
+          name: actual_output_${{ runner.os }}_${{ matrix.options.framework }}${{ matrix.options.runtime }}.zip
+          path: tests/Images/ActualOutput/
+
+  Publish:
+    needs: [Build]
+
+    runs-on: ubuntu-latest
+
+    if: (github.event_name == 'push')
+
+    steps:
+      - name: Git Config
+        shell: bash
+        run: |
+          git config --global core.autocrlf false
+          git config --global core.longpaths true
+
+      - name: Git Checkout
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+          submodules: recursive
+
+      - name: NuGet Install
+        uses: NuGet/setup-nuget@v1
+
+      - name: NuGet Setup Cache
+        uses: actions/cache@v2
+        id: nuget-cache
+        with:
+          path: ~/.nuget
+          key: ${{ runner.os }}-nuget-${{ hashFiles('**/*.csproj', '**/*.props', '**/*.targets') }}
+          restore-keys: ${{ runner.os }}-nuget-
+
+      - name: DotNet Pack
+        shell: pwsh
+        run: ./ci-pack.ps1
+
+      - name: MyGet Publish
+        shell: pwsh
+        run: |
+          dotnet nuget push .\artifacts\*.nupkg -k ${{secrets.MYGET_TOKEN}} -s https://www.myget.org/F/sixlabors/api/v2/package
+          dotnet nuget push .\artifacts\*.snupkg -k ${{secrets.MYGET_TOKEN}} -s https://www.myget.org/F/sixlabors/api/v3/index.json
+        # TODO: If github.ref starts with 'refs/tags' then it was tag push and we can optionally push out package to nuget.org

.github/workflows/code-coverage.yml

@@ -0,0 +1,81 @@
+name: CodeCoverage
+
+on:
+  schedule:
+    # 2AM every Tuesday/Thursday
+    - cron: "0 2 * * 2,4"
+jobs:
+  Build:
+    strategy:
+      matrix:
+        options:
+          - os: ubuntu-latest
+            framework: netcoreapp3.1
+            runtime: -x64
+            codecov: true
+
+    runs-on: ${{matrix.options.os}}
+
+    steps:
+      - name: Git Config
+        shell: bash
+        run: |
+          git config --global core.autocrlf false
+          git config --global core.longpaths true
+
+      - name: Git Checkout
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+          submodules: recursive
+
+      # See https://github.com/actions/checkout/issues/165#issuecomment-657673315
+      - name: Git Create LFS FileList
+        run: git lfs ls-files -l | cut -d' ' -f1 | sort > .lfs-assets-id
+
+      - name: Git Setup LFS Cache
+        uses: actions/cache@v2
+        id: lfs-cache
+        with:
+          path: .git/lfs
+          key: ${{ runner.os }}-lfs-${{ hashFiles('.lfs-assets-id') }}-v1
+
+      - name: Git Pull LFS
+        run: git lfs pull
+
+      - name: NuGet Install
+        uses: NuGet/setup-nuget@v1
+
+      - name: NuGet Setup Cache
+        uses: actions/cache@v2
+        id: nuget-cache
+        with:
+          path: ~/.nuget
+          key: ${{ runner.os }}-nuget-${{ hashFiles('**/*.csproj', '**/*.props', '**/*.targets') }}
+          restore-keys: ${{ runner.os }}-nuget-
+
+      - name: DotNet Build
+        shell: pwsh
+        run: ./ci-build.ps1 "${{matrix.options.framework}}"
+        env:
+          SIXLABORS_TESTING: True
+
+      - name: DotNet Test
+        shell: pwsh
+        run: ./ci-test.ps1 "${{matrix.options.os}}" "${{matrix.options.framework}}" "${{matrix.options.runtime}}" "${{matrix.options.codecov}}"
+        env:
+          SIXLABORS_TESTING: True
+          XUNIT_PATH: .\tests\ImageSharp.Tests # Required for xunit
+
+      - name: Export Failed Output
+        uses: actions/upload-artifact@v2
+        if: failure()
+        with:
+          name: actual_output_${{ runner.os }}_${{ matrix.options.framework }}${{ matrix.options.runtime }}.zip
+          path: tests/Images/ActualOutput/
+
+      - name: Codecov Update
+        uses: codecov/codecov-action@v1
+        if: matrix.options.codecov == true && startsWith(github.repository, 'SixLabors')
+        with:
+          flags: unittests

ImageSharp.sln

@@ -551,6 +551,7 @@ EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "workflows", "workflows", "{C0D7754B-5277-438E-ABEB-2BA34401B5A7}"
 	ProjectSection(SolutionItems) = preProject
 		.github\workflows\build-and-test.yml = .github\workflows\build-and-test.yml
+		.github\workflows\code-coverage.yml = .github\workflows\code-coverage.yml
 	EndProjectSection
 EndProject
 Project("{D954291E-2A0B-460D-934E-DC6B0785DB48}") = "SharedInfrastructure", "shared-infrastructure\src\SharedInfrastructure\SharedInfrastructure.shproj", "{68A8CC40-6AED-4E96-B524-31B1158FDEEA}"

README.md

@@ -1,14 +1,14 @@
 <h1 align="center">
 
-<img src="https://github.com/SixLabors/Branding/raw/master/icons/imagesharp/sixlabors.imagesharp.svg?sanitize=true" alt="SixLabors.ImageSharp" width="256"/>
+<img src="https://github.com/SixLabors/Branding/raw/main/icons/imagesharp/sixlabors.imagesharp.svg?sanitize=true" alt="SixLabors.ImageSharp" width="256"/>
 <br/>
 SixLabors.ImageSharp
 </h1>
 
 <div align="center">
 
-[![Build Status](https://img.shields.io/github/workflow/status/SixLabors/ImageSharp/Build/master)](https://github.com/SixLabors/ImageSharp/actions)
-[![Code coverage](https://codecov.io/gh/SixLabors/ImageSharp/branch/master/graph/badge.svg)](https://codecov.io/gh/SixLabors/ImageSharp)
+[![Build Status](https://img.shields.io/github/workflow/status/SixLabors/ImageSharp/Build/main)](https://github.com/SixLabors/ImageSharp/actions)
+[![Code coverage](https://codecov.io/gh/SixLabors/ImageSharp/branch/main/graph/badge.svg)](https://codecov.io/gh/SixLabors/ImageSharp)
 [![License: Apache 2.0](https://img.shields.io/badge/license-Apache%202.0-blue.svg)](https://opensource.org/licenses/Apache-2.0)
 [![Twitter](https://img.shields.io/twitter/url/http/shields.io.svg?style=flat&logo=twitter)](https://twitter.com/intent/tweet?hashtags=imagesharp,dotnet,oss&text=ImageSharp.+A+new+cross-platform+2D+graphics+API+in+C%23&url=https%3a%2f%2fgithub.com%2fSixLabors%2fImageSharp&via=sixlabors)
 
@@ -39,12 +39,12 @@ Support the efforts of the development of the Six Labors projects.
 ## Documentation
 
 - [Detailed documentation](https://sixlabors.github.io/docs/) for the ImageSharp API is available. This includes additional conceptual documentation to help you get started.
-- Our [Samples Repository](https://github.com/SixLabors/Samples/tree/master/ImageSharp) is also available containing buildable code samples demonstrating common activities.
+- Our [Samples Repository](https://github.com/SixLabors/Samples/tree/main/ImageSharp) is also available containing buildable code samples demonstrating common activities.
 
 ## Questions
 
 - Do you have questions? We are happy to help! Please [join our Discussions Forum](https://github.com/SixLabors/ImageSharp/discussions/category_choices), or ask them on [Stack Overflow](https://stackoverflow.com) using the `ImageSharp` tag. Please do not open issues for questions.
-- Please read our [Contribution Guide](https://github.com/SixLabors/ImageSharp/blob/master/.github/CONTRIBUTING.md) before opening issues or pull requests!
+- Please read our [Contribution Guide](https://github.com/SixLabors/ImageSharp/blob/main/.github/CONTRIBUTING.md) before opening issues or pull requests!
 
 ## Code of Conduct  
 This project has adopted the code of conduct defined by the [Contributor Covenant](https://contributor-covenant.org/) to clarify expected behavior in our community.
@@ -93,7 +93,7 @@ git submodule update --init --recursive
 
 ## How can you help?
 
-Please... Spread the word, contribute algorithms, submit performance improvements, unit tests, no input is too little. Make sure to read our [Contribution Guide](https://github.com/SixLabors/ImageSharp/blob/master/.github/CONTRIBUTING.md) before opening a PR.
+Please... Spread the word, contribute algorithms, submit performance improvements, unit tests, no input is too little. Make sure to read our [Contribution Guide](https://github.com/SixLabors/ImageSharp/blob/main/.github/CONTRIBUTING.md) before opening a PR.
 
 ## The ImageSharp Team
 

src/ImageSharp/Common/Helpers/HexConverter.cs

@@ -0,0 +1,98 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Runtime.CompilerServices;
+
+namespace SixLabors.ImageSharp.Common.Helpers
+{
+    internal static class HexConverter
+    {
+        /// <summary>
+        /// Parses a hexadecimal string into a byte array without allocations. Throws on non-hexadecimal character.
+        /// Adapted from https://source.dot.net/#System.Private.CoreLib/Convert.cs,c9e4fbeaca708991.
+        /// </summary>
+        /// <param name="chars">The hexadecimal string to parse.</param>
+        /// <param name="bytes">The destination for the parsed bytes. Must be at least <paramref name="chars"/>.Length / 2 bytes long.</param>
+        /// <returns>The number of bytes written to <paramref name="bytes"/>.</returns>
+        public static int HexStringToBytes(ReadOnlySpan<char> chars, Span<byte> bytes)
+        {
+            if ((chars.Length % 2) != 0)
+            {
+                throw new ArgumentException("Input string length must be a multiple of 2", nameof(chars));
+            }
+
+            if ((bytes.Length * 2) < chars.Length)
+            {
+                throw new ArgumentException("Output span must be at least half the length of the input string");
+            }
+            else
+            {
+                // Slightly better performance in the loop below, allows us to skip a bounds check
+                // while still supporting output buffers that are larger than necessary
+                bytes = bytes.Slice(0, chars.Length / 2);
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            static int FromChar(int c)
+            {
+                // Map from an ASCII char to its hex value, e.g. arr['b'] == 11. 0xFF means it's not a hex digit.
+                // This doesn't actually allocate.
+                ReadOnlySpan<byte> charToHexLookup = new byte[]
+                {
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 15
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 31
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 47
+                    0x0,  0x1,  0x2,  0x3,  0x4,  0x5,  0x6,  0x7,  0x8,  0x9,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 63
+                    0xFF, 0xA,  0xB,  0xC,  0xD,  0xE,  0xF,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 79
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 95
+                    0xFF, 0xa,  0xb,  0xc,  0xd,  0xe,  0xf,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 111
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 127
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 143
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 159
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 175
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 191
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 207
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 223
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 239
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 255
+                };
+
+                return c >= charToHexLookup.Length ? 0xFF : charToHexLookup[c];
+            }
+
+            // See https://source.dot.net/#System.Private.CoreLib/HexConverter.cs,4681d45a0aa0b361
+            int i = 0;
+            int j = 0;
+            int byteLo = 0;
+            int byteHi = 0;
+            while (j < bytes.Length)
+            {
+                byteLo = FromChar(chars[i + 1]);
+                byteHi = FromChar(chars[i]);
+
+                // byteHi hasn't been shifted to the high half yet, so the only way the bitwise or produces this pattern
+                // is if either byteHi or byteLo was not a hex character.
+                if ((byteLo | byteHi) == 0xFF)
+                {
+                    break;
+                }
+
+                bytes[j++] = (byte)((byteHi << 4) | byteLo);
+                i += 2;
+            }
+
+            if (byteLo == 0xFF)
+            {
+                i++;
+            }
+
+            if ((byteLo | byteHi) == 0xFF)
+            {
+                throw new ArgumentException("Input string contained non-hexadecimal characters", nameof(chars));
+            }
+
+            return j;
+        }
+    }
+}

src/ImageSharp/Configuration.cs

@@ -123,25 +123,25 @@ namespace SixLabors.ImageSharp
         public ReadOrigin ReadOrigin { get; set; } = ReadOrigin.Current;
 
         /// <summary>
-        /// Gets or sets the <see cref="ImageFormatManager"/> that is currently in use.
+        /// Gets or the <see cref="ImageFormatManager"/> that is currently in use.
         /// </summary>
-        public ImageFormatManager ImageFormatsManager { get; set; } = new();
+        public ImageFormatManager ImageFormatsManager { get; private set; } = new ImageFormatManager();
 
         /// <summary>
-        /// Gets or sets the <see cref="ImageSharp.Memory.MemoryAllocator"/> that is currently in use.
-        /// Defaults to <see cref="ImageSharp.Memory.MemoryAllocator.Default"/>.
+        /// Gets or sets the <see cref="Memory.MemoryAllocator"/> that is currently in use.
+        /// Defaults to <see cref="MemoryAllocator.Default"/>.
         /// <para />
         /// Allocators are expensive, so it is strongly recommended to use only one busy instance per process.
         /// In case you need to customize it, you can ensure this by changing
         /// </summary>
         /// <remarks>
         /// It's possible to reduce allocator footprint by assigning a custom instance created with
-        /// <see cref="Memory.MemoryAllocator.Create(MemoryAllocatorOptions)"/>, but note that since the default pooling
+        /// <see cref="MemoryAllocator.Create(MemoryAllocatorOptions)"/>, but note that since the default pooling
         /// allocators are expensive, it is strictly recommended to use a single process-wide allocator.
         /// You can ensure this by altering the allocator of <see cref="Default"/>, or by implementing custom application logic that
         /// manages allocator lifetime.
         /// <para />
-        /// If an allocator has to be dropped for some reason, <see cref="Memory.MemoryAllocator.ReleaseRetainedResources"/>
+        /// If an allocator has to be dropped for some reason, <see cref="MemoryAllocator.ReleaseRetainedResources"/>
         /// shall be invoked after disposing all associated <see cref="Image"/> instances.
         /// </remarks>
         public MemoryAllocator MemoryAllocator

src/ImageSharp/Diagnostics/MemoryDiagnostics.cs

@@ -0,0 +1,83 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Threading;
+
+namespace SixLabors.ImageSharp.Diagnostics
+{
+    /// <summary>
+    /// Represents the method to handle <see cref="MemoryDiagnostics.UndisposedAllocation"/>.
+    /// </summary>
+    public delegate void UndisposedAllocationDelegate(string allocationStackTrace);
+
+    /// <summary>
+    /// Utilities to track memory usage and detect memory leaks from not disposing ImageSharp objects.
+    /// </summary>
+    public static class MemoryDiagnostics
+    {
+        private static int totalUndisposedAllocationCount;
+
+        private static UndisposedAllocationDelegate undisposedAllocation;
+        private static int undisposedAllocationSubscriptionCounter;
+        private static readonly object SyncRoot = new();
+
+        /// <summary>
+        /// Fires when an ImageSharp object's undisposed memory resource leaks to the finalizer.
+        /// The event brings significant overhead, and is intended to be used for troubleshooting only.
+        /// For production diagnostics, use <see cref="TotalUndisposedAllocationCount"/>.
+        /// </summary>
+        public static event UndisposedAllocationDelegate UndisposedAllocation
+        {
+            add
+            {
+                lock (SyncRoot)
+                {
+                    undisposedAllocationSubscriptionCounter++;
+                    undisposedAllocation += value;
+                }
+            }
+
+            remove
+            {
+                lock (SyncRoot)
+                {
+                    undisposedAllocation -= value;
+                    undisposedAllocationSubscriptionCounter--;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Gets a value indicating the total number of memory resource objects leaked to the finalizer.
+        /// </summary>
+        public static int TotalUndisposedAllocationCount => totalUndisposedAllocationCount;
+
+        internal static bool UndisposedAllocationSubscribed => Volatile.Read(ref undisposedAllocationSubscriptionCounter) > 0;
+
+        internal static void IncrementTotalUndisposedAllocationCount() =>
+            Interlocked.Increment(ref totalUndisposedAllocationCount);
+
+        internal static void DecrementTotalUndisposedAllocationCount() =>
+            Interlocked.Decrement(ref totalUndisposedAllocationCount);
+
+        internal static void RaiseUndisposedMemoryResource(string allocationStackTrace)
+        {
+            if (undisposedAllocation is null)
+            {
+                return;
+            }
+
+            // Schedule on the ThreadPool, to avoid user callback messing up the finalizer thread.
+#if NETSTANDARD2_1 || NETCOREAPP2_1_OR_GREATER
+            ThreadPool.QueueUserWorkItem(
+                stackTrace => undisposedAllocation?.Invoke(stackTrace),
+                allocationStackTrace,
+                preferLocal: false);
+#else
+            ThreadPool.QueueUserWorkItem(
+                stackTrace => undisposedAllocation?.Invoke((string)stackTrace),
+                allocationStackTrace);
+#endif
+        }
+    }
+}

src/ImageSharp/Formats/Gif/GifConstants.cs

@@ -121,5 +121,16 @@ namespace SixLabors.ImageSharp.Formats.Gif
             (byte)'P', (byte)'E',
             (byte)'2', (byte)'.', (byte)'0'
         };
+
+        /// <summary>
+        /// Gets the ASCII encoded application identification bytes.
+        /// </summary>
+        internal static ReadOnlySpan<byte> XmpApplicationIdentificationBytes => new[]
+        {
+            (byte)'X', (byte)'M', (byte)'P',
+            (byte)' ', (byte)'D', (byte)'a',
+            (byte)'t', (byte)'a',
+            (byte)'X', (byte)'M', (byte)'P'
+        };
     }
 }

src/ImageSharp/Formats/Gif/GifDecoderCore.cs

@@ -11,6 +11,7 @@ using System.Threading;
 using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Gif
@@ -250,7 +251,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
         }
 
         /// <summary>
-        /// Reads the application extension block parsing any animation information
+        /// Reads the application extension block parsing any animation or XMP information
         /// if present.
         /// </summary>
         private void ReadApplicationExtension()
@@ -258,25 +259,37 @@ namespace SixLabors.ImageSharp.Formats.Gif
             int appLength = this.stream.ReadByte();
 
             // If the length is 11 then it's a valid extension and most likely
-            // a NETSCAPE or ANIMEXTS extension. We want the loop count from this.
+            // a NETSCAPE, XMP or ANIMEXTS extension. We want the loop count from this.
             if (appLength == GifConstants.ApplicationBlockSize)
             {
-                this.stream.Skip(appLength);
-                int subBlockSize = this.stream.ReadByte();
+                this.stream.Read(this.buffer, 0, GifConstants.ApplicationBlockSize);
+                bool isXmp = this.buffer.AsSpan().StartsWith(GifConstants.XmpApplicationIdentificationBytes);
 
-                // TODO: There's also a NETSCAPE buffer extension.
-                // http://www.vurdalakov.net/misc/gif/netscape-buffering-application-extension
-                if (subBlockSize == GifConstants.NetscapeLoopingSubBlockSize)
+                if (isXmp)
                 {
-                    this.stream.Read(this.buffer, 0, GifConstants.NetscapeLoopingSubBlockSize);
-                    this.gifMetadata.RepeatCount = GifNetscapeLoopingApplicationExtension.Parse(this.buffer.AsSpan(1)).RepeatCount;
-                    this.stream.Skip(1); // Skip the terminator.
+                    var extension = GifXmpApplicationExtension.Read(this.stream);
+                    this.metadata.XmpProfile = new XmpProfile(extension.Data);
                     return;
                 }
+                else
+                {
+                    int subBlockSize = this.stream.ReadByte();
+
+                    // TODO: There's also a NETSCAPE buffer extension.
+                    // http://www.vurdalakov.net/misc/gif/netscape-buffering-application-extension
+                    if (subBlockSize == GifConstants.NetscapeLoopingSubBlockSize)
+                    {
+                        this.stream.Read(this.buffer, 0, GifConstants.NetscapeLoopingSubBlockSize);
+                        this.gifMetadata.RepeatCount = GifNetscapeLoopingApplicationExtension.Parse(this.buffer.AsSpan(1)).RepeatCount;
+                        this.stream.Skip(1); // Skip the terminator.
+                        return;
+                    }
+
+                    // Could be something else not supported yet.
+                    // Skip the subblock and terminator.
+                    this.SkipBlock(subBlockSize);
+                }
 
-                // Could be XMP or something else not supported yet.
-                // Skip the subblock and terminator.
-                this.SkipBlock(subBlockSize);
                 return;
             }
 
@@ -363,7 +376,17 @@ namespace SixLabors.ImageSharp.Formats.Gif
                 indices = this.Configuration.MemoryAllocator.Allocate2D<byte>(this.imageDescriptor.Width, this.imageDescriptor.Height, AllocationOptions.Clean);
 
                 this.ReadFrameIndices(indices);
-                ReadOnlySpan<Rgb24> colorTable = MemoryMarshal.Cast<byte, Rgb24>((localColorTable ?? this.globalColorTable).GetSpan());
+                Span<byte> rawColorTable = default;
+                if (localColorTable != null)
+                {
+                    rawColorTable = localColorTable.GetSpan();
+                }
+                else if (this.globalColorTable != null)
+                {
+                    rawColorTable = this.globalColorTable.GetSpan();
+                }
+
+                ReadOnlySpan<Rgb24> colorTable = MemoryMarshal.Cast<byte, Rgb24>(rawColorTable);
                 this.ReadFrameColors(ref image, ref previousFrame, indices, colorTable, this.imageDescriptor);
 
                 // Skip any remaining blocks
@@ -402,6 +425,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
         {
             int imageWidth = this.logicalScreenDescriptor.Width;
             int imageHeight = this.logicalScreenDescriptor.Height;
+            bool transFlag = this.graphicsControlExtension.TransparencyFlag;
 
             ImageFrame<TPixel> prevFrame = null;
             ImageFrame<TPixel> currentFrame = null;
@@ -409,8 +433,15 @@ namespace SixLabors.ImageSharp.Formats.Gif
 
             if (previousFrame is null)
             {
-                // This initializes the image to become fully transparent because the alpha channel is zero.
-                image = new Image<TPixel>(this.Configuration, imageWidth, imageHeight, this.metadata);
+                if (!transFlag)
+                {
+                    image = new Image<TPixel>(this.Configuration, imageWidth, imageHeight, Color.Black.ToPixel<TPixel>(), this.metadata);
+                }
+                else
+                {
+                    // This initializes the image to become fully transparent because the alpha channel is zero.
+                    image = new Image<TPixel>(this.Configuration, imageWidth, imageHeight, this.metadata);
+                }
 
                 this.SetFrameMetadata(image.Frames.RootFrame.Metadata);
 
@@ -432,6 +463,11 @@ namespace SixLabors.ImageSharp.Formats.Gif
                 this.RestoreToBackground(imageFrame);
             }
 
+            if (colorTable.Length == 0)
+            {
+                return;
+            }
+
             int interlacePass = 0; // The interlace pass
             int interlaceIncrement = 8; // The interlacing line increment
             int interlaceY = 0; // The current interlaced line
@@ -439,7 +475,6 @@ namespace SixLabors.ImageSharp.Formats.Gif
             int descriptorBottom = descriptorTop + descriptor.Height;
             int descriptorLeft = descriptor.Left;
             int descriptorRight = descriptorLeft + descriptor.Width;
-            bool transFlag = this.graphicsControlExtension.TransparencyFlag;
             byte transIndex = this.graphicsControlExtension.TransparencyIndex;
             int colorTableMaxIdx = colorTable.Length - 1;
 
@@ -622,10 +657,13 @@ namespace SixLabors.ImageSharp.Formats.Gif
                 int globalColorTableLength = this.logicalScreenDescriptor.GlobalColorTableSize * 3;
                 this.gifMetadata.GlobalColorTableLength = globalColorTableLength;
 
-                this.globalColorTable = this.MemoryAllocator.Allocate<byte>(globalColorTableLength, AllocationOptions.Clean);
+                if (globalColorTableLength > 0)
+                {
+                    this.globalColorTable = this.MemoryAllocator.Allocate<byte>(globalColorTableLength, AllocationOptions.Clean);
 
-                // Read the global color table data from the stream
-                stream.Read(this.globalColorTable.GetSpan());
+                    // Read the global color table data from the stream
+                    stream.Read(this.globalColorTable.GetSpan());
+                }
             }
         }
     }

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -10,6 +10,7 @@ using System.Threading;
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
@@ -121,11 +122,8 @@ namespace SixLabors.ImageSharp.Formats.Gif
             // Write the comments.
             this.WriteComments(gifMetadata, stream);
 
-            // Write application extension to allow additional frames.
-            if (image.Frames.Count > 1)
-            {
-                this.WriteApplicationExtension(stream, gifMetadata.RepeatCount);
-            }
+            // Write application extensions.
+            this.WriteApplicationExtensions(stream, image.Frames.Count, gifMetadata.RepeatCount, metadata.XmpProfile);
 
             if (useGlobalTable)
             {
@@ -326,15 +324,24 @@ namespace SixLabors.ImageSharp.Formats.Gif
         /// Writes the application extension to the stream.
         /// </summary>
         /// <param name="stream">The stream to write to.</param>
+        /// <param name="frameCount">The frame count fo this image.</param>
         /// <param name="repeatCount">The animated image repeat count.</param>
-        private void WriteApplicationExtension(Stream stream, ushort repeatCount)
+        /// <param name="xmpProfile">The XMP metadata profile. Null if profile is not to be written.</param>
+        private void WriteApplicationExtensions(Stream stream, int frameCount, ushort repeatCount, XmpProfile xmpProfile)
         {
-            // Application Extension Header
-            if (repeatCount != 1)
+            // Application Extension: Loop repeat count.
+            if (frameCount > 1 && repeatCount != 1)
             {
                 var loopingExtension = new GifNetscapeLoopingApplicationExtension(repeatCount);
                 this.WriteExtension(loopingExtension, stream);
             }
+
+            // Application Extension: XMP Profile.
+            if (xmpProfile != null)
+            {
+                var xmpExtension = new GifXmpApplicationExtension(xmpProfile.Data);
+                this.WriteExtension(xmpExtension, stream);
+            }
         }
 
         /// <summary>
@@ -420,14 +427,28 @@ namespace SixLabors.ImageSharp.Formats.Gif
         private void WriteExtension<TGifExtension>(TGifExtension extension, Stream stream)
             where TGifExtension : struct, IGifExtension
         {
-            this.buffer[0] = GifConstants.ExtensionIntroducer;
-            this.buffer[1] = extension.Label;
+            IMemoryOwner<byte> owner = null;
+            Span<byte> buffer;
+            int extensionSize = extension.ContentLength;
+            if (extensionSize > this.buffer.Length - 3)
+            {
+                owner = this.memoryAllocator.Allocate<byte>(extensionSize + 3);
+                buffer = owner.GetSpan();
+            }
+            else
+            {
+                buffer = this.buffer;
+            }
+
+            buffer[0] = GifConstants.ExtensionIntroducer;
+            buffer[1] = extension.Label;
 
-            int extensionSize = extension.WriteTo(this.buffer.AsSpan(2));
+            extension.WriteTo(buffer.Slice(2));
 
-            this.buffer[extensionSize + 2] = GifConstants.Terminator;
+            buffer[extensionSize + 2] = GifConstants.Terminator;
 
-            stream.Write(this.buffer, 0, extensionSize + 3);
+            stream.Write(buffer, 0, extensionSize + 3);
+            owner?.Dispose();
         }
 
         /// <summary>

src/ImageSharp/Formats/Gif/Sections/GifGraphicControlExtension.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -63,6 +63,8 @@ namespace SixLabors.ImageSharp.Formats.Gif
 
         byte IGifExtension.Label => GifConstants.GraphicControlLabel;
 
+        int IGifExtension.ContentLength => 5;
+
         public int WriteTo(Span<byte> buffer)
         {
             ref GifGraphicControlExtension dest = ref Unsafe.As<byte, GifGraphicControlExtension>(ref MemoryMarshal.GetReference(buffer));

src/ImageSharp/Formats/Gif/Sections/GifNetscapeLoopingApplicationExtension.cs

@@ -12,6 +12,8 @@ namespace SixLabors.ImageSharp.Formats.Gif
 
         public byte Label => GifConstants.ApplicationExtensionLabel;
 
+        public int ContentLength => 16;
+
         /// <summary>
         /// Gets the repeat count.
         /// 0 means loop indefinitely. Count is set as play n + 1 times.

src/ImageSharp/Formats/Gif/Sections/GifXmpApplicationExtension.cs

@@ -0,0 +1,97 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
+
+namespace SixLabors.ImageSharp.Formats.Gif
+{
+    internal readonly struct GifXmpApplicationExtension : IGifExtension
+    {
+        public GifXmpApplicationExtension(byte[] data) => this.Data = data;
+
+        public byte Label => GifConstants.ApplicationExtensionLabel;
+
+        public int ContentLength => this.Data.Length + 269; // 12 + Data Length + 1 + 256
+
+        /// <summary>
+        /// Gets the raw Data.
+        /// </summary>
+        public byte[] Data { get; }
+
+        /// <summary>
+        /// Reads the XMP metadata from the specified stream.
+        /// </summary>
+        /// <param name="stream">The stream to read from.</param>
+        /// <returns>The XMP metadata</returns>
+        /// <exception cref="ImageFormatException">Thrown if the XMP block is not properly terminated.</exception>
+        public static GifXmpApplicationExtension Read(Stream stream)
+        {
+            // Read data in blocks, until an \0 character is encountered.
+            // We overshoot, indicated by the terminatorIndex variable.
+            const int bufferSize = 256;
+            var list = new List<byte[]>();
+            int terminationIndex = -1;
+            while (terminationIndex < 0)
+            {
+                byte[] temp = new byte[bufferSize];
+                int bytesRead = stream.Read(temp);
+                list.Add(temp);
+                terminationIndex = Array.IndexOf(temp, (byte)1);
+            }
+
+            // Pack all the blocks (except magic trailer) into one single array again.
+            int dataSize = ((list.Count - 1) * bufferSize) + terminationIndex;
+            byte[] buffer = new byte[dataSize];
+            Span<byte> bufferSpan = buffer;
+            int pos = 0;
+            for (int j = 0; j < list.Count - 1; j++)
+            {
+                list[j].CopyTo(bufferSpan.Slice(pos));
+                pos += bufferSize;
+            }
+
+            // Last one only needs the portion until terminationIndex copied over.
+            Span<byte> lastBytes = list[list.Count - 1];
+            lastBytes.Slice(0, terminationIndex).CopyTo(bufferSpan.Slice(pos));
+
+            // Skip the remainder of the magic trailer.
+            stream.Skip(258 - (bufferSize - terminationIndex));
+            return new GifXmpApplicationExtension(buffer);
+        }
+
+        public int WriteTo(Span<byte> buffer)
+        {
+            int totalSize = this.ContentLength;
+            if (buffer.Length < totalSize)
+            {
+                throw new InsufficientMemoryException("Unable to write XMP metadata to GIF image");
+            }
+
+            int bytesWritten = 0;
+            buffer[bytesWritten++] = GifConstants.ApplicationBlockSize;
+
+            // Write "XMP DataXMP"
+            ReadOnlySpan<byte> idBytes = GifConstants.XmpApplicationIdentificationBytes;
+            idBytes.CopyTo(buffer.Slice(bytesWritten));
+            bytesWritten += idBytes.Length;
+
+            // XMP Data itself
+            this.Data.CopyTo(buffer.Slice(bytesWritten));
+            bytesWritten += this.Data.Length;
+
+            // Write the Magic Trailer
+            buffer[bytesWritten++] = 0x01;
+            for (byte i = 255; i > 0; i--)
+            {
+                buffer[bytesWritten++] = i;
+            }
+
+            buffer[bytesWritten++] = 0x00;
+
+            return totalSize;
+        }
+    }
+}

src/ImageSharp/Formats/Gif/Sections/IGifExtension.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -15,6 +15,11 @@ namespace SixLabors.ImageSharp.Formats.Gif
         /// </summary>
         byte Label { get; }
 
+        /// <summary>
+        /// Gets the length of the contents of this extension.
+        /// </summary>
+        int ContentLength { get; }
+
         /// <summary>
         /// Writes the extension data to the buffer.
         /// </summary>

src/ImageSharp/Formats/ImageExtensions.Save.cs

@@ -106,7 +106,6 @@ namespace SixLabors.ImageSharp
         /// <param name="stream">The stream to save the image to.</param>
         /// <param name="encoder">The encoder to save the image with.</param>
         /// <exception cref="System.ArgumentNullException">Thrown if the stream is null.</exception>
-        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
         public static void SaveAsBmp(this Image source, Stream stream, BmpEncoder encoder)
             => source.Save(
                 stream,
@@ -209,7 +208,6 @@ namespace SixLabors.ImageSharp
         /// <param name="stream">The stream to save the image to.</param>
         /// <param name="encoder">The encoder to save the image with.</param>
         /// <exception cref="System.ArgumentNullException">Thrown if the stream is null.</exception>
-        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
         public static void SaveAsGif(this Image source, Stream stream, GifEncoder encoder)
             => source.Save(
                 stream,
@@ -312,7 +310,6 @@ namespace SixLabors.ImageSharp
         /// <param name="stream">The stream to save the image to.</param>
         /// <param name="encoder">The encoder to save the image with.</param>
         /// <exception cref="System.ArgumentNullException">Thrown if the stream is null.</exception>
-        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
         public static void SaveAsJpeg(this Image source, Stream stream, JpegEncoder encoder)
             => source.Save(
                 stream,
@@ -415,7 +412,6 @@ namespace SixLabors.ImageSharp
         /// <param name="stream">The stream to save the image to.</param>
         /// <param name="encoder">The encoder to save the image with.</param>
         /// <exception cref="System.ArgumentNullException">Thrown if the stream is null.</exception>
-        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
         public static void SaveAsPbm(this Image source, Stream stream, PbmEncoder encoder)
             => source.Save(
                 stream,
@@ -518,7 +514,6 @@ namespace SixLabors.ImageSharp
         /// <param name="stream">The stream to save the image to.</param>
         /// <param name="encoder">The encoder to save the image with.</param>
         /// <exception cref="System.ArgumentNullException">Thrown if the stream is null.</exception>
-        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
         public static void SaveAsPng(this Image source, Stream stream, PngEncoder encoder)
             => source.Save(
                 stream,
@@ -621,7 +616,6 @@ namespace SixLabors.ImageSharp
         /// <param name="stream">The stream to save the image to.</param>
         /// <param name="encoder">The encoder to save the image with.</param>
         /// <exception cref="System.ArgumentNullException">Thrown if the stream is null.</exception>
-        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
         public static void SaveAsTga(this Image source, Stream stream, TgaEncoder encoder)
             => source.Save(
                 stream,
@@ -724,7 +718,6 @@ namespace SixLabors.ImageSharp
         /// <param name="stream">The stream to save the image to.</param>
         /// <param name="encoder">The encoder to save the image with.</param>
         /// <exception cref="System.ArgumentNullException">Thrown if the stream is null.</exception>
-        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
         public static void SaveAsWebp(this Image source, Stream stream, WebpEncoder encoder)
             => source.Save(
                 stream,
@@ -827,7 +820,6 @@ namespace SixLabors.ImageSharp
         /// <param name="stream">The stream to save the image to.</param>
         /// <param name="encoder">The encoder to save the image with.</param>
         /// <exception cref="System.ArgumentNullException">Thrown if the stream is null.</exception>
-        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
         public static void SaveAsTiff(this Image source, Stream stream, TiffEncoder encoder)
             => source.Save(
                 stream,

src/ImageSharp/Formats/ImageExtensions.Save.tt

@@ -124,7 +124,6 @@ namespace SixLabors.ImageSharp
         /// <param name="stream">The stream to save the image to.</param>
         /// <param name="encoder">The encoder to save the image with.</param>
         /// <exception cref="System.ArgumentNullException">Thrown if the stream is null.</exception>
-        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
         public static void SaveAs<#= fmt #>(this Image source, Stream stream, <#= fmt #>Encoder encoder)
             => source.Save(
                 stream,

src/ImageSharp/Formats/ImageFormatManager.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -17,27 +17,27 @@ namespace SixLabors.ImageSharp.Formats
         /// Used for locking against as there is no ConcurrentSet type.
         /// <see href="https://github.com/dotnet/corefx/issues/6318"/>
         /// </summary>
-        private static readonly object HashLock = new object();
+        private static readonly object HashLock = new();
 
         /// <summary>
         /// The list of supported <see cref="IImageEncoder"/> keyed to mime types.
         /// </summary>
-        private readonly ConcurrentDictionary<IImageFormat, IImageEncoder> mimeTypeEncoders = new ConcurrentDictionary<IImageFormat, IImageEncoder>();
+        private readonly ConcurrentDictionary<IImageFormat, IImageEncoder> mimeTypeEncoders = new();
 
         /// <summary>
         /// The list of supported <see cref="IImageEncoder"/> keyed to mime types.
         /// </summary>
-        private readonly ConcurrentDictionary<IImageFormat, IImageDecoder> mimeTypeDecoders = new ConcurrentDictionary<IImageFormat, IImageDecoder>();
+        private readonly ConcurrentDictionary<IImageFormat, IImageDecoder> mimeTypeDecoders = new();
 
         /// <summary>
         /// The list of supported <see cref="IImageFormat"/>s.
         /// </summary>
-        private readonly HashSet<IImageFormat> imageFormats = new HashSet<IImageFormat>();
+        private readonly HashSet<IImageFormat> imageFormats = new();
 
         /// <summary>
         /// The list of supported <see cref="IImageFormatDetector"/>s.
         /// </summary>
-        private ConcurrentBag<IImageFormatDetector> imageFormatDetectors = new ConcurrentBag<IImageFormatDetector>();
+        private ConcurrentBag<IImageFormatDetector> imageFormatDetectors = new();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ImageFormatManager" /> class.
@@ -113,9 +113,7 @@ namespace SixLabors.ImageSharp.Formats
         /// <param name="mimeType">The mime-type to discover</param>
         /// <returns>The <see cref="IImageFormat"/> if found; otherwise null</returns>
         public IImageFormat FindFormatByMimeType(string mimeType)
-        {
-            return this.imageFormats.FirstOrDefault(x => x.MimeTypes.Contains(mimeType, StringComparer.OrdinalIgnoreCase));
-        }
+            => this.imageFormats.FirstOrDefault(x => x.MimeTypes.Contains(mimeType, StringComparer.OrdinalIgnoreCase));
 
         /// <summary>
         /// Sets a specific image encoder as the encoder for a specific image format.
@@ -146,10 +144,7 @@ namespace SixLabors.ImageSharp.Formats
         /// <summary>
         /// Removes all the registered image format detectors.
         /// </summary>
-        public void ClearImageFormatDetectors()
-        {
-            this.imageFormatDetectors = new ConcurrentBag<IImageFormatDetector>();
-        }
+        public void ClearImageFormatDetectors() => this.imageFormatDetectors = new();
 
         /// <summary>
         /// Adds a new detector for detecting mime types.
@@ -193,9 +188,6 @@ namespace SixLabors.ImageSharp.Formats
         /// <summary>
         /// Sets the max header size.
         /// </summary>
-        private void SetMaxHeaderSize()
-        {
-            this.MaxHeaderSize = this.imageFormatDetectors.Max(x => x.HeaderSize);
-        }
+        private void SetMaxHeaderSize() => this.MaxHeaderSize = this.imageFormatDetectors.Max(x => x.HeaderSize);
     }
 }

src/ImageSharp/Formats/Jpeg/Components/Block8x8F.cs

@@ -280,7 +280,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
         }
 
         /// <summary>
-        /// Quantize input block, apply zig-zag ordering and store result as 16bit integers.
+        /// Quantize input block, transpose, apply zig-zag ordering and store as <see cref="Block8x8"/>.
         /// </summary>
         /// <param name="block">Source block.</param>
         /// <param name="dest">Destination block.</param>
@@ -291,19 +291,19 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
             if (Avx2.IsSupported)
             {
                 MultiplyIntoInt16_Avx2(ref block, ref qt, ref dest);
-                ZigZag.ApplyZigZagOrderingAvx2(ref dest);
+                ZigZag.ApplyTransposingZigZagOrderingAvx2(ref dest);
             }
             else if (Ssse3.IsSupported)
             {
                 MultiplyIntoInt16_Sse2(ref block, ref qt, ref dest);
-                ZigZag.ApplyZigZagOrderingSsse3(ref dest);
+                ZigZag.ApplyTransposingZigZagOrderingSsse3(ref dest);
             }
             else
 #endif
             {
                 for (int i = 0; i < Size; i++)
                 {
-                    int idx = ZigZag.ZigZagOrder[i];
+                    int idx = ZigZag.TransposingOrder[i];
                     float quantizedVal = block[idx] * qt[idx];
                     quantizedVal += quantizedVal < 0 ? -0.5f : 0.5f;
                     dest[i] = (short)quantizedVal;

src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanScanDecoder.cs

@@ -31,7 +31,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// <summary>
         /// Number of component in the current scan.
         /// </summary>
-        private int componentsCount;
+        private int scanComponentCount;
 
         /// <summary>
         /// The reset interval determined by RST markers.
@@ -112,11 +112,12 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// <summary>
         /// Decodes the entropy coded data.
         /// </summary>
-        public void ParseEntropyCodedData(int componentCount)
+        /// <param name="scanComponentCount">Component count in the current scan.</param>
+        public void ParseEntropyCodedData(int scanComponentCount)
         {
             this.cancellationToken.ThrowIfCancellationRequested();
 
-            this.componentsCount = componentCount;
+            this.scanComponentCount = scanComponentCount;
 
             this.scanBuffer = new HuffmanScanBuffer(this.stream);
 
@@ -148,11 +149,16 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
         private void ParseBaselineData()
         {
-            if (this.componentsCount == this.frame.ComponentCount)
+            if (this.scanComponentCount != 1)
             {
                 this.ParseBaselineDataInterleaved();
                 this.spectralConverter.CommitConversion();
             }
+            else if (this.frame.ComponentCount == 1)
+            {
+                this.ParseBaselineDataSingleComponent();
+                this.spectralConverter.CommitConversion();
+            }
             else
             {
                 this.ParseBaselineDataNonInterleaved();
@@ -161,24 +167,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
         private void ParseBaselineDataInterleaved()
         {
-            // Interleaved
             int mcu = 0;
             int mcusPerColumn = this.frame.McusPerColumn;
             int mcusPerLine = this.frame.McusPerLine;
             ref HuffmanScanBuffer buffer = ref this.scanBuffer;
 
-            // Pre-derive the huffman table to avoid in-loop checks.
-            for (int i = 0; i < this.componentsCount; i++)
-            {
-                int order = this.frame.ComponentOrder[i];
-                JpegComponent component = this.components[order];
-
-                ref HuffmanTable dcHuffmanTable = ref this.dcHuffmanTables[component.DCHuffmanTableId];
-                ref HuffmanTable acHuffmanTable = ref this.acHuffmanTables[component.ACHuffmanTableId];
-                dcHuffmanTable.Configure();
-                acHuffmanTable.Configure();
-            }
-
             for (int j = 0; j < mcusPerColumn; j++)
             {
                 this.cancellationToken.ThrowIfCancellationRequested();
@@ -188,7 +181,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                 {
                     // Scan an interleaved mcu... process components in order
                     int mcuCol = mcu % mcusPerLine;
-                    for (int k = 0; k < this.componentsCount; k++)
+                    for (int k = 0; k < this.scanComponentCount; k++)
                     {
                         int order = this.frame.ComponentOrder[k];
                         JpegComponent component = this.components[order];
@@ -210,7 +203,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                             {
                                 if (buffer.NoData)
                                 {
-                                    // It is very likely that some spectral data was decoded before we encountered EOI marker
+                                    // It is very likely that some spectral data was decoded before we've encountered 'end of scan'
                                     // so we need to decode what's left and return (or maybe throw?)
                                     this.spectralConverter.ConvertStrideBaseline();
                                     return;
@@ -233,7 +226,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                     this.HandleRestart();
                 }
 
-                // convert from spectral to actual pixels via given converter
+                // Convert from spectral to actual pixels via given converter
                 this.spectralConverter.ConvertStrideBaseline();
             }
         }
@@ -248,8 +241,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
             ref HuffmanTable dcHuffmanTable = ref this.dcHuffmanTables[component.DCHuffmanTableId];
             ref HuffmanTable acHuffmanTable = ref this.acHuffmanTables[component.ACHuffmanTableId];
-            dcHuffmanTable.Configure();
-            acHuffmanTable.Configure();
 
             for (int j = 0; j < h; j++)
             {
@@ -275,6 +266,52 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             }
         }
 
+        private void ParseBaselineDataSingleComponent()
+        {
+            JpegComponent component = this.frame.Components[0];
+            int mcuLines = this.frame.McusPerColumn;
+            int w = component.WidthInBlocks;
+            int h = component.SamplingFactors.Height;
+            ref HuffmanTable dcHuffmanTable = ref this.dcHuffmanTables[component.DCHuffmanTableId];
+            ref HuffmanTable acHuffmanTable = ref this.acHuffmanTables[component.ACHuffmanTableId];
+
+            ref HuffmanScanBuffer buffer = ref this.scanBuffer;
+
+            for (int i = 0; i < mcuLines; i++)
+            {
+                this.cancellationToken.ThrowIfCancellationRequested();
+
+                // decode from binary to spectral
+                for (int j = 0; j < h; j++)
+                {
+                    Span<Block8x8> blockSpan = component.SpectralBlocks.DangerousGetRowSpan(j);
+                    ref Block8x8 blockRef = ref MemoryMarshal.GetReference(blockSpan);
+
+                    for (int k = 0; k < w; k++)
+                    {
+                        if (buffer.NoData)
+                        {
+                            // It is very likely that some spectral data was decoded before we've encountered 'end of scan'
+                            // so we need to decode what's left and return (or maybe throw?)
+                            this.spectralConverter.ConvertStrideBaseline();
+                            return;
+                        }
+
+                        this.DecodeBlockBaseline(
+                            component,
+                            ref Unsafe.Add(ref blockRef, k),
+                            ref dcHuffmanTable,
+                            ref acHuffmanTable);
+
+                        this.HandleRestart();
+                    }
+                }
+
+                // Convert from spectral to actual pixels via given converter
+                this.spectralConverter.ConvertStrideBaseline();
+            }
+        }
+
         private void CheckProgressiveData()
         {
             // Validate successive scan parameters.
@@ -297,7 +334,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                 }
 
                 // AC scans may have only one component.
-                if (this.componentsCount != 1)
+                if (this.scanComponentCount != 1)
                 {
                     invalid = true;
                 }
@@ -329,7 +366,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         {
             this.CheckProgressiveData();
 
-            if (this.componentsCount == 1)
+            if (this.scanComponentCount == 1)
             {
                 this.ParseProgressiveDataNonInterleaved();
             }
@@ -347,15 +384,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             int mcusPerLine = this.frame.McusPerLine;
             ref HuffmanScanBuffer buffer = ref this.scanBuffer;
 
-            // Pre-derive the huffman table to avoid in-loop checks.
-            for (int k = 0; k < this.componentsCount; k++)
-            {
-                int order = this.frame.ComponentOrder[k];
-                JpegComponent component = this.components[order];
-                ref HuffmanTable dcHuffmanTable = ref this.dcHuffmanTables[component.DCHuffmanTableId];
-                dcHuffmanTable.Configure();
-            }
-
             for (int j = 0; j < mcusPerColumn; j++)
             {
                 for (int i = 0; i < mcusPerLine; i++)
@@ -363,7 +391,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                     // Scan an interleaved mcu... process components in order
                     int mcuRow = mcu / mcusPerLine;
                     int mcuCol = mcu % mcusPerLine;
-                    for (int k = 0; k < this.componentsCount; k++)
+                    for (int k = 0; k < this.scanComponentCount; k++)
                     {
                         int order = this.frame.ComponentOrder[k];
                         JpegComponent component = this.components[order];
@@ -416,7 +444,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             if (this.SpectralStart == 0)
             {
                 ref HuffmanTable dcHuffmanTable = ref this.dcHuffmanTables[component.DCHuffmanTableId];
-                dcHuffmanTable.Configure();
 
                 for (int j = 0; j < h; j++)
                 {
@@ -444,7 +471,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             else
             {
                 ref HuffmanTable acHuffmanTable = ref this.acHuffmanTables[component.ACHuffmanTableId];
-                acHuffmanTable.Configure();
 
                 for (int j = 0; j < h; j++)
                 {
@@ -752,11 +778,12 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// <param name="index">Table index.</param>
         /// <param name="codeLengths">Code lengths.</param>
         /// <param name="values">Code values.</param>
+        /// <param name="workspace">The provided spare workspace memory, can be dirty.</param>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public void BuildHuffmanTable(int type, int index, ReadOnlySpan<byte> codeLengths, ReadOnlySpan<byte> values)
+        public void BuildHuffmanTable(int type, int index, ReadOnlySpan<byte> codeLengths, ReadOnlySpan<byte> values, Span<uint> workspace)
         {
             HuffmanTable[] tables = type == 0 ? this.dcHuffmanTables : this.acHuffmanTables;
-            tables[index] = new HuffmanTable(codeLengths, values);
+            tables[index] = new HuffmanTable(codeLengths, values, workspace);
         }
     }
 }

src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanTable.cs

@@ -13,12 +13,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
     [StructLayout(LayoutKind.Sequential)]
     internal unsafe struct HuffmanTable
     {
-        private bool isConfigured;
-
         /// <summary>
-        /// Derived from the DHT marker. Sizes[k] = # of symbols with codes of length k bits; Sizes[0] is unused.
+        /// Memory workspace buffer size used in <see cref="HuffmanTable"/> ctor.
         /// </summary>
-        public fixed byte Sizes[17];
+        public const int WorkspaceByteSize = 256 * sizeof(uint);
 
         /// <summary>
         /// Derived from the DHT marker. Contains the symbols, in order of incremental code length.
@@ -58,51 +56,35 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// <summary>
         /// Initializes a new instance of the <see cref="HuffmanTable"/> struct.
         /// </summary>
-        /// <param name="codeLengths">The code lengths</param>
-        /// <param name="values">The huffman values</param>
-        public HuffmanTable(ReadOnlySpan<byte> codeLengths, ReadOnlySpan<byte> values)
+        /// <param name="codeLengths">The code lengths.</param>
+        /// <param name="values">The huffman values.</param>
+        /// <param name="workspace">The provided spare workspace memory, can be dirty.</param>
+        public HuffmanTable(ReadOnlySpan<byte> codeLengths, ReadOnlySpan<byte> values, Span<uint> workspace)
         {
-            this.isConfigured = false;
-            Unsafe.CopyBlockUnaligned(ref this.Sizes[0], ref MemoryMarshal.GetReference(codeLengths), (uint)codeLengths.Length);
             Unsafe.CopyBlockUnaligned(ref this.Values[0], ref MemoryMarshal.GetReference(values), (uint)values.Length);
-        }
-
-        /// <summary>
-        /// Expands the HuffmanTable into its readable form.
-        /// </summary>
-        public void Configure()
-        {
-            if (this.isConfigured)
-            {
-                return;
-            }
 
-            Span<char> huffSize = stackalloc char[257];
-            Span<uint> huffCode = stackalloc uint[257];
-
-            // Figure C.1: make table of Huffman code length for each symbol
+            // Generate codes
+            uint code = 0;
+            int si = 1;
             int p = 0;
-            for (int j = 1; j <= 16; j++)
+            for (int i = 1; i <= 16; i++)
             {
-                int i = this.Sizes[j];
-                while (i-- != 0)
+                int count = codeLengths[i];
+                for (int j = 0; j < count; j++)
                 {
-                    huffSize[p++] = (char)j;
+                    workspace[p++] = code;
+                    code++;
                 }
-            }
 
-            huffSize[p] = (char)0;
-
-            // Figure C.2: generate the codes themselves
-            uint code = 0;
-            int si = huffSize[0];
-            p = 0;
-            while (huffSize[p] != 0)
-            {
-                while (huffSize[p] == si)
+                // 'code' is now 1 more than the last code used for codelength 'si'
+                // in the valid worst possible case 'code' would have the least
+                // significant bit set to 1, e.g. 1111(0) +1 => 1111(1)
+                // but it must still fit in 'si' bits since no huffman code can be equal to all 1s
+                // if last code is all ones, e.g. 1111(1), then incrementing it by 1 would yield
+                // a new code which occupies one extra bit, e.g. 1111(1) +1 => (1)1111(0)
+                if (code >= (1 << si))
                 {
-                    huffCode[p++] = code;
-                    code++;
+                    JpegThrowHelper.ThrowInvalidImageContentException("Bad huffman table.");
                 }
 
                 code <<= 1;
@@ -113,11 +95,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             p = 0;
             for (int j = 1; j <= 16; j++)
             {
-                if (this.Sizes[j] != 0)
+                if (codeLengths[j] != 0)
                 {
-                    this.ValOffset[j] = p - (int)huffCode[p];
-                    p += this.Sizes[j];
-                    this.MaxCode[j] = huffCode[p - 1]; // Maximum code of length l
+                    this.ValOffset[j] = p - (int)workspace[p];
+                    p += codeLengths[j];
+                    this.MaxCode[j] = workspace[p - 1]; // Maximum code of length l
                     this.MaxCode[j] <<= JpegConstants.Huffman.RegisterSize - j; // Left justify
                     this.MaxCode[j] |= (1ul << (JpegConstants.Huffman.RegisterSize - j)) - 1;
                 }
@@ -142,11 +124,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             for (int length = 1; length <= JpegConstants.Huffman.LookupBits; length++)
             {
                 int jShift = JpegConstants.Huffman.LookupBits - length;
-                for (int i = 1; i <= this.Sizes[length]; i++, p++)
+                for (int i = 1; i <= codeLengths[length]; i++, p++)
                 {
                     // length = current code's length, p = its index in huffCode[] & Values[].
                     // Generate left-justified code followed by all possible bit sequences
-                    int lookBits = (int)(huffCode[p] << jShift);
+                    int lookBits = (int)(workspace[p] << jShift);
                     for (int ctr = 1 << (JpegConstants.Huffman.LookupBits - length); ctr > 0; ctr--)
                     {
                         this.LookaheadSize[lookBits] = (byte)length;
@@ -155,8 +137,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
                     }
                 }
             }
-
-            this.isConfigured = true;
         }
     }
 }

src/ImageSharp/Formats/Jpeg/Components/Decoder/JFifMarker.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -103,26 +103,22 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
         /// <inheritdoc/>
         public bool Equals(JFifMarker other)
-        {
-            return this.MajorVersion == other.MajorVersion
+            => this.MajorVersion == other.MajorVersion
                 && this.MinorVersion == other.MinorVersion
                 && this.DensityUnits == other.DensityUnits
                 && this.XDensity == other.XDensity
                 && this.YDensity == other.YDensity;
-        }
 
         /// <inheritdoc/>
         public override bool Equals(object obj) => obj is JFifMarker other && this.Equals(other);
 
         /// <inheritdoc/>
         public override int GetHashCode()
-        {
-            return HashCode.Combine(
+            => HashCode.Combine(
                 this.MajorVersion,
                 this.MinorVersion,
                 this.DensityUnits,
                 this.XDensity,
                 this.YDensity);
-        }
     }
 }

src/ImageSharp/Formats/Jpeg/Components/Decoder/ProfileResolver.cs

@@ -60,6 +60,18 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             (byte)'E', (byte)'x', (byte)'i', (byte)'f', (byte)'\0', (byte)'\0'
         };
 
+        /// <summary>
+        /// Gets the XMP specific markers.
+        /// </summary>
+        public static ReadOnlySpan<byte> XmpMarker => new[]
+        {
+            (byte)'h', (byte)'t', (byte)'t', (byte)'p', (byte)':', (byte)'/', (byte)'/',
+            (byte)'n', (byte)'s', (byte)'.', (byte)'a', (byte)'d', (byte)'o', (byte)'b',
+            (byte)'e', (byte)'.', (byte)'c', (byte)'o', (byte)'m', (byte)'/', (byte)'x',
+            (byte)'a', (byte)'p', (byte)'/', (byte)'1', (byte)'.', (byte)'0', (byte)'/',
+            (byte)0
+        };
+
         /// <summary>
         /// Gets the Adobe specific markers <see href="http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html#Adobe"/>.
         /// </summary>

src/ImageSharp/Formats/Jpeg/Components/Decoder/SpectralConverter{TPixel}.cs

@@ -111,7 +111,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             this.pixelRowsPerStep = majorVerticalSamplingFactor * blockPixelHeight;
 
             // pixel buffer for resulting image
-            this.pixelBuffer = allocator.Allocate2D<TPixel>(frame.PixelWidth, frame.PixelHeight);
+            this.pixelBuffer = allocator.Allocate2D<TPixel>(
+                frame.PixelWidth,
+                frame.PixelHeight,
+                this.configuration.PreferContiguousImageBuffers);
             this.paddedProxyPixelRow = allocator.Allocate<TPixel>(frame.PixelWidth + 3);
 
             // component processors from spectral to Rgba32

src/ImageSharp/Formats/Jpeg/Components/FastFloatingPointDCT.Intrinsic.cs

@@ -29,11 +29,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
         {
             DebugGuard.IsTrue(Avx.IsSupported, "Avx support is required to execute this operation.");
 
-            // First pass - process rows
-            block.TransposeInplace();
+            // First pass - process columns
             FDCT8x8_1D_Avx(ref block);
 
-            // Second pass - process columns
+            // Second pass - process rows
             block.TransposeInplace();
             FDCT8x8_1D_Avx(ref block);
 

src/ImageSharp/Formats/Jpeg/Components/FastFloatingPointDCT.cs

@@ -92,6 +92,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
                 tableRef = 0.125f / (tableRef * Unsafe.Add(ref multipliersRef, i));
                 tableRef = ref Unsafe.Add(ref tableRef, 1);
             }
+
+            // Spectral macroblocks are not transposed before quantization
+            // Transpose is done after quantization at zig-zag stage
+            // so we must transpose quantization table
+            quantTable.TransposeInplace();
         }
 
         /// <summary>
@@ -133,24 +138,21 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
             }
             else
 #endif
-            if (Vector.IsHardwareAccelerated)
             {
                 FDCT_Vector4(ref block);
             }
-            else
-            {
-                FDCT_Scalar(ref block);
-            }
         }
 
         /// <summary>
         /// Apply floating point IDCT inplace using <see cref="Vector4"/> API.
         /// </summary>
+        /// <remarks>
+        /// This method can be used even if there's no SIMD intrinsics available
+        /// as <see cref="Vector4"/> can be compiled to scalar instructions.
+        /// </remarks>
         /// <param name="transposedBlock">Input block.</param>
         private static void IDCT_Vector4(ref Block8x8F transposedBlock)
         {
-            DebugGuard.IsTrue(Vector.IsHardwareAccelerated, "Scalar implementation should be called for non-accelerated hardware.");
-
             // First pass - process columns
             IDCT8x4_Vector4(ref transposedBlock.V0L);
             IDCT8x4_Vector4(ref transposedBlock.V0R);
@@ -215,136 +217,17 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
             }
         }
 
-        /// <summary>
-        /// Apply 2D floating point FDCT inplace using scalar operations.
-        /// </summary>
-        /// <remarks>
-        /// Ported from libjpeg-turbo https://github.com/libjpeg-turbo/libjpeg-turbo/blob/main/jfdctflt.c.
-        /// </remarks>
-        /// <param name="block">Input block.</param>
-        private static void FDCT_Scalar(ref Block8x8F block)
-        {
-            const int dctSize = 8;
-
-            float tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
-            float tmp10, tmp11, tmp12, tmp13;
-            float z1, z2, z3, z4, z5, z11, z13;
-
-            // First pass - process rows
-            ref float blockRef = ref Unsafe.As<Block8x8F, float>(ref block);
-            for (int ctr = 7; ctr >= 0; ctr--)
-            {
-                tmp0 = Unsafe.Add(ref blockRef, 0) + Unsafe.Add(ref blockRef, 7);
-                tmp7 = Unsafe.Add(ref blockRef, 0) - Unsafe.Add(ref blockRef, 7);
-                tmp1 = Unsafe.Add(ref blockRef, 1) + Unsafe.Add(ref blockRef, 6);
-                tmp6 = Unsafe.Add(ref blockRef, 1) - Unsafe.Add(ref blockRef, 6);
-                tmp2 = Unsafe.Add(ref blockRef, 2) + Unsafe.Add(ref blockRef, 5);
-                tmp5 = Unsafe.Add(ref blockRef, 2) - Unsafe.Add(ref blockRef, 5);
-                tmp3 = Unsafe.Add(ref blockRef, 3) + Unsafe.Add(ref blockRef, 4);
-                tmp4 = Unsafe.Add(ref blockRef, 3) - Unsafe.Add(ref blockRef, 4);
-
-                // Even part
-                tmp10 = tmp0 + tmp3;
-                tmp13 = tmp0 - tmp3;
-                tmp11 = tmp1 + tmp2;
-                tmp12 = tmp1 - tmp2;
-
-                Unsafe.Add(ref blockRef, 0) = tmp10 + tmp11;
-                Unsafe.Add(ref blockRef, 4) = tmp10 - tmp11;
-
-                z1 = (tmp12 + tmp13) * 0.707106781f;
-                Unsafe.Add(ref blockRef, 2) = tmp13 + z1;
-                Unsafe.Add(ref blockRef, 6) = tmp13 - z1;
-
-                // Odd part
-                tmp10 = tmp4 + tmp5;
-                tmp11 = tmp5 + tmp6;
-                tmp12 = tmp6 + tmp7;
-
-                z5 = (tmp10 - tmp12) * 0.382683433f;
-                z2 = (0.541196100f * tmp10) + z5;
-                z4 = (1.306562965f * tmp12) + z5;
-                z3 = tmp11 * 0.707106781f;
-
-                z11 = tmp7 + z3;
-                z13 = tmp7 - z3;
-
-                Unsafe.Add(ref blockRef, 5) = z13 + z2;
-                Unsafe.Add(ref blockRef, 3) = z13 - z2;
-                Unsafe.Add(ref blockRef, 1) = z11 + z4;
-                Unsafe.Add(ref blockRef, 7) = z11 - z4;
-
-                blockRef = ref Unsafe.Add(ref blockRef, dctSize);
-            }
-
-            // Second pass - process columns
-            blockRef = ref Unsafe.As<Block8x8F, float>(ref block);
-            for (int ctr = 7; ctr >= 0; ctr--)
-            {
-                tmp0 = Unsafe.Add(ref blockRef, dctSize * 0) + Unsafe.Add(ref blockRef, dctSize * 7);
-                tmp7 = Unsafe.Add(ref blockRef, dctSize * 0) - Unsafe.Add(ref blockRef, dctSize * 7);
-                tmp1 = Unsafe.Add(ref blockRef, dctSize * 1) + Unsafe.Add(ref blockRef, dctSize * 6);
-                tmp6 = Unsafe.Add(ref blockRef, dctSize * 1) - Unsafe.Add(ref blockRef, dctSize * 6);
-                tmp2 = Unsafe.Add(ref blockRef, dctSize * 2) + Unsafe.Add(ref blockRef, dctSize * 5);
-                tmp5 = Unsafe.Add(ref blockRef, dctSize * 2) - Unsafe.Add(ref blockRef, dctSize * 5);
-                tmp3 = Unsafe.Add(ref blockRef, dctSize * 3) + Unsafe.Add(ref blockRef, dctSize * 4);
-                tmp4 = Unsafe.Add(ref blockRef, dctSize * 3) - Unsafe.Add(ref blockRef, dctSize * 4);
-
-                // Even part
-                tmp10 = tmp0 + tmp3;
-                tmp13 = tmp0 - tmp3;
-                tmp11 = tmp1 + tmp2;
-                tmp12 = tmp1 - tmp2;
-
-                Unsafe.Add(ref blockRef, dctSize * 0) = tmp10 + tmp11;
-                Unsafe.Add(ref blockRef, dctSize * 4) = tmp10 - tmp11;
-
-                z1 = (tmp12 + tmp13) * 0.707106781f;
-                Unsafe.Add(ref blockRef, dctSize * 2) = tmp13 + z1;
-                Unsafe.Add(ref blockRef, dctSize * 6) = tmp13 - z1;
-
-                // Odd part
-                tmp10 = tmp4 + tmp5;
-                tmp11 = tmp5 + tmp6;
-                tmp12 = tmp6 + tmp7;
-
-                z5 = (tmp10 - tmp12) * 0.382683433f;
-                z2 = (0.541196100f * tmp10) + z5;
-                z4 = (1.306562965f * tmp12) + z5;
-                z3 = tmp11 * 0.707106781f;
-
-                z11 = tmp7 + z3;
-                z13 = tmp7 - z3;
-
-                Unsafe.Add(ref blockRef, dctSize * 5) = z13 + z2;
-                Unsafe.Add(ref blockRef, dctSize * 3) = z13 - z2;
-                Unsafe.Add(ref blockRef, dctSize * 1) = z11 + z4;
-                Unsafe.Add(ref blockRef, dctSize * 7) = z11 - z4;
-
-                blockRef = ref Unsafe.Add(ref blockRef, 1);
-            }
-        }
-
         /// <summary>
         /// Apply floating point FDCT inplace using <see cref="Vector4"/> API.
         /// </summary>
-        /// <remarks>
-        /// This implementation must be called only if hardware supports 4
-        /// floating point numbers vector. Otherwise explicit scalar
-        /// implementation <see cref="FDCT_Scalar"/> is faster
-        /// because it does not rely on block transposition.
-        /// </remarks>
         /// <param name="block">Input block.</param>
         public static void FDCT_Vector4(ref Block8x8F block)
         {
-            DebugGuard.IsTrue(Vector.IsHardwareAccelerated, "Scalar implementation should be called for non-accelerated hardware.");
-
-            // First pass - process rows
-            block.TransposeInplace();
+            // First pass - process columns
             FDCT8x4_Vector4(ref block.V0L);
             FDCT8x4_Vector4(ref block.V0R);
 
-            // Second pass - process columns
+            // Second pass - process rows
             block.TransposeInplace();
             FDCT8x4_Vector4(ref block.V0L);
             FDCT8x4_Vector4(ref block.V0R);

src/ImageSharp/Formats/Jpeg/Components/ZigZag.Intrinsic.cs

@@ -3,6 +3,7 @@
 
 #if SUPPORTS_RUNTIME_INTRINSICS
 using System;
+using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics;
 using System.Runtime.Intrinsics.X86;
 
@@ -18,120 +19,138 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
 #pragma warning restore SA1309
 
         /// <summary>
-        /// Gets shuffle vectors for <see cref="ApplyZigZagOrderingSsse3"/>
+        /// Gets shuffle vectors for <see cref="ApplyTransposingZigZagOrderingSsse3"/>
         /// zig zag implementation.
         /// </summary>
         private static ReadOnlySpan<byte> SseShuffleMasks => new byte[]
         {
-            // row0
-            0, 1, 2, 3, _, _, _, _, _, _, 4, 5, 6, 7, _, _,
-            _, _, _, _, 0, 1, _, _, 2, 3, _, _, _, _, 4, 5,
-            _, _, _, _, _, _, 0, 1, _, _, _, _, _, _, _, _,
-
-            // row1
-            _, _, _, _, _, _, _, _, _, _, _, _, 8, 9, 10, 11,
-            2, 3, _, _, _, _, _, _, 4, 5, _, _, _, _, _, _,
-            _, _, 0, 1, _, _, 2, 3, _, _, _, _, _, _, _, _,
-
-            // row2
-            _, _, _, _, _, _, 2, 3, _, _, _, _, _, _, 4, 5,
-            _, _, _, _, _, _, _, _, 0, 1, _, _, 2, 3, _, _,
-
-            // row3
-            _, _, _, _, _, _, 12, 13, 14, 15, _, _, _, _, _, _,
-            _, _, _, _, 10, 11, _, _, _, _, 12, 13, _, _, _, _,
-            _, _, 8, 9, _, _, _, _, _, _, _, _, 10, 11, _, _,
-            6, 7, _, _, _, _, _, _, _, _, _, _, _, _, 8, 9,
-
-            // row4
-            _, _, 4, 5, _, _, _, _, _, _, _, _, 6, 7, _, _,
-            _, _, _, _, 2, 3, _, _, _, _, 4, 5, _, _, _, _,
-            _, _, _, _, _, _, 0, 1, 2, 3, _, _, _, _, _, _,
-
-            // row5
-            _, _, 12, 13, _, _, 14, 15, _, _, _, _, _, _, _, _,
-            10, 11, _, _, _, _, _, _, 12, 13, _, _, _, _, _, _,
-
-            // row6
-            _, _, _, _, _, _, _, _, 12, 13, _, _, 14, 15, _, _,
-            _, _, _, _, _, _, 10, 11, _, _, _, _, _, _, 12, 13,
-            4, 5, 6, 7, _, _, _, _, _, _, _, _, _, _, _, _,
-
-            // row7
-            10, 11, _, _, _, _, 12, 13, _, _, 14, 15, _, _, _, _,
-            _, _, 8, 9, 10, 11, _, _, _, _, _, _, 12, 13, 14, 15
+#pragma warning disable SA1515
+            /* row0 - A0 B0 A1 A2 B1 C0 D0 C1 */
+            // A
+            0, 1, _, _, 2, 3, 4, 5, _, _, _, _, _, _, _, _,
+            // B
+            _, _, 0, 1, _, _, _, _, 2, 3, _, _, _, _, _, _,
+            // C
+            _, _, _, _, _, _, _, _, _, _, 0, 1, _, _, 2, 3,
+
+            /* row1 - B2 A3 A4 B3 C2 D1 E0 F0 */
+            // A
+            _, _, 6, 7, 8, 9, _, _, _, _, _, _, _, _, _, _,
+            // B
+            4, 5, _, _, _, _, 6, 7, _, _, _, _, _, _, _, _,
+
+            /* row2 - E1 D2 C3 B4 A5 A6 B5 C4 */
+            // A
+            _, _, _, _, _, _, _, _, 10, 11, 12, 13,  _,  _, _, _,
+            // B
+            _, _, _, _, _, _, 8, 9,  _,  _,  _,  _, 10, 11, _, _,
+            // C
+            _, _, _, _, 6, 7, _, _,  _,  _,  _,  _,  _,  _, 8, 9,
+
+            /* row3 - D3 E2 F1 G0 H0 G1 F2 E3 */
+            // E
+            _, _, 4, 5, _, _, _, _, _, _, _, _, _, _, 6, 7,
+            // F
+            _, _, _, _, 2, 3, _, _, _, _, _, _, 4, 5, _, _,
+            // G
+            _, _, _, _, _, _, 0, 1, _, _, 2, 3, _, _, _, _,
+
+            /* row4 - D4 C5 B6 A7 B7 C6 D5 E4 */
+            // B
+            _, _,  _,  _, 12, 13, _, _, 14, 15,  _,  _,  _,  _, _, _,
+            // C
+            _, _, 10, 11,  _,  _, _, _,  _,  _, 12, 13,  _,  _, _, _,
+            // D
+            8, 9,  _,  _,  _,  _, _, _,  _,  _,  _,  _, 10, 11, _, _,
+
+            /* row5 - F3 G2 H1 H2 G3 F4 E5 D6 */
+            // F
+            6, 7, _, _, _, _, _, _, _, _, 8, 9, _, _, _, _,
+            // G
+            _, _, 4, 5, _, _, _, _, 6, 7, _, _, _, _, _, _,
+            // H
+            _, _, _, _, 2, 3, 4, 5, _, _, _, _, _, _, _, _,
+
+            /* row6 - C7 D7 E6 F5 G4 H3 H4 G5 */
+            // G
+            _, _, _, _, _, _, _, _, 8, 9, _, _, _, _, 10, 11,
+            // H
+            _, _, _, _, _, _, _, _, _, _, 6, 7, 8, 9,  _,  _,
+
+            /* row7 - F6 E7 F7 G6 H5 H6 G7 H7 */
+            // F
+            12, 13, _, _, 14, 15,  _,  _,  _,  _,  _,  _,  _,  _, _, _,
+            // G
+            _,  _, _, _,  _,  _, 12, 13,  _,  _,  _,  _, 14, 15, _, _,
+            // H
+            _,  _, _, _,  _,  _,  _,  _, 10, 11, 12, 13,  _,  _, 14, 15,
+#pragma warning restore SA1515
         };
 
         /// <summary>
-        /// Gets shuffle vectors for <see cref="ApplyZigZagOrderingAvx2"/>
+        /// Gets shuffle vectors for <see cref="ApplyTransposingZigZagOrderingAvx2"/>
         /// zig zag implementation.
         /// </summary>
         private static ReadOnlySpan<byte> AvxShuffleMasks => new byte[]
         {
-                // 01_AB/01_EF/23_CD - cross-lane
-                0, 0, 0, 0,   1, 0, 0, 0,   4, 0, 0, 0,   5, 0, 0, 0,   0, 0, 0, 0,   2, 0, 0, 0,   5, 0, 0, 0,   6, 0, 0, 0,
-
-                // 01_AB - inner-lane
-                0, 1, 2, 3,   8, 9, _, _,   10, 11, 4, 5,   6, 7, 12, 13,  _, _, _, _,   _, _, _, _,   _, _, 10, 11,   4, 5, 6, 7,
-
-                // 01_CD/23_GH - cross-lane
-                0, 0, 0, 0,   1, 0, 0, 0,   4, 0, 0, 0,   _, _, _, _,   0, 0, 0, 0,   1, 0, 0, 0,   4, 0, 0, 0,   _, _, _, _,
-
-                // 01_CD - inner-lane
-                _, _, _, _,   _, _, 0, 1,   _, _, _, _,   _, _, _, _,   2, 3, 8, 9,   _, _, 10, 11,   4, 5, _, _,   _, _, _, _,
-
-                // 01_EF - inner-lane
-                _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   0, 1, _, _,   _, _, _, _,   _, _, _, _,
-
-                // 23_AB/45_CD/67_EF - cross-lane
-                3, 0, 0, 0,   6, 0, 0, 0,   7, 0, 0, 0,   _, _, _, _,   3, 0, 0, 0,   6, 0, 0, 0,   7, 0, 0, 0,   _, _, _, _,
-
-                // 23_AB - inner-lane
-                4, 5, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   6, 7, 0, 1,   2, 3, 8, 9,   _, _, _, _,
-
-                // 23_CD - inner-lane
-                _, _, 6, 7,   12, 13, _, _,   _, _, _, _,   _, _, _, _,   10, 11, 4, 5,   _, _, _, _,   _, _, _, _,   6, 7, 12, 13,
-
-                // 23_EF - inner-lane
-                _, _, _, _,   _, _, 2, 3,   8, 9, _, _,   10, 11, 4, 5,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,
-
-                // 23_GH - inner-lane
-                _, _, _, _,   _, _, _, _,   _, _, 0, 1,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,
-
-                // 45_AB - inner-lane
-                _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   10, 11, _, _,   _, _, _, _,   _, _, _, _,
-
-                // 45_CD - inner-lane
-                _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   6, 7, 0, 1,   _, _, 2, 3,   8, 9, _, _,   _, _, _, _,
-
-                // 45_EF - cross-lane
-                1, 0, 0, 0,   2, 0, 0, 0,   5, 0, 0, 0,   _, _, _, _,   2, 0, 0, 0,   3, 0, 0, 0,   6, 0, 0, 0,   7, 0, 0, 0,
-
-                // 45_EF - inner-lane
-                2, 3, 8, 9,   _, _, _, _,   _, _, _, _,   10, 11, 4, 5,  _, _, _, _,   _, _, _, _,   _, _, 2, 3,   8, 9, _, _,
-
-                // 45_GH - inner-lane
-                _, _, _, _,   2, 3, 8, 9,   10, 11, 4, 5,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, 6, 7,
-
-                // 67_CD - inner-lane
-                _, _, _, _,   _, _, _, _,   _, _, 10, 11,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,
-
-                // 67_EF - inner-lane
-                _, _, _, _,   _, _, 6, 7,   0, 1, _, _,   2, 3, 8, 9,   _, _, _, _,   _, _, _, _,   10, 11, _, _,   _, _, _, _,
-
-                // 67_GH - inner-lane
-                8, 9, 10, 11,   4, 5, _, _,   _, _, _, _,   _, _, _, _,   2, 3, 8, 9,   10, 11, 4, 5,   _, _, 6, 7,   12, 13, 14, 15
+#pragma warning disable SA1515
+            /* 01 */
+            // [cr] crln_01_AB_CD
+            0, 0, 0, 0,   1, 0, 0, 0,   4, 0, 0, 0,   _, _, _, _,   1, 0, 0, 0,   2, 0, 0, 0,   4, 0, 0, 0,   5, 0, 0, 0,
+            // (in) AB
+            0, 1, 8, 9,   2, 3, 4, 5,   10, 11, _, _,   _, _, _, _,   12, 13, 2, 3,   4, 5, 14, 15,   _, _, _, _,   _, _, _, _,
+            // (in) CD
+            _, _, _, _,   _, _, _, _,   _, _, 0, 1,   8, 9, 2, 3,   _, _, _, _,   _, _, _, _,   0, 1, 10, 11,   _, _, _, _,
+            // [cr] crln_01_23_EF_23_CD
+            0, 0, 0, 0,   1, 0, 0, 0,   2, 0, 0, 0,   5, 0, 0, 0,   0, 0, 0, 0,   1, 0, 0, 0,   4, 0, 0, 0,   5, 0, 0, 0,
+            // (in) EF
+            _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   0, 1, 8, 9,
+
+            /* 23 */
+            // [cr] crln_23_AB_23_45_GH
+            2, 0, 0, 0,   3, 0, 0, 0,   6, 0, 0, 0,   7, 0, 0, 0,   0, 0, 0, 0,   1, 0, 0, 0,   4, 0, 0, 0,   5, 0, 0, 0,
+            // (in) AB
+            _, _, _, _,   _, _, 8, 9,   2, 3, 4, 5,   10, 11, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,
+            // (in) CDe
+            _, _, 12, 13,   6, 7, _, _,   _, _, _, _,   _, _, 8, 9,   14, 15, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,
+            // (in) EF
+            2, 3, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, 4, 5,   10, 11, _, _,   _, _, _, _,   12, 13, 6, 7,
+            // (in) GH
+            _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, 0, 1,   8, 9, 2, 3,   _, _, _, _,
+
+            /* 45 */
+            // (in) AB
+            _, _, _, _,   12, 13, 6, 7,   14, 15, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,
+            // [cr] crln_45_67_CD_45_EF
+            2, 0, 0, 0,   3, 0, 0, 0,   6, 0, 0, 0,   7, 0, 0, 0,   2, 0, 0, 0,   5, 0, 0, 0,   6, 0, 0, 0,   7, 0, 0, 0,
+            // (in) CD
+            8, 9, 2, 3,   _, _, _, _,   _, _, 4, 5,   10, 11, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, 12, 13,
+            // (in) EF
+            _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, 0, 1,   6, 7, _, _,   _, _, _, _,   _, _, 8, 9,   2, 3, _, _,
+            // (in) GH
+            _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, 4, 5,   10, 11, 12, 13,   6, 7, _, _,   _, _, _, _,
+
+            /* 67 */
+            // (in) CD
+            6, 7, 14, 15,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,   _, _, _, _,
+            // [cr] crln_67_EF_67_GH
+            2, 0, 0, 0,   3, 0, 0, 0,   5, 0, 0, 0,   6, 0, 0, 0,   3, 0, 0, 0,   6, 0, 0, 0,   7, 0, 0, 0,   _, _, _, _,
+            // (in) EF
+            _, _, _, _,   4, 5, 14, 15,   _, _, _, _,   _, _, _, _,   8, 9, 2, 3,   10, 11, _, _,   _, _, _, _,   _, _, _, _,
+            // (in) GH
+            _, _, _, _,   _, _, _, _,   0, 1, 10, 11,   12, 13, 2, 3,   _, _, _, _,   _, _, 0, 1,   6, 7, 8, 9,   2, 3, 10, 11,
+#pragma warning restore SA1515
         };
 
         /// <summary>
         /// Applies zig zag ordering for given 8x8 matrix using SSE cpu intrinsics.
         /// </summary>
         /// <param name="block">Input matrix.</param>
-        public static unsafe void ApplyZigZagOrderingSsse3(ref Block8x8 block)
+        public static unsafe void ApplyTransposingZigZagOrderingSsse3(ref Block8x8 block)
         {
             DebugGuard.IsTrue(Ssse3.IsSupported, "Ssse3 support is required to run this operation!");
 
-            fixed (byte* maskPtr = SseShuffleMasks)
+            fixed (byte* shuffleVectorsPtr = &MemoryMarshal.GetReference(SseShuffleMasks))
             {
                 Vector128<byte> rowA = block.V0.AsByte();
                 Vector128<byte> rowB = block.V1.AsByte();
@@ -142,73 +161,69 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
                 Vector128<byte> rowG = block.V6.AsByte();
                 Vector128<byte> rowH = block.V7.AsByte();
 
-                // row0 - A0  A1  B0  C0  B1  A2  A3  B2
-                Vector128<short> rowA0 = Ssse3.Shuffle(rowA, Sse2.LoadVector128(maskPtr + (16 * 0))).AsInt16();
-                Vector128<short> rowB0 = Ssse3.Shuffle(rowB, Sse2.LoadVector128(maskPtr + (16 * 1))).AsInt16();
-                Vector128<short> row0 = Sse2.Or(rowA0, rowB0);
-                Vector128<short> rowC0 = Ssse3.Shuffle(rowC, Sse2.LoadVector128(maskPtr + (16 * 2))).AsInt16();
-                row0 = Sse2.Or(row0, rowC0);
-
-                // row1 - C1  D0  E0  D1  C2  B3  A4  A5
-                Vector128<short> rowA1 = Ssse3.Shuffle(rowA, Sse2.LoadVector128(maskPtr + (16 * 3))).AsInt16();
-                Vector128<short> rowC1 = Ssse3.Shuffle(rowC, Sse2.LoadVector128(maskPtr + (16 * 4))).AsInt16();
-                Vector128<short> row1 = Sse2.Or(rowA1, rowC1);
-                Vector128<short> rowD1 = Ssse3.Shuffle(rowD, Sse2.LoadVector128(maskPtr + (16 * 5))).AsInt16();
-                row1 = Sse2.Or(row1, rowD1);
-                row1 = Sse2.Insert(row1.AsUInt16(), Sse2.Extract(rowB.AsUInt16(), 3), 5).AsInt16();
-                row1 = Sse2.Insert(row1.AsUInt16(), Sse2.Extract(rowE.AsUInt16(), 0), 2).AsInt16();
-
-                // row2
-                Vector128<short> rowE2 = Ssse3.Shuffle(rowE, Sse2.LoadVector128(maskPtr + (16 * 6))).AsInt16();
-                Vector128<short> rowF2 = Ssse3.Shuffle(rowF, Sse2.LoadVector128(maskPtr + (16 * 7))).AsInt16();
-                Vector128<short> row2 = Sse2.Or(rowE2, rowF2);
-                row2 = Sse2.Insert(row2.AsUInt16(), Sse2.Extract(rowB.AsUInt16(), 4), 0).AsInt16();
-                row2 = Sse2.Insert(row2.AsUInt16(), Sse2.Extract(rowC.AsUInt16(), 3), 1).AsInt16();
-                row2 = Sse2.Insert(row2.AsUInt16(), Sse2.Extract(rowD.AsUInt16(), 2), 2).AsInt16();
-                row2 = Sse2.Insert(row2.AsUInt16(), Sse2.Extract(rowG.AsUInt16(), 0), 5).AsInt16();
-
-                // row3
-                Vector128<short> rowA3 = Ssse3.Shuffle(rowA, Sse2.LoadVector128(maskPtr + (16 * 8))).AsInt16().AsInt16();
-                Vector128<short> rowB3 = Ssse3.Shuffle(rowB, Sse2.LoadVector128(maskPtr + (16 * 9))).AsInt16().AsInt16();
-                Vector128<short> row3 = Sse2.Or(rowA3, rowB3);
-                Vector128<short> rowC3 = Ssse3.Shuffle(rowC, Sse2.LoadVector128(maskPtr + (16 * 10))).AsInt16();
-                row3 = Sse2.Or(row3, rowC3);
-                Vector128<byte> shuffleRowD3EF = Sse2.LoadVector128(maskPtr + (16 * 11));
-                Vector128<short> rowD3 = Ssse3.Shuffle(rowD, shuffleRowD3EF).AsInt16();
-                row3 = Sse2.Or(row3, rowD3);
-
-                // row4
-                Vector128<short> rowE4 = Ssse3.Shuffle(rowE, shuffleRowD3EF).AsInt16();
-                Vector128<short> rowF4 = Ssse3.Shuffle(rowF, Sse2.LoadVector128(maskPtr + (16 * 12))).AsInt16();
-                Vector128<short> row4 = Sse2.Or(rowE4, rowF4);
-                Vector128<short> rowG4 = Ssse3.Shuffle(rowG, Sse2.LoadVector128(maskPtr + (16 * 13))).AsInt16();
-                row4 = Sse2.Or(row4, rowG4);
-                Vector128<short> rowH4 = Ssse3.Shuffle(rowH, Sse2.LoadVector128(maskPtr + (16 * 14))).AsInt16();
-                row4 = Sse2.Or(row4, rowH4);
-
-                // row5
-                Vector128<short> rowC5 = Ssse3.Shuffle(rowC, Sse2.LoadVector128(maskPtr + (16 * 15))).AsInt16();
-                Vector128<short> rowD5 = Ssse3.Shuffle(rowD, Sse2.LoadVector128(maskPtr + (16 * 16))).AsInt16();
-                Vector128<short> row5 = Sse2.Or(rowC5, rowD5);
-                row5 = Sse2.Insert(row5.AsUInt16(), Sse2.Extract(rowB.AsUInt16(), 7), 2).AsInt16();
-                row5 = Sse2.Insert(row5.AsUInt16(), Sse2.Extract(rowE.AsUInt16(), 5), 5).AsInt16();
-                row5 = Sse2.Insert(row5.AsUInt16(), Sse2.Extract(rowF.AsUInt16(), 4), 6).AsInt16();
-                row5 = Sse2.Insert(row5.AsUInt16(), Sse2.Extract(rowG.AsUInt16(), 3), 7).AsInt16();
-
-                // row6
-                Vector128<short> rowE6 = Ssse3.Shuffle(rowE, Sse2.LoadVector128(maskPtr + (16 * 17))).AsInt16();
-                Vector128<short> rowF6 = Ssse3.Shuffle(rowF, Sse2.LoadVector128(maskPtr + (16 * 18))).AsInt16();
-                Vector128<short> row6 = Sse2.Or(rowE6, rowF6);
-                Vector128<short> rowH6 = Ssse3.Shuffle(rowH, Sse2.LoadVector128(maskPtr + (16 * 19))).AsInt16();
-                row6 = Sse2.Or(row6, rowH6);
-                row6 = Sse2.Insert(row6.AsUInt16(), Sse2.Extract(rowD.AsUInt16(), 7), 5).AsInt16();
-                row6 = Sse2.Insert(row6.AsUInt16(), Sse2.Extract(rowG.AsUInt16(), 4), 2).AsInt16();
-
-                // row7
-                Vector128<short> rowG7 = Ssse3.Shuffle(rowG, Sse2.LoadVector128(maskPtr + (16 * 20))).AsInt16();
-                Vector128<short> rowH7 = Ssse3.Shuffle(rowH, Sse2.LoadVector128(maskPtr + (16 * 21))).AsInt16();
-                Vector128<short> row7 = Sse2.Or(rowG7, rowH7);
-                row7 = Sse2.Insert(row7.AsUInt16(), Sse2.Extract(rowF.AsUInt16(), 7), 4).AsInt16();
+                // row0 - A0 B0 A1 A2 B1 C0 D0 C1
+                Vector128<short> row0_A = Ssse3.Shuffle(rowA, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 0))).AsInt16();
+                Vector128<short> row0_B = Ssse3.Shuffle(rowB, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 1))).AsInt16();
+                Vector128<short> row0_C = Ssse3.Shuffle(rowC, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 2))).AsInt16();
+                Vector128<short> row0 = Sse2.Or(Sse2.Or(row0_A, row0_B), row0_C);
+                row0 = Sse2.Insert(row0.AsUInt16(), Sse2.Extract(rowD.AsUInt16(), 0), 6).AsInt16();
+
+                // row1 - B2 A3 A4 B3 C2 D1 E0 F0
+                Vector128<short> row1_A = Ssse3.Shuffle(rowA, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 3))).AsInt16();
+                Vector128<short> row1_B = Ssse3.Shuffle(rowB, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 4))).AsInt16();
+                Vector128<short> row1 = Sse2.Or(row1_A, row1_B);
+                row1 = Sse2.Insert(row1.AsUInt16(), Sse2.Extract(rowC.AsUInt16(), 2), 4).AsInt16();
+                row1 = Sse2.Insert(row1.AsUInt16(), Sse2.Extract(rowD.AsUInt16(), 1), 5).AsInt16();
+                row1 = Sse2.Insert(row1.AsUInt16(), Sse2.Extract(rowE.AsUInt16(), 0), 6).AsInt16();
+                row1 = Sse2.Insert(row1.AsUInt16(), Sse2.Extract(rowF.AsUInt16(), 0), 7).AsInt16();
+
+                // row2 - E1 D2 C3 B4 A5 A6 B5 C4
+                Vector128<short> row2_A = Ssse3.Shuffle(rowA, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 5))).AsInt16();
+                Vector128<short> row2_B = Ssse3.Shuffle(rowB, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 6))).AsInt16();
+                Vector128<short> row2_C = Ssse3.Shuffle(rowC, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 7))).AsInt16();
+                Vector128<short> row2 = Sse2.Or(Sse2.Or(row2_A, row2_B), row2_C);
+                row2 = Sse2.Insert(row2.AsUInt16(), Sse2.Extract(rowD.AsUInt16(), 2), 1).AsInt16();
+                row2 = Sse2.Insert(row2.AsUInt16(), Sse2.Extract(rowE.AsUInt16(), 1), 0).AsInt16();
+
+                // row3 - D3 E2 F1 G0 H0 G1 F2 E3
+                Vector128<short> row3_E = Ssse3.Shuffle(rowE, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 8))).AsInt16();
+                Vector128<short> row3_F = Ssse3.Shuffle(rowF, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 9))).AsInt16();
+                Vector128<short> row3_G = Ssse3.Shuffle(rowG, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 10))).AsInt16();
+                Vector128<short> row3 = Sse2.Or(Sse2.Or(row3_E, row3_F), row3_G);
+                row3 = Sse2.Insert(row3.AsUInt16(), Sse2.Extract(rowD.AsUInt16(), 3), 0).AsInt16();
+                row3 = Sse2.Insert(row3.AsUInt16(), Sse2.Extract(rowH.AsUInt16(), 0), 4).AsInt16();
+
+                // row4 - D4 C5 B6 A7 B7 C6 D5 E4
+                Vector128<short> row4_B = Ssse3.Shuffle(rowB, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 11))).AsInt16();
+                Vector128<short> row4_C = Ssse3.Shuffle(rowC, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 12))).AsInt16();
+                Vector128<short> row4_D = Ssse3.Shuffle(rowD, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 13))).AsInt16();
+                Vector128<short> row4 = Sse2.Or(Sse2.Or(row4_B, row4_C), row4_D);
+                row4 = Sse2.Insert(row4.AsUInt16(), Sse2.Extract(rowA.AsUInt16(), 7), 3).AsInt16();
+                row4 = Sse2.Insert(row4.AsUInt16(), Sse2.Extract(rowE.AsUInt16(), 4), 7).AsInt16();
+
+                // row5 - F3 G2 H1 H2 G3 F4 E5 D6
+                Vector128<short> row5_F = Ssse3.Shuffle(rowF, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 14))).AsInt16();
+                Vector128<short> row5_G = Ssse3.Shuffle(rowG, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 15))).AsInt16();
+                Vector128<short> row5_H = Ssse3.Shuffle(rowH, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 16))).AsInt16();
+                Vector128<short> row5 = Sse2.Or(Sse2.Or(row5_F, row5_G), row5_H);
+                row5 = Sse2.Insert(row5.AsUInt16(), Sse2.Extract(rowD.AsUInt16(), 6), 7).AsInt16();
+                row5 = Sse2.Insert(row5.AsUInt16(), Sse2.Extract(rowE.AsUInt16(), 5), 6).AsInt16();
+
+                // row6 - C7 D7 E6 F5 G4 H3 H4 G5
+                Vector128<short> row6_G = Ssse3.Shuffle(rowG, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 17))).AsInt16();
+                Vector128<short> row6_H = Ssse3.Shuffle(rowH, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 18))).AsInt16();
+                Vector128<short> row6 = Sse2.Or(row6_G, row6_H);
+                row6 = Sse2.Insert(row6.AsUInt16(), Sse2.Extract(rowC.AsUInt16(), 7), 0).AsInt16();
+                row6 = Sse2.Insert(row6.AsUInt16(), Sse2.Extract(rowD.AsUInt16(), 7), 1).AsInt16();
+                row6 = Sse2.Insert(row6.AsUInt16(), Sse2.Extract(rowE.AsUInt16(), 6), 2).AsInt16();
+                row6 = Sse2.Insert(row6.AsUInt16(), Sse2.Extract(rowF.AsUInt16(), 5), 3).AsInt16();
+
+                // row7 - F6 E7 F7 G6 H5 H6 G7 H7
+                Vector128<short> row7_F = Ssse3.Shuffle(rowF, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 19))).AsInt16();
+                Vector128<short> row7_G = Ssse3.Shuffle(rowG, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 20))).AsInt16();
+                Vector128<short> row7_H = Ssse3.Shuffle(rowH, Sse2.LoadVector128(shuffleVectorsPtr + (16 * 21))).AsInt16();
+                Vector128<short> row7 = Sse2.Or(Sse2.Or(row7_F, row7_G), row7_H);
+                row7 = Sse2.Insert(row7.AsUInt16(), Sse2.Extract(rowE.AsUInt16(), 7), 1).AsInt16();
 
                 block.V0 = row0;
                 block.V1 = row1;
@@ -225,69 +240,61 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
         /// Applies zig zag ordering for given 8x8 matrix using AVX cpu intrinsics.
         /// </summary>
         /// <param name="block">Input matrix.</param>
-        public static unsafe void ApplyZigZagOrderingAvx2(ref Block8x8 block)
+        public static unsafe void ApplyTransposingZigZagOrderingAvx2(ref Block8x8 block)
         {
             DebugGuard.IsTrue(Avx2.IsSupported, "Avx2 support is required to run this operation!");
 
-            fixed (byte* shuffleVectorsPtr = AvxShuffleMasks)
+            fixed (byte* shuffleVectorsPtr = &MemoryMarshal.GetReference(AvxShuffleMasks))
             {
-                Vector256<byte> rowsAB = block.V01.AsByte();
-                Vector256<byte> rowsCD = block.V23.AsByte();
-                Vector256<byte> rowsEF = block.V45.AsByte();
-                Vector256<byte> rowsGH = block.V67.AsByte();
-
-                // rows 0 1
-                Vector256<int> rows_AB01_EF01_CD23_shuffleMask = Avx.LoadVector256(shuffleVectorsPtr + (0 * 32)).AsInt32();
-                Vector256<byte> row01_AB = Avx2.PermuteVar8x32(rowsAB.AsInt32(), rows_AB01_EF01_CD23_shuffleMask).AsByte();
+                Vector256<byte> rowAB = block.V01.AsByte();
+                Vector256<byte> rowCD = block.V23.AsByte();
+                Vector256<byte> rowEF = block.V45.AsByte();
+                Vector256<byte> rowGH = block.V67.AsByte();
+
+                /* row01 - A0 B0 A1 A2 B1 C0 D0 C1 | B2 A3 A4 B3 C2 D1 E0 F0 */
+                Vector256<int> crln_01_AB_CD = Avx.LoadVector256(shuffleVectorsPtr + (0 * 32)).AsInt32();
+                Vector256<byte> row01_AB = Avx2.PermuteVar8x32(rowAB.AsInt32(), crln_01_AB_CD).AsByte();
                 row01_AB = Avx2.Shuffle(row01_AB, Avx.LoadVector256(shuffleVectorsPtr + (1 * 32))).AsByte();
-
-                Vector256<int> rows_CD01_GH23_shuffleMask = Avx.LoadVector256(shuffleVectorsPtr + (2 * 32)).AsInt32();
-                Vector256<byte> row01_CD = Avx2.PermuteVar8x32(rowsCD.AsInt32(), rows_CD01_GH23_shuffleMask).AsByte();
-                row01_CD = Avx2.Shuffle(row01_CD, Avx.LoadVector256(shuffleVectorsPtr + (3 * 32))).AsByte();
-
-                Vector256<byte> row0123_EF = Avx2.PermuteVar8x32(rowsEF.AsInt32(), rows_AB01_EF01_CD23_shuffleMask).AsByte();
-                Vector256<byte> row01_EF = Avx2.Shuffle(row0123_EF, Avx.LoadVector256(shuffleVectorsPtr + (4 * 32))).AsByte();
-
-                Vector256<byte> row01 = Avx2.Or(Avx2.Or(row01_AB, row01_CD), row01_EF);
-
-                // rows 2 3
-                Vector256<int> rows_AB23_CD45_EF67_shuffleMask = Avx.LoadVector256(shuffleVectorsPtr + (5 * 32)).AsInt32();
-                Vector256<byte> row2345_AB = Avx2.PermuteVar8x32(rowsAB.AsInt32(), rows_AB23_CD45_EF67_shuffleMask).AsByte();
-                Vector256<byte> row23_AB = Avx2.Shuffle(row2345_AB, Avx.LoadVector256(shuffleVectorsPtr + (6 * 32))).AsByte();
-
-                Vector256<byte> row23_CD = Avx2.PermuteVar8x32(rowsCD.AsInt32(), rows_AB01_EF01_CD23_shuffleMask).AsByte();
+                Vector256<byte> row01_CD = Avx2.PermuteVar8x32(rowCD.AsInt32(), crln_01_AB_CD).AsByte();
+                row01_CD = Avx2.Shuffle(row01_CD, Avx.LoadVector256(shuffleVectorsPtr + (2 * 32))).AsByte();
+                Vector256<int> crln_01_23_EF_23_CD = Avx.LoadVector256(shuffleVectorsPtr + (3 * 32)).AsInt32();
+                Vector256<byte> row01_23_EF = Avx2.PermuteVar8x32(rowEF.AsInt32(), crln_01_23_EF_23_CD).AsByte();
+                Vector256<byte> row01_EF = Avx2.Shuffle(row01_23_EF, Avx.LoadVector256(shuffleVectorsPtr + (4 * 32))).AsByte();
+
+                Vector256<byte> row01 = Avx2.Or(row01_AB, Avx2.Or(row01_CD, row01_EF));
+
+                /* row23 - E1 D2 C3 B4 A5 A6 B5 C4 | D3 E2 F1 G0 H0 G1 F2 E3 */
+                Vector256<int> crln_23_AB_23_45_GH = Avx.LoadVector256(shuffleVectorsPtr + (5 * 32)).AsInt32();
+                Vector256<byte> row23_45_AB = Avx2.PermuteVar8x32(rowAB.AsInt32(), crln_23_AB_23_45_GH).AsByte();
+                Vector256<byte> row23_AB = Avx2.Shuffle(row23_45_AB, Avx.LoadVector256(shuffleVectorsPtr + (6 * 32))).AsByte();
+                Vector256<byte> row23_CD = Avx2.PermuteVar8x32(rowCD.AsInt32(), crln_01_23_EF_23_CD).AsByte();
                 row23_CD = Avx2.Shuffle(row23_CD, Avx.LoadVector256(shuffleVectorsPtr + (7 * 32))).AsByte();
-
-                Vector256<byte> row23_EF = Avx2.Shuffle(row0123_EF, Avx.LoadVector256(shuffleVectorsPtr + (8 * 32))).AsByte();
-
-                Vector256<byte> row2345_GH = Avx2.PermuteVar8x32(rowsGH.AsInt32(), rows_CD01_GH23_shuffleMask).AsByte();
-                Vector256<byte> row23_GH = Avx2.Shuffle(row2345_GH, Avx.LoadVector256(shuffleVectorsPtr + (9 * 32)).AsByte());
+                Vector256<byte> row23_EF = Avx2.Shuffle(row01_23_EF, Avx.LoadVector256(shuffleVectorsPtr + (8 * 32))).AsByte();
+                Vector256<byte> row23_45_GH = Avx2.PermuteVar8x32(rowGH.AsInt32(), crln_23_AB_23_45_GH).AsByte();
+                Vector256<byte> row23_GH = Avx2.Shuffle(row23_45_GH, Avx.LoadVector256(shuffleVectorsPtr + (9 * 32))).AsByte();
 
                 Vector256<byte> row23 = Avx2.Or(Avx2.Or(row23_AB, row23_CD), Avx2.Or(row23_EF, row23_GH));
 
-                // rows 4 5
-                Vector256<byte> row45_AB = Avx2.Shuffle(row2345_AB, Avx.LoadVector256(shuffleVectorsPtr + (10 * 32)).AsByte());
-                Vector256<byte> row4567_CD = Avx2.PermuteVar8x32(rowsCD.AsInt32(), rows_AB23_CD45_EF67_shuffleMask).AsByte();
-                Vector256<byte> row45_CD = Avx2.Shuffle(row4567_CD, Avx.LoadVector256(shuffleVectorsPtr + (11 * 32)).AsByte());
-
-                Vector256<int> rows_EF45_GH67_shuffleMask = Avx.LoadVector256(shuffleVectorsPtr + (12 * 32)).AsInt32();
-                Vector256<byte> row45_EF = Avx2.PermuteVar8x32(rowsEF.AsInt32(), rows_EF45_GH67_shuffleMask).AsByte();
-                row45_EF = Avx2.Shuffle(row45_EF, Avx.LoadVector256(shuffleVectorsPtr + (13 * 32)).AsByte());
-
-                Vector256<byte> row45_GH = Avx2.Shuffle(row2345_GH, Avx.LoadVector256(shuffleVectorsPtr + (14 * 32)).AsByte());
+                /* row45 - D4 C5 B6 A7 B7 C6 D5 E4 | F3 G2 H1 H2 G3 F4 E5 D6 */
+                Vector256<byte> row45_AB = Avx2.Shuffle(row23_45_AB, Avx.LoadVector256(shuffleVectorsPtr + (10 * 32))).AsByte();
+                Vector256<int> crln_45_67_CD_45_EF = Avx.LoadVector256(shuffleVectorsPtr + (11 * 32)).AsInt32();
+                Vector256<byte> row45_67_CD = Avx2.PermuteVar8x32(rowCD.AsInt32(), crln_45_67_CD_45_EF).AsByte();
+                Vector256<byte> row45_CD = Avx2.Shuffle(row45_67_CD, Avx.LoadVector256(shuffleVectorsPtr + (12 * 32))).AsByte();
+                Vector256<byte> row45_EF = Avx2.PermuteVar8x32(rowEF.AsInt32(), crln_45_67_CD_45_EF).AsByte();
+                row45_EF = Avx2.Shuffle(row45_EF, Avx.LoadVector256(shuffleVectorsPtr + (13 * 32))).AsByte();
+                Vector256<byte> row45_GH = Avx2.Shuffle(row23_45_GH, Avx.LoadVector256(shuffleVectorsPtr + (14 * 32))).AsByte();
 
                 Vector256<byte> row45 = Avx2.Or(Avx2.Or(row45_AB, row45_CD), Avx2.Or(row45_EF, row45_GH));
 
-                // rows 6 7
-                Vector256<byte> row67_CD = Avx2.Shuffle(row4567_CD, Avx.LoadVector256(shuffleVectorsPtr + (15 * 32)).AsByte());
-
-                Vector256<byte> row67_EF = Avx2.PermuteVar8x32(rowsEF.AsInt32(), rows_AB23_CD45_EF67_shuffleMask).AsByte();
-                row67_EF = Avx2.Shuffle(row67_EF, Avx.LoadVector256(shuffleVectorsPtr + (16 * 32)).AsByte());
-
-                Vector256<byte> row67_GH = Avx2.PermuteVar8x32(rowsGH.AsInt32(), rows_EF45_GH67_shuffleMask).AsByte();
-                row67_GH = Avx2.Shuffle(row67_GH, Avx.LoadVector256(shuffleVectorsPtr + (17 * 32)).AsByte());
+                /* row67 - C7 D7 E6 F5 G4 H3 H4 G5 | F6 E7 F7 G6 H5 H6 G7 H7 */
+                Vector256<byte> row67_CD = Avx2.Shuffle(row45_67_CD, Avx.LoadVector256(shuffleVectorsPtr + (15 * 32))).AsByte();
+                Vector256<int> crln_67_EF_67_GH = Avx.LoadVector256(shuffleVectorsPtr + (16 * 32)).AsInt32();
+                Vector256<byte> row67_EF = Avx2.PermuteVar8x32(rowEF.AsInt32(), crln_67_EF_67_GH).AsByte();
+                row67_EF = Avx2.Shuffle(row67_EF, Avx.LoadVector256(shuffleVectorsPtr + (17 * 32))).AsByte();
+                Vector256<byte> row67_GH = Avx2.PermuteVar8x32(rowGH.AsInt32(), crln_67_EF_67_GH).AsByte();
+                row67_GH = Avx2.Shuffle(row67_GH, Avx.LoadVector256(shuffleVectorsPtr + (18 * 32))).AsByte();
 
-                Vector256<byte> row67 = Avx2.Or(Avx2.Or(row67_CD, row67_EF), row67_GH);
+                Vector256<byte> row67 = Avx2.Or(row67_CD, Avx2.Or(row67_EF, row67_GH));
 
                 block.V01 = row01.AsInt16();
                 block.V23 = row23.AsInt16();

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -17,6 +17,7 @@ using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.Metadata.Profiles.Icc;
 using SixLabors.ImageSharp.Metadata.Profiles.Iptc;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg
@@ -46,7 +47,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <summary>
         /// Whether the image has an EXIF marker.
         /// </summary>
-        private bool isExif;
+        private bool hasExif;
 
         /// <summary>
         /// Contains exif data.
@@ -56,7 +57,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <summary>
         /// Whether the image has an ICC marker.
         /// </summary>
-        private bool isIcc;
+        private bool hasIcc;
 
         /// <summary>
         /// Contains ICC data.
@@ -66,13 +67,23 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <summary>
         /// Whether the image has a IPTC data.
         /// </summary>
-        private bool isIptc;
+        private bool hasIptc;
 
         /// <summary>
         /// Contains IPTC data.
         /// </summary>
         private byte[] iptcData;
 
+        /// <summary>
+        /// Whether the image has a XMP data.
+        /// </summary>
+        private bool hasXmp;
+
+        /// <summary>
+        /// Contains XMP data.
+        /// </summary>
+        private byte[] xmpData;
+
         /// <summary>
         /// Contains information about the JFIF marker.
         /// </summary>
@@ -183,6 +194,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             this.InitExifProfile();
             this.InitIccProfile();
             this.InitIptcProfile();
+            this.InitXmpProfile();
             this.InitDerivedMetadataProperties();
 
             return new Image<TPixel>(
@@ -198,6 +210,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             this.InitExifProfile();
             this.InitIccProfile();
             this.InitIptcProfile();
+            this.InitXmpProfile();
             this.InitDerivedMetadataProperties();
 
             Size pixelSize = this.Frame.PixelSize;
@@ -472,7 +485,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                     : JpegColorSpace.Cmyk;
             }
 
-            JpegThrowHelper.ThrowInvalidImageContentException($"Unsupported color mode. Supported component counts 1, 3, and 4; found {componentCount}");
+            JpegThrowHelper.ThrowNotSupportedComponentCount(componentCount);
             return default;
         }
 
@@ -539,7 +552,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// </summary>
         private void InitExifProfile()
         {
-            if (this.isExif)
+            if (this.hasExif)
             {
                 this.Metadata.ExifProfile = new ExifProfile(this.exifData);
             }
@@ -550,7 +563,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// </summary>
         private void InitIccProfile()
         {
-            if (this.isIcc)
+            if (this.hasIcc)
             {
                 var profile = new IccProfile(this.iccData);
                 if (profile.CheckIsValid())
@@ -565,13 +578,25 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// </summary>
         private void InitIptcProfile()
         {
-            if (this.isIptc)
+            if (this.hasIptc)
             {
                 var profile = new IptcProfile(this.iptcData);
                 this.Metadata.IptcProfile = profile;
             }
         }
 
+        /// <summary>
+        /// Initializes the XMP profile.
+        /// </summary>
+        private void InitXmpProfile()
+        {
+            if (this.hasXmp)
+            {
+                var profile = new XmpProfile(this.xmpData);
+                this.Metadata.XmpProfile = profile;
+            }
+        }
+
         /// <summary>
         /// Assigns derived metadata properties to <see cref="Metadata"/>, eg. horizontal and vertical resolution if it has a JFIF header.
         /// </summary>
@@ -583,7 +608,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                 this.Metadata.VerticalResolution = this.jFif.YDensity;
                 this.Metadata.ResolutionUnits = this.jFif.DensityUnits;
             }
-            else if (this.isExif)
+            else if (this.hasExif)
             {
                 double horizontalValue = this.GetExifResolutionValue(ExifTag.XResolution);
                 double verticalValue = this.GetExifResolutionValue(ExifTag.YResolution);
@@ -625,7 +650,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         private void ProcessApplicationHeaderMarker(BufferedReadStream stream, int remaining)
         {
             // We can only decode JFif identifiers.
-            if (remaining < JFifMarker.Length)
+            // Some images contain multiple JFIF markers (Issue 1932) so we check to see
+            // if it's already been read.
+            if (remaining < JFifMarker.Length || (!this.jFif.Equals(default)))
             {
                 // Skip the application header length
                 stream.Skip(remaining);
@@ -656,8 +683,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <param name="remaining">The remaining bytes in the segment block.</param>
         private void ProcessApp1Marker(BufferedReadStream stream, int remaining)
         {
-            const int Exif00 = 6;
-            if (remaining < Exif00 || this.IgnoreMetadata)
+            const int ExifMarkerLength = 6;
+            const int XmpMarkerLength = 29;
+            if (remaining < ExifMarkerLength || this.IgnoreMetadata)
             {
                 // Skip the application header length
                 stream.Skip(remaining);
@@ -669,23 +697,55 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                 JpegThrowHelper.ThrowInvalidImageContentException("Bad App1 Marker length.");
             }
 
-            byte[] profile = new byte[remaining];
-            stream.Read(profile, 0, remaining);
+            // XMP marker is the longest, so read at least that many bytes into temp.
+            stream.Read(this.temp, 0, ExifMarkerLength);
 
-            if (ProfileResolver.IsProfile(profile, ProfileResolver.ExifMarker))
+            if (ProfileResolver.IsProfile(this.temp, ProfileResolver.ExifMarker))
             {
-                this.isExif = true;
+                remaining -= ExifMarkerLength;
+                this.hasExif = true;
+                byte[] profile = new byte[remaining];
+                stream.Read(profile, 0, remaining);
+
                 if (this.exifData is null)
                 {
-                    // The first 6 bytes (Exif00) will be skipped, because this is Jpeg specific
-                    this.exifData = profile.AsSpan(Exif00).ToArray();
+                    this.exifData = profile;
                 }
                 else
                 {
                     // If the EXIF information exceeds 64K, it will be split over multiple APP1 markers
-                    this.ExtendProfile(ref this.exifData, profile.AsSpan(Exif00).ToArray());
+                    this.ExtendProfile(ref this.exifData, profile);
                 }
+
+                remaining = 0;
             }
+
+            if (ProfileResolver.IsProfile(this.temp, ProfileResolver.XmpMarker.Slice(0, ExifMarkerLength)))
+            {
+                stream.Read(this.temp, 0, XmpMarkerLength - ExifMarkerLength);
+                remaining -= XmpMarkerLength;
+                if (ProfileResolver.IsProfile(this.temp, ProfileResolver.XmpMarker.Slice(ExifMarkerLength)))
+                {
+                    this.hasXmp = true;
+                    byte[] profile = new byte[remaining];
+                    stream.Read(profile, 0, remaining);
+
+                    if (this.xmpData is null)
+                    {
+                        this.xmpData = profile;
+                    }
+                    else
+                    {
+                        // If the XMP information exceeds 64K, it will be split over multiple APP1 markers
+                        this.ExtendProfile(ref this.xmpData, profile);
+                    }
+
+                    remaining = 0;
+                }
+            }
+
+            // Skip over any remaining bytes of this header.
+            stream.Skip(remaining);
         }
 
         /// <summary>
@@ -709,7 +769,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
 
             if (ProfileResolver.IsProfile(identifier, ProfileResolver.IccMarker))
             {
-                this.isIcc = true;
+                this.hasIcc = true;
                 byte[] profile = new byte[remaining];
                 stream.Read(profile, 0, remaining);
 
@@ -768,7 +828,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                         int dataStartIdx = 2 + resourceBlockNameLength + 4;
                         if (resourceDataSize > 0 && blockDataSpan.Length >= dataStartIdx + resourceDataSize)
                         {
-                            this.isIptc = true;
+                            this.hasIptc = true;
                             this.iptcData = blockDataSpan.Slice(dataStartIdx, resourceDataSize).ToArray();
                             break;
                         }
@@ -788,6 +848,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                     }
                 }
             }
+            else
+            {
+                // If the profile is unknown skip over the rest of it.
+                stream.Skip(remaining);
+            }
         }
 
         /// <summary>
@@ -998,6 +1063,14 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             // 1 byte: Number of components
             byte componentCount = this.temp[5];
 
+            // Validate: componentCount more than 4 can lead to a buffer overflow during stream
+            // reading so we must limit it to 4
+            // We do not support jpeg images with more than 4 components anyway
+            if (componentCount > 4)
+            {
+                JpegThrowHelper.ThrowNotSupportedComponentCount(componentCount);
+            }
+
             this.Frame = new JpegFrame(frameMarker, precision, frameWidth, frameHeight, componentCount);
 
             remaining -= length;
@@ -1087,12 +1160,18 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <param name="remaining">The remaining bytes in the segment block.</param>
         private void ProcessDefineHuffmanTablesMarker(BufferedReadStream stream, int remaining)
         {
-            int length = remaining;
+            const int codeLengthsByteSize = 17;
+            const int codeValuesMaxByteSize = 256;
+            const int totalBufferSize = codeLengthsByteSize + codeValuesMaxByteSize + HuffmanTable.WorkspaceByteSize;
 
-            using (IMemoryOwner<byte> huffmanData = this.Configuration.MemoryAllocator.Allocate<byte>(256, AllocationOptions.Clean))
+            int length = remaining;
+            using (IMemoryOwner<byte> buffer = this.Configuration.MemoryAllocator.Allocate<byte>(totalBufferSize))
             {
-                Span<byte> huffmanDataSpan = huffmanData.GetSpan();
-                ref byte huffmanDataRef = ref MemoryMarshal.GetReference(huffmanDataSpan);
+                Span<byte> bufferSpan = buffer.GetSpan();
+                Span<byte> huffmanLegthsSpan = bufferSpan.Slice(0, codeLengthsByteSize);
+                Span<byte> huffmanValuesSpan = bufferSpan.Slice(codeLengthsByteSize, codeValuesMaxByteSize);
+                Span<uint> tableWorkspace = MemoryMarshal.Cast<byte, uint>(bufferSpan.Slice(codeLengthsByteSize + codeValuesMaxByteSize));
+
                 for (int i = 2; i < remaining;)
                 {
                     byte huffmanTableSpec = (byte)stream.ReadByte();
@@ -1102,49 +1181,40 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                     // Types 0..1 DC..AC
                     if (tableType > 1)
                     {
-                        JpegThrowHelper.ThrowInvalidImageContentException($"Bad huffman table type: {tableType}");
+                        JpegThrowHelper.ThrowInvalidImageContentException($"Bad huffman table type: {tableType}.");
                     }
 
                     // Max tables of each type
                     if (tableIndex > 3)
                     {
-                        JpegThrowHelper.ThrowInvalidImageContentException($"Bad huffman table index: {tableIndex}");
+                        JpegThrowHelper.ThrowInvalidImageContentException($"Bad huffman table index: {tableIndex}.");
                     }
 
-                    stream.Read(huffmanDataSpan, 0, 16);
+                    stream.Read(huffmanLegthsSpan, 1, 16);
 
-                    using (IMemoryOwner<byte> codeLengths = this.Configuration.MemoryAllocator.Allocate<byte>(17, AllocationOptions.Clean))
+                    int codeLengthSum = 0;
+                    for (int j = 1; j < 17; j++)
                     {
-                        Span<byte> codeLengthsSpan = codeLengths.GetSpan();
-                        ref byte codeLengthsRef = ref MemoryMarshal.GetReference(codeLengthsSpan);
-                        int codeLengthSum = 0;
-
-                        for (int j = 1; j < 17; j++)
-                        {
-                            codeLengthSum += Unsafe.Add(ref codeLengthsRef, j) = Unsafe.Add(ref huffmanDataRef, j - 1);
-                        }
+                        codeLengthSum += huffmanLegthsSpan[j];
+                    }
 
-                        length -= 17;
+                    length -= 17;
 
-                        if (codeLengthSum > 256 || codeLengthSum > length)
-                        {
-                            JpegThrowHelper.ThrowInvalidImageContentException("Huffman table has excessive length.");
-                        }
+                    if (codeLengthSum > 256 || codeLengthSum > length)
+                    {
+                        JpegThrowHelper.ThrowInvalidImageContentException("Huffman table has excessive length.");
+                    }
 
-                        using (IMemoryOwner<byte> huffmanValues = this.Configuration.MemoryAllocator.Allocate<byte>(256, AllocationOptions.Clean))
-                        {
-                            Span<byte> huffmanValuesSpan = huffmanValues.GetSpan();
-                            stream.Read(huffmanValuesSpan, 0, codeLengthSum);
+                    stream.Read(huffmanValuesSpan, 0, codeLengthSum);
 
-                            i += 17 + codeLengthSum;
+                    i += 17 + codeLengthSum;
 
-                            this.scanDecoder.BuildHuffmanTable(
-                                tableType,
-                                tableIndex,
-                                codeLengthsSpan,
-                                huffmanValuesSpan);
-                        }
-                    }
+                    this.scanDecoder.BuildHuffmanTable(
+                        tableType,
+                        tableIndex,
+                        huffmanLegthsSpan,
+                        huffmanValuesSpan.Slice(0, codeLengthSum),
+                        tableWorkspace);
                 }
             }
         }

src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs

@@ -14,6 +14,7 @@ using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.Metadata.Profiles.Icc;
 using SixLabors.ImageSharp.Metadata.Profiles.Iptc;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg
@@ -109,7 +110,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                 this.WriteJfifApplicationHeader(metadata);
             }
 
-            // Write Exif, ICC and IPTC profiles
+            // Write Exif, XMP, ICC and IPTC profiles
             this.WriteProfiles(metadata);
 
             if (this.colorType == JpegColorType.Rgb)
@@ -466,6 +467,54 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             this.outputStream.Write(data, 0, data.Length);
         }
 
+        /// <summary>
+        /// Writes the XMP metadata.
+        /// </summary>
+        /// <param name="xmpProfile">The XMP metadata to write.</param>
+        /// <exception cref="ImageFormatException">
+        /// Thrown if the XMP profile size exceeds the limit of 65533 bytes.
+        /// </exception>
+        private void WriteXmpProfile(XmpProfile xmpProfile)
+        {
+            if (xmpProfile is null)
+            {
+                return;
+            }
+
+            const int XmpOverheadLength = 29;
+            const int Max = 65533;
+            const int MaxData = Max - XmpOverheadLength;
+
+            byte[] data = xmpProfile.Data;
+
+            if (data is null || data.Length == 0)
+            {
+                return;
+            }
+
+            int dataLength = data.Length;
+            int offset = 0;
+
+            while (dataLength > 0)
+            {
+                int length = dataLength; // Number of bytes to write.
+
+                if (length > MaxData)
+                {
+                    length = MaxData;
+                }
+
+                dataLength -= length;
+
+                int app1Length = 2 + ProfileResolver.XmpMarker.Length + length;
+                this.WriteApp1Header(app1Length);
+                this.outputStream.Write(ProfileResolver.XmpMarker);
+                this.outputStream.Write(data, offset, length);
+
+                offset += length;
+            }
+        }
+
         /// <summary>
         /// Writes the App1 header.
         /// </summary>
@@ -579,8 +628,14 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                 return;
             }
 
+            // For compatibility, place the profiles in the following order:
+            // - APP1 EXIF
+            // - APP1 XMP
+            // - APP2 ICC
+            // - APP13 IPTC
             metadata.SyncProfiles();
             this.WriteExifProfile(metadata.ExifProfile);
+            this.WriteXmpProfile(metadata.XmpProfile);
             this.WriteIccProfile(metadata.IccProfile);
             this.WriteIptcProfile(metadata.IptcProfile);
         }

src/ImageSharp/Formats/Jpeg/JpegThrowHelper.cs

@@ -45,5 +45,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
 
         [MethodImpl(InliningOptions.ColdPath)]
         public static void ThrowDimensionsTooLarge(int width, int height) => throw new ImageFormatException($"Image is too large to encode at {width}x{height} for JPEG format.");
+
+        [MethodImpl(InliningOptions.ColdPath)]
+        public static void ThrowNotSupportedComponentCount(int componentCount) => throw new NotSupportedException($"Images with {componentCount} components are not supported.");
     }
 }

src/ImageSharp/Formats/PixelTypeInfo.cs

@@ -15,8 +15,17 @@ namespace SixLabors.ImageSharp.Formats
         /// Initializes a new instance of the <see cref="PixelTypeInfo"/> class.
         /// </summary>
         /// <param name="bitsPerPixel">Color depth, in number of bits per pixel.</param>
-        /// <param name="alpha">Tthe pixel alpha transparency behavior.</param>
-        internal PixelTypeInfo(int bitsPerPixel, PixelAlphaRepresentation? alpha = null)
+        public PixelTypeInfo(int bitsPerPixel)
+        {
+            this.BitsPerPixel = bitsPerPixel;
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PixelTypeInfo"/> class.
+        /// </summary>
+        /// <param name="bitsPerPixel">Color depth, in number of bits per pixel.</param>
+        /// <param name="alpha">The pixel alpha transparency behavior.</param>
+        public PixelTypeInfo(int bitsPerPixel, PixelAlphaRepresentation alpha)
         {
             this.BitsPerPixel = bitsPerPixel;
             this.AlphaRepresentation = alpha;

src/ImageSharp/Formats/Png/PngConstants.cs

@@ -78,5 +78,29 @@ namespace SixLabors.ImageSharp.Formats.Png
             0x1A, // EOF
             0x0A // LF
         };
+
+        /// <summary>
+        /// Gets the keyword of the XMP metadata, encoded in an iTXT chunk.
+        /// </summary>
+        public static ReadOnlySpan<byte> XmpKeyword => new byte[]
+        {
+            (byte)'X',
+            (byte)'M',
+            (byte)'L',
+            (byte)':',
+            (byte)'c',
+            (byte)'o',
+            (byte)'m',
+            (byte)'.',
+            (byte)'a',
+            (byte)'d',
+            (byte)'o',
+            (byte)'b',
+            (byte)'e',
+            (byte)'.',
+            (byte)'x',
+            (byte)'m',
+            (byte)'p'
+        };
     }
 }

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -11,6 +11,7 @@ using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading;
+using SixLabors.ImageSharp.Common.Helpers;
 using SixLabors.ImageSharp.Compression.Zlib;
 using SixLabors.ImageSharp.Formats.Png.Chunks;
 using SixLabors.ImageSharp.Formats.Png.Filters;
@@ -18,6 +19,7 @@ using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Png
@@ -187,20 +189,20 @@ namespace SixLabors.ImageSharp.Formats.Png
                                 this.AssignTransparentMarkers(alpha, pngMetadata);
                                 break;
                             case PngChunkType.Text:
-                                this.ReadTextChunk(pngMetadata, chunk.Data.GetSpan());
+                                this.ReadTextChunk(metadata, pngMetadata, chunk.Data.GetSpan());
                                 break;
                             case PngChunkType.CompressedText:
-                                this.ReadCompressedTextChunk(pngMetadata, chunk.Data.GetSpan());
+                                this.ReadCompressedTextChunk(metadata, pngMetadata, chunk.Data.GetSpan());
                                 break;
                             case PngChunkType.InternationalText:
-                                this.ReadInternationalTextChunk(pngMetadata, chunk.Data.GetSpan());
+                                this.ReadInternationalTextChunk(metadata, chunk.Data.GetSpan());
                                 break;
                             case PngChunkType.Exif:
                                 if (!this.ignoreMetadata)
                                 {
                                     byte[] exifData = new byte[chunk.Length];
                                     chunk.Data.GetSpan().CopyTo(exifData);
-                                    metadata.ExifProfile = new ExifProfile(exifData);
+                                    this.MergeOrSetExifProfile(metadata, new ExifProfile(exifData), replaceExistingKeys: true);
                                 }
 
                                 break;
@@ -297,7 +299,7 @@ namespace SixLabors.ImageSharp.Formats.Png
                                     break;
                                 }
 
-                                this.ReadTextChunk(pngMetadata, chunk.Data.GetSpan());
+                                this.ReadTextChunk(metadata, pngMetadata, chunk.Data.GetSpan());
                                 break;
                             case PngChunkType.CompressedText:
                                 if (this.colorMetadataOnly)
@@ -306,7 +308,7 @@ namespace SixLabors.ImageSharp.Formats.Png
                                     break;
                                 }
 
-                                this.ReadCompressedTextChunk(pngMetadata, chunk.Data.GetSpan());
+                                this.ReadCompressedTextChunk(metadata, pngMetadata, chunk.Data.GetSpan());
                                 break;
                             case PngChunkType.InternationalText:
                                 if (this.colorMetadataOnly)
@@ -315,7 +317,7 @@ namespace SixLabors.ImageSharp.Formats.Png
                                     break;
                                 }
 
-                                this.ReadInternationalTextChunk(pngMetadata, chunk.Data.GetSpan());
+                                this.ReadInternationalTextChunk(metadata, chunk.Data.GetSpan());
                                 break;
                             case PngChunkType.Exif:
                                 if (this.colorMetadataOnly)
@@ -328,7 +330,7 @@ namespace SixLabors.ImageSharp.Formats.Png
                                 {
                                     byte[] exifData = new byte[chunk.Length];
                                     chunk.Data.GetSpan().CopyTo(exifData);
-                                    metadata.ExifProfile = new ExifProfile(exifData);
+                                    this.MergeOrSetExifProfile(metadata, new ExifProfile(exifData), replaceExistingKeys: true);
                                 }
 
                                 break;
@@ -967,9 +969,10 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <summary>
         /// Reads a text chunk containing image properties from the data.
         /// </summary>
+        /// <param name="baseMetadata">The <see cref="ImageMetadata"/> object.</param>
         /// <param name="metadata">The metadata to decode to.</param>
         /// <param name="data">The <see cref="T:Span"/> containing the data.</param>
-        private void ReadTextChunk(PngMetadata metadata, ReadOnlySpan<byte> data)
+        private void ReadTextChunk(ImageMetadata baseMetadata, PngMetadata metadata, ReadOnlySpan<byte> data)
         {
             if (this.ignoreMetadata)
             {
@@ -992,15 +995,19 @@ namespace SixLabors.ImageSharp.Formats.Png
 
             string value = PngConstants.Encoding.GetString(data.Slice(zeroIndex + 1));
 
-            metadata.TextData.Add(new PngTextData(name, value, string.Empty, string.Empty));
+            if (!this.TryReadTextChunkMetadata(baseMetadata, name, value))
+            {
+                metadata.TextData.Add(new PngTextData(name, value, string.Empty, string.Empty));
+            }
         }
 
         /// <summary>
         /// Reads the compressed text chunk. Contains a uncompressed keyword and a compressed text string.
         /// </summary>
+        /// <param name="baseMetadata">The <see cref="ImageMetadata"/> object.</param>
         /// <param name="metadata">The metadata to decode to.</param>
         /// <param name="data">The <see cref="T:Span"/> containing the data.</param>
-        private void ReadCompressedTextChunk(PngMetadata metadata, ReadOnlySpan<byte> data)
+        private void ReadCompressedTextChunk(ImageMetadata baseMetadata, PngMetadata metadata, ReadOnlySpan<byte> data)
         {
             if (this.ignoreMetadata)
             {
@@ -1028,12 +1035,185 @@ namespace SixLabors.ImageSharp.Formats.Png
 
             ReadOnlySpan<byte> compressedData = data.Slice(zeroIndex + 2);
 
-            if (this.TryUncompressTextData(compressedData, PngConstants.Encoding, out string uncompressed))
+            if (this.TryUncompressTextData(compressedData, PngConstants.Encoding, out string uncompressed) &&
+                !this.TryReadTextChunkMetadata(baseMetadata, name, uncompressed))
             {
                 metadata.TextData.Add(new PngTextData(name, uncompressed, string.Empty, string.Empty));
             }
         }
 
+        /// <summary>
+        /// Checks if the given text chunk is actually storing parsable metadata.
+        /// </summary>
+        /// <param name="baseMetadata">The <see cref="ImageMetadata"/> object to store the parsed metadata in.</param>
+        /// <param name="chunkName">The name of the text chunk.</param>
+        /// <param name="chunkText">The contents of the text chunk.</param>
+        /// <returns>True if metadata was successfully parsed from the text chunk. False if the
+        /// text chunk was not identified as metadata, and should be stored in the metadata
+        /// object unmodified.</returns>
+        private bool TryReadTextChunkMetadata(ImageMetadata baseMetadata, string chunkName, string chunkText)
+        {
+            if (chunkName.Equals("Raw profile type exif", StringComparison.OrdinalIgnoreCase) &&
+                this.TryReadLegacyExifTextChunk(baseMetadata, chunkText))
+            {
+                // Successfully parsed legacy exif data from text
+                return true;
+            }
+
+            // TODO: "Raw profile type iptc", potentially others?
+
+            // No special chunk data identified
+            return false;
+        }
+
+        /// <summary>
+        /// Reads exif data encoded into a text chunk with the name "raw profile type exif".
+        /// This method was used by ImageMagick, exiftool, exiv2, digiKam, etc, before the
+        /// 2017 update to png that allowed a true exif chunk.
+        /// </summary>
+        /// <param name="metadata">The <see cref="ImageMetadata"/> to store the decoded exif tags into.</param>
+        /// <param name="data">The contents of the "raw profile type exif" text chunk.</param>
+        private bool TryReadLegacyExifTextChunk(ImageMetadata metadata, string data)
+        {
+            ReadOnlySpan<char> dataSpan = data.AsSpan();
+            dataSpan = dataSpan.TrimStart();
+
+            if (!StringEqualsInsensitive(dataSpan.Slice(0, 4), "exif".AsSpan()))
+            {
+                // "exif" identifier is missing from the beginning of the text chunk
+                return false;
+            }
+
+            // Skip to the data length
+            dataSpan = dataSpan.Slice(4).TrimStart();
+            int dataLengthEnd = dataSpan.IndexOf('\n');
+            int dataLength = ParseInt32(dataSpan.Slice(0, dataSpan.IndexOf('\n')));
+
+            // Skip to the hex-encoded data
+            dataSpan = dataSpan.Slice(dataLengthEnd).Trim();
+
+            // Sequence of bytes for the exif header ("Exif" ASCII and two zero bytes).
+            // This doesn't actually allocate.
+            ReadOnlySpan<byte> exifHeader = new byte[] { 0x45, 0x78, 0x69, 0x66, 0x00, 0x00 };
+
+            if (dataLength < exifHeader.Length)
+            {
+                // Not enough room for the required exif header, this data couldn't possibly be valid
+                return false;
+            }
+
+            // Parse the hex-encoded data into the byte array we are going to hand off to ExifProfile
+            byte[] exifBlob = new byte[dataLength - exifHeader.Length];
+
+            try
+            {
+                // Check for the presence of the exif header in the hex-encoded binary data
+                byte[] tempExifBuf = exifBlob;
+                if (exifBlob.Length < exifHeader.Length)
+                {
+                    // Need to allocate a temporary array, this should be an extremely uncommon (TODO: impossible?) case
+                    tempExifBuf = new byte[exifHeader.Length];
+                }
+
+                HexConverter.HexStringToBytes(dataSpan.Slice(0, exifHeader.Length * 2), tempExifBuf);
+                if (!tempExifBuf.AsSpan().Slice(0, exifHeader.Length).SequenceEqual(exifHeader))
+                {
+                    // Exif header in the hex data is not valid
+                    return false;
+                }
+
+                // Skip over the exif header we just tested
+                dataSpan = dataSpan.Slice(exifHeader.Length * 2);
+                dataLength -= exifHeader.Length;
+
+                // Load the hex-encoded data, one line at a time
+                for (int i = 0; i < dataLength;)
+                {
+                    ReadOnlySpan<char> lineSpan = dataSpan;
+
+                    int newlineIndex = dataSpan.IndexOf('\n');
+                    if (newlineIndex != -1)
+                    {
+                        lineSpan = dataSpan.Slice(0, newlineIndex);
+                    }
+
+                    i += HexConverter.HexStringToBytes(lineSpan, exifBlob.AsSpan().Slice(i));
+
+                    dataSpan = dataSpan.Slice(newlineIndex + 1);
+                }
+            }
+            catch
+            {
+                return false;
+            }
+
+            this.MergeOrSetExifProfile(metadata, new ExifProfile(exifBlob), replaceExistingKeys: false);
+            return true;
+        }
+
+        /// <summary>
+        /// Compares two ReadOnlySpan&lt;char&gt;s in a case-insensitive method.
+        /// This is only needed because older frameworks are missing the extension method.
+        /// </summary>
+        /// <param name="span1">The first <see cref="Span{T}"/> to compare.</param>
+        /// <param name="span2">The second <see cref="Span{T}"/> to compare.</param>
+        /// <returns>True if the spans were identical, false otherwise.</returns>
+        private static bool StringEqualsInsensitive(ReadOnlySpan<char> span1, ReadOnlySpan<char> span2)
+        {
+#pragma warning disable IDE0022 // Use expression body for methods
+#if NETSTANDARD2_1 || NETCOREAPP2_1_OR_GREATER
+            return span1.Equals(span2, StringComparison.OrdinalIgnoreCase);
+#else
+            return span1.ToString().Equals(span2.ToString(), StringComparison.OrdinalIgnoreCase);
+#endif
+#pragma warning restore IDE0022 // Use expression body for methods
+        }
+
+        /// <summary>
+        /// int.Parse() a ReadOnlySpan&lt;char&gt;, with a fallback for older frameworks.
+        /// </summary>
+        /// <param name="span">The <see cref="int"/> to parse.</param>
+        /// <returns>The parsed <see cref="int"/>.</returns>
+        private static int ParseInt32(ReadOnlySpan<char> span)
+        {
+#pragma warning disable IDE0022 // Use expression body for methods
+#if NETSTANDARD2_1 || NETCOREAPP2_1_OR_GREATER
+            return int.Parse(span);
+#else
+            return int.Parse(span.ToString());
+#endif
+#pragma warning restore IDE0022 // Use expression body for methods
+        }
+
+        /// <summary>
+        /// Sets the <see cref="ExifProfile"/> in <paramref name="metadata"/> to <paramref name="newProfile"/>,
+        /// or copies exif tags if <paramref name="metadata"/> already contains an <see cref="ExifProfile"/>.
+        /// </summary>
+        /// <param name="metadata">The <see cref="ImageMetadata"/> to store the exif data in.</param>
+        /// <param name="newProfile">The <see cref="ExifProfile"/> to copy exif tags from.</param>
+        /// <param name="replaceExistingKeys">If <paramref name="metadata"/> already contains an <see cref="ExifProfile"/>,
+        /// controls whether existing exif tags in <paramref name="metadata"/> will be overwritten with any conflicting
+        /// tags from <paramref name="newProfile"/>.</param>
+        private void MergeOrSetExifProfile(ImageMetadata metadata, ExifProfile newProfile, bool replaceExistingKeys)
+        {
+            if (metadata.ExifProfile is null)
+            {
+                // No exif metadata was loaded yet, so just assign it
+                metadata.ExifProfile = newProfile;
+            }
+            else
+            {
+                // Try to merge existing keys with the ones from the new profile
+                foreach (IExifValue newKey in newProfile.Values)
+                {
+                    if (replaceExistingKeys || metadata.ExifProfile.GetValueInternal(newKey.Tag) is null)
+                    {
+                        metadata.ExifProfile.SetValueInternal(newKey.Tag, newKey.GetValue());
+                    }
+                }
+            }
+        }
+
         /// <summary>
         /// Reads a iTXt chunk, which contains international text data. It contains:
         /// - A uncompressed keyword.
@@ -1045,13 +1225,14 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// </summary>
         /// <param name="metadata">The metadata to decode to.</param>
         /// <param name="data">The <see cref="T:Span"/> containing the data.</param>
-        private void ReadInternationalTextChunk(PngMetadata metadata, ReadOnlySpan<byte> data)
+        private void ReadInternationalTextChunk(ImageMetadata metadata, ReadOnlySpan<byte> data)
         {
             if (this.ignoreMetadata)
             {
                 return;
             }
 
+            PngMetadata pngMetadata = metadata.GetPngMetadata();
             int zeroIndexKeyword = data.IndexOf((byte)0);
             if (zeroIndexKeyword < PngConstants.MinTextKeywordLength || zeroIndexKeyword > PngConstants.MaxTextKeywordLength)
             {
@@ -1097,13 +1278,18 @@ namespace SixLabors.ImageSharp.Formats.Png
 
                 if (this.TryUncompressTextData(compressedData, PngConstants.TranslatedEncoding, out string uncompressed))
                 {
-                    metadata.TextData.Add(new PngTextData(keyword, uncompressed, language, translatedKeyword));
+                    pngMetadata.TextData.Add(new PngTextData(keyword, uncompressed, language, translatedKeyword));
                 }
             }
+            else if (this.IsXmpTextData(keywordBytes))
+            {
+                XmpProfile xmpProfile = new XmpProfile(data.Slice(dataStartIdx).ToArray());
+                metadata.XmpProfile = xmpProfile;
+            }
             else
             {
                 string value = PngConstants.TranslatedEncoding.GetString(data.Slice(dataStartIdx));
-                metadata.TextData.Add(new PngTextData(keyword, value, language, translatedKeyword));
+                pngMetadata.TextData.Add(new PngTextData(keyword, value, language, translatedKeyword));
             }
         }
 
@@ -1371,6 +1557,8 @@ namespace SixLabors.ImageSharp.Formats.Png
             return true;
         }
 
+        private bool IsXmpTextData(ReadOnlySpan<byte> keywordBytes) => keywordBytes.SequenceEqual(PngConstants.XmpKeyword);
+
         private void SwapScanlineBuffers()
         {
             IMemoryOwner<byte> temp = this.previousScanline;

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -138,6 +138,7 @@ namespace SixLabors.ImageSharp.Formats.Png
             this.WriteTransparencyChunk(stream, pngMetadata);
             this.WritePhysicalChunk(stream, metadata);
             this.WriteExifChunk(stream, metadata);
+            this.WriteXmpChunk(stream, metadata);
             this.WriteTextChunks(stream, pngMetadata);
             this.WriteDataChunks(clearTransparency ? clonedImage : image, quantized, stream);
             this.WriteEndChunk(stream);
@@ -654,6 +655,51 @@ namespace SixLabors.ImageSharp.Formats.Png
             this.WriteChunk(stream, PngChunkType.Exif, meta.ExifProfile.ToByteArray());
         }
 
+        /// <summary>
+        /// Writes an iTXT chunk, containing the XMP metdata to the stream, if such profile is present in the metadata.
+        /// </summary>
+        /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+        /// <param name="meta">The image metadata.</param>
+        private void WriteXmpChunk(Stream stream, ImageMetadata meta)
+        {
+            const int iTxtHeaderSize = 5;
+            if (((this.options.ChunkFilter ?? PngChunkFilter.None) & PngChunkFilter.ExcludeTextChunks) == PngChunkFilter.ExcludeTextChunks)
+            {
+                return;
+            }
+
+            if (meta.XmpProfile is null)
+            {
+                return;
+            }
+
+            var xmpData = meta.XmpProfile.Data;
+
+            if (xmpData.Length == 0)
+            {
+                return;
+            }
+
+            int payloadLength = xmpData.Length + PngConstants.XmpKeyword.Length + iTxtHeaderSize;
+            using (IMemoryOwner<byte> owner = this.memoryAllocator.Allocate<byte>(payloadLength))
+            {
+                Span<byte> payload = owner.GetSpan();
+                PngConstants.XmpKeyword.CopyTo(payload);
+                int bytesWritten = PngConstants.XmpKeyword.Length;
+
+                // Write the iTxt header (all zeros in this case)
+                payload[bytesWritten++] = 0;
+                payload[bytesWritten++] = 0;
+                payload[bytesWritten++] = 0;
+                payload[bytesWritten++] = 0;
+                payload[bytesWritten++] = 0;
+
+                // And the XMP data itself
+                xmpData.CopyTo(payload.Slice(bytesWritten));
+                this.WriteChunk(stream, PngChunkType.InternationalText, payload);
+            }
+        }
+
         /// <summary>
         /// Writes a text chunk to the stream. Can be either a tTXt, iTXt or zTXt chunk,
         /// depending whether the text contains any latin characters or should be compressed.
@@ -693,21 +739,33 @@ namespace SixLabors.ImageSharp.Formats.Png
                     byte[] translatedKeyword = PngConstants.TranslatedEncoding.GetBytes(textData.TranslatedKeyword);
                     byte[] languageTag = PngConstants.LanguageEncoding.GetBytes(textData.LanguageTag);
 
-                    Span<byte> outputBytes = new byte[keywordBytes.Length + textBytes.Length +
-                                                      translatedKeyword.Length + languageTag.Length + 5];
-                    keywordBytes.CopyTo(outputBytes);
-                    if (textData.Value.Length > this.options.TextCompressionThreshold)
+                    int payloadLength = keywordBytes.Length + textBytes.Length + translatedKeyword.Length + languageTag.Length + 5;
+                    using (IMemoryOwner<byte> owner = this.memoryAllocator.Allocate<byte>(payloadLength))
                     {
-                        // Indicate that the text is compressed.
-                        outputBytes[keywordBytes.Length + 1] = 1;
-                    }
+                        Span<byte> outputBytes = owner.GetSpan();
+                        keywordBytes.CopyTo(outputBytes);
+                        int bytesWritten = keywordBytes.Length;
+                        outputBytes[bytesWritten++] = 0;
+                        if (textData.Value.Length > this.options.TextCompressionThreshold)
+                        {
+                            // Indicate that the text is compressed.
+                            outputBytes[bytesWritten++] = 1;
+                        }
+                        else
+                        {
+                            outputBytes[bytesWritten++] = 0;
+                        }
 
-                    int keywordStart = keywordBytes.Length + 3;
-                    languageTag.CopyTo(outputBytes.Slice(keywordStart));
-                    int translatedKeywordStart = keywordStart + languageTag.Length + 1;
-                    translatedKeyword.CopyTo(outputBytes.Slice(translatedKeywordStart));
-                    textBytes.CopyTo(outputBytes.Slice(translatedKeywordStart + translatedKeyword.Length + 1));
-                    this.WriteChunk(stream, PngChunkType.InternationalText, outputBytes.ToArray());
+                        outputBytes[bytesWritten++] = 0;
+                        languageTag.CopyTo(outputBytes.Slice(bytesWritten));
+                        bytesWritten += languageTag.Length;
+                        outputBytes[bytesWritten++] = 0;
+                        translatedKeyword.CopyTo(outputBytes.Slice(bytesWritten));
+                        bytesWritten += translatedKeyword.Length;
+                        outputBytes[bytesWritten++] = 0;
+                        textBytes.CopyTo(outputBytes.Slice(bytesWritten));
+                        this.WriteChunk(stream, PngChunkType.InternationalText, outputBytes);
+                    }
                 }
                 else
                 {
@@ -716,19 +774,32 @@ namespace SixLabors.ImageSharp.Formats.Png
                         // Write zTXt chunk.
                         byte[] compressedData =
                             this.GetCompressedTextBytes(PngConstants.Encoding.GetBytes(textData.Value));
-                        Span<byte> outputBytes = new byte[textData.Keyword.Length + compressedData.Length + 2];
-                        PngConstants.Encoding.GetBytes(textData.Keyword).CopyTo(outputBytes);
-                        compressedData.CopyTo(outputBytes.Slice(textData.Keyword.Length + 2));
-                        this.WriteChunk(stream, PngChunkType.CompressedText, outputBytes.ToArray());
+                        int payloadLength = textData.Keyword.Length + compressedData.Length + 2;
+                        using (IMemoryOwner<byte> owner = this.memoryAllocator.Allocate<byte>(payloadLength))
+                        {
+                            Span<byte> outputBytes = owner.GetSpan();
+                            PngConstants.Encoding.GetBytes(textData.Keyword).CopyTo(outputBytes);
+                            int bytesWritten = textData.Keyword.Length;
+                            outputBytes[bytesWritten++] = 0;
+                            outputBytes[bytesWritten++] = 0;
+                            compressedData.CopyTo(outputBytes.Slice(bytesWritten));
+                            this.WriteChunk(stream, PngChunkType.CompressedText, outputBytes.ToArray());
+                        }
                     }
                     else
                     {
                         // Write tEXt chunk.
-                        Span<byte> outputBytes = new byte[textData.Keyword.Length + textData.Value.Length + 1];
-                        PngConstants.Encoding.GetBytes(textData.Keyword).CopyTo(outputBytes);
-                        PngConstants.Encoding.GetBytes(textData.Value)
-                            .CopyTo(outputBytes.Slice(textData.Keyword.Length + 1));
-                        this.WriteChunk(stream, PngChunkType.Text, outputBytes.ToArray());
+                        int payloadLength = textData.Keyword.Length + textData.Value.Length + 1;
+                        using (IMemoryOwner<byte> owner = this.memoryAllocator.Allocate<byte>(payloadLength))
+                        {
+                            Span<byte> outputBytes = owner.GetSpan();
+                            PngConstants.Encoding.GetBytes(textData.Keyword).CopyTo(outputBytes);
+                            int bytesWritten = textData.Keyword.Length;
+                            outputBytes[bytesWritten++] = 0;
+                            PngConstants.Encoding.GetBytes(textData.Value)
+                                .CopyTo(outputBytes.Slice(bytesWritten));
+                            this.WriteChunk(stream, PngChunkType.Text, outputBytes.ToArray());
+                        }
                     }
                 }
             }

src/ImageSharp/Formats/Tiff/Compression/Compressors/T4BitCompressor.cs

@@ -2,8 +2,6 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
-using System.Buffers;
-using System.Collections.Generic;
 using System.IO;
 using SixLabors.ImageSharp.Formats.Tiff.Constants;
 using SixLabors.ImageSharp.Memory;
@@ -13,222 +11,35 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Compressors
     /// <summary>
     /// Bitwriter for writing compressed CCITT T4 1D data.
     /// </summary>
-    internal sealed class T4BitCompressor : TiffBaseCompressor
+    internal sealed class T4BitCompressor : TiffCcittCompressor
     {
-        private const uint WhiteZeroRunTermCode = 0x35;
-
-        private const uint BlackZeroRunTermCode = 0x37;
-
-        private static readonly uint[] MakeupRunLength =
-        {
-            64, 128, 192, 256, 320, 384, 448, 512, 576, 640, 704, 768, 832, 896, 960, 1024, 1088, 1152, 1216, 1280, 1344, 1408, 1472, 1536, 1600, 1664, 1728, 1792, 1856, 1920, 1984, 2048, 2112, 2176, 2240, 2304, 2368, 2432, 2496, 2560
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen4TermCodes = new Dictionary<uint, uint>()
-        {
-            { 2, 0x7 }, { 3, 0x8 }, { 4, 0xB }, { 5, 0xC }, { 6, 0xE }, { 7, 0xF }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen5TermCodes = new Dictionary<uint, uint>()
-        {
-            { 8, 0x13 }, { 9, 0x14 }, { 10, 0x7 }, { 11, 0x8 }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen6TermCodes = new Dictionary<uint, uint>()
-        {
-            { 1, 0x7 }, { 12, 0x8 }, { 13, 0x3 }, { 14, 0x34 }, { 15, 0x35 }, { 16, 0x2A }, { 17, 0x2B }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen7TermCodes = new Dictionary<uint, uint>()
-        {
-            { 18, 0x27 }, { 19, 0xC }, { 20, 0x8 }, { 21, 0x17 }, { 22, 0x3 }, { 23, 0x4 }, { 24, 0x28 }, { 25, 0x2B }, { 26, 0x13 },
-            { 27, 0x24 }, { 28, 0x18 }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen8TermCodes = new Dictionary<uint, uint>()
-        {
-            { 0, WhiteZeroRunTermCode }, { 29, 0x2 }, { 30, 0x3 }, { 31, 0x1A }, { 32, 0x1B }, { 33, 0x12 }, { 34, 0x13 }, { 35, 0x14 },
-            { 36, 0x15 }, { 37, 0x16 }, { 38, 0x17 }, { 39, 0x28 }, { 40, 0x29 }, { 41, 0x2A }, { 42, 0x2B }, { 43, 0x2C }, { 44, 0x2D },
-            { 45, 0x4 }, { 46, 0x5 }, { 47, 0xA }, { 48, 0xB }, { 49, 0x52 }, { 50, 0x53 }, { 51, 0x54 }, { 52, 0x55 }, { 53, 0x24 },
-            { 54, 0x25 }, { 55, 0x58 }, { 56, 0x59 }, { 57, 0x5A }, { 58, 0x5B }, { 59, 0x4A }, { 60, 0x4B }, { 61, 0x32 }, { 62, 0x33 },
-            { 63, 0x34 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen2TermCodes = new Dictionary<uint, uint>()
-        {
-            { 2, 0x3 }, { 3, 0x2 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen3TermCodes = new Dictionary<uint, uint>()
-        {
-            { 1, 0x2 }, { 4, 0x3 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen4TermCodes = new Dictionary<uint, uint>()
-        {
-            { 5, 0x3 }, { 6, 0x2 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen5TermCodes = new Dictionary<uint, uint>()
-        {
-            { 7, 0x3 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen6TermCodes = new Dictionary<uint, uint>()
-        {
-            { 8, 0x5 }, { 9, 0x4 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen7TermCodes = new Dictionary<uint, uint>()
-        {
-            { 10, 0x4 }, { 11, 0x5 }, { 12, 0x7 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen8TermCodes = new Dictionary<uint, uint>()
-        {
-            { 13, 0x4 }, { 14, 0x7 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen9TermCodes = new Dictionary<uint, uint>()
-        {
-            { 15, 0x18 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen10TermCodes = new Dictionary<uint, uint>()
-        {
-            { 0, BlackZeroRunTermCode }, { 16, 0x17 }, { 17, 0x18 }, { 18, 0x8 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen11TermCodes = new Dictionary<uint, uint>()
-        {
-            { 19, 0x67 }, { 20, 0x68 }, { 21, 0x6C }, { 22, 0x37 }, { 23, 0x28 }, { 24, 0x17 }, { 25, 0x18 }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen12TermCodes = new Dictionary<uint, uint>()
-        {
-            { 26, 0xCA }, { 27, 0xCB }, { 28, 0xCC }, { 29, 0xCD }, { 30, 0x68 }, { 31, 0x69 }, { 32, 0x6A }, { 33, 0x6B }, { 34, 0xD2 },
-            { 35, 0xD3 }, { 36, 0xD4 }, { 37, 0xD5 }, { 38, 0xD6 }, { 39, 0xD7 }, { 40, 0x6C }, { 41, 0x6D }, { 42, 0xDA }, { 43, 0xDB },
-            { 44, 0x54 }, { 45, 0x55 }, { 46, 0x56 }, { 47, 0x57 }, { 48, 0x64 }, { 49, 0x65 }, { 50, 0x52 }, { 51, 0x53 }, { 52, 0x24 },
-            { 53, 0x37 }, { 54, 0x38 }, { 55, 0x27 }, { 56, 0x28 }, { 57, 0x58 }, { 58, 0x59 }, { 59, 0x2B }, { 60, 0x2C }, { 61, 0x5A },
-            { 62, 0x66 }, { 63, 0x67 }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen5MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 64, 0x1B }, { 128, 0x12 }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen6MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 192, 0x17 }, { 1664, 0x18 }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen8MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 320, 0x36 }, { 384, 0x37 }, { 448, 0x64 }, { 512, 0x65 }, { 576, 0x68 }, { 640, 0x67 }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen7MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 256, 0x37 }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen9MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 704, 0xCC }, { 768, 0xCD }, { 832, 0xD2 }, { 896, 0xD3 }, { 960, 0xD4 }, { 1024, 0xD5 }, { 1088, 0xD6 },
-            { 1152, 0xD7 }, { 1216, 0xD8 }, { 1280, 0xD9 }, { 1344, 0xDA }, { 1408, 0xDB }, { 1472, 0x98 }, { 1536, 0x99 },
-            { 1600, 0x9A }, { 1728, 0x9B }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen11MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 1792, 0x8 }, { 1856, 0xC }, { 1920, 0xD }
-        };
-
-        private static readonly Dictionary<uint, uint> WhiteLen12MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 1984, 0x12 }, { 2048, 0x13 }, { 2112, 0x14 }, { 2176, 0x15 }, { 2240, 0x16 }, { 2304, 0x17 }, { 2368, 0x1C },
-            { 2432, 0x1D }, { 2496, 0x1E }, { 2560, 0x1F }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen10MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 64, 0xF }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen11MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 1792, 0x8 }, { 1856, 0xC }, { 1920, 0xD }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen12MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 128, 0xC8 }, { 192, 0xC9 }, { 256, 0x5B }, { 320, 0x33 }, { 384, 0x34 }, { 448, 0x35 },
-            { 1984, 0x12 }, { 2048, 0x13 }, { 2112, 0x14 }, { 2176, 0x15 }, { 2240, 0x16 }, { 2304, 0x17 }, { 2368, 0x1C },
-            { 2432, 0x1D }, { 2496, 0x1E }, { 2560, 0x1F }
-        };
-
-        private static readonly Dictionary<uint, uint> BlackLen13MakeupCodes = new Dictionary<uint, uint>()
-        {
-            { 512, 0x6C }, { 576, 0x6D }, { 640, 0x4A }, { 704, 0x4B }, { 768, 0x4C }, { 832, 0x4D }, { 896, 0x72 },
-            { 960, 0x73 }, { 1024, 0x74 }, { 1088, 0x75 }, { 1152, 0x76 }, { 1216, 0x77 }, { 1280,  0x52 }, { 1344, 0x53 },
-            { 1408, 0x54 }, { 1472, 0x55 }, { 1536, 0x5A }, { 1600, 0x5B }, { 1664, 0x64 }, { 1728, 0x65 }
-        };
-
         /// <summary>
         /// The modified huffman is basically the same as CCITT T4, but without EOL markers and padding at the end of the rows.
         /// </summary>
         private readonly bool useModifiedHuffman;
 
-        private IMemoryOwner<byte> compressedDataBuffer;
-
-        private int bytePosition;
-
-        private byte bitPosition;
-
         /// <summary>
         /// Initializes a new instance of the <see cref="T4BitCompressor" /> class.
         /// </summary>
-        /// <param name="output">The output.</param>
-        /// <param name="allocator">The allocator.</param>
-        /// <param name="width">The width.</param>
+        /// <param name="output">The output stream to write the compressed data.</param>
+        /// <param name="allocator">The memory allocator.</param>
+        /// <param name="width">The width of the image.</param>
         /// <param name="bitsPerPixel">The bits per pixel.</param>
         /// <param name="useModifiedHuffman">Indicates if the modified huffman RLE should be used.</param>
         public T4BitCompressor(Stream output, MemoryAllocator allocator, int width, int bitsPerPixel, bool useModifiedHuffman = false)
-            : base(output, allocator, width, bitsPerPixel)
-        {
-            this.bytePosition = 0;
-            this.bitPosition = 0;
-            this.useModifiedHuffman = useModifiedHuffman;
-        }
+            : base(output, allocator, width, bitsPerPixel) => this.useModifiedHuffman = useModifiedHuffman;
 
         /// <inheritdoc/>
         public override TiffCompression Method => this.useModifiedHuffman ? TiffCompression.Ccitt1D : TiffCompression.CcittGroup3Fax;
 
-        /// <inheritdoc/>
-        public override void Initialize(int rowsPerStrip)
-        {
-            // This is too much memory allocated, but just 1 bit per pixel will not do, if the compression rate is not good.
-            int maxNeededBytes = this.Width * rowsPerStrip;
-            this.compressedDataBuffer = this.Allocator.Allocate<byte>(maxNeededBytes);
-        }
-
         /// <summary>
-        /// Writes a image compressed with CCITT T4 to the stream.
+        /// Writes a image compressed with CCITT T4 to the output buffer.
         /// </summary>
         /// <param name="pixelsAsGray">The pixels as 8-bit gray array.</param>
         /// <param name="height">The strip height.</param>
-        public override void CompressStrip(Span<byte> pixelsAsGray, int height)
+        /// <param name="compressedData">The destination for the compressed data.</param>
+        protected override void CompressStrip(Span<byte> pixelsAsGray, int height, Span<byte> compressedData)
         {
-            DebugGuard.IsTrue(pixelsAsGray.Length / height == this.Width, "Values must be equals");
-            DebugGuard.IsTrue(pixelsAsGray.Length % height == 0, "Values must be equals");
-
-            this.compressedDataBuffer.Clear();
-            Span<byte> compressedData = this.compressedDataBuffer.GetSpan();
-
-            this.bytePosition = 0;
-            this.bitPosition = 0;
-
             if (!this.useModifiedHuffman)
             {
                 // An EOL code is expected at the start of the data.
@@ -315,25 +126,13 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Compressors
 
                 this.WriteEndOfLine(compressedData);
             }
-
-            // Write the compressed data to the stream.
-            int bytesToWrite = this.bitPosition != 0 ? this.bytePosition + 1 : this.bytePosition;
-            this.Output.Write(compressedData.Slice(0, bytesToWrite));
         }
 
-        protected override void Dispose(bool disposing) => this.compressedDataBuffer?.Dispose();
-
         private void WriteEndOfLine(Span<byte> compressedData)
         {
             if (this.useModifiedHuffman)
             {
-                // Check if padding is necessary.
-                if (this.bitPosition % 8 != 0)
-                {
-                    // Skip padding bits, move to next byte.
-                    this.bytePosition++;
-                    this.bitPosition = 0;
-                }
+                this.PadByte();
             }
             else
             {
@@ -341,254 +140,5 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Compressors
                 this.WriteCode(12, 1, compressedData);
             }
         }
-
-        private void WriteCode(uint codeLength, uint code, Span<byte> compressedData)
-        {
-            while (codeLength > 0)
-            {
-                int bitNumber = (int)codeLength;
-                bool bit = (code & (1 << (bitNumber - 1))) != 0;
-                if (bit)
-                {
-                    BitWriterUtils.WriteBit(compressedData, this.bytePosition, this.bitPosition);
-                }
-                else
-                {
-                    BitWriterUtils.WriteZeroBit(compressedData, this.bytePosition, this.bitPosition);
-                }
-
-                this.bitPosition++;
-                if (this.bitPosition == 8)
-                {
-                    this.bytePosition++;
-                    this.bitPosition = 0;
-                }
-
-                codeLength--;
-            }
-        }
-
-        private uint GetBestFittingMakeupRunLength(uint runLength)
-        {
-            for (int i = 0; i < MakeupRunLength.Length - 1; i++)
-            {
-                if (MakeupRunLength[i] <= runLength && MakeupRunLength[i + 1] > runLength)
-                {
-                    return MakeupRunLength[i];
-                }
-            }
-
-            return MakeupRunLength[MakeupRunLength.Length - 1];
-        }
-
-        private uint GetTermCode(uint runLength, out uint codeLength, bool isWhiteRun)
-        {
-            if (isWhiteRun)
-            {
-                return this.GetWhiteTermCode(runLength, out codeLength);
-            }
-
-            return this.GetBlackTermCode(runLength, out codeLength);
-        }
-
-        private uint GetMakeupCode(uint runLength, out uint codeLength, bool isWhiteRun)
-        {
-            if (isWhiteRun)
-            {
-                return this.GetWhiteMakeupCode(runLength, out codeLength);
-            }
-
-            return this.GetBlackMakeupCode(runLength, out codeLength);
-        }
-
-        private uint GetWhiteMakeupCode(uint runLength, out uint codeLength)
-        {
-            codeLength = 0;
-
-            if (WhiteLen5MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 5;
-                return WhiteLen5MakeupCodes[runLength];
-            }
-
-            if (WhiteLen6MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 6;
-                return WhiteLen6MakeupCodes[runLength];
-            }
-
-            if (WhiteLen7MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 7;
-                return WhiteLen7MakeupCodes[runLength];
-            }
-
-            if (WhiteLen8MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 8;
-                return WhiteLen8MakeupCodes[runLength];
-            }
-
-            if (WhiteLen9MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 9;
-                return WhiteLen9MakeupCodes[runLength];
-            }
-
-            if (WhiteLen11MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 11;
-                return WhiteLen11MakeupCodes[runLength];
-            }
-
-            if (WhiteLen12MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 12;
-                return WhiteLen12MakeupCodes[runLength];
-            }
-
-            return 0;
-        }
-
-        private uint GetBlackMakeupCode(uint runLength, out uint codeLength)
-        {
-            codeLength = 0;
-
-            if (BlackLen10MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 10;
-                return BlackLen10MakeupCodes[runLength];
-            }
-
-            if (BlackLen11MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 11;
-                return BlackLen11MakeupCodes[runLength];
-            }
-
-            if (BlackLen12MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 12;
-                return BlackLen12MakeupCodes[runLength];
-            }
-
-            if (BlackLen13MakeupCodes.ContainsKey(runLength))
-            {
-                codeLength = 13;
-                return BlackLen13MakeupCodes[runLength];
-            }
-
-            return 0;
-        }
-
-        private uint GetWhiteTermCode(uint runLength, out uint codeLength)
-        {
-            codeLength = 0;
-
-            if (WhiteLen4TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 4;
-                return WhiteLen4TermCodes[runLength];
-            }
-
-            if (WhiteLen5TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 5;
-                return WhiteLen5TermCodes[runLength];
-            }
-
-            if (WhiteLen6TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 6;
-                return WhiteLen6TermCodes[runLength];
-            }
-
-            if (WhiteLen7TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 7;
-                return WhiteLen7TermCodes[runLength];
-            }
-
-            if (WhiteLen8TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 8;
-                return WhiteLen8TermCodes[runLength];
-            }
-
-            return 0;
-        }
-
-        private uint GetBlackTermCode(uint runLength, out uint codeLength)
-        {
-            codeLength = 0;
-
-            if (BlackLen2TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 2;
-                return BlackLen2TermCodes[runLength];
-            }
-
-            if (BlackLen3TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 3;
-                return BlackLen3TermCodes[runLength];
-            }
-
-            if (BlackLen4TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 4;
-                return BlackLen4TermCodes[runLength];
-            }
-
-            if (BlackLen5TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 5;
-                return BlackLen5TermCodes[runLength];
-            }
-
-            if (BlackLen6TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 6;
-                return BlackLen6TermCodes[runLength];
-            }
-
-            if (BlackLen7TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 7;
-                return BlackLen7TermCodes[runLength];
-            }
-
-            if (BlackLen8TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 8;
-                return BlackLen8TermCodes[runLength];
-            }
-
-            if (BlackLen9TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 9;
-                return BlackLen9TermCodes[runLength];
-            }
-
-            if (BlackLen10TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 10;
-                return BlackLen10TermCodes[runLength];
-            }
-
-            if (BlackLen11TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 11;
-                return BlackLen11TermCodes[runLength];
-            }
-
-            if (BlackLen12TermCodes.ContainsKey(runLength))
-            {
-                codeLength = 12;
-                return BlackLen12TermCodes[runLength];
-            }
-
-            return 0;
-        }
     }
 }

src/ImageSharp/Formats/Tiff/Compression/Compressors/T6BitCompressor.cs

@@ -0,0 +1,201 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Buffers;
+using System.IO;
+using SixLabors.ImageSharp.Formats.Tiff.Constants;
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Compressors
+{
+    /// <summary>
+    /// Bitwriter for writing compressed CCITT T6 2D data.
+    /// </summary>
+    internal sealed class T6BitCompressor : TiffCcittCompressor
+    {
+        /// <summary>
+        /// Vertical codes from -3 to +3.
+        /// </summary>
+        private static readonly (uint Length, uint Code)[] VerticalCodes =
+        {
+            (7u, 3u),
+            (6u, 3u),
+            (3u, 3u),
+            (1u, 1u),
+            (3u, 2u),
+            (6u, 2u),
+            (7u, 2u)
+        };
+
+        private IMemoryOwner<byte> referenceLineBuffer;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="T6BitCompressor"/> class.
+        /// </summary>
+        /// <param name="output">The output stream to write the compressed data.</param>
+        /// <param name="allocator">The memory allocator.</param>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="bitsPerPixel">The bits per pixel.</param>
+        public T6BitCompressor(Stream output, MemoryAllocator allocator, int width, int bitsPerPixel)
+            : base(output, allocator, width, bitsPerPixel)
+        {
+        }
+
+        /// <inheritdoc />
+        public override TiffCompression Method => TiffCompression.CcittGroup4Fax;
+
+        /// <summary>
+        /// Writes a image compressed with CCITT T6 to the output buffer.
+        /// </summary>
+        /// <param name="pixelsAsGray">The pixels as 8-bit gray array.</param>
+        /// <param name="height">The strip height.</param>
+        /// <param name="compressedData">The destination for the compressed data.</param>
+        protected override void CompressStrip(Span<byte> pixelsAsGray, int height, Span<byte> compressedData)
+        {
+            // Initial reference line is all white.
+            Span<byte> referenceLine = this.referenceLineBuffer.GetSpan();
+            referenceLine.Fill(0xff);
+
+            for (int y = 0; y < height; y++)
+            {
+                Span<byte> row = pixelsAsGray.Slice(y * this.Width, this.Width);
+                uint a0 = 0;
+                uint a1 = row[0] == 0 ? 0 : this.FindRunEnd(row, 0);
+                uint b1 = referenceLine[0] == 0 ? 0 : this.FindRunEnd(referenceLine, 0);
+
+                while (true)
+                {
+                    uint b2 = this.FindRunEnd(referenceLine, b1);
+                    if (b2 < a1)
+                    {
+                        // Pass mode.
+                        this.WriteCode(4, 1, compressedData);
+                        a0 = b2;
+                    }
+                    else
+                    {
+                        int d = int.MaxValue;
+                        if ((b1 >= a1) && (b1 - a1 <= 3))
+                        {
+                            d = (int)(b1 - a1);
+                        }
+                        else if ((b1 < a1) && (a1 - b1 <= 3))
+                        {
+                            d = -(int)(a1 - b1);
+                        }
+
+                        if ((d >= -3) && (d <= 3))
+                        {
+                            // Vertical mode.
+                            (uint length, uint code) = VerticalCodes[d + 3];
+                            this.WriteCode(length, code, compressedData);
+                            a0 = a1;
+                        }
+                        else
+                        {
+                            // Horizontal mode.
+                            this.WriteCode(3, 1, compressedData);
+
+                            uint a2 = this.FindRunEnd(row, a1);
+                            if ((a0 + a1 == 0) || (row[(int)a0] != 0))
+                            {
+                                this.WriteRun(a1 - a0, true, compressedData);
+                                this.WriteRun(a2 - a1, false, compressedData);
+                            }
+                            else
+                            {
+                                this.WriteRun(a1 - a0, false, compressedData);
+                                this.WriteRun(a2 - a1, true, compressedData);
+                            }
+
+                            a0 = a2;
+                        }
+                    }
+
+                    if (a0 >= row.Length)
+                    {
+                        break;
+                    }
+
+                    byte thisPixel = row[(int)a0];
+                    a1 = this.FindRunEnd(row, a0, thisPixel);
+                    b1 = this.FindRunEnd(referenceLine, a0, (byte)~thisPixel);
+                    b1 = this.FindRunEnd(referenceLine, b1, thisPixel);
+                }
+
+                // This row is now the reference line.
+                row.CopyTo(referenceLine);
+            }
+
+            this.WriteCode(12, 1, compressedData);
+            this.WriteCode(12, 1, compressedData);
+        }
+
+        /// <inheritdoc />
+        protected override void Dispose(bool disposing)
+        {
+            this.referenceLineBuffer?.Dispose();
+            base.Dispose(disposing);
+        }
+
+        /// <summary>
+        /// Finds the end of a pixel run.
+        /// </summary>
+        /// <param name="row">The row of pixels to examine.</param>
+        /// <param name="startIndex">The index of the first pixel in <paramref name="row"/> to examine.</param>
+        /// <param name="color">Color of pixels in the run.  If not specified, the color at
+        /// <paramref name="startIndex"/> will be used.</param>
+        /// <returns>The index of the first pixel at or after <paramref name="startIndex"/>
+        /// that does not match <paramref name="color"/>, or the length of <paramref name="row"/>,
+        /// whichever comes first.</returns>
+        private uint FindRunEnd(Span<byte> row, uint startIndex, byte? color = null)
+        {
+            if (startIndex >= row.Length)
+            {
+                return (uint)row.Length;
+            }
+
+            byte colorValue = color.GetValueOrDefault(row[(int)startIndex]);
+            for (int i = (int)startIndex; i < row.Length; i++)
+            {
+                if (row[i] != colorValue)
+                {
+                    return (uint)i;
+                }
+            }
+
+            return (uint)row.Length;
+        }
+
+        /// <inheritdoc />
+        public override void Initialize(int rowsPerStrip)
+        {
+            base.Initialize(rowsPerStrip);
+            this.referenceLineBuffer = this.Allocator.Allocate<byte>(this.Width);
+        }
+
+        /// <summary>
+        /// Writes a run to the output buffer.
+        /// </summary>
+        /// <param name="runLength">The length of the run.</param>
+        /// <param name="isWhiteRun">If <c>true</c> the run is white pixels,
+        /// if <c>false</c> the run is black pixels.</param>
+        /// <param name="compressedData">The destination to write the run to.</param>
+        private void WriteRun(uint runLength, bool isWhiteRun, Span<byte> compressedData)
+        {
+            uint code;
+            uint codeLength;
+            while (runLength > 63)
+            {
+                uint makeupLength = this.GetBestFittingMakeupRunLength(runLength);
+                code = this.GetMakeupCode(makeupLength, out codeLength, isWhiteRun);
+                this.WriteCode(codeLength, code, compressedData);
+                runLength -= makeupLength;
+            }
+
+            code = this.GetTermCode(runLength, out codeLength, isWhiteRun);
+            this.WriteCode(codeLength, code, compressedData);
+        }
+    }
+}

src/ImageSharp/Formats/Tiff/Compression/Compressors/TiffCcittCompressor.cs

@@ -0,0 +1,536 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Buffers;
+using System.Collections.Generic;
+using System.IO;
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Compressors
+{
+    /// <summary>
+    /// Common functionality for CCITT T4 and T6 Compression
+    /// </summary>
+    internal abstract class TiffCcittCompressor : TiffBaseCompressor
+    {
+        protected const uint WhiteZeroRunTermCode = 0x35;
+
+        protected const uint BlackZeroRunTermCode = 0x37;
+
+        private static readonly uint[] MakeupRunLength =
+        {
+            64, 128, 192, 256, 320, 384, 448, 512, 576, 640, 704, 768, 832, 896, 960, 1024, 1088, 1152, 1216, 1280, 1344, 1408, 1472, 1536, 1600, 1664, 1728, 1792, 1856, 1920, 1984, 2048, 2112, 2176, 2240, 2304, 2368, 2432, 2496, 2560
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen4TermCodes = new Dictionary<uint, uint>()
+        {
+            { 2, 0x7 }, { 3, 0x8 }, { 4, 0xB }, { 5, 0xC }, { 6, 0xE }, { 7, 0xF }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen5TermCodes = new Dictionary<uint, uint>()
+        {
+            { 8, 0x13 }, { 9, 0x14 }, { 10, 0x7 }, { 11, 0x8 }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen6TermCodes = new Dictionary<uint, uint>()
+        {
+            { 1, 0x7 }, { 12, 0x8 }, { 13, 0x3 }, { 14, 0x34 }, { 15, 0x35 }, { 16, 0x2A }, { 17, 0x2B }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen7TermCodes = new Dictionary<uint, uint>()
+        {
+            { 18, 0x27 }, { 19, 0xC }, { 20, 0x8 }, { 21, 0x17 }, { 22, 0x3 }, { 23, 0x4 }, { 24, 0x28 }, { 25, 0x2B }, { 26, 0x13 },
+            { 27, 0x24 }, { 28, 0x18 }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen8TermCodes = new Dictionary<uint, uint>()
+        {
+            { 0, WhiteZeroRunTermCode }, { 29, 0x2 }, { 30, 0x3 }, { 31, 0x1A }, { 32, 0x1B }, { 33, 0x12 }, { 34, 0x13 }, { 35, 0x14 },
+            { 36, 0x15 }, { 37, 0x16 }, { 38, 0x17 }, { 39, 0x28 }, { 40, 0x29 }, { 41, 0x2A }, { 42, 0x2B }, { 43, 0x2C }, { 44, 0x2D },
+            { 45, 0x4 }, { 46, 0x5 }, { 47, 0xA }, { 48, 0xB }, { 49, 0x52 }, { 50, 0x53 }, { 51, 0x54 }, { 52, 0x55 }, { 53, 0x24 },
+            { 54, 0x25 }, { 55, 0x58 }, { 56, 0x59 }, { 57, 0x5A }, { 58, 0x5B }, { 59, 0x4A }, { 60, 0x4B }, { 61, 0x32 }, { 62, 0x33 },
+            { 63, 0x34 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen2TermCodes = new Dictionary<uint, uint>()
+        {
+            { 2, 0x3 }, { 3, 0x2 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen3TermCodes = new Dictionary<uint, uint>()
+        {
+            { 1, 0x2 }, { 4, 0x3 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen4TermCodes = new Dictionary<uint, uint>()
+        {
+            { 5, 0x3 }, { 6, 0x2 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen5TermCodes = new Dictionary<uint, uint>()
+        {
+            { 7, 0x3 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen6TermCodes = new Dictionary<uint, uint>()
+        {
+            { 8, 0x5 }, { 9, 0x4 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen7TermCodes = new Dictionary<uint, uint>()
+        {
+            { 10, 0x4 }, { 11, 0x5 }, { 12, 0x7 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen8TermCodes = new Dictionary<uint, uint>()
+        {
+            { 13, 0x4 }, { 14, 0x7 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen9TermCodes = new Dictionary<uint, uint>()
+        {
+            { 15, 0x18 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen10TermCodes = new Dictionary<uint, uint>()
+        {
+            { 0, BlackZeroRunTermCode }, { 16, 0x17 }, { 17, 0x18 }, { 18, 0x8 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen11TermCodes = new Dictionary<uint, uint>()
+        {
+            { 19, 0x67 }, { 20, 0x68 }, { 21, 0x6C }, { 22, 0x37 }, { 23, 0x28 }, { 24, 0x17 }, { 25, 0x18 }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen12TermCodes = new Dictionary<uint, uint>()
+        {
+            { 26, 0xCA }, { 27, 0xCB }, { 28, 0xCC }, { 29, 0xCD }, { 30, 0x68 }, { 31, 0x69 }, { 32, 0x6A }, { 33, 0x6B }, { 34, 0xD2 },
+            { 35, 0xD3 }, { 36, 0xD4 }, { 37, 0xD5 }, { 38, 0xD6 }, { 39, 0xD7 }, { 40, 0x6C }, { 41, 0x6D }, { 42, 0xDA }, { 43, 0xDB },
+            { 44, 0x54 }, { 45, 0x55 }, { 46, 0x56 }, { 47, 0x57 }, { 48, 0x64 }, { 49, 0x65 }, { 50, 0x52 }, { 51, 0x53 }, { 52, 0x24 },
+            { 53, 0x37 }, { 54, 0x38 }, { 55, 0x27 }, { 56, 0x28 }, { 57, 0x58 }, { 58, 0x59 }, { 59, 0x2B }, { 60, 0x2C }, { 61, 0x5A },
+            { 62, 0x66 }, { 63, 0x67 }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen5MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 64, 0x1B }, { 128, 0x12 }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen6MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 192, 0x17 }, { 1664, 0x18 }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen8MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 320, 0x36 }, { 384, 0x37 }, { 448, 0x64 }, { 512, 0x65 }, { 576, 0x68 }, { 640, 0x67 }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen7MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 256, 0x37 }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen9MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 704, 0xCC }, { 768, 0xCD }, { 832, 0xD2 }, { 896, 0xD3 }, { 960, 0xD4 }, { 1024, 0xD5 }, { 1088, 0xD6 },
+            { 1152, 0xD7 }, { 1216, 0xD8 }, { 1280, 0xD9 }, { 1344, 0xDA }, { 1408, 0xDB }, { 1472, 0x98 }, { 1536, 0x99 },
+            { 1600, 0x9A }, { 1728, 0x9B }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen11MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 1792, 0x8 }, { 1856, 0xC }, { 1920, 0xD }
+        };
+
+        private static readonly Dictionary<uint, uint> WhiteLen12MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 1984, 0x12 }, { 2048, 0x13 }, { 2112, 0x14 }, { 2176, 0x15 }, { 2240, 0x16 }, { 2304, 0x17 }, { 2368, 0x1C },
+            { 2432, 0x1D }, { 2496, 0x1E }, { 2560, 0x1F }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen10MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 64, 0xF }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen11MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 1792, 0x8 }, { 1856, 0xC }, { 1920, 0xD }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen12MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 128, 0xC8 }, { 192, 0xC9 }, { 256, 0x5B }, { 320, 0x33 }, { 384, 0x34 }, { 448, 0x35 },
+            { 1984, 0x12 }, { 2048, 0x13 }, { 2112, 0x14 }, { 2176, 0x15 }, { 2240, 0x16 }, { 2304, 0x17 }, { 2368, 0x1C },
+            { 2432, 0x1D }, { 2496, 0x1E }, { 2560, 0x1F }
+        };
+
+        private static readonly Dictionary<uint, uint> BlackLen13MakeupCodes = new Dictionary<uint, uint>()
+        {
+            { 512, 0x6C }, { 576, 0x6D }, { 640, 0x4A }, { 704, 0x4B }, { 768, 0x4C }, { 832, 0x4D }, { 896, 0x72 },
+            { 960, 0x73 }, { 1024, 0x74 }, { 1088, 0x75 }, { 1152, 0x76 }, { 1216, 0x77 }, { 1280,  0x52 }, { 1344, 0x53 },
+            { 1408, 0x54 }, { 1472, 0x55 }, { 1536, 0x5A }, { 1600, 0x5B }, { 1664, 0x64 }, { 1728, 0x65 }
+        };
+
+        private int bytePosition;
+
+        private byte bitPosition;
+
+        private IMemoryOwner<byte> compressedDataBuffer;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="TiffCcittCompressor" /> class.
+        /// </summary>
+        /// <param name="output">The output.</param>
+        /// <param name="allocator">The allocator.</param>
+        /// <param name="width">The width.</param>
+        /// <param name="bitsPerPixel">The bits per pixel.</param>
+        protected TiffCcittCompressor(Stream output, MemoryAllocator allocator, int width, int bitsPerPixel)
+            : base(output, allocator, width, bitsPerPixel)
+        {
+            DebugGuard.IsTrue(bitsPerPixel == 1, nameof(bitsPerPixel), "CCITT compression requires one bit per pixel");
+            this.bytePosition = 0;
+            this.bitPosition = 0;
+        }
+
+        private uint GetWhiteMakeupCode(uint runLength, out uint codeLength)
+        {
+            codeLength = 0;
+
+            if (WhiteLen5MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 5;
+                return WhiteLen5MakeupCodes[runLength];
+            }
+
+            if (WhiteLen6MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 6;
+                return WhiteLen6MakeupCodes[runLength];
+            }
+
+            if (WhiteLen7MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 7;
+                return WhiteLen7MakeupCodes[runLength];
+            }
+
+            if (WhiteLen8MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 8;
+                return WhiteLen8MakeupCodes[runLength];
+            }
+
+            if (WhiteLen9MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 9;
+                return WhiteLen9MakeupCodes[runLength];
+            }
+
+            if (WhiteLen11MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 11;
+                return WhiteLen11MakeupCodes[runLength];
+            }
+
+            if (WhiteLen12MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 12;
+                return WhiteLen12MakeupCodes[runLength];
+            }
+
+            return 0;
+        }
+
+        private uint GetBlackMakeupCode(uint runLength, out uint codeLength)
+        {
+            codeLength = 0;
+
+            if (BlackLen10MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 10;
+                return BlackLen10MakeupCodes[runLength];
+            }
+
+            if (BlackLen11MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 11;
+                return BlackLen11MakeupCodes[runLength];
+            }
+
+            if (BlackLen12MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 12;
+                return BlackLen12MakeupCodes[runLength];
+            }
+
+            if (BlackLen13MakeupCodes.ContainsKey(runLength))
+            {
+                codeLength = 13;
+                return BlackLen13MakeupCodes[runLength];
+            }
+
+            return 0;
+        }
+
+        private uint GetWhiteTermCode(uint runLength, out uint codeLength)
+        {
+            codeLength = 0;
+
+            if (WhiteLen4TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 4;
+                return WhiteLen4TermCodes[runLength];
+            }
+
+            if (WhiteLen5TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 5;
+                return WhiteLen5TermCodes[runLength];
+            }
+
+            if (WhiteLen6TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 6;
+                return WhiteLen6TermCodes[runLength];
+            }
+
+            if (WhiteLen7TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 7;
+                return WhiteLen7TermCodes[runLength];
+            }
+
+            if (WhiteLen8TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 8;
+                return WhiteLen8TermCodes[runLength];
+            }
+
+            return 0;
+        }
+
+        private uint GetBlackTermCode(uint runLength, out uint codeLength)
+        {
+            codeLength = 0;
+
+            if (BlackLen2TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 2;
+                return BlackLen2TermCodes[runLength];
+            }
+
+            if (BlackLen3TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 3;
+                return BlackLen3TermCodes[runLength];
+            }
+
+            if (BlackLen4TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 4;
+                return BlackLen4TermCodes[runLength];
+            }
+
+            if (BlackLen5TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 5;
+                return BlackLen5TermCodes[runLength];
+            }
+
+            if (BlackLen6TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 6;
+                return BlackLen6TermCodes[runLength];
+            }
+
+            if (BlackLen7TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 7;
+                return BlackLen7TermCodes[runLength];
+            }
+
+            if (BlackLen8TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 8;
+                return BlackLen8TermCodes[runLength];
+            }
+
+            if (BlackLen9TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 9;
+                return BlackLen9TermCodes[runLength];
+            }
+
+            if (BlackLen10TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 10;
+                return BlackLen10TermCodes[runLength];
+            }
+
+            if (BlackLen11TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 11;
+                return BlackLen11TermCodes[runLength];
+            }
+
+            if (BlackLen12TermCodes.ContainsKey(runLength))
+            {
+                codeLength = 12;
+                return BlackLen12TermCodes[runLength];
+            }
+
+            return 0;
+        }
+
+        /// <summary>
+        /// Gets the best makeup run length for a given run length
+        /// </summary>
+        /// <param name="runLength">A run length needing a makeup code</param>
+        /// <returns>The makeup length for <paramref name="runLength"/>.</returns>
+        protected uint GetBestFittingMakeupRunLength(uint runLength)
+        {
+            DebugGuard.MustBeGreaterThanOrEqualTo(runLength, MakeupRunLength[0], nameof(runLength));
+
+            for (int i = 0; i < MakeupRunLength.Length - 1; i++)
+            {
+                if (MakeupRunLength[i] <= runLength && MakeupRunLength[i + 1] > runLength)
+                {
+                    return MakeupRunLength[i];
+                }
+            }
+
+            return MakeupRunLength[MakeupRunLength.Length - 1];
+        }
+
+        /// <summary>
+        /// Gets the terminating code for a run length.
+        /// </summary>
+        /// <param name="runLength">The run length to get the terminating code for.</param>
+        /// <param name="codeLength">The length of the terminating code.</param>
+        /// <param name="isWhiteRun">If <c>true</c>, the run is of white pixels.
+        /// If <c>false</c> the run is of black pixels</param>
+        /// <returns>The terminating code for a run of length <paramref name="runLength"/></returns>
+        protected uint GetTermCode(uint runLength, out uint codeLength, bool isWhiteRun)
+        {
+            if (isWhiteRun)
+            {
+                return this.GetWhiteTermCode(runLength, out codeLength);
+            }
+
+            return this.GetBlackTermCode(runLength, out codeLength);
+        }
+
+        /// <summary>
+        /// Gets the makeup code for a run length.
+        /// </summary>
+        /// <param name="runLength">The run length to get the makeup code for.</param>
+        /// <param name="codeLength">The length of the makeup code.</param>
+        /// <param name="isWhiteRun">If <c>true</c>, the run is of white pixels.
+        /// If <c>false</c> the run is of black pixels</param>
+        /// <returns>The makeup code for a run of length <paramref name="runLength"/></returns>
+        protected uint GetMakeupCode(uint runLength, out uint codeLength, bool isWhiteRun)
+        {
+            if (isWhiteRun)
+            {
+                return this.GetWhiteMakeupCode(runLength, out codeLength);
+            }
+
+            return this.GetBlackMakeupCode(runLength, out codeLength);
+        }
+
+        /// <summary>
+        /// Pads output to the next byte
+        /// </summary>
+        /// <remarks>
+        /// If the output is not currently on a byte boundary,
+        /// zero-pad it to the next byte
+        /// </remarks>
+        protected void PadByte()
+        {
+            // Check if padding is necessary.
+            if (this.bitPosition % 8 != 0)
+            {
+                // Skip padding bits, move to next byte.
+                this.bytePosition++;
+                this.bitPosition = 0;
+            }
+        }
+
+        /// <summary>
+        /// Writes a code to the output.
+        /// </summary>
+        /// <param name="codeLength">The length of the code to write.</param>
+        /// <param name="code">The code to be written.</param>
+        /// <param name="compressedData">The destination buffer to write the code to.</param>
+        protected void WriteCode(uint codeLength, uint code, Span<byte> compressedData)
+        {
+            while (codeLength > 0)
+            {
+                int bitNumber = (int)codeLength;
+                bool bit = (code & (1 << (bitNumber - 1))) != 0;
+                if (bit)
+                {
+                    BitWriterUtils.WriteBit(compressedData, this.bytePosition, this.bitPosition);
+                }
+                else
+                {
+                    BitWriterUtils.WriteZeroBit(compressedData, this.bytePosition, this.bitPosition);
+                }
+
+                this.bitPosition++;
+                if (this.bitPosition == 8)
+                {
+                    this.bytePosition++;
+                    this.bitPosition = 0;
+                }
+
+                codeLength--;
+            }
+        }
+
+        /// <summary>
+        /// Writes a image compressed with CCITT T6 to the stream.
+        /// </summary>
+        /// <param name="pixelsAsGray">The pixels as 8-bit gray array.</param>
+        /// <param name="height">The strip height.</param>
+        public override void CompressStrip(Span<byte> pixelsAsGray, int height)
+        {
+            DebugGuard.IsTrue(pixelsAsGray.Length / height == this.Width, "Values must be equals");
+            DebugGuard.IsTrue(pixelsAsGray.Length % height == 0, "Values must be equals");
+
+            this.compressedDataBuffer.Clear();
+            Span<byte> compressedData = this.compressedDataBuffer.GetSpan();
+
+            this.bytePosition = 0;
+            this.bitPosition = 0;
+
+            this.CompressStrip(pixelsAsGray, height, compressedData);
+
+            // Write the compressed data to the stream.
+            int bytesToWrite = this.bitPosition != 0 ? this.bytePosition + 1 : this.bytePosition;
+            this.Output.Write(compressedData.Slice(0, bytesToWrite));
+        }
+
+        /// <summary>
+        /// Compress a data strip
+        /// </summary>
+        /// <param name="pixelsAsGray">The pixels as 8-bit gray array.</param>
+        /// <param name="height">The strip height.</param>
+        /// <param name="compressedData">The destination for the compressed data.</param>
+        protected abstract void CompressStrip(Span<byte> pixelsAsGray, int height, Span<byte> compressedData);
+
+        /// <inheritdoc/>
+        protected override void Dispose(bool disposing) => this.compressedDataBuffer?.Dispose();
+
+        /// <inheritdoc/>
+        public override void Initialize(int rowsPerStrip)
+        {
+            // This is too much memory allocated, but just 1 bit per pixel will not do, if the compression rate is not good.
+            int maxNeededBytes = this.Width * rowsPerStrip;
+            this.compressedDataBuffer = this.Allocator.Allocate<byte>(maxNeededBytes);
+        }
+    }
+}

src/ImageSharp/Formats/Tiff/Compression/TiffBaseDecompressor.cs

@@ -34,17 +34,15 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression
         /// <param name="stripByteCount">The number of bytes to read from the input stream.</param>
         /// <param name="stripHeight">The height of the strip.</param>
         /// <param name="buffer">The output buffer for uncompressed data.</param>
-        public void Decompress(BufferedReadStream stream, uint stripOffset, uint stripByteCount, int stripHeight, Span<byte> buffer)
+        public void Decompress(BufferedReadStream stream, ulong stripOffset, ulong stripByteCount, int stripHeight, Span<byte> buffer)
         {
-            if (stripByteCount > int.MaxValue)
-            {
-                TiffThrowHelper.ThrowImageFormatException("The StripByteCount value is too big.");
-            }
+            DebugGuard.MustBeLessThanOrEqualTo(stripOffset, (ulong)long.MaxValue, nameof(stripOffset));
+            DebugGuard.MustBeLessThanOrEqualTo(stripByteCount, (ulong)long.MaxValue, nameof(stripByteCount));
 
-            stream.Seek(stripOffset, SeekOrigin.Begin);
+            stream.Seek((long)stripOffset, SeekOrigin.Begin);
             this.Decompress(stream, (int)stripByteCount, stripHeight, buffer);
 
-            if (stripOffset + stripByteCount < stream.Position)
+            if ((long)stripOffset + (long)stripByteCount < stream.Position)
             {
                 TiffThrowHelper.ThrowImageFormatException("Out of range when reading a strip.");
             }

src/ImageSharp/Formats/Tiff/Compression/TiffCompressorFactory.cs

@@ -55,6 +55,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression
                     DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
                     return new T4BitCompressor(output, allocator, width, bitsPerPixel, false);
 
+                case TiffCompression.CcittGroup4Fax:
+                    DebugGuard.IsTrue(compressionLevel == DeflateCompressionLevel.DefaultCompression, "No deflate compression level is expected to be set");
+                    DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
+                    return new T6BitCompressor(output, allocator, width, bitsPerPixel);
+
                 case TiffCompression.Ccitt1D:
                     DebugGuard.IsTrue(compressionLevel == DeflateCompressionLevel.DefaultCompression, "No deflate compression level is expected to be set");
                     DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");

src/ImageSharp/Formats/Tiff/Constants/TiffCompression.cs

@@ -35,9 +35,6 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Constants
 
         /// <summary>
         /// T6-encoding: CCITT T.6 bi-level encoding (see Section 11 of the TIFF 6.0 specification).
-        ///
-        /// Note: The TIFF encoder does not yet support this compression and will default to use no compression instead,
-        /// if this is choosen.
         /// </summary>
         CcittGroup4Fax = 4,
 

src/ImageSharp/Formats/Tiff/Constants/TiffConstants.cs

@@ -35,6 +35,16 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Constants
         /// </summary>
         public const ushort HeaderMagicNumber = 42;
 
+        /// <summary>
+        /// The big tiff header magic number
+        /// </summary>
+        public const ushort BigTiffHeaderMagicNumber = 43;
+
+        /// <summary>
+        /// The big tiff bytesize of offsets value.
+        /// </summary>
+        public const ushort BigTiffBytesize = 8;
+
         /// <summary>
         /// RowsPerStrip default value, which is effectively infinity.
         /// </summary>

src/ImageSharp/Formats/Tiff/Ifd/DirectoryReader.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using SixLabors.ImageSharp.Formats.Tiff.Constants;
+using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 
 namespace SixLabors.ImageSharp.Formats.Tiff
@@ -14,23 +15,27 @@ namespace SixLabors.ImageSharp.Formats.Tiff
     /// </summary>
     internal class DirectoryReader
     {
-        private readonly Stream stream;
+        private const int DirectoryMax = 65534;
 
-        private uint nextIfdOffset;
+        private readonly Stream stream;
 
-        private const int DirectoryMax = 65534;
+        private readonly MemoryAllocator allocator;
 
-        // used for sequential read big values (actual for multiframe big files)
-        // todo: different tags can link to the same data (stream offset) - investigate
-        private readonly SortedList<uint, Action> lazyLoaders = new(new DuplicateKeyComparer<uint>());
+        private ulong nextIfdOffset;
 
-        public DirectoryReader(Stream stream) => this.stream = stream;
+        public DirectoryReader(Stream stream, MemoryAllocator allocator)
+        {
+            this.stream = stream;
+            this.allocator = allocator;
+        }
 
         /// <summary>
         /// Gets the byte order.
         /// </summary>
         public ByteOrder ByteOrder { get; private set; }
 
+        public bool IsBigTiff { get; private set; }
+
         /// <summary>
         /// Reads image file directories.
         /// </summary>
@@ -38,14 +43,19 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         public IEnumerable<ExifProfile> Read()
         {
             this.ByteOrder = ReadByteOrder(this.stream);
-            this.nextIfdOffset = new HeaderReader(this.stream, this.ByteOrder).ReadFileHeader();
-            return this.ReadIfds();
+            var headerReader = new HeaderReader(this.stream, this.ByteOrder);
+            headerReader.ReadFileHeader();
+
+            this.nextIfdOffset = headerReader.FirstIfdOffset;
+            this.IsBigTiff = headerReader.IsBigTiff;
+
+            return this.ReadIfds(headerReader.IsBigTiff);
         }
 
         private static ByteOrder ReadByteOrder(Stream stream)
         {
-            var headerBytes = new byte[2];
-            stream.Read(headerBytes, 0, 2);
+            Span<byte> headerBytes = stackalloc byte[2];
+            stream.Read(headerBytes);
             if (headerBytes[0] == TiffConstants.ByteOrderLittleEndian && headerBytes[1] == TiffConstants.ByteOrderLittleEndian)
             {
                 return ByteOrder.LittleEndian;
@@ -59,16 +69,26 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             throw TiffThrowHelper.ThrowInvalidHeader();
         }
 
-        private IEnumerable<ExifProfile> ReadIfds()
+        private IEnumerable<ExifProfile> ReadIfds(bool isBigTiff)
         {
             var readers = new List<EntryReader>();
-            while (this.nextIfdOffset != 0 && this.nextIfdOffset < this.stream.Length)
+            while (this.nextIfdOffset != 0 && this.nextIfdOffset < (ulong)this.stream.Length)
             {
-                var reader = new EntryReader(this.stream, this.ByteOrder, this.nextIfdOffset, this.lazyLoaders);
-                reader.ReadTags();
+                var reader = new EntryReader(this.stream, this.ByteOrder, this.allocator);
+                reader.ReadTags(isBigTiff, this.nextIfdOffset);
 
-                this.nextIfdOffset = reader.NextIfdOffset;
+                if (reader.BigValues.Count > 0)
+                {
+                    reader.BigValues.Sort((t1, t2) => t1.Offset.CompareTo(t2.Offset));
+
+                    // this means that most likely all elements are placed  before next IFD
+                    if (reader.BigValues[0].Offset < reader.NextIfdOffset)
+                    {
+                        reader.ReadBigValues();
+                    }
+                }
 
+                this.nextIfdOffset = reader.NextIfdOffset;
                 readers.Add(reader);
 
                 if (readers.Count >= DirectoryMax)
@@ -77,36 +97,15 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 }
             }
 
-            // Sequential reading big values.
-            foreach (Action loader in this.lazyLoaders.Values)
-            {
-                loader();
-            }
-
-            var list = new List<ExifProfile>();
+            var list = new List<ExifProfile>(readers.Count);
             foreach (EntryReader reader in readers)
             {
+                reader.ReadBigValues();
                 var profile = new ExifProfile(reader.Values, reader.InvalidTags);
                 list.Add(profile);
             }
 
             return list;
         }
-
-        /// <summary>
-        /// <see cref="DuplicateKeyComparer{TKey}"/> used for possibility add a duplicate offsets (but tags don't duplicate).
-        /// </summary>
-        /// <typeparam name="TKey">The type of the key.</typeparam>
-        private class DuplicateKeyComparer<TKey> : IComparer<TKey>
-            where TKey : IComparable
-        {
-            public int Compare(TKey x, TKey y)
-            {
-                int result = x.CompareTo(y);
-
-                // Handle equality as being greater.
-                return (result == 0) ? 1 : result;
-            }
-        }
     }
 }

src/ImageSharp/Formats/Tiff/Ifd/EntryReader.cs

@@ -1,64 +1,78 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
-using System;
 using System.Collections.Generic;
 using System.IO;
 using SixLabors.ImageSharp.Formats.Tiff.Constants;
+using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 
 namespace SixLabors.ImageSharp.Formats.Tiff
 {
     internal class EntryReader : BaseExifReader
     {
-        private readonly uint startOffset;
-
-        private readonly SortedList<uint, Action> lazyLoaders;
-
-        public EntryReader(Stream stream, ByteOrder byteOrder, uint ifdOffset, SortedList<uint, Action> lazyLoaders)
-            : base(stream)
-        {
+        public EntryReader(Stream stream, ByteOrder byteOrder, MemoryAllocator allocator)
+            : base(stream, allocator) =>
             this.IsBigEndian = byteOrder == ByteOrder.BigEndian;
-            this.startOffset = ifdOffset;
-            this.lazyLoaders = lazyLoaders;
-        }
 
         public List<IExifValue> Values { get; } = new();
 
-        public uint NextIfdOffset { get; private set; }
+        public ulong NextIfdOffset { get; private set; }
 
-        public void ReadTags()
+        public void ReadTags(bool isBigTiff, ulong ifdOffset)
         {
-            this.ReadValues(this.Values, this.startOffset);
-            this.NextIfdOffset = this.ReadUInt32();
+            if (!isBigTiff)
+            {
+                this.ReadValues(this.Values, (uint)ifdOffset);
+                this.NextIfdOffset = this.ReadUInt32();
+
+                this.ReadSubIfd(this.Values);
+            }
+            else
+            {
+                this.ReadValues64(this.Values, ifdOffset);
+                this.NextIfdOffset = this.ReadUInt64();
 
-            this.ReadSubIfd(this.Values);
+                //// this.ReadSubIfd64(this.Values);
+            }
         }
 
-        protected override void RegisterExtLoader(uint offset, Action reader) =>
-            this.lazyLoaders.Add(offset, reader);
+        public void ReadBigValues() => this.ReadBigValues(this.Values);
     }
 
     internal class HeaderReader : BaseExifReader
     {
         public HeaderReader(Stream stream, ByteOrder byteOrder)
-            : base(stream) =>
+            : base(stream, null) =>
             this.IsBigEndian = byteOrder == ByteOrder.BigEndian;
 
-        public uint FirstIfdOffset { get; private set; }
+        public bool IsBigTiff { get; private set; }
 
-        public uint ReadFileHeader()
+        public ulong FirstIfdOffset { get; private set; }
+
+        public void ReadFileHeader()
         {
             ushort magic = this.ReadUInt16();
-            if (magic != TiffConstants.HeaderMagicNumber)
+            if (magic == TiffConstants.HeaderMagicNumber)
             {
-                TiffThrowHelper.ThrowInvalidHeader();
+                this.IsBigTiff = false;
+                this.FirstIfdOffset = this.ReadUInt32();
+                return;
             }
+            else if (magic == TiffConstants.BigTiffHeaderMagicNumber)
+            {
+                this.IsBigTiff = true;
 
-            this.FirstIfdOffset = this.ReadUInt32();
-            return this.FirstIfdOffset;
-        }
+                ushort bytesize = this.ReadUInt16();
+                ushort reserve = this.ReadUInt16();
+                if (bytesize == TiffConstants.BigTiffBytesize && reserve == 0)
+                {
+                    this.FirstIfdOffset = this.ReadUInt64();
+                    return;
+                }
+            }
 
-        protected override void RegisterExtLoader(uint offset, Action reader) => throw new NotSupportedException();
+            TiffThrowHelper.ThrowInvalidHeader();
+        }
     }
 }

src/ImageSharp/Formats/Tiff/README.md

@@ -45,7 +45,7 @@
 |Ccitt1D                    |   Y   |   Y   |                          |
 |PackBits                   |   Y   |   Y   |                          |
 |CcittGroup3Fax             |   Y   |   Y   |                          |
-|CcittGroup4Fax             |       |   Y   |                          |
+|CcittGroup4Fax             |   Y   |   Y   |                          |
 |Lzw                        |   Y   |   Y   | Based on ImageSharp GIF LZW implementation - this code could be modified to be (i) shared, or (ii) optimised for each case |
 |Old Jpeg                   |       |       | We should not even try to support this |
 |Jpeg (Technote 2)          |   Y   |   Y   |                          |

src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.Buffers;
 using System.Collections.Generic;
 using System.Linq;
@@ -12,6 +13,7 @@ using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Tiff
@@ -41,6 +43,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// </summary>
         private ByteOrder byteOrder;
 
+        /// <summary>
+        /// Indicating whether is BigTiff format.
+        /// </summary>
+        private bool isBigTiff;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="TiffDecoderCore" /> class.
         /// </summary>
@@ -141,10 +148,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             where TPixel : unmanaged, IPixel<TPixel>
         {
             this.inputStream = stream;
-            var reader = new DirectoryReader(stream);
+            var reader = new DirectoryReader(stream, this.Configuration.MemoryAllocator);
 
             IEnumerable<ExifProfile> directories = reader.Read();
             this.byteOrder = reader.ByteOrder;
+            this.isBigTiff = reader.IsBigTiff;
 
             var frames = new List<ImageFrame<TPixel>>();
             foreach (ExifProfile ifd in directories)
@@ -154,7 +162,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 frames.Add(frame);
             }
 
-            ImageMetadata metadata = TiffDecoderMetadataCreator.Create(frames, this.ignoreMetadata, reader.ByteOrder);
+            ImageMetadata metadata = TiffDecoderMetadataCreator.Create(frames, this.ignoreMetadata, reader.ByteOrder, reader.IsBigTiff);
 
             // TODO: Tiff frames can have different sizes
             ImageFrame<TPixel> root = frames[0];
@@ -174,13 +182,13 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         public IImageInfo Identify(BufferedReadStream stream, CancellationToken cancellationToken)
         {
             this.inputStream = stream;
-            var reader = new DirectoryReader(stream);
+            var reader = new DirectoryReader(stream, this.Configuration.MemoryAllocator);
             IEnumerable<ExifProfile> directories = reader.Read();
 
             ExifProfile rootFrameExifProfile = directories.First();
             var rootMetadata = TiffFrameMetadata.Parse(rootFrameExifProfile);
 
-            ImageMetadata metadata = TiffDecoderMetadataCreator.Create(reader.ByteOrder, rootFrameExifProfile);
+            ImageMetadata metadata = TiffDecoderMetadataCreator.Create(reader.ByteOrder, reader.IsBigTiff, rootFrameExifProfile);
             int width = GetImageWidth(rootFrameExifProfile);
             int height = GetImageHeight(rootFrameExifProfile);
 
@@ -197,9 +205,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         private ImageFrame<TPixel> DecodeFrame<TPixel>(ExifProfile tags, CancellationToken cancellationToken)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            ImageFrameMetadata imageFrameMetaData = this.ignoreMetadata ?
-                new ImageFrameMetadata() :
-                new ImageFrameMetadata { ExifProfile = tags, XmpProfile = tags.GetValue(ExifTag.XMP)?.Value };
+            var imageFrameMetaData = new ImageFrameMetadata();
+            if (!this.ignoreMetadata)
+            {
+                imageFrameMetaData.ExifProfile = tags;
+            }
 
             TiffFrameMetadata tiffFrameMetaData = imageFrameMetaData.GetTiffMetadata();
             TiffFrameMetadata.Parse(tiffFrameMetaData, tags);
@@ -211,21 +221,58 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             var frame = new ImageFrame<TPixel>(this.Configuration, width, height, imageFrameMetaData);
 
             int rowsPerStrip = tags.GetValue(ExifTag.RowsPerStrip) != null ? (int)tags.GetValue(ExifTag.RowsPerStrip).Value : TiffConstants.RowsPerStripInfinity;
-            Number[] stripOffsets = tags.GetValue(ExifTag.StripOffsets)?.Value;
-            Number[] stripByteCounts = tags.GetValue(ExifTag.StripByteCounts)?.Value;
+
+            var stripOffsetsArray = (Array)tags.GetValueInternal(ExifTag.StripOffsets).GetValue();
+            var stripByteCountsArray = (Array)tags.GetValueInternal(ExifTag.StripByteCounts).GetValue();
+
+            IMemoryOwner<ulong> stripOffsetsMemory = this.ConvertNumbers(stripOffsetsArray, out Span<ulong> stripOffsets);
+            IMemoryOwner<ulong> stripByteCountsMemory = this.ConvertNumbers(stripByteCountsArray, out Span<ulong> stripByteCounts);
 
             if (this.PlanarConfiguration == TiffPlanarConfiguration.Planar)
             {
-                this.DecodeStripsPlanar(frame, rowsPerStrip, stripOffsets, stripByteCounts, cancellationToken);
+                this.DecodeStripsPlanar(
+                    frame,
+                    rowsPerStrip,
+                    stripOffsets,
+                    stripByteCounts,
+                    cancellationToken);
             }
             else
             {
-                this.DecodeStripsChunky(frame, rowsPerStrip, stripOffsets, stripByteCounts, cancellationToken);
+                this.DecodeStripsChunky(
+                    frame,
+                    rowsPerStrip,
+                    stripOffsets,
+                    stripByteCounts,
+                    cancellationToken);
             }
 
+            stripOffsetsMemory?.Dispose();
+            stripByteCountsMemory?.Dispose();
             return frame;
         }
 
+        private IMemoryOwner<ulong> ConvertNumbers(Array array, out Span<ulong> span)
+        {
+            if (array is Number[] numbers)
+            {
+                IMemoryOwner<ulong> memory = this.memoryAllocator.Allocate<ulong>(numbers.Length);
+                span = memory.GetSpan();
+                for (int i = 0; i < numbers.Length; i++)
+                {
+                    span[i] = (uint)numbers[i];
+                }
+
+                return memory;
+            }
+            else
+            {
+                DebugGuard.IsTrue(array is ulong[], $"Expected {nameof(UInt64)} array.");
+                span = (ulong[])array;
+                return null;
+            }
+        }
+
         /// <summary>
         /// Calculates the size (in bytes) for a pixel buffer using the determined color format.
         /// </summary>
@@ -276,7 +323,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// <param name="stripOffsets">An array of byte offsets to each strip in the image.</param>
         /// <param name="stripByteCounts">An array of the size of each strip (in bytes).</param>
         /// <param name="cancellationToken">The token to monitor cancellation.</param>
-        private void DecodeStripsPlanar<TPixel>(ImageFrame<TPixel> frame, int rowsPerStrip, Number[] stripOffsets, Number[] stripByteCounts, CancellationToken cancellationToken)
+        private void DecodeStripsPlanar<TPixel>(ImageFrame<TPixel> frame, int rowsPerStrip, Span<ulong> stripOffsets, Span<ulong> stripByteCounts, CancellationToken cancellationToken)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             int stripsPerPixel = this.BitsPerSample.Channels;
@@ -329,10 +376,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     {
                         decompressor.Decompress(
                             this.inputStream,
-                            (uint)stripOffsets[stripIndex],
-                            (uint)stripByteCounts[stripIndex],
+                            stripOffsets[stripIndex],
+                            stripByteCounts[stripIndex],
                             stripHeight,
                             stripBuffers[planeIndex].GetSpan());
+
                         stripIndex += stripsPerPlane;
                     }
 
@@ -357,7 +405,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// <param name="stripOffsets">The strip offsets.</param>
         /// <param name="stripByteCounts">The strip byte counts.</param>
         /// <param name="cancellationToken">The token to monitor cancellation.</param>
-        private void DecodeStripsChunky<TPixel>(ImageFrame<TPixel> frame, int rowsPerStrip, Number[] stripOffsets, Number[] stripByteCounts, CancellationToken cancellationToken)
+        private void DecodeStripsChunky<TPixel>(ImageFrame<TPixel> frame, int rowsPerStrip, Span<ulong> stripOffsets, Span<ulong> stripByteCounts, CancellationToken cancellationToken)
            where TPixel : unmanaged, IPixel<TPixel>
         {
             // If the rowsPerStrip has the default value, which is effectively infinity. That is, the entire image is one strip.
@@ -370,7 +418,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             int bitsPerPixel = this.BitsPerPixel;
 
             using IMemoryOwner<byte> stripBuffer = this.memoryAllocator.Allocate<byte>(uncompressedStripSize, AllocationOptions.Clean);
-            System.Span<byte> stripBufferSpan = stripBuffer.GetSpan();
+            Span<byte> stripBufferSpan = stripBuffer.GetSpan();
             Buffer2D<TPixel> pixels = frame.PixelBuffer;
 
             using TiffBaseDecompressor decompressor = TiffDecompressorsFactory.Create(
@@ -413,7 +461,12 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     break;
                 }
 
-                decompressor.Decompress(this.inputStream, (uint)stripOffsets[stripIndex], (uint)stripByteCounts[stripIndex], stripHeight, stripBufferSpan);
+                decompressor.Decompress(
+                    this.inputStream,
+                    stripOffsets[stripIndex],
+                    stripByteCounts[stripIndex],
+                    stripHeight,
+                    stripBufferSpan);
 
                 colorDecoder.Decode(stripBufferSpan, pixels, 0, top, frame.Width, stripHeight);
             }
@@ -432,6 +485,8 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 TiffThrowHelper.ThrowImageFormatException("The TIFF image frame is missing the ImageWidth");
             }
 
+            DebugGuard.MustBeLessThanOrEqualTo((ulong)width.Value, (ulong)int.MaxValue, nameof(ExifTag.ImageWidth));
+
             return (int)width.Value;
         }
 

src/ImageSharp/Formats/Tiff/TiffDecoderMetadataCreator.cs

@@ -9,6 +9,7 @@ using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.Metadata.Profiles.Icc;
 using SixLabors.ImageSharp.Metadata.Profiles.Iptc;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Tiff
@@ -18,7 +19,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
     /// </summary>
     internal static class TiffDecoderMetadataCreator
     {
-        public static ImageMetadata Create<TPixel>(List<ImageFrame<TPixel>> frames, bool ignoreMetadata, ByteOrder byteOrder)
+        public static ImageMetadata Create<TPixel>(List<ImageFrame<TPixel>> frames, bool ignoreMetadata, ByteOrder byteOrder, bool isBigTiff)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             if (frames.Count < 1)
@@ -26,13 +27,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 TiffThrowHelper.ThrowImageFormatException("Expected at least one frame.");
             }
 
-            var imageMetaData = new ImageMetadata();
-            ExifProfile exifProfileRootFrame = frames[0].Metadata.ExifProfile;
-
-            SetResolution(imageMetaData, exifProfileRootFrame);
-
-            TiffMetadata tiffMetadata = imageMetaData.GetTiffMetadata();
-            tiffMetadata.ByteOrder = byteOrder;
+            ImageMetadata imageMetaData = Create(byteOrder, isBigTiff, frames[0].Metadata.ExifProfile);
 
             if (!ignoreMetadata)
             {
@@ -45,6 +40,12 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                         frameMetaData.IptcProfile = new IptcProfile(iptcBytes);
                     }
 
+                    IExifValue<byte[]> xmpProfileBytes = frameMetaData.ExifProfile.GetValue(ExifTag.XMP);
+                    if (xmpProfileBytes != null)
+                    {
+                        frameMetaData.XmpProfile = new XmpProfile(xmpProfileBytes.Value);
+                    }
+
                     IExifValue<byte[]> iccProfileBytes = frameMetaData.ExifProfile.GetValue(ExifTag.IccProfile);
                     if (iccProfileBytes != null)
                     {
@@ -56,13 +57,14 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             return imageMetaData;
         }
 
-        public static ImageMetadata Create(ByteOrder byteOrder, ExifProfile exifProfile)
+        public static ImageMetadata Create(ByteOrder byteOrder, bool isBigTiff, ExifProfile exifProfile)
         {
             var imageMetaData = new ImageMetadata();
             SetResolution(imageMetaData, exifProfile);
 
             TiffMetadata tiffMetadata = imageMetaData.GetTiffMetadata();
             tiffMetadata.ByteOrder = byteOrder;
+            tiffMetadata.FormatType = isBigTiff ? TiffFormatType.BigTIFF : TiffFormatType.Default;
 
             return imageMetaData;
         }

src/ImageSharp/Formats/Tiff/TiffDecoderOptionsParser.cs

@@ -24,12 +24,12 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// <param name="frameMetadata">The IFD entries container to read the image format information for current frame.</param>
         public static void VerifyAndParse(this TiffDecoderCore options, ExifProfile exifProfile, TiffFrameMetadata frameMetadata)
         {
-            if (exifProfile.GetValue(ExifTag.TileOffsets)?.Value != null)
+            if (exifProfile.GetValueInternal(ExifTag.TileOffsets) is not null || exifProfile.GetValueInternal(ExifTag.TileByteCounts) is not null)
             {
                 TiffThrowHelper.ThrowNotSupported("Tiled images are not supported.");
             }
 
-            if (exifProfile.GetValue(ExifTag.ExtraSamples)?.Value != null)
+            if (exifProfile.GetValueInternal(ExifTag.ExtraSamples) is not null)
             {
                 TiffThrowHelper.ThrowNotSupported("ExtraSamples is not supported.");
             }
@@ -95,12 +95,12 @@ namespace SixLabors.ImageSharp.Formats.Tiff
 
         private static void VerifyRequiredFieldsArePresent(ExifProfile exifProfile, TiffFrameMetadata frameMetadata)
         {
-            if (exifProfile.GetValue(ExifTag.StripOffsets) == null)
+            if (exifProfile.GetValueInternal(ExifTag.StripOffsets) is null)
             {
                 TiffThrowHelper.ThrowImageFormatException("StripOffsets are missing and are required for decoding the TIFF image!");
             }
 
-            if (exifProfile.GetValue(ExifTag.StripByteCounts) == null)
+            if (exifProfile.GetValueInternal(ExifTag.StripByteCounts) is null)
             {
                 TiffThrowHelper.ThrowImageFormatException("StripByteCounts are missing and are required for decoding the TIFF image!");
             }
@@ -384,7 +384,8 @@ namespace SixLabors.ImageSharp.Formats.Tiff
 
         private static void ParseCompression(this TiffDecoderCore options, TiffCompression? compression, ExifProfile exifProfile)
         {
-            switch (compression)
+            // Default 1 (No compression) https://www.awaresystems.be/imaging/tiff/tifftags/compression.html
+            switch (compression ?? TiffCompression.None)
             {
                 case TiffCompression.None:
                 {
@@ -441,7 +442,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
 
                 default:
                 {
-                    TiffThrowHelper.ThrowNotSupported($"The specified TIFF compression format {compression} is not supported");
+                    TiffThrowHelper.ThrowNotSupported($"The specified TIFF compression format '{compression}' is not supported");
                     break;
                 }
             }

src/ImageSharp/Formats/Tiff/TiffEncoderEntriesCollector.cs

@@ -6,6 +6,7 @@ using SixLabors.ImageSharp.Common.Helpers;
 using SixLabors.ImageSharp.Formats.Tiff.Constants;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 
 namespace SixLabors.ImageSharp.Formats.Tiff
 {
@@ -57,9 +58,9 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             {
                 ImageFrame rootFrame = image.Frames.RootFrame;
                 ExifProfile rootFrameExifProfile = rootFrame.Metadata.ExifProfile ?? new ExifProfile();
-                byte[] foorFrameXmpBytes = rootFrame.Metadata.XmpProfile;
+                XmpProfile rootFrameXmpProfile = rootFrame.Metadata.XmpProfile;
 
-                this.ProcessProfiles(image.Metadata, rootFrameExifProfile, foorFrameXmpBytes);
+                this.ProcessProfiles(image.Metadata, rootFrameExifProfile, rootFrameXmpProfile);
                 this.ProcessMetadata(rootFrameExifProfile);
 
                 if (!this.Collector.Entries.Exists(t => t.Tag == ExifTag.Software))
@@ -149,7 +150,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 }
             }
 
-            private void ProcessProfiles(ImageMetadata imageMetadata, ExifProfile exifProfile, byte[] xmpProfile)
+            private void ProcessProfiles(ImageMetadata imageMetadata, ExifProfile exifProfile, XmpProfile xmpProfile)
             {
                 if (exifProfile != null && exifProfile.Parts != ExifParts.None)
                 {
@@ -203,7 +204,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 {
                     var xmp = new ExifByteArray(ExifTagValue.XMP, ExifDataType.Byte)
                     {
-                        Value = xmpProfile
+                        Value = xmpProfile.Data
                     };
 
                     this.Collector.Add(xmp);
@@ -394,6 +395,9 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     case TiffCompression.CcittGroup3Fax:
                         return (ushort)TiffCompression.CcittGroup3Fax;
 
+                    case TiffCompression.CcittGroup4Fax:
+                        return (ushort)TiffCompression.CcittGroup4Fax;
+
                     case TiffCompression.Ccitt1D:
                         return (ushort)TiffCompression.Ccitt1D;
 

src/ImageSharp/Formats/Tiff/TiffFormatType.cs

@@ -0,0 +1,21 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Tiff
+{
+    /// <summary>
+    /// The TIFF format type enum.
+    /// </summary>
+    public enum TiffFormatType
+    {
+        /// <summary>
+        /// The TIFF file format type.
+        /// </summary>
+        Default,
+
+        /// <summary>
+        /// The BigTIFF format type.
+        /// </summary>
+        BigTIFF
+    }
+}

src/ImageSharp/Formats/Tiff/TiffImageFormatDetector.cs

@@ -11,7 +11,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
     public sealed class TiffImageFormatDetector : IImageFormatDetector
     {
         /// <inheritdoc/>
-        public int HeaderSize => 4;
+        public int HeaderSize => 8;
 
         /// <inheritdoc/>
         public IImageFormat DetectFormat(ReadOnlySpan<byte> header)
@@ -26,9 +26,42 @@ namespace SixLabors.ImageSharp.Formats.Tiff
 
         private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)
         {
-            return header.Length >= this.HeaderSize &&
-                   ((header[0] == 0x49 && header[1] == 0x49 && header[2] == 0x2A && header[3] == 0x00) || // Little-endian
-                    (header[0] == 0x4D && header[1] == 0x4D && header[2] == 0x00 && header[3] == 0x2A)); // Big-endian
+            if (header.Length >= this.HeaderSize)
+            {
+                if (header[0] == 0x49 && header[1] == 0x49)
+                {
+                    // Little-endian
+                    if (header[2] == 0x2A && header[3] == 0x00)
+                    {
+                        // tiff
+                        return true;
+                    }
+                    else if (header[2] == 0x2B && header[3] == 0x00
+                         && header[4] == 8 && header[5] == 0 && header[6] == 0 && header[7] == 0)
+                    {
+                        // big tiff
+                        return true;
+                    }
+                }
+                else if (header[0] == 0x4D && header[1] == 0x4D)
+                {
+                    // Big-endian
+                    if (header[2] == 0 && header[3] == 0x2A)
+                    {
+                        // tiff
+                        return true;
+                    }
+                    else
+                    if (header[2] == 0 && header[3] == 0x2B
+                        && header[4] == 0 && header[5] == 8 && header[6] == 0 && header[7] == 0)
+                    {
+                        // big tiff
+                        return true;
+                    }
+                }
+            }
+
+            return false;
         }
     }
 }

src/ImageSharp/Formats/Tiff/TiffMetadata.cs

@@ -26,6 +26,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// </summary>
         public ByteOrder ByteOrder { get; set; }
 
+        /// <summary>
+        /// Gets or sets the format type.
+        /// </summary>
+        public TiffFormatType FormatType { get; set; }
+
         /// <inheritdoc/>
         public IDeepCloneable DeepClone() => new TiffMetadata(this);
     }

src/ImageSharp/Formats/Tiff/TiffThrowHelper.cs

@@ -16,7 +16,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// </summary>
         /// <param name="errorMessage">The error message for the exception.</param>
         [MethodImpl(MethodImplOptions.NoInlining)]
-        public static void ThrowImageFormatException(string errorMessage) => throw new ImageFormatException(errorMessage);
+        public static Exception ThrowImageFormatException(string errorMessage) => throw new ImageFormatException(errorMessage);
 
         [MethodImpl(InliningOptions.ColdPath)]
         public static Exception NotSupportedDecompressor(string compressionType) => throw new NotSupportedException($"Not supported decoder compression method: {compressionType}");

src/ImageSharp/Formats/Tiff/Writers/TiffBiColorWriter{TPixel}.cs

@@ -37,7 +37,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Writers
         {
             int width = this.Image.Width;
 
-            if (compressor.Method == TiffCompression.CcittGroup3Fax || compressor.Method == TiffCompression.Ccitt1D)
+            if (compressor.Method == TiffCompression.CcittGroup3Fax || compressor.Method == TiffCompression.Ccitt1D || compressor.Method == TiffCompression.CcittGroup4Fax)
             {
                 // Special case for T4BitCompressor.
                 int stripPixels = width * height;

src/ImageSharp/Formats/Webp/AlphaDecoder.cs

@@ -9,6 +9,10 @@ using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Formats.Webp.BitReader;
 using SixLabors.ImageSharp.Formats.Webp.Lossless;
 using SixLabors.ImageSharp.Memory;
+#if SUPPORTS_RUNTIME_INTRINSICS
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.X86;
+#endif
 
 namespace SixLabors.ImageSharp.Formats.Webp
 {
@@ -307,34 +311,94 @@ namespace SixLabors.ImageSharp.Formats.Webp
 
         private static void HorizontalUnfilter(Span<byte> prev, Span<byte> input, Span<byte> dst, int width)
         {
-            byte pred = (byte)(prev == null ? 0 : prev[0]);
+#if SUPPORTS_RUNTIME_INTRINSICS
+            if (Sse2.IsSupported)
+            {
+                dst[0] = (byte)(input[0] + (prev.IsEmpty ? 0 : prev[0]));
+                if (width <= 1)
+                {
+                    return;
+                }
+
+                nint i;
+                Vector128<int> last = Vector128<int>.Zero.WithElement(0, dst[0]);
+                ref byte srcRef = ref MemoryMarshal.GetReference(input);
+                for (i = 1; i + 8 <= width; i += 8)
+                {
+                    var a0 = Vector128.Create(Unsafe.As<byte, long>(ref Unsafe.Add(ref srcRef, i)), 0);
+                    Vector128<byte> a1 = Sse2.Add(a0.AsByte(), last.AsByte());
+                    Vector128<byte> a2 = Sse2.ShiftLeftLogical128BitLane(a1, 1);
+                    Vector128<byte> a3 = Sse2.Add(a1, a2);
+                    Vector128<byte> a4 = Sse2.ShiftLeftLogical128BitLane(a3, 2);
+                    Vector128<byte> a5 = Sse2.Add(a3, a4);
+                    Vector128<byte> a6 = Sse2.ShiftLeftLogical128BitLane(a5, 4);
+                    Vector128<byte> a7 = Sse2.Add(a5, a6);
+
+                    ref byte outputRef = ref Unsafe.Add(ref MemoryMarshal.GetReference(dst), i);
+                    Unsafe.As<byte, Vector64<byte>>(ref outputRef) = a7.GetLower();
+                    last = Sse2.ShiftRightLogical(a7.AsInt64(), 56).AsInt32();
+                }
 
-            for (int i = 0; i < width; i++)
+                for (; i < width; ++i)
+                {
+                    dst[(int)i] = (byte)(input[(int)i] + dst[(int)i - 1]);
+                }
+            }
+            else
+#endif
             {
-                byte val = (byte)(pred + input[i]);
-                pred = val;
-                dst[i] = val;
+                byte pred = (byte)(prev.IsEmpty ? 0 : prev[0]);
+
+                for (int i = 0; i < width; i++)
+                {
+                    byte val = (byte)(pred + input[i]);
+                    pred = val;
+                    dst[i] = val;
+                }
             }
         }
 
         private static void VerticalUnfilter(Span<byte> prev, Span<byte> input, Span<byte> dst, int width)
         {
-            if (prev == null)
+            if (prev.IsEmpty)
             {
                 HorizontalUnfilter(null, input, dst, width);
             }
             else
             {
-                for (int i = 0; i < width; i++)
+#if SUPPORTS_RUNTIME_INTRINSICS
+                if (Avx2.IsSupported)
                 {
-                    dst[i] = (byte)(prev[i] + input[i]);
+                    nint i;
+                    int maxPos = width & ~31;
+                    for (i = 0; i < maxPos; i += 32)
+                    {
+                        Vector256<int> a0 = Unsafe.As<byte, Vector256<int>>(ref Unsafe.Add(ref MemoryMarshal.GetReference(input), i));
+                        Vector256<int> b0 = Unsafe.As<byte, Vector256<int>>(ref Unsafe.Add(ref MemoryMarshal.GetReference(prev), i));
+                        Vector256<byte> c0 = Avx2.Add(a0.AsByte(), b0.AsByte());
+                        ref byte outputRef = ref Unsafe.Add(ref MemoryMarshal.GetReference(dst), i);
+                        Unsafe.As<byte, Vector256<byte>>(ref outputRef) = c0;
+                    }
+
+                    for (; i < width; i++)
+                    {
+                        dst[(int)i] = (byte)(prev[(int)i] + input[(int)i]);
+                    }
+                }
+                else
+#endif
+                {
+                    for (int i = 0; i < width; i++)
+                    {
+                        dst[i] = (byte)(prev[i] + input[i]);
+                    }
                 }
             }
         }
 
         private static void GradientUnfilter(Span<byte> prev, Span<byte> input, Span<byte> dst, int width)
         {
-            if (prev == null)
+            if (prev.IsEmpty)
             {
                 HorizontalUnfilter(null, input, dst, width);
             }

src/ImageSharp/Formats/Webp/AlphaEncoder.cs

@@ -0,0 +1,133 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Buffers;
+using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.Formats.Webp.Lossless;
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Formats.Webp
+{
+    /// <summary>
+    /// Methods for encoding the alpha data of a VP8 image.
+    /// </summary>
+    internal class AlphaEncoder : IDisposable
+    {
+        private IMemoryOwner<byte> alphaData;
+
+        /// <summary>
+        /// Encodes the alpha channel data.
+        /// Data is either compressed as lossless webp image or uncompressed.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel format.</typeparam>
+        /// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
+        /// <param name="configuration">The global configuration.</param>
+        /// <param name="memoryAllocator">The memory manager.</param>
+        /// <param name="compress">Indicates, if the data should be compressed with the lossless webp compression.</param>
+        /// <param name="size">The size in bytes of the alpha data.</param>
+        /// <returns>The encoded alpha data.</returns>
+        public IMemoryOwner<byte> EncodeAlpha<TPixel>(Image<TPixel> image, Configuration configuration, MemoryAllocator memoryAllocator, bool compress, out int size)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            int width = image.Width;
+            int height = image.Height;
+            this.alphaData = ExtractAlphaChannel(image, configuration, memoryAllocator);
+
+            if (compress)
+            {
+                WebpEncodingMethod effort = WebpEncodingMethod.Default;
+                int quality = 8 * (int)effort;
+                using var lossLessEncoder = new Vp8LEncoder(
+                    memoryAllocator,
+                    configuration,
+                    width,
+                    height,
+                    quality,
+                    effort,
+                    WebpTransparentColorMode.Preserve,
+                    false,
+                    0);
+
+                // The transparency information will be stored in the green channel of the ARGB quadruplet.
+                // The green channel is allowed extra transformation steps in the specification -- unlike the other channels,
+                // that can improve compression.
+                using Image<Rgba32> alphaAsImage = DispatchAlphaToGreen(image, this.alphaData.GetSpan());
+
+                size = lossLessEncoder.EncodeAlphaImageData(alphaAsImage, this.alphaData);
+
+                return this.alphaData;
+            }
+
+            size = width * height;
+            return this.alphaData;
+        }
+
+        /// <summary>
+        /// Store the transparency in the green channel.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel format.</typeparam>
+        /// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
+        /// <param name="alphaData">A byte sequence of length width * height, containing all the 8-bit transparency values in scan order.</param>
+        /// <returns>The transparency image.</returns>
+        private static Image<Rgba32> DispatchAlphaToGreen<TPixel>(Image<TPixel> image, Span<byte> alphaData)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            int width = image.Width;
+            int height = image.Height;
+            var alphaAsImage = new Image<Rgba32>(width, height);
+
+            for (int y = 0; y < height; y++)
+            {
+                Memory<Rgba32> rowBuffer = alphaAsImage.DangerousGetPixelRowMemory(y);
+                Span<Rgba32> pixelRow = rowBuffer.Span;
+                Span<byte> alphaRow = alphaData.Slice(y * width, width);
+                for (int x = 0; x < width; x++)
+                {
+                    // Leave A/R/B channels zero'd.
+                    pixelRow[x] = new Rgba32(0, alphaRow[x], 0, 0);
+                }
+            }
+
+            return alphaAsImage;
+        }
+
+        /// <summary>
+        /// Extract the alpha data of the image.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel format.</typeparam>
+        /// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
+        /// <param name="configuration">The global configuration.</param>
+        /// <param name="memoryAllocator">The memory manager.</param>
+        /// <returns>A byte sequence of length width * height, containing all the 8-bit transparency values in scan order.</returns>
+        private static IMemoryOwner<byte> ExtractAlphaChannel<TPixel>(Image<TPixel> image, Configuration configuration, MemoryAllocator memoryAllocator)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            Buffer2D<TPixel> imageBuffer = image.Frames.RootFrame.PixelBuffer;
+            int height = image.Height;
+            int width = image.Width;
+            IMemoryOwner<byte> alphaDataBuffer = memoryAllocator.Allocate<byte>(width * height);
+            Span<byte> alphaData = alphaDataBuffer.GetSpan();
+
+            using IMemoryOwner<Rgba32> rowBuffer = memoryAllocator.Allocate<Rgba32>(width);
+            Span<Rgba32> rgbaRow = rowBuffer.GetSpan();
+
+            for (int y = 0; y < height; y++)
+            {
+                Span<TPixel> rowSpan = imageBuffer.DangerousGetRowSpan(y);
+                PixelOperations<TPixel>.Instance.ToRgba32(configuration, rowSpan, rgbaRow);
+                int offset = y * width;
+                for (int x = 0; x < width; x++)
+                {
+                    alphaData[offset + x] = rgbaRow[x].A;
+                }
+            }
+
+            return alphaDataBuffer;
+        }
+
+        /// <inheritdoc/>
+        public void Dispose() => this.alphaData?.Dispose();
+    }
+}

src/ImageSharp/Formats/Webp/BitWriter/BitWriterBase.cs

@@ -5,6 +5,7 @@ using System;
 using System.Buffers.Binary;
 using System.IO;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 
 namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
 {
@@ -46,6 +47,12 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
         /// <param name="stream">The stream to write to.</param>
         public void WriteToStream(Stream stream) => stream.Write(this.Buffer.AsSpan(0, this.NumBytes()));
 
+        /// <summary>
+        /// Writes the encoded bytes of the image to the given buffer. Call Finish() before this.
+        /// </summary>
+        /// <param name="dest">The destination buffer.</param>
+        public void WriteToBuffer(Span<byte> dest) => this.Buffer.AsSpan(0, this.NumBytes()).CopyTo(dest);
+
         /// <summary>
         /// Resizes the buffer to write to.
         /// </summary>
@@ -90,34 +97,79 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
         }
 
         /// <summary>
-        /// Calculates the exif chunk size.
+        /// Calculates the chunk size of EXIF or XMP metadata.
+        /// </summary>
+        /// <param name="metadataBytes">The metadata profile bytes.</param>
+        /// <returns>The metadata chunk size in bytes.</returns>
+        protected uint MetadataChunkSize(byte[] metadataBytes)
+        {
+            uint metaSize = (uint)metadataBytes.Length;
+            uint metaChunkSize = WebpConstants.ChunkHeaderSize + metaSize + (metaSize & 1);
+
+            return metaChunkSize;
+        }
+
+        /// <summary>
+        /// Calculates the chunk size of a alpha chunk.
         /// </summary>
-        /// <param name="exifBytes">The exif profile bytes.</param>
-        /// <returns>The exif chunk size in bytes.</returns>
-        protected uint ExifChunkSize(byte[] exifBytes)
+        /// <param name="alphaBytes">The alpha chunk bytes.</param>
+        /// <returns>The alpha data chunk size in bytes.</returns>
+        protected uint AlphaChunkSize(Span<byte> alphaBytes)
         {
-            uint exifSize = (uint)exifBytes.Length;
-            uint exifChunkSize = WebpConstants.ChunkHeaderSize + exifSize + (exifSize & 1);
+            uint alphaSize = (uint)alphaBytes.Length + 1;
+            uint alphaChunkSize = WebpConstants.ChunkHeaderSize + alphaSize + (alphaSize & 1);
 
-            return exifChunkSize;
+            return alphaChunkSize;
         }
 
         /// <summary>
-        /// Writes the Exif profile to the stream.
+        /// Writes a metadata profile (EXIF or XMP) to the stream.
         /// </summary>
         /// <param name="stream">The stream to write to.</param>
-        /// <param name="exifBytes">The exif profile bytes.</param>
-        protected void WriteExifProfile(Stream stream, byte[] exifBytes)
+        /// <param name="metadataBytes">The metadata profile's bytes.</param>
+        /// <param name="chunkType">The chuck type to write.</param>
+        protected void WriteMetadataProfile(Stream stream, byte[] metadataBytes, WebpChunkType chunkType)
         {
-            DebugGuard.NotNull(exifBytes, nameof(exifBytes));
+            DebugGuard.NotNull(metadataBytes, nameof(metadataBytes));
+
+            uint size = (uint)metadataBytes.Length;
+            Span<byte> buf = this.scratchBuffer.AsSpan(0, 4);
+            BinaryPrimitives.WriteUInt32BigEndian(buf, (uint)chunkType);
+            stream.Write(buf);
+            BinaryPrimitives.WriteUInt32LittleEndian(buf, size);
+            stream.Write(buf);
+            stream.Write(metadataBytes);
+
+            // Add padding byte if needed.
+            if ((size & 1) == 1)
+            {
+                stream.WriteByte(0);
+            }
+        }
 
-            uint size = (uint)exifBytes.Length;
+        /// <summary>
+        /// Writes the alpha chunk to the stream.
+        /// </summary>
+        /// <param name="stream">The stream to write to.</param>
+        /// <param name="dataBytes">The alpha channel data bytes.</param>
+        /// <param name="alphaDataIsCompressed">Indicates, if the alpha channel data is compressed.</param>
+        protected void WriteAlphaChunk(Stream stream, Span<byte> dataBytes, bool alphaDataIsCompressed)
+        {
+            uint size = (uint)dataBytes.Length + 1;
             Span<byte> buf = this.scratchBuffer.AsSpan(0, 4);
-            BinaryPrimitives.WriteUInt32BigEndian(buf, (uint)WebpChunkType.Exif);
+            BinaryPrimitives.WriteUInt32BigEndian(buf, (uint)WebpChunkType.Alpha);
             stream.Write(buf);
             BinaryPrimitives.WriteUInt32LittleEndian(buf, size);
             stream.Write(buf);
-            stream.Write(exifBytes);
+
+            byte flags = 0;
+            if (alphaDataIsCompressed)
+            {
+                flags |= 1;
+            }
+
+            stream.WriteByte(flags);
+            stream.Write(dataBytes);
 
             // Add padding byte if needed.
             if ((size & 1) == 1)
@@ -131,10 +183,11 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
         /// </summary>
         /// <param name="stream">The stream to write to.</param>
         /// <param name="exifProfile">A exif profile or null, if it does not exist.</param>
+        /// <param name="xmpProfile">A XMP profile or null, if it does not exist.</param>
         /// <param name="width">The width of the image.</param>
         /// <param name="height">The height of the image.</param>
         /// <param name="hasAlpha">Flag indicating, if a alpha channel is present.</param>
-        protected void WriteVp8XHeader(Stream stream, ExifProfile exifProfile, uint width, uint height, bool hasAlpha)
+        protected void WriteVp8XHeader(Stream stream, ExifProfile exifProfile, XmpProfile xmpProfile, uint width, uint height, bool hasAlpha)
         {
             if (width > MaxDimension || height > MaxDimension)
             {
@@ -154,6 +207,12 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
                 flags |= 8;
             }
 
+            if (xmpProfile != null)
+            {
+                // Set xmp bit.
+                flags |= 4;
+            }
+
             if (hasAlpha)
             {
                 // Set alpha bit.

src/ImageSharp/Formats/Webp/BitWriter/Vp8BitWriter.cs

@@ -6,6 +6,7 @@ using System.Buffers.Binary;
 using System.IO;
 using SixLabors.ImageSharp.Formats.Webp.Lossy;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 
 namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
 {
@@ -404,20 +405,49 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
         /// </summary>
         /// <param name="stream">The stream to write to.</param>
         /// <param name="exifProfile">The exif profile.</param>
+        /// <param name="xmpProfile">The XMP profile.</param>
         /// <param name="width">The width of the image.</param>
         /// <param name="height">The height of the image.</param>
         /// <param name="hasAlpha">Flag indicating, if a alpha channel is present.</param>
-        public void WriteEncodedImageToStream(Stream stream, ExifProfile exifProfile, uint width, uint height, bool hasAlpha)
+        /// <param name="alphaData">The alpha channel data.</param>
+        /// <param name="alphaDataIsCompressed">Indicates, if the alpha data is compressed.</param>
+        public void WriteEncodedImageToStream(
+            Stream stream,
+            ExifProfile exifProfile,
+            XmpProfile xmpProfile,
+            uint width,
+            uint height,
+            bool hasAlpha,
+            Span<byte> alphaData,
+            bool alphaDataIsCompressed)
         {
             bool isVp8X = false;
             byte[] exifBytes = null;
+            byte[] xmpBytes = null;
             uint riffSize = 0;
             if (exifProfile != null)
             {
                 isVp8X = true;
-                riffSize += ExtendedFileChunkSize;
                 exifBytes = exifProfile.ToByteArray();
-                riffSize += this.ExifChunkSize(exifBytes);
+                riffSize += this.MetadataChunkSize(exifBytes);
+            }
+
+            if (xmpProfile != null)
+            {
+                isVp8X = true;
+                xmpBytes = xmpProfile.Data;
+                riffSize += this.MetadataChunkSize(xmpBytes);
+            }
+
+            if (hasAlpha)
+            {
+                isVp8X = true;
+                riffSize += this.AlphaChunkSize(alphaData);
+            }
+
+            if (isVp8X)
+            {
+                riffSize += ExtendedFileChunkSize;
             }
 
             this.Finish();
@@ -440,7 +470,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
             riffSize += WebpConstants.TagSize + WebpConstants.ChunkHeaderSize + vp8Size;
 
             // Emit headers and partition #0
-            this.WriteWebpHeaders(stream, size0, vp8Size, riffSize, isVp8X, width, height, exifProfile, hasAlpha);
+            this.WriteWebpHeaders(stream, size0, vp8Size, riffSize, isVp8X, width, height, exifProfile, xmpProfile, hasAlpha, alphaData, alphaDataIsCompressed);
             bitWriterPartZero.WriteToStream(stream);
 
             // Write the encoded image to the stream.
@@ -452,7 +482,12 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
 
             if (exifProfile != null)
             {
-                this.WriteExifProfile(stream, exifBytes);
+                this.WriteMetadataProfile(stream, exifBytes, WebpChunkType.Exif);
+            }
+
+            if (xmpProfile != null)
+            {
+                this.WriteMetadataProfile(stream, xmpBytes, WebpChunkType.Xmp);
             }
         }
 
@@ -623,14 +658,30 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
             while (it.Next());
         }
 
-        private void WriteWebpHeaders(Stream stream, uint size0, uint vp8Size, uint riffSize, bool isVp8X, uint width, uint height, ExifProfile exifProfile, bool hasAlpha)
+        private void WriteWebpHeaders(
+            Stream stream,
+            uint size0,
+            uint vp8Size,
+            uint riffSize,
+            bool isVp8X,
+            uint width,
+            uint height,
+            ExifProfile exifProfile,
+            XmpProfile xmpProfile,
+            bool hasAlpha,
+            Span<byte> alphaData,
+            bool alphaDataIsCompressed)
         {
             this.WriteRiffHeader(stream, riffSize);
 
             // Write VP8X, header if necessary.
             if (isVp8X)
             {
-                this.WriteVp8XHeader(stream, exifProfile, width, height, hasAlpha);
+                this.WriteVp8XHeader(stream, exifProfile, xmpProfile, width, height, hasAlpha);
+                if (hasAlpha)
+                {
+                    this.WriteAlphaChunk(stream, alphaData, alphaDataIsCompressed);
+                }
             }
 
             this.WriteVp8Header(stream, vp8Size);

src/ImageSharp/Formats/Webp/BitWriter/Vp8LBitWriter.cs

@@ -6,6 +6,7 @@ using System.Buffers.Binary;
 using System.IO;
 using SixLabors.ImageSharp.Formats.Webp.Lossless;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 
 namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
 {
@@ -132,20 +133,30 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
         /// </summary>
         /// <param name="stream">The stream to write to.</param>
         /// <param name="exifProfile">The exif profile.</param>
+        /// <param name="xmpProfile">The XMP profile.</param>
         /// <param name="width">The width of the image.</param>
         /// <param name="height">The height of the image.</param>
         /// <param name="hasAlpha">Flag indicating, if a alpha channel is present.</param>
-        public void WriteEncodedImageToStream(Stream stream, ExifProfile exifProfile, uint width, uint height, bool hasAlpha)
+        public void WriteEncodedImageToStream(Stream stream, ExifProfile exifProfile, XmpProfile xmpProfile, uint width, uint height, bool hasAlpha)
         {
             bool isVp8X = false;
             byte[] exifBytes = null;
+            byte[] xmpBytes = null;
             uint riffSize = 0;
             if (exifProfile != null)
             {
                 isVp8X = true;
                 riffSize += ExtendedFileChunkSize;
                 exifBytes = exifProfile.ToByteArray();
-                riffSize += this.ExifChunkSize(exifBytes);
+                riffSize += this.MetadataChunkSize(exifBytes);
+            }
+
+            if (xmpProfile != null)
+            {
+                isVp8X = true;
+                riffSize += ExtendedFileChunkSize;
+                xmpBytes = xmpProfile.Data;
+                riffSize += this.MetadataChunkSize(xmpBytes);
             }
 
             this.Finish();
@@ -160,7 +171,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
             // Write VP8X, header if necessary.
             if (isVp8X)
             {
-                this.WriteVp8XHeader(stream, exifProfile, width, height, hasAlpha);
+                this.WriteVp8XHeader(stream, exifProfile, xmpProfile, width, height, hasAlpha);
             }
 
             // Write magic bytes indicating its a lossless webp.
@@ -180,7 +191,12 @@ namespace SixLabors.ImageSharp.Formats.Webp.BitWriter
 
             if (exifProfile != null)
             {
-                this.WriteExifProfile(stream, exifBytes);
+                this.WriteMetadataProfile(stream, exifBytes, WebpChunkType.Exif);
+            }
+
+            if (xmpProfile != null)
+            {
+                this.WriteMetadataProfile(stream, xmpBytes, WebpChunkType.Xmp);
             }
         }
 

src/ImageSharp/Formats/Webp/IWebpEncoderOptions.cs

@@ -10,6 +10,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
     {
         /// <summary>
         /// Gets the webp file format used. Either lossless or lossy.
+        /// Defaults to lossy.
         /// </summary>
         WebpFileFormatType? FileFormat { get; }
 
@@ -30,6 +31,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
 
         /// <summary>
         /// Gets a value indicating whether the alpha plane should be compressed with Webp lossless format.
+        /// Defaults to true.
         /// </summary>
         bool UseAlphaCompression { get; }
 

src/ImageSharp/Formats/Webp/Lossless/LosslessUtils.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
-using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Memory;

src/ImageSharp/Formats/Webp/Lossless/Vp8LEncoder.cs

@@ -10,6 +10,7 @@ using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Formats.Webp.BitWriter;
 using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Webp.Lossless
@@ -227,7 +228,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         public Vp8LHashChain HashChain { get; }
 
         /// <summary>
-        /// Encodes the image to the specified stream from the <see cref="Image{TPixel}"/>.
+        /// Encodes the image as lossless webp to the specified stream.
         /// </summary>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="image">The <see cref="Image{TPixel}"/> to encode from.</param>
@@ -235,10 +236,12 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         public void Encode<TPixel>(Image<TPixel> image, Stream stream)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            image.Metadata.SyncProfiles();
             int width = image.Width;
             int height = image.Height;
 
+            ImageMetadata metadata = image.Metadata;
+            metadata.SyncProfiles();
+
             // Convert image pixels to bgra array.
             bool hasAlpha = this.ConvertPixelsToBgra(image, width, height);
 
@@ -252,7 +255,40 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
             this.EncodeStream(image);
 
             // Write bytes from the bitwriter buffer to the stream.
-            this.bitWriter.WriteEncodedImageToStream(stream, image.Metadata.ExifProfile, (uint)width, (uint)height, hasAlpha);
+            this.bitWriter.WriteEncodedImageToStream(stream, metadata.ExifProfile, metadata.XmpProfile, (uint)width, (uint)height, hasAlpha);
+        }
+
+        /// <summary>
+        /// Encodes the alpha image data using the webp lossless compression.
+        /// </summary>
+        /// <typeparam name="TPixel">The type of the pixel.</typeparam>
+        /// <param name="image">The <see cref="Image{TPixel}"/> to encode from.</param>
+        /// <param name="alphaData">The destination buffer to write the encoded alpha data to.</param>
+        /// <returns>The size of the compressed data in bytes.
+        /// If the size of the data is the same as the pixel count, the compression would not yield in smaller data and is left uncompressed.
+        /// </returns>
+        public int EncodeAlphaImageData<TPixel>(Image<TPixel> image, IMemoryOwner<byte> alphaData)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            int width = image.Width;
+            int height = image.Height;
+            int pixelCount = width * height;
+
+            // Convert image pixels to bgra array.
+            this.ConvertPixelsToBgra(image, width, height);
+
+            // The image-stream will NOT contain any headers describing the image dimension, the dimension is already known.
+            this.EncodeStream(image);
+            this.bitWriter.Finish();
+            int size = this.bitWriter.NumBytes();
+            if (size >= pixelCount)
+            {
+                // Compressing would not yield in smaller data -> leave the data uncompressed.
+                return pixelCount;
+            }
+
+            this.bitWriter.WriteToBuffer(alphaData.GetSpan());
+            return size;
         }
 
         /// <summary>

src/ImageSharp/Formats/Webp/Lossy/Vp8Encoder.cs

@@ -7,6 +7,7 @@ using System.IO;
 using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.Formats.Webp.BitWriter;
 using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Webp.Lossy
@@ -70,12 +71,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
         /// </summary>
         private int uvAlpha;
 
-        /// <summary>
-        /// Scratch buffer to reduce allocations.
-        /// </summary>
-        private readonly int[] scratch = new int[16];
-
-        private readonly byte[] averageBytesPerMb = { 50, 24, 16, 9, 7, 5, 3, 2 };
+        private readonly bool alphaCompression;
 
         private const int NumMbSegments = 4;
 
@@ -104,6 +100,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
         /// <param name="entropyPasses">Number of entropy-analysis passes (in [1..10]).</param>
         /// <param name="filterStrength">The filter the strength of the deblocking filter, between 0 (no filtering) and 100 (maximum filtering).</param>
         /// <param name="spatialNoiseShaping">The spatial noise shaping. 0=off, 100=maximum.</param>
+        /// <param name="alphaCompression">If true, the alpha channel will be compressed with the lossless compression.</param>
         public Vp8Encoder(
             MemoryAllocator memoryAllocator,
             Configuration configuration,
@@ -113,7 +110,8 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
             WebpEncodingMethod method,
             int entropyPasses,
             int filterStrength,
-            int spatialNoiseShaping)
+            int spatialNoiseShaping,
+            bool alphaCompression)
         {
             this.memoryAllocator = memoryAllocator;
             this.configuration = configuration;
@@ -124,6 +122,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
             this.entropyPasses = Numerics.Clamp(entropyPasses, 1, 10);
             this.filterStrength = Numerics.Clamp(filterStrength, 0, 100);
             this.spatialNoiseShaping = Numerics.Clamp(spatialNoiseShaping, 0, 100);
+            this.alphaCompression = alphaCompression;
             this.rdOptLevel = method is WebpEncodingMethod.BestQuality ? Vp8RdLevel.RdOptTrellisAll
                 : method >= WebpEncodingMethod.Level5 ? Vp8RdLevel.RdOptTrellis
                 : method >= WebpEncodingMethod.Level3 ? Vp8RdLevel.RdOptBasic
@@ -173,6 +172,9 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
             this.ResetBoundaryPredictions();
         }
 
+        // This uses C#'s optimization to refer to the static data segment of the assembly, no allocation occurs.
+        private static ReadOnlySpan<byte> AverageBytesPerMb => new byte[] { 50, 24, 16, 9, 7, 5, 3, 2 };
+
         public int BaseQuant { get; set; }
 
         /// <summary>
@@ -296,10 +298,11 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
         {
             int width = image.Width;
             int height = image.Height;
+            int pixelCount = width * height;
             Span<byte> y = this.Y.GetSpan();
             Span<byte> u = this.U.GetSpan();
             Span<byte> v = this.V.GetSpan();
-            YuvConversion.ConvertRgbToYuv(image, this.configuration, this.memoryAllocator, y, u, v);
+            bool hasAlpha = YuvConversion.ConvertRgbToYuv(image, this.configuration, this.memoryAllocator, y, u, v);
 
             int yStride = width;
             int uvStride = (yStride + 1) >> 1;
@@ -317,12 +320,26 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
             this.SetLoopParams(this.quality);
 
             // Initialize the bitwriter.
-            int averageBytesPerMacroBlock = this.averageBytesPerMb[this.BaseQuant >> 4];
+            int averageBytesPerMacroBlock = AverageBytesPerMb[this.BaseQuant >> 4];
             int expectedSize = this.Mbw * this.Mbh * averageBytesPerMacroBlock;
             this.bitWriter = new Vp8BitWriter(expectedSize, this);
 
-            // TODO: EncodeAlpha();
-            bool hasAlpha = false;
+            // Extract and encode alpha channel data, if present.
+            int alphaDataSize = 0;
+            bool alphaCompressionSucceeded = false;
+            using var alphaEncoder = new AlphaEncoder();
+            Span<byte> alphaData = Span<byte>.Empty;
+            if (hasAlpha)
+            {
+                // TODO: This can potentially run in an separate task.
+                IMemoryOwner<byte> encodedAlphaData = alphaEncoder.EncodeAlpha(image, this.configuration, this.memoryAllocator, this.alphaCompression, out alphaDataSize);
+                alphaData = encodedAlphaData.GetSpan();
+                if (alphaDataSize < pixelCount)
+                {
+                    // Only use compressed data, if the compressed data is actually smaller then the uncompressed data.
+                    alphaCompressionSucceeded = true;
+                }
+            }
 
             // Stats-collection loop.
             this.StatLoop(width, height, yStride, uvStride);
@@ -355,8 +372,17 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
             this.AdjustFilterStrength();
 
             // Write bytes from the bitwriter buffer to the stream.
-            image.Metadata.SyncProfiles();
-            this.bitWriter.WriteEncodedImageToStream(stream, image.Metadata.ExifProfile, (uint)width, (uint)height, hasAlpha);
+            ImageMetadata metadata = image.Metadata;
+            metadata.SyncProfiles();
+            this.bitWriter.WriteEncodedImageToStream(
+                stream,
+                metadata.ExifProfile,
+                metadata.XmpProfile,
+                (uint)width,
+                (uint)height,
+                hasAlpha,
+                alphaData,
+                this.alphaCompression && alphaCompressionSucceeded);
         }
 
         /// <inheritdoc/>

src/ImageSharp/Formats/Webp/Lossy/YuvConversion.cs

@@ -318,7 +318,8 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
         /// <param name="y">Span to store the luma component of the image.</param>
         /// <param name="u">Span to store the u component of the image.</param>
         /// <param name="v">Span to store the v component of the image.</param>
-        public static void ConvertRgbToYuv<TPixel>(Image<TPixel> image, Configuration configuration, MemoryAllocator memoryAllocator, Span<byte> y, Span<byte> u, Span<byte> v)
+        /// <returns>true, if the image contains alpha data.</returns>
+        public static bool ConvertRgbToYuv<TPixel>(Image<TPixel> image, Configuration configuration, MemoryAllocator memoryAllocator, Span<byte> y, Span<byte> u, Span<byte> v)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             Buffer2D<TPixel> imageBuffer = image.Frames.RootFrame.PixelBuffer;
@@ -335,6 +336,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
             Span<Bgra32> bgraRow1 = bgraRow1Buffer.GetSpan();
             int uvRowIndex = 0;
             int rowIndex;
+            bool hasAlpha = false;
             for (rowIndex = 0; rowIndex < height - 1; rowIndex += 2)
             {
                 Span<TPixel> rowSpan = imageBuffer.DangerousGetRowSpan(rowIndex);
@@ -343,6 +345,10 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
                 PixelOperations<TPixel>.Instance.ToBgra32(configuration, nextRowSpan, bgraRow1);
 
                 bool rowsHaveAlpha = WebpCommonUtils.CheckNonOpaque(bgraRow0) && WebpCommonUtils.CheckNonOpaque(bgraRow1);
+                if (rowsHaveAlpha)
+                {
+                    hasAlpha = true;
+                }
 
                 // Downsample U/V planes, two rows at a time.
                 if (!rowsHaveAlpha)
@@ -375,10 +381,13 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
                 else
                 {
                     AccumulateRgba(bgraRow0, bgraRow0, tmpRgbSpan, width);
+                    hasAlpha = true;
                 }
 
                 ConvertRgbaToUv(tmpRgbSpan, u.Slice(uvRowIndex * uvWidth), v.Slice(uvRowIndex * uvWidth), uvWidth);
             }
+
+            return hasAlpha;
         }
 
         /// <summary>

src/ImageSharp/Formats/Webp/WebpDecoderCore.cs

@@ -13,6 +13,7 @@ using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.Metadata.Profiles.Icc;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Webp
@@ -177,6 +178,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// Reads an the extended webp file header. An extended file header consists of:
         /// - A 'VP8X' chunk with information about features used in the file.
         /// - An optional 'ICCP' chunk with color profile.
+        /// - An optional 'XMP' chunk with metadata.
         /// - An optional 'ANIM' chunk with animation control data.
         /// - An optional 'ALPH' chunk with alpha channel data.
         /// After the image header, image data will follow. After that optional image metadata chunks (EXIF and XMP) can follow.
@@ -228,12 +230,27 @@ namespace SixLabors.ImageSharp.Formats.Webp
             this.buffer[3] = 0;
             uint height = (uint)BinaryPrimitives.ReadInt32LittleEndian(this.buffer) + 1;
 
-            // Optional chunks ICCP, ALPH and ANIM can follow here.
-            WebpChunkType chunkType = this.ReadChunkType();
-            while (IsOptionalVp8XChunk(chunkType))
+            // Read all the chunks in the order they occur.
+            var info = new WebpImageInfo();
+            while (this.currentStream.Position < this.currentStream.Length)
             {
-                this.ParseOptionalExtendedChunks(chunkType, features);
-                chunkType = this.ReadChunkType();
+                WebpChunkType chunkType = this.ReadChunkType();
+                if (chunkType == WebpChunkType.Vp8)
+                {
+                    info = this.ReadVp8Header(features);
+                }
+                else if (chunkType == WebpChunkType.Vp8L)
+                {
+                    info = this.ReadVp8LHeader(features);
+                }
+                else if (IsOptionalVp8XChunk(chunkType))
+                {
+                    this.ParseOptionalExtendedChunks(chunkType, features);
+                }
+                else
+                {
+                    WebpThrowHelper.ThrowImageFormatException("Unexpected chunk followed VP8X header");
+                }
             }
 
             if (features.Animation)
@@ -242,17 +259,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
                 return new WebpImageInfo() { Width = width, Height = height, Features = features };
             }
 
-            switch (chunkType)
-            {
-                case WebpChunkType.Vp8:
-                    return this.ReadVp8Header(features);
-                case WebpChunkType.Vp8L:
-                    return this.ReadVp8LHeader(features);
-            }
-
-            WebpThrowHelper.ThrowImageFormatException("Unexpected chunk followed VP8X header");
-
-            return new WebpImageInfo();
+            return info;
         }
 
         /// <summary>
@@ -413,7 +420,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
         }
 
         /// <summary>
-        /// Parses optional VP8X chunks, which can be ICCP, ANIM or ALPH chunks.
+        /// Parses optional VP8X chunks, which can be ICCP, XMP, ANIM or ALPH chunks.
         /// </summary>
         /// <param name="chunkType">The chunk type.</param>
         /// <param name="features">The webp image features.</param>
@@ -440,6 +447,38 @@ namespace SixLabors.ImageSharp.Formats.Webp
 
                     break;
 
+                case WebpChunkType.Exif:
+                    uint exifChunkSize = this.ReadChunkSize();
+                    if (this.IgnoreMetadata)
+                    {
+                        this.currentStream.Skip((int)exifChunkSize);
+                    }
+                    else
+                    {
+                        byte[] exifData = new byte[exifChunkSize];
+                        this.currentStream.Read(exifData, 0, (int)exifChunkSize);
+                        var profile = new ExifProfile(exifData);
+                        this.Metadata.ExifProfile = profile;
+                    }
+
+                    break;
+
+                case WebpChunkType.Xmp:
+                    uint xmpChunkSize = this.ReadChunkSize();
+                    if (this.IgnoreMetadata)
+                    {
+                        this.currentStream.Skip((int)xmpChunkSize);
+                    }
+                    else
+                    {
+                        byte[] xmpData = new byte[xmpChunkSize];
+                        this.currentStream.Read(xmpData, 0, (int)xmpChunkSize);
+                        var profile = new XmpProfile(xmpData);
+                        this.Metadata.XmpProfile = profile;
+                    }
+
+                    break;
+
                 case WebpChunkType.Animation:
                     // TODO: Decoding animation is not implemented yet.
                     break;
@@ -451,6 +490,9 @@ namespace SixLabors.ImageSharp.Formats.Webp
                     features.AlphaData = this.memoryAllocator.Allocate<byte>(alphaDataSize);
                     this.currentStream.Read(features.AlphaData.Memory.Span, 0, alphaDataSize);
                     break;
+                default:
+                    WebpThrowHelper.ThrowImageFormatException("Unexpected chunk followed VP8X header");
+                    break;
             }
         }
 
@@ -530,7 +572,9 @@ namespace SixLabors.ImageSharp.Formats.Webp
         {
             WebpChunkType.Alpha => true,
             WebpChunkType.Animation => true,
+            WebpChunkType.Exif => true,
             WebpChunkType.Iccp => true,
+            WebpChunkType.Xmp => true,
             _ => false
         };
     }

src/ImageSharp/Formats/Webp/WebpEncoder.cs

@@ -24,7 +24,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
         public WebpEncodingMethod Method { get; set; } = WebpEncodingMethod.Default;
 
         /// <inheritdoc/>
-        public bool UseAlphaCompression { get; set; }
+        public bool UseAlphaCompression { get; set; } = true;
 
         /// <inheritdoc/>
         public int EntropyPasses { get; set; } = 1;

src/ImageSharp/Formats/Webp/WebpEncoderCore.cs

@@ -22,8 +22,8 @@ namespace SixLabors.ImageSharp.Formats.Webp
         private readonly MemoryAllocator memoryAllocator;
 
         /// <summary>
-        /// TODO: not used at the moment.
         /// Indicating whether the alpha plane should be compressed with Webp lossless format.
+        /// Defaults to true.
         /// </summary>
         private readonly bool alphaCompression;
 
@@ -70,6 +70,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
 
         /// <summary>
         /// Indicating what file format compression should be used.
+        /// Defaults to lossy.
         /// </summary>
         private readonly WebpFileFormatType? fileFormat;
 
@@ -99,7 +100,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
         }
 
         /// <summary>
-        /// Encodes the image to the specified stream from the <see cref="ImageFrame{TPixel}"/>.
+        /// Encodes the image as webp to the specified stream.
         /// </summary>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
@@ -112,43 +113,44 @@ namespace SixLabors.ImageSharp.Formats.Webp
             Guard.NotNull(stream, nameof(stream));
 
             this.configuration = image.GetConfiguration();
-            bool lossy;
+            bool lossless;
             if (this.fileFormat is not null)
             {
-                lossy = this.fileFormat == WebpFileFormatType.Lossy;
+                lossless = this.fileFormat == WebpFileFormatType.Lossless;
             }
             else
             {
                 WebpMetadata webpMetadata = image.Metadata.GetWebpMetadata();
-                lossy = webpMetadata.FileFormat == WebpFileFormatType.Lossy;
+                lossless = webpMetadata.FileFormat == WebpFileFormatType.Lossless;
             }
 
-            if (lossy)
+            if (lossless)
             {
-                using var enc = new Vp8Encoder(
+                using var enc = new Vp8LEncoder(
                     this.memoryAllocator,
                     this.configuration,
                     image.Width,
                     image.Height,
                     this.quality,
                     this.method,
-                    this.entropyPasses,
-                    this.filterStrength,
-                    this.spatialNoiseShaping);
+                    this.transparentColorMode,
+                    this.nearLossless,
+                    this.nearLosslessQuality);
                 enc.Encode(image, stream);
             }
             else
             {
-                using var enc = new Vp8LEncoder(
+                using var enc = new Vp8Encoder(
                     this.memoryAllocator,
                     this.configuration,
                     image.Width,
                     image.Height,
                     this.quality,
                     this.method,
-                    this.transparentColorMode,
-                    this.nearLossless,
-                    this.nearLosslessQuality);
+                    this.entropyPasses,
+                    this.filterStrength,
+                    this.spatialNoiseShaping,
+                    this.alphaCompression);
                 enc.Encode(image, stream);
             }
         }

src/ImageSharp/IO/BufferedReadStream.cs

@@ -87,7 +87,6 @@ namespace SixLabors.ImageSharp.IO
             set
             {
                 Guard.MustBeGreaterThanOrEqualTo(value, 0, nameof(this.Position));
-                Guard.MustBeLessThanOrEqualTo(value, this.Length, nameof(this.Position));
 
                 // Only reset readBufferIndex if we are out of bounds of our working buffer
                 // otherwise we should simply move the value by the diff.

src/ImageSharp/IO/ChunkedMemoryStream.cs

@@ -168,7 +168,6 @@ namespace SixLabors.ImageSharp.IO
                     // Position is out of range
                     this.readChunk = backupReadChunk;
                     this.readOffset = backupReadOffset;
-                    ThrowArgumentOutOfRange(nameof(value));
                 }
             }
         }

src/ImageSharp/Image.Decode.cs

@@ -35,8 +35,10 @@ namespace SixLabors.ImageSharp
             ImageMetadata metadata)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            Buffer2D<TPixel> uninitializedMemoryBuffer =
-                configuration.MemoryAllocator.Allocate2D<TPixel>(width, height);
+            Buffer2D<TPixel> uninitializedMemoryBuffer = configuration.MemoryAllocator.Allocate2D<TPixel>(
+                    width,
+                    height,
+                    configuration.PreferContiguousImageBuffers);
             return new Image<TPixel>(configuration, uninitializedMemoryBuffer.FastMemoryGroup, width, height, metadata);
         }
 

src/ImageSharp/ImageSharp.csproj

@@ -10,7 +10,7 @@
     <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
     <RepositoryUrl Condition="'$(RepositoryUrl)' == ''">https://github.com/SixLabors/ImageSharp/</RepositoryUrl>
     <PackageProjectUrl>$(RepositoryUrl)</PackageProjectUrl>
-    <PackageTags>Image Resize Crop Gif Jpg Jpeg Bitmap Pbm Png Tga NetCore</PackageTags>
+    <PackageTags>Image Resize Crop Gif Jpg Jpeg Bitmap Pbm Png Tga Tiff WebP NetCore</PackageTags>
     <Description>A new, fully featured, fully managed, cross-platform, 2D graphics API for .NET</Description>
     <Configurations>Debug;Release;Debug-InnerLoop;Release-InnerLoop</Configurations>
   </PropertyGroup>
@@ -49,6 +49,7 @@
 
   <ItemGroup>
     <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="5.0.0" />
+    <PackageReference Include="System.Text.Encoding.CodePages" Version="5.0.0" />
   </ItemGroup>
 
   <ItemGroup Condition=" $(TargetFramework.StartsWith('netstandard')) OR '$(TargetFramework)' == 'net472'">
@@ -57,13 +58,6 @@
     <PackageReference Include="System.Memory" Version="4.5.4" />
   </ItemGroup>
 
-  <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard1.3'">
-    <PackageReference Include="System.IO.Compression" Version="4.3.0" />
-    <PackageReference Include="System.IO.UnmanagedMemoryStream" Version="4.3.0" />
-    <PackageReference Include="System.Threading.Tasks.Parallel" Version="4.3.0" />
-    <PackageReference Include="System.ValueTuple" Version="4.5.0" />
-  </ItemGroup>
-
   <ItemGroup>
     <Compile Update="Formats\Jpeg\Components\Block8x8F.Generated.cs">
       <DesignTime>True</DesignTime>

src/ImageSharp/Memory/Allocators/Internals/RefCountedLifetimeGuard.cs

@@ -1,56 +0,0 @@
-// Copyright (c) Six Labors.
-// Licensed under the Apache License, Version 2.0.
-
-using System;
-using System.Runtime.InteropServices;
-using System.Threading;
-
-namespace SixLabors.ImageSharp.Memory.Internals
-{
-    /// <summary>
-    /// Implements reference counting lifetime guard mechanism similar to the one provided by <see cref="SafeHandle"/>,
-    /// but without the restriction of the guarded object being a handle.
-    /// </summary>
-    internal abstract class RefCountedLifetimeGuard : IDisposable
-    {
-        private int refCount = 1;
-        private int disposed;
-        private int released;
-
-        ~RefCountedLifetimeGuard()
-        {
-            Interlocked.Exchange(ref this.disposed, 1);
-            this.ReleaseRef();
-        }
-
-        public bool IsDisposed => this.disposed == 1;
-
-        public void AddRef() => Interlocked.Increment(ref this.refCount);
-
-        public void ReleaseRef()
-        {
-            Interlocked.Decrement(ref this.refCount);
-            if (this.refCount == 0)
-            {
-                int wasReleased = Interlocked.Exchange(ref this.released, 1);
-
-                if (wasReleased == 0)
-                {
-                    this.Release();
-                }
-            }
-        }
-
-        public void Dispose()
-        {
-            int wasDisposed = Interlocked.Exchange(ref this.disposed, 1);
-            if (wasDisposed == 0)
-            {
-                this.ReleaseRef();
-                GC.SuppressFinalize(this);
-            }
-        }
-
-        protected abstract void Release();
-    }
-}

src/ImageSharp/Memory/Allocators/Internals/RefCountedMemoryLifetimeGuard.cs

@@ -0,0 +1,79 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Runtime.InteropServices;
+using System.Threading;
+using SixLabors.ImageSharp.Diagnostics;
+
+namespace SixLabors.ImageSharp.Memory.Internals
+{
+    /// <summary>
+    /// Implements reference counting lifetime guard mechanism for memory resources
+    /// and maintains the value of <see cref="MemoryDiagnostics.TotalUndisposedAllocationCount"/>.
+    /// </summary>
+    internal abstract class RefCountedMemoryLifetimeGuard : IDisposable
+    {
+        private int refCount = 1;
+        private int disposed;
+        private int released;
+        private string allocationStackTrace;
+
+        protected RefCountedMemoryLifetimeGuard()
+        {
+            if (MemoryDiagnostics.UndisposedAllocationSubscribed)
+            {
+                this.allocationStackTrace = Environment.StackTrace;
+            }
+
+            MemoryDiagnostics.IncrementTotalUndisposedAllocationCount();
+        }
+
+        ~RefCountedMemoryLifetimeGuard()
+        {
+            Interlocked.Exchange(ref this.disposed, 1);
+            this.ReleaseRef(true);
+        }
+
+        public bool IsDisposed => this.disposed == 1;
+
+        public void AddRef() => Interlocked.Increment(ref this.refCount);
+
+        public void ReleaseRef() => this.ReleaseRef(false);
+
+        public void Dispose()
+        {
+            int wasDisposed = Interlocked.Exchange(ref this.disposed, 1);
+            if (wasDisposed == 0)
+            {
+                this.ReleaseRef();
+                GC.SuppressFinalize(this);
+            }
+        }
+
+        protected abstract void Release();
+
+        private void ReleaseRef(bool finalizing)
+        {
+            Interlocked.Decrement(ref this.refCount);
+            if (this.refCount == 0)
+            {
+                int wasReleased = Interlocked.Exchange(ref this.released, 1);
+
+                if (wasReleased == 0)
+                {
+                    if (!finalizing)
+                    {
+                        MemoryDiagnostics.DecrementTotalUndisposedAllocationCount();
+                    }
+                    else if (this.allocationStackTrace != null)
+                    {
+                        MemoryDiagnostics.RaiseUndisposedMemoryResource(this.allocationStackTrace);
+                    }
+
+                    this.Release();
+                }
+            }
+        }
+    }
+}

src/ImageSharp/Memory/Allocators/Internals/SharedArrayPoolBuffer{T}.cs

@@ -60,7 +60,7 @@ namespace SixLabors.ImageSharp.Memory.Internals
             }
         }
 
-        private sealed class LifetimeGuard : RefCountedLifetimeGuard
+        private sealed class LifetimeGuard : RefCountedMemoryLifetimeGuard
         {
             private byte[] array;
 

src/ImageSharp/Memory/Allocators/Internals/UniformUnmanagedMemoryPool.LifetimeGuards.cs

@@ -20,9 +20,9 @@ namespace SixLabors.ImageSharp.Memory.Internals
             return buffer;
         }
 
-        public RefCountedLifetimeGuard CreateGroupLifetimeGuard(UnmanagedMemoryHandle[] handles) => new GroupLifetimeGuard(this, handles);
+        public RefCountedMemoryLifetimeGuard CreateGroupLifetimeGuard(UnmanagedMemoryHandle[] handles) => new GroupLifetimeGuard(this, handles);
 
-        private sealed class GroupLifetimeGuard : RefCountedLifetimeGuard
+        private sealed class GroupLifetimeGuard : RefCountedMemoryLifetimeGuard
         {
             private readonly UniformUnmanagedMemoryPool pool;
             private readonly UnmanagedMemoryHandle[] handles;

src/ImageSharp/Memory/Allocators/Internals/UnmanagedBufferLifetimeGuard.cs

@@ -6,7 +6,7 @@ namespace SixLabors.ImageSharp.Memory.Internals
     /// <summary>
     /// Defines a strategy for managing unmanaged memory ownership.
     /// </summary>
-    internal abstract class UnmanagedBufferLifetimeGuard : RefCountedLifetimeGuard
+    internal abstract class UnmanagedBufferLifetimeGuard : RefCountedMemoryLifetimeGuard
     {
         private UnmanagedMemoryHandle handle;
 

src/ImageSharp/Memory/Buffer2DRegion{T}.cs

@@ -88,7 +88,7 @@ namespace SixLabors.ImageSharp.Memory
         /// <param name="y">The row index</param>
         /// <returns>The span</returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public Span<T> GetRowSpan(int y)
+        public Span<T> DangerousGetRowSpan(int y)
         {
             int yy = this.Rectangle.Y + y;
             int xx = this.Rectangle.X;
@@ -152,7 +152,7 @@ namespace SixLabors.ImageSharp.Memory
 
             for (int y = 0; y < this.Rectangle.Height; y++)
             {
-                Span<T> row = this.GetRowSpan(y);
+                Span<T> row = this.DangerousGetRowSpan(y);
                 row.Clear();
             }
         }

src/ImageSharp/Memory/DiscontiguousBuffers/MemoryGroup{T}.Owned.cs

@@ -18,7 +18,7 @@ namespace SixLabors.ImageSharp.Memory
         public sealed class Owned : MemoryGroup<T>, IEnumerable<Memory<T>>
         {
             private IMemoryOwner<T>[] memoryOwners;
-            private RefCountedLifetimeGuard groupLifetimeGuard;
+            private RefCountedMemoryLifetimeGuard groupLifetimeGuard;
 
             public Owned(IMemoryOwner<T>[] memoryOwners, int bufferLength, long totalLength, bool swappable)
                 : base(bufferLength, totalLength)

src/ImageSharp/Metadata/ImageFrameMetadata.cs

@@ -1,12 +1,12 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
-using System;
 using System.Collections.Generic;
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.Metadata.Profiles.Icc;
 using SixLabors.ImageSharp.Metadata.Profiles.Iptc;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 
 namespace SixLabors.ImageSharp.Metadata
 {
@@ -43,8 +43,7 @@ namespace SixLabors.ImageSharp.Metadata
             this.ExifProfile = other.ExifProfile?.DeepClone();
             this.IccProfile = other.IccProfile?.DeepClone();
             this.IptcProfile = other.IptcProfile?.DeepClone();
-            this.XmpProfile = other.XmpProfile != null ? new byte[other.XmpProfile.Length] : null;
-            other.XmpProfile?.AsSpan().CopyTo(this.XmpProfile.AsSpan());
+            this.XmpProfile = other.XmpProfile?.DeepClone();
         }
 
         /// <summary>
@@ -55,7 +54,7 @@ namespace SixLabors.ImageSharp.Metadata
         /// <summary>
         /// Gets or sets the XMP profile.
         /// </summary>
-        internal byte[] XmpProfile { get; set; }
+        public XmpProfile XmpProfile { get; set; }
 
         /// <summary>
         /// Gets or sets the list of ICC profiles.

src/ImageSharp/Metadata/ImageMetadata.cs

@@ -6,6 +6,7 @@ using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.Metadata.Profiles.Icc;
 using SixLabors.ImageSharp.Metadata.Profiles.Iptc;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 
 namespace SixLabors.ImageSharp.Metadata
 {
@@ -39,7 +40,7 @@ namespace SixLabors.ImageSharp.Metadata
         /// <summary>
         /// Initializes a new instance of the <see cref="ImageMetadata"/> class.
         /// </summary>
-        internal ImageMetadata()
+        public ImageMetadata()
         {
             this.horizontalResolution = DefaultHorizontalResolution;
             this.verticalResolution = DefaultVerticalResolution;
@@ -71,7 +72,7 @@ namespace SixLabors.ImageSharp.Metadata
 
         /// <summary>
         /// Gets or sets the resolution of the image in x- direction.
-        /// It is defined as the number of dots per inch and should be an positive value.
+        /// It is defined as the number of dots per <see cref="ResolutionUnits"/> and should be an positive value.
         /// </summary>
         /// <value>The density of the image in x- direction.</value>
         public double HorizontalResolution
@@ -89,7 +90,7 @@ namespace SixLabors.ImageSharp.Metadata
 
         /// <summary>
         /// Gets or sets the resolution of the image in y- direction.
-        /// It is defined as the number of dots per inch and should be an positive value.
+        /// It is defined as the number of dots per <see cref="ResolutionUnits"/> and should be an positive value.
         /// </summary>
         /// <value>The density of the image in y- direction.</value>
         public double VerticalResolution
@@ -107,10 +108,28 @@ namespace SixLabors.ImageSharp.Metadata
 
         /// <summary>
         /// Gets or sets unit of measure used when reporting resolution.
-        ///  00 : No units; width:height pixel aspect ratio = Ydensity:Xdensity
-        ///  01 : Pixels per inch (2.54 cm)
-        ///  02 : Pixels per centimeter
-        ///  03 : Pixels per meter
+        /// <list type="table">
+        ///   <listheader>
+        ///     <term>Value</term>
+        ///     <description>Unit</description>
+        ///   </listheader>
+        ///   <item>
+        ///     <term>AspectRatio (00)</term>
+        ///     <description>No units; width:height pixel aspect ratio = Ydensity:Xdensity</description>
+        ///   </item>
+        ///   <item>
+        ///     <term>PixelsPerInch (01)</term>
+        ///     <description>Pixels per inch (2.54 cm)</description>
+        ///   </item>
+        ///   <item>
+        ///     <term>PixelsPerCentimeter (02)</term>
+        ///     <description>Pixels per centimeter</description>
+        ///   </item>
+        ///   <item>
+        ///     <term>PixelsPerMeter (03)</term>
+        ///     <description>Pixels per meter (100 cm)</description>
+        ///   </item>
+        /// </list>
         /// </summary>
         public PixelResolutionUnit ResolutionUnits { get; set; }
 
@@ -119,13 +138,18 @@ namespace SixLabors.ImageSharp.Metadata
         /// </summary>
         public ExifProfile ExifProfile { get; set; }
 
+        /// <summary>
+        /// Gets or sets the XMP profile.
+        /// </summary>
+        public XmpProfile XmpProfile { get; set; }
+
         /// <summary>
         /// Gets or sets the list of ICC profiles.
         /// </summary>
         public IccProfile IccProfile { get; set; }
 
         /// <summary>
-        /// Gets or sets the iptc profile.
+        /// Gets or sets the IPTC profile.
         /// </summary>
         public IptcProfile IptcProfile { get; set; }
 

src/ImageSharp/Metadata/Profiles/Exif/ExifConstants.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Text;
 
 namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 {
@@ -22,5 +23,8 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             0x00,
             0x2A
         };
+
+        // UTF-8 is better than ASCII, UTF-8 encodes the ASCII codes the same way
+        public static Encoding DefaultEncoding => Encoding.UTF8;
     }
 }

src/ImageSharp/Metadata/Profiles/Exif/ExifDataType.cs

@@ -80,6 +80,21 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
         /// <summary>
         /// Reference to an IFD (32-bit (4-byte) unsigned integer).
         /// </summary>
-        Ifd = 13
+        Ifd = 13,
+
+        /// <summary>
+        /// A 64-bit (8-byte) unsigned integer.
+        /// </summary>
+        Long8 = 16,
+
+        /// <summary>
+        /// A 64-bit (8-byte) signed integer (2's complement notation).
+        /// </summary>
+        SignedLong8 = 17,
+
+        /// <summary>
+        /// Reference to an IFD (64-bit (8-byte) unsigned integer).
+        /// </summary>
+        Ifd8 = 18,
     }
 }

src/ImageSharp/Metadata/Profiles/Exif/ExifDataTypes.cs

@@ -32,10 +32,14 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
                 case ExifDataType.Long:
                 case ExifDataType.SignedLong:
                 case ExifDataType.SingleFloat:
+                case ExifDataType.Ifd:
                     return 4;
                 case ExifDataType.DoubleFloat:
                 case ExifDataType.Rational:
                 case ExifDataType.SignedRational:
+                case ExifDataType.Long8:
+                case ExifDataType.SignedLong8:
+                case ExifDataType.Ifd8:
                     return 8;
                 default:
                     throw new NotSupportedException(dataType.ToString());

src/ImageSharp/Metadata/Profiles/Exif/ExifEncodedStringHelpers.cs

@@ -0,0 +1,121 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Buffers.Binary;
+using System.Text;
+using static SixLabors.ImageSharp.Metadata.Profiles.Exif.EncodedString;
+
+namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
+{
+    internal static class ExifEncodedStringHelpers
+    {
+        public const int CharacterCodeBytesLength = 8;
+
+        private const ulong AsciiCode = 0x_00_00_00_49_49_43_53_41;
+        private const ulong JISCode = 0x_00_00_00_00_00_53_49_4A;
+        private const ulong UnicodeCode = 0x_45_44_4F_43_49_4E_55;
+        private const ulong UndefinedCode = 0x_00_00_00_00_00_00_00_00;
+
+        private static ReadOnlySpan<byte> AsciiCodeBytes => new byte[] { 0x41, 0x53, 0x43, 0x49, 0x49, 0, 0, 0 };
+
+        private static ReadOnlySpan<byte> JISCodeBytes => new byte[] { 0x4A, 0x49, 0x53, 0, 0, 0, 0, 0 };
+
+        private static ReadOnlySpan<byte> UnicodeCodeBytes => new byte[] { 0x55, 0x4E, 0x49, 0x43, 0x4F, 0x44, 0x45, 0 };
+
+        private static ReadOnlySpan<byte> UndefinedCodeBytes => new byte[] { 0, 0, 0, 0, 0, 0, 0, 0 };
+
+        // 20932 EUC-JP Japanese (JIS 0208-1990 and 0212-1990)
+        // https://docs.microsoft.com/en-us/dotnet/api/system.text.encoding?view=net-6.0
+        private static Encoding JIS0208Encoding => CodePagesEncodingProvider.Instance.GetEncoding(20932);
+
+        public static bool IsEncodedString(ExifTagValue tag) => tag switch
+        {
+            ExifTagValue.UserComment or ExifTagValue.GPSProcessingMethod or ExifTagValue.GPSAreaInformation => true,
+            _ => false
+        };
+
+        public static ReadOnlySpan<byte> GetCodeBytes(CharacterCode code) => code switch
+        {
+            CharacterCode.ASCII => AsciiCodeBytes,
+            CharacterCode.JIS => JISCodeBytes,
+            CharacterCode.Unicode => UnicodeCodeBytes,
+            CharacterCode.Undefined => UndefinedCodeBytes,
+            _ => UndefinedCodeBytes
+        };
+
+        public static Encoding GetEncoding(CharacterCode code) => code switch
+        {
+            CharacterCode.ASCII => Encoding.ASCII,
+            CharacterCode.JIS => JIS0208Encoding,
+            CharacterCode.Unicode => Encoding.Unicode,
+            CharacterCode.Undefined => Encoding.UTF8,
+            _ => Encoding.UTF8
+        };
+
+        public static bool TryParse(ReadOnlySpan<byte> buffer, out EncodedString encodedString)
+        {
+            if (TryDetect(buffer, out CharacterCode code))
+            {
+                string text = GetEncoding(code).GetString(buffer.Slice(CharacterCodeBytesLength));
+                encodedString = new EncodedString(code, text);
+                return true;
+            }
+
+            encodedString = default;
+            return false;
+        }
+
+        public static uint GetDataLength(EncodedString encodedString) =>
+            (uint)GetEncoding(encodedString.Code).GetByteCount(encodedString.Text) + CharacterCodeBytesLength;
+
+        public static int Write(EncodedString encodedString, Span<byte> destination)
+        {
+            GetCodeBytes(encodedString.Code).CopyTo(destination);
+
+            string text = encodedString.Text;
+            int count = Write(GetEncoding(encodedString.Code), text, destination.Slice(CharacterCodeBytesLength));
+
+            return CharacterCodeBytesLength + count;
+        }
+
+        public static unsafe int Write(Encoding encoding, string value, Span<byte> destination)
+        {
+            fixed (char* c = value)
+            {
+                fixed (byte* b = destination)
+                {
+                    return encoding.GetBytes(c, value.Length, b, destination.Length);
+                }
+            }
+        }
+
+        private static bool TryDetect(ReadOnlySpan<byte> buffer, out CharacterCode code)
+        {
+            if (buffer.Length >= CharacterCodeBytesLength)
+            {
+                ulong test = BinaryPrimitives.ReadUInt64LittleEndian(buffer);
+                switch (test)
+                {
+                    case AsciiCode:
+                        code = CharacterCode.ASCII;
+                        return true;
+                    case JISCode:
+                        code = CharacterCode.JIS;
+                        return true;
+                    case UnicodeCode:
+                        code = CharacterCode.Unicode;
+                        return true;
+                    case UndefinedCode:
+                        code = CharacterCode.Undefined;
+                        return true;
+                    default:
+                        break;
+                }
+            }
+
+            code = default;
+            return false;
+        }
+    }
+}

src/ImageSharp/Metadata/Profiles/Exif/ExifReader.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
 using System.Buffers.Binary;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
@@ -9,15 +10,19 @@ using System.Diagnostics;
 using System.IO;
 using System.Runtime.CompilerServices;
 using System.Text;
+using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 {
     internal class ExifReader : BaseExifReader
     {
-        private readonly List<Action> loaders = new List<Action>();
-
         public ExifReader(byte[] exifData)
-            : base(new MemoryStream(exifData ?? throw new ArgumentNullException(nameof(exifData))))
+            : this(exifData, null)
+        {
+        }
+
+        public ExifReader(byte[] exifData, MemoryAllocator allocator)
+            : base(new MemoryStream(exifData ?? throw new ArgumentNullException(nameof(exifData))), allocator)
         {
         }
 
@@ -47,16 +52,11 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 
             this.ReadSubIfd(values);
 
-            foreach (Action loader in this.loaders)
-            {
-                loader();
-            }
+            this.ReadBigValues(values);
 
             return values;
         }
 
-        protected override void RegisterExtLoader(uint offset, Action loader) => this.loaders.Add(loader);
-
         private void GetThumbnail(uint offset)
         {
             if (offset == 0)
@@ -86,19 +86,21 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
     /// </summary>
     internal abstract class BaseExifReader
     {
-        private readonly byte[] offsetBuffer = new byte[4];
+        private readonly byte[] buf8 = new byte[8];
         private readonly byte[] buf4 = new byte[4];
         private readonly byte[] buf2 = new byte[2];
 
+        private readonly MemoryAllocator allocator;
         private readonly Stream data;
         private List<ExifTag> invalidTags;
 
-        private uint exifOffset;
-
-        private uint gpsOffset;
+        private List<ulong> subIfds;
 
-        protected BaseExifReader(Stream stream) =>
+        protected BaseExifReader(Stream stream, MemoryAllocator allocator)
+        {
             this.data = stream ?? throw new ArgumentNullException(nameof(stream));
+            this.allocator = allocator;
+        }
 
         private delegate TDataType ConverterMethod<TDataType>(ReadOnlySpan<byte> data);
 
@@ -119,7 +121,51 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 
         public bool IsBigEndian { get; protected set; }
 
-        protected abstract void RegisterExtLoader(uint offset, Action loader);
+        public List<(ulong Offset, ExifDataType DataType, ulong NumberOfComponents, ExifValue Exif)> BigValues { get; } = new();
+
+        protected void ReadBigValues(List<IExifValue> values)
+        {
+            if (this.BigValues.Count == 0)
+            {
+                return;
+            }
+
+            int maxSize = 0;
+            foreach ((ulong offset, ExifDataType dataType, ulong numberOfComponents, ExifValue exif) in this.BigValues)
+            {
+                ulong size = numberOfComponents * ExifDataTypes.GetSize(dataType);
+                DebugGuard.MustBeLessThanOrEqualTo<ulong>(size, int.MaxValue, nameof(size));
+
+                if ((int)size > maxSize)
+                {
+                    maxSize = (int)size;
+                }
+            }
+
+            if (this.allocator != null)
+            {
+                // tiff, bigTiff
+                using IMemoryOwner<byte> memory = this.allocator.Allocate<byte>(maxSize);
+                Span<byte> buf = memory.GetSpan();
+                foreach ((ulong Offset, ExifDataType DataType, ulong NumberOfComponents, ExifValue Exif) tag in this.BigValues)
+                {
+                    ulong size = tag.NumberOfComponents * ExifDataTypes.GetSize(tag.DataType);
+                    this.ReadBigValue(values, tag, buf.Slice(0, (int)size));
+                }
+            }
+            else
+            {
+                // embedded exif
+                Span<byte> buf = maxSize <= 256 ? stackalloc byte[256] : new byte[maxSize];
+                foreach ((ulong Offset, ExifDataType DataType, ulong NumberOfComponents, ExifValue Exif) tag in this.BigValues)
+                {
+                    ulong size = tag.NumberOfComponents * ExifDataTypes.GetSize(tag.DataType);
+                    this.ReadBigValue(values, tag, buf.Slice(0, (int)size));
+                }
+            }
+
+            this.BigValues.Clear();
+        }
 
         /// <summary>
         /// Reads the values to the values collection.
@@ -136,22 +182,45 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             this.Seek(offset);
             int count = this.ReadUInt16();
 
+            Span<byte> offsetBuffer = stackalloc byte[4];
             for (int i = 0; i < count; i++)
             {
-                this.ReadValue(values);
+                this.ReadValue(values, offsetBuffer);
             }
         }
 
         protected void ReadSubIfd(List<IExifValue> values)
         {
-            if (this.exifOffset != 0)
+            if (this.subIfds is not null)
+            {
+                foreach (ulong subIfdOffset in this.subIfds)
+                {
+                    this.ReadValues(values, (uint)subIfdOffset);
+                }
+            }
+        }
+
+        protected void ReadValues64(List<IExifValue> values, ulong offset)
+        {
+            DebugGuard.MustBeLessThanOrEqualTo(offset, (ulong)this.data.Length, "By spec UInt64.MaxValue is supported, but .Net Stream.Length can Int64.MaxValue.");
+
+            this.Seek(offset);
+            ulong count = this.ReadUInt64();
+
+            Span<byte> offsetBuffer = stackalloc byte[8];
+            for (ulong i = 0; i < count; i++)
             {
-                this.ReadValues(values, this.exifOffset);
+                this.ReadValue64(values, offsetBuffer);
             }
+        }
 
-            if (this.gpsOffset != 0)
+        protected void ReadBigValue(IList<IExifValue> values, (ulong Offset, ExifDataType DataType, ulong NumberOfComponents, ExifValue Exif) tag, Span<byte> buffer)
+        {
+            this.Seek(tag.Offset);
+            if (this.TryReadSpan(buffer))
             {
-                this.ReadValues(values, this.gpsOffset);
+                object value = this.ConvertValue(tag.DataType, buffer, tag.NumberOfComponents > 1 || tag.Exif.IsArray);
+                this.Add(values, tag.Exif, value);
             }
         }
 
@@ -172,9 +241,7 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             return result;
         }
 
-        private byte ConvertToByte(ReadOnlySpan<byte> buffer) => buffer[0];
-
-        private string ConvertToString(ReadOnlySpan<byte> buffer)
+        private static string ConvertToString(Encoding encoding, ReadOnlySpan<byte> buffer)
         {
             int nullCharIndex = buffer.IndexOf((byte)0);
 
@@ -183,10 +250,12 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
                 buffer = buffer.Slice(0, nullCharIndex);
             }
 
-            return Encoding.UTF8.GetString(buffer);
+            return encoding.GetString(buffer);
         }
 
-        private object ConvertValue(ExifDataType dataType, ReadOnlySpan<byte> buffer, uint numberOfComponents)
+        private byte ConvertToByte(ReadOnlySpan<byte> buffer) => buffer[0];
+
+        private object ConvertValue(ExifDataType dataType, ReadOnlySpan<byte> buffer, bool isArray)
         {
             if (buffer.Length == 0)
             {
@@ -198,90 +267,101 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
                 case ExifDataType.Unknown:
                     return null;
                 case ExifDataType.Ascii:
-                    return this.ConvertToString(buffer);
+                    return ConvertToString(ExifConstants.DefaultEncoding, buffer);
                 case ExifDataType.Byte:
-                    if (numberOfComponents == 1)
+                case ExifDataType.Undefined:
+                    if (!isArray)
                     {
                         return this.ConvertToByte(buffer);
                     }
 
                     return buffer.ToArray();
                 case ExifDataType.DoubleFloat:
-                    if (numberOfComponents == 1)
+                    if (!isArray)
                     {
                         return this.ConvertToDouble(buffer);
                     }
 
                     return ToArray(dataType, buffer, this.ConvertToDouble);
                 case ExifDataType.Long:
-                    if (numberOfComponents == 1)
+                case ExifDataType.Ifd:
+                    if (!isArray)
                     {
                         return this.ConvertToUInt32(buffer);
                     }
 
                     return ToArray(dataType, buffer, this.ConvertToUInt32);
                 case ExifDataType.Rational:
-                    if (numberOfComponents == 1)
+                    if (!isArray)
                     {
                         return this.ToRational(buffer);
                     }
 
                     return ToArray(dataType, buffer, this.ToRational);
                 case ExifDataType.Short:
-                    if (numberOfComponents == 1)
+                    if (!isArray)
                     {
                         return this.ConvertToShort(buffer);
                     }
 
                     return ToArray(dataType, buffer, this.ConvertToShort);
                 case ExifDataType.SignedByte:
-                    if (numberOfComponents == 1)
+                    if (!isArray)
                     {
                         return this.ConvertToSignedByte(buffer);
                     }
 
                     return ToArray(dataType, buffer, this.ConvertToSignedByte);
                 case ExifDataType.SignedLong:
-                    if (numberOfComponents == 1)
+                    if (!isArray)
                     {
                         return this.ConvertToInt32(buffer);
                     }
 
                     return ToArray(dataType, buffer, this.ConvertToInt32);
                 case ExifDataType.SignedRational:
-                    if (numberOfComponents == 1)
+                    if (!isArray)
                     {
                         return this.ToSignedRational(buffer);
                     }
 
                     return ToArray(dataType, buffer, this.ToSignedRational);
                 case ExifDataType.SignedShort:
-                    if (numberOfComponents == 1)
+                    if (!isArray)
                     {
                         return this.ConvertToSignedShort(buffer);
                     }
 
                     return ToArray(dataType, buffer, this.ConvertToSignedShort);
                 case ExifDataType.SingleFloat:
-                    if (numberOfComponents == 1)
+                    if (!isArray)
                     {
                         return this.ConvertToSingle(buffer);
                     }
 
                     return ToArray(dataType, buffer, this.ConvertToSingle);
-                case ExifDataType.Undefined:
-                    if (numberOfComponents == 1)
+                case ExifDataType.Long8:
+                case ExifDataType.Ifd8:
+                    if (!isArray)
                     {
-                        return this.ConvertToByte(buffer);
+                        return this.ConvertToUInt64(buffer);
                     }
 
-                    return buffer.ToArray();
+                    return ToArray(dataType, buffer, this.ConvertToUInt64);
+                case ExifDataType.SignedLong8:
+                    if (!isArray)
+                    {
+                        return this.ConvertToInt64(buffer);
+                    }
+
+                    return ToArray(dataType, buffer, this.ConvertToUInt64);
+
                 default:
-                    throw new NotSupportedException();
+                    throw new NotSupportedException($"Data type {dataType} is not supported.");
             }
         }
 
-        private void ReadValue(List<IExifValue> values)
+        private void ReadValue(List<IExifValue> values, Span<byte> offsetBuffer)
         {
             // 2   | 2    | 4     | 4
             // tag | type | count | value offset
@@ -295,7 +375,7 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 
             uint numberOfComponents = this.ReadUInt32();
 
-            this.TryReadSpan(this.offsetBuffer);
+            this.TryReadSpan(offsetBuffer);
 
             // Ensure that the data type is valid
             if (dataType == ExifDataType.Unknown)
@@ -305,9 +385,9 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 
             // Issue #132: ExifDataType == Undefined is treated like a byte array.
             // If numberOfComponents == 0 this value can only be handled as an inline value and must fallback to 4 (bytes)
-            if (dataType == ExifDataType.Undefined && numberOfComponents == 0)
+            if (numberOfComponents == 0)
             {
-                numberOfComponents = 4;
+                numberOfComponents = 4 / ExifDataTypes.GetSize(dataType);
             }
 
             ExifValue exifValue = ExifValues.Create(tag) ?? ExifValues.Create(tag, dataType, numberOfComponents);
@@ -321,7 +401,7 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             uint size = numberOfComponents * ExifDataTypes.GetSize(dataType);
             if (size > 4)
             {
-                uint newOffset = this.ConvertToUInt32(this.offsetBuffer);
+                uint newOffset = this.ConvertToUInt32(offsetBuffer);
 
                 // Ensure that the new index does not overrun the data.
                 if (newOffset > int.MaxValue || (newOffset + size) > this.data.Length)
@@ -330,21 +410,85 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
                     return;
                 }
 
-                this.RegisterExtLoader(newOffset, () =>
-                {
-                    byte[] dataBuffer = new byte[size];
-                    this.Seek(newOffset);
-                    if (this.TryReadSpan(dataBuffer))
-                    {
-                        object value = this.ConvertValue(dataType, dataBuffer, numberOfComponents);
-                        this.Add(values, exifValue, value);
-                    }
-                });
+                this.BigValues.Add((newOffset, dataType, numberOfComponents, exifValue));
             }
             else
             {
-                object value = this.ConvertValue(dataType, this.offsetBuffer, numberOfComponents);
+                object value = this.ConvertValue(dataType, offsetBuffer.Slice(0, (int)size), numberOfComponents > 1 || exifValue.IsArray);
+                this.Add(values, exifValue, value);
+            }
+        }
+
+        private void ReadValue64(List<IExifValue> values, Span<byte> offsetBuffer)
+        {
+            if ((this.data.Length - this.data.Position) < 20)
+            {
+                return;
+            }
+
+            var tag = (ExifTagValue)this.ReadUInt16();
+            ExifDataType dataType = EnumUtils.Parse(this.ReadUInt16(), ExifDataType.Unknown);
+
+            ulong numberOfComponents = this.ReadUInt64();
+
+            this.TryReadSpan(offsetBuffer);
+
+            if (dataType == ExifDataType.Unknown)
+            {
+                return;
+            }
 
+            if (numberOfComponents == 0)
+            {
+                numberOfComponents = 8 / ExifDataTypes.GetSize(dataType);
+            }
+
+            // The StripOffsets, StripByteCounts, TileOffsets, and TileByteCounts tags are allowed to have the datatype TIFF_LONG8 in BigTIFF.
+            // Old datatypes TIFF_LONG, and TIFF_SHORT where allowed in the TIFF 6.0 specification, are still valid in BigTIFF, too.
+            // Likewise, tags that point to other IFDs, like e.g. the SubIFDs tag, are now allowed to have the datatype TIFF_IFD8 in BigTIFF.
+            // Again, the old datatypes TIFF_IFD, and the hardly recommendable TIFF_LONG, are still valid, too.
+            // https://www.awaresystems.be/imaging/tiff/bigtiff.html
+            ExifValue exifValue;
+            switch (tag)
+            {
+                case ExifTagValue.StripOffsets:
+                    exifValue = new ExifLong8Array(ExifTagValue.StripOffsets);
+                    break;
+                case ExifTagValue.StripByteCounts:
+                    exifValue = new ExifLong8Array(ExifTagValue.StripByteCounts);
+                    break;
+                case ExifTagValue.TileOffsets:
+                    exifValue = new ExifLong8Array(ExifTagValue.TileOffsets);
+                    break;
+                case ExifTagValue.TileByteCounts:
+                    exifValue = new ExifLong8Array(ExifTagValue.TileByteCounts);
+                    break;
+                default:
+                    exifValue = ExifValues.Create(tag) ?? ExifValues.Create(tag, dataType, numberOfComponents);
+                    break;
+            }
+
+            if (exifValue is null)
+            {
+                this.AddInvalidTag(new UnkownExifTag(tag));
+                return;
+            }
+
+            ulong size = numberOfComponents * ExifDataTypes.GetSize(dataType);
+            if (size > 8)
+            {
+                ulong newOffset = this.ConvertToUInt64(offsetBuffer);
+                if (newOffset > ulong.MaxValue || newOffset > ((ulong)this.data.Length - size))
+                {
+                    this.AddInvalidTag(new UnkownExifTag(tag));
+                    return;
+                }
+
+                this.BigValues.Add((newOffset, dataType, numberOfComponents, exifValue));
+            }
+            else
+            {
+                object value = this.ConvertValue(dataType, offsetBuffer.Slice(0, (int)size), numberOfComponents > 1 || exifValue.IsArray);
                 this.Add(values, exifValue, value);
             }
         }
@@ -368,11 +512,11 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 
             if (exif.Tag == ExifTag.SubIFDOffset)
             {
-                this.exifOffset = (uint)value;
+                this.AddSubIfd(value);
             }
             else if (exif.Tag == ExifTag.GPSIFDOffset)
             {
-                this.gpsOffset = (uint)value;
+                this.AddSubIfd(value);
             }
             else
             {
@@ -383,8 +527,11 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
         private void AddInvalidTag(ExifTag tag)
             => (this.invalidTags ??= new List<ExifTag>()).Add(tag);
 
-        private void Seek(long pos)
-            => this.data.Seek(pos, SeekOrigin.Begin);
+        private void AddSubIfd(object val)
+            => (this.subIfds ??= new List<ulong>()).Add(Convert.ToUInt64(val));
+
+        private void Seek(ulong pos)
+            => this.data.Seek((long)pos, SeekOrigin.Begin);
 
         private bool TryReadSpan(Span<byte> span)
         {
@@ -398,6 +545,11 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             return read == length;
         }
 
+        protected ulong ReadUInt64() =>
+            this.TryReadSpan(this.buf8)
+                ? this.ConvertToUInt64(this.buf8)
+                : default;
+
         // Known as Long in Exif Specification.
         protected uint ReadUInt32() =>
             this.TryReadSpan(this.buf4)
@@ -408,6 +560,30 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
                 ? this.ConvertToShort(this.buf2)
                 : default;
 
+        private long ConvertToInt64(ReadOnlySpan<byte> buffer)
+        {
+            if (buffer.Length < 8)
+            {
+                return default;
+            }
+
+            return this.IsBigEndian
+                ? BinaryPrimitives.ReadInt64BigEndian(buffer)
+                : BinaryPrimitives.ReadInt64LittleEndian(buffer);
+        }
+
+        private ulong ConvertToUInt64(ReadOnlySpan<byte> buffer)
+        {
+            if (buffer.Length < 8)
+            {
+                return default;
+            }
+
+            return this.IsBigEndian
+                ? BinaryPrimitives.ReadUInt64BigEndian(buffer)
+                : BinaryPrimitives.ReadUInt64LittleEndian(buffer);
+        }
+
         private double ConvertToDouble(ReadOnlySpan<byte> buffer)
         {
             if (buffer.Length < 8)

src/ImageSharp/Metadata/Profiles/Exif/ExifUcs2StringHelpers.cs

@@ -0,0 +1,21 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Text;
+
+namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
+{
+    internal static class ExifUcs2StringHelpers
+    {
+        public static Encoding Ucs2Encoding => Encoding.GetEncoding("UCS-2");
+
+        public static bool IsUcs2Tag(ExifTagValue tag) => tag switch
+        {
+            ExifTagValue.XPAuthor or ExifTagValue.XPComment or ExifTagValue.XPKeywords or ExifTagValue.XPSubject or ExifTagValue.XPTitle => true,
+            _ => false,
+        };
+
+        public static int Write(string value, Span<byte> destination) => ExifEncodedStringHelpers.Write(Ucs2Encoding, value, destination);
+    }
+}

src/ImageSharp/Metadata/Profiles/Exif/ExifWriter.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Buffers.Binary;
 using System.Collections.Generic;
-using System.Text;
 
 namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 {
@@ -46,23 +45,17 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
         public byte[] GetData()
         {
             const uint startIndex = 0;
-            uint length;
 
             IExifValue exifOffset = GetOffsetValue(this.ifdValues, this.exifValues, ExifTag.SubIFDOffset);
             IExifValue gpsOffset = GetOffsetValue(this.ifdValues, this.gpsValues, ExifTag.GPSIFDOffset);
 
-            if (this.ifdValues.Count == 0 && this.exifValues.Count == 0 && this.gpsValues.Count == 0)
-            {
-                return Array.Empty<byte>();
-            }
-
-            uint ifdLength = this.GetLength(this.ifdValues) + 4U;
+            uint ifdLength = this.GetLength(this.ifdValues);
             uint exifLength = this.GetLength(this.exifValues);
             uint gpsLength = this.GetLength(this.gpsValues);
 
-            length = ifdLength + exifLength + gpsLength;
+            uint length = ifdLength + exifLength + gpsLength;
 
-            if (length == 4U)
+            if (length == 0)
             {
                 return Array.Empty<byte>();
             }
@@ -70,9 +63,10 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             // two bytes for the byte Order marker 'II' or 'MM', followed by the number 42 (0x2A) and a 0, making 4 bytes total
             length += (uint)ExifConstants.LittleEndianByteOrderMarker.Length;
 
-            length += 4 + 2;
+            // first IFD offset
+            length += 4;
 
-            var result = new byte[length];
+            byte[] result = new byte[length];
 
             int i = 0;
 
@@ -80,15 +74,13 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             ExifConstants.LittleEndianByteOrderMarker.CopyTo(result.AsSpan(start: i));
             i += ExifConstants.LittleEndianByteOrderMarker.Length;
 
-            uint ifdOffset = ((uint)i - startIndex) + 4U;
-            uint thumbnailOffset = ifdOffset + ifdLength + exifLength + gpsLength;
+            uint ifdOffset = (uint)i - startIndex + 4U;
 
             exifOffset?.TrySetValue(ifdOffset + ifdLength);
             gpsOffset?.TrySetValue(ifdOffset + ifdLength + exifLength);
 
             i = WriteUInt32(ifdOffset, result, i);
             i = this.WriteHeaders(this.ifdValues, result, i);
-            i = WriteUInt32(thumbnailOffset, result, i);
             i = this.WriteData(startIndex, this.ifdValues, result, i);
 
             if (exifLength > 0)
@@ -103,8 +95,6 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
                 i = this.WriteData(startIndex, this.gpsValues, result, i);
             }
 
-            WriteUInt16(0, result, i);
-
             return result;
         }
 
@@ -150,6 +140,20 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             return offset + 4;
         }
 
+        private static int WriteInt64(long value, Span<byte> destination, int offset)
+        {
+            BinaryPrimitives.WriteInt64LittleEndian(destination.Slice(offset, 8), value);
+
+            return offset + 8;
+        }
+
+        private static int WriteUInt64(ulong value, Span<byte> destination, int offset)
+        {
+            BinaryPrimitives.WriteUInt64LittleEndian(destination.Slice(offset, 8), value);
+
+            return offset + 8;
+        }
+
         private static int WriteInt32(int value, Span<byte> destination, int offset)
         {
             BinaryPrimitives.WriteInt32LittleEndian(destination.Slice(offset, 4), value);
@@ -249,7 +253,7 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             {
                 uint valueLength = GetLength(value);
 
-                length += 2 + 2 + 4 + 4;
+                length += 12;
 
                 if (valueLength > 4)
                 {
@@ -257,6 +261,9 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
                 }
             }
 
+            // next IFD offset
+            length += 4;
+
             return length;
         }
 
@@ -266,9 +273,19 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
         {
             object value = exifValue.GetValue();
 
+            if (ExifUcs2StringHelpers.IsUcs2Tag((ExifTagValue)(ushort)exifValue.Tag))
+            {
+                return (uint)ExifUcs2StringHelpers.Ucs2Encoding.GetByteCount((string)value);
+            }
+
+            if (value is EncodedString encodedString)
+            {
+                return ExifEncodedStringHelpers.GetDataLength(encodedString);
+            }
+
             if (exifValue.DataType == ExifDataType.Ascii)
             {
-                return (uint)Encoding.UTF8.GetBytes((string)value).Length + 1;
+                return (uint)ExifConstants.DefaultEncoding.GetByteCount((string)value) + 1;
             }
 
             if (value is Array arrayValue)
@@ -281,11 +298,6 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 
         private static int WriteArray(IExifValue value, Span<byte> destination, int offset)
         {
-            if (value.DataType == ExifDataType.Ascii)
-            {
-                return WriteValue(ExifDataType.Ascii, value.GetValue(), destination, offset);
-            }
-
             int newOffset = offset;
             foreach (object obj in (Array)value.GetValue())
             {
@@ -347,6 +359,9 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
                 newOffset += 4;
             }
 
+            // next IFD offset
+            newOffset = WriteUInt32(0, destination, newOffset);
+
             return newOffset;
         }
 
@@ -367,7 +382,7 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             switch (dataType)
             {
                 case ExifDataType.Ascii:
-                    offset = Write(Encoding.UTF8.GetBytes((string)value), destination, offset);
+                    offset = Write(ExifConstants.DefaultEncoding.GetBytes((string)value), destination, offset);
                     destination[offset] = 0;
                     return offset + 1;
                 case ExifDataType.Byte:
@@ -390,6 +405,10 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
                     }
 
                     return WriteUInt32((uint)value, destination, offset);
+                case ExifDataType.Long8:
+                    return WriteUInt64((ulong)value, destination, offset);
+                case ExifDataType.SignedLong8:
+                    return WriteInt64((long)value, destination, offset);
                 case ExifDataType.Rational:
                     WriteRational(destination.Slice(offset, 8), (Rational)value);
                     return offset + 8;
@@ -410,14 +429,25 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             }
         }
 
-        internal static int WriteValue(IExifValue value, Span<byte> destination, int offset)
+        internal static int WriteValue(IExifValue exifValue, Span<byte> destination, int offset)
         {
-            if (value.IsArray && value.DataType != ExifDataType.Ascii)
+            object value = exifValue.GetValue();
+
+            if (ExifUcs2StringHelpers.IsUcs2Tag((ExifTagValue)(ushort)exifValue.Tag))
+            {
+                return offset + ExifUcs2StringHelpers.Write((string)value, destination.Slice(offset));
+            }
+            else if (value is EncodedString encodedString)
+            {
+                return offset + ExifEncodedStringHelpers.Write(encodedString, destination.Slice(offset));
+            }
+
+            if (exifValue.IsArray)
             {
-                return WriteArray(value, destination, offset);
+                return WriteArray(exifValue, destination, offset);
             }
 
-            return WriteValue(value.DataType, value.GetValue(), destination, offset);
+            return WriteValue(exifValue.DataType, value, destination, offset);
         }
     }
 }

src/ImageSharp/Metadata/Profiles/Exif/Tags/ExifTag.ByteArray.cs

@@ -41,31 +41,6 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
         /// </summary>
         public static ExifTag<byte[]> TIFFEPStandardID => new ExifTag<byte[]>(ExifTagValue.TIFFEPStandardID);
 
-        /// <summary>
-        /// Gets the XPTitle exif tag.
-        /// </summary>
-        public static ExifTag<byte[]> XPTitle => new ExifTag<byte[]>(ExifTagValue.XPTitle);
-
-        /// <summary>
-        /// Gets the XPComment exif tag.
-        /// </summary>
-        public static ExifTag<byte[]> XPComment => new ExifTag<byte[]>(ExifTagValue.XPComment);
-
-        /// <summary>
-        /// Gets the XPAuthor exif tag.
-        /// </summary>
-        public static ExifTag<byte[]> XPAuthor => new ExifTag<byte[]>(ExifTagValue.XPAuthor);
-
-        /// <summary>
-        /// Gets the XPKeywords exif tag.
-        /// </summary>
-        public static ExifTag<byte[]> XPKeywords => new ExifTag<byte[]>(ExifTagValue.XPKeywords);
-
-        /// <summary>
-        /// Gets the XPSubject exif tag.
-        /// </summary>
-        public static ExifTag<byte[]> XPSubject => new ExifTag<byte[]>(ExifTagValue.XPSubject);
-
         /// <summary>
         /// Gets the GPSVersionID exif tag.
         /// </summary>

src/ImageSharp/Metadata/Profiles/Exif/Tags/ExifTag.EncodedString.cs

@@ -0,0 +1,24 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
+{
+    /// <content/>
+    public abstract partial class ExifTag
+    {
+        /// <summary>
+        /// Gets the UserComment exif tag.
+        /// </summary>
+        public static ExifTag<EncodedString> UserComment { get; } = new ExifTag<EncodedString>(ExifTagValue.UserComment);
+
+        /// <summary>
+        /// Gets the GPSProcessingMethod exif tag.
+        /// </summary>
+        public static ExifTag<EncodedString> GPSProcessingMethod { get; } = new ExifTag<EncodedString>(ExifTagValue.GPSProcessingMethod);
+
+        /// <summary>
+        /// Gets the GPSAreaInformation exif tag.
+        /// </summary>
+        public static ExifTag<EncodedString> GPSAreaInformation { get; } = new ExifTag<EncodedString>(ExifTagValue.GPSAreaInformation);
+    }
+}

src/ImageSharp/Metadata/Profiles/Exif/Tags/ExifTag.LongArray.cs

@@ -65,5 +65,10 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
         /// Gets the TimeZoneOffset exif tag.
         /// </summary>
         public static ExifTag<uint[]> TimeZoneOffset { get; } = new ExifTag<uint[]>(ExifTagValue.TimeZoneOffset);
+
+        /// <summary>
+        /// Gets the offset to child IFDs exif tag.
+        /// </summary>
+        public static ExifTag<uint[]> SubIFDs { get; } = new ExifTag<uint[]>(ExifTagValue.SubIFDs);
     }
 }

src/ImageSharp/Metadata/Profiles/Exif/Tags/ExifTag.Ucs2String.cs

@@ -0,0 +1,34 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
+{
+    /// <content/>
+    public abstract partial class ExifTag
+    {
+        /// <summary>
+        /// Gets the title tag used by Windows (encoded in UCS2).
+        /// </summary>
+        public static ExifTag<string> XPTitle => new ExifTag<string>(ExifTagValue.XPTitle);
+
+        /// <summary>
+        /// Gets the comment tag used by Windows (encoded in UCS2).
+        /// </summary>
+        public static ExifTag<string> XPComment => new ExifTag<string>(ExifTagValue.XPComment);
+
+        /// <summary>
+        /// Gets the author tag used by Windows (encoded in UCS2).
+        /// </summary>
+        public static ExifTag<string> XPAuthor => new ExifTag<string>(ExifTagValue.XPAuthor);
+
+        /// <summary>
+        /// Gets the keywords tag used by Windows (encoded in UCS2).
+        /// </summary>
+        public static ExifTag<string> XPKeywords => new ExifTag<string>(ExifTagValue.XPKeywords);
+
+        /// <summary>
+        /// Gets the subject tag used by Windows (encoded in UCS2).
+        /// </summary>
+        public static ExifTag<string> XPSubject => new ExifTag<string>(ExifTagValue.XPSubject);
+    }
+}

src/ImageSharp/Metadata/Profiles/Exif/Tags/ExifTag.Undefined.cs

@@ -31,11 +31,6 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
         /// </summary>
         public static ExifTag<byte[]> MakerNote { get; } = new ExifTag<byte[]>(ExifTagValue.MakerNote);
 
-        /// <summary>
-        /// Gets the UserComment exif tag.
-        /// </summary>
-        public static ExifTag<byte[]> UserComment { get; } = new ExifTag<byte[]>(ExifTagValue.UserComment);
-
         /// <summary>
         /// Gets the FlashpixVersion exif tag.
         /// </summary>
@@ -71,16 +66,6 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
         /// </summary>
         public static ExifTag<byte[]> ImageSourceData { get; } = new ExifTag<byte[]>(ExifTagValue.ImageSourceData);
 
-        /// <summary>
-        /// Gets the GPSProcessingMethod exif tag.
-        /// </summary>
-        public static ExifTag<byte[]> GPSProcessingMethod { get; } = new ExifTag<byte[]>(ExifTagValue.GPSProcessingMethod);
-
-        /// <summary>
-        /// Gets the GPSAreaInformation exif tag.
-        /// </summary>
-        public static ExifTag<byte[]> GPSAreaInformation { get; } = new ExifTag<byte[]>(ExifTagValue.GPSAreaInformation);
-
         /// <summary>
         /// Gets the FileSource exif tag.
         /// </summary>

src/ImageSharp/Metadata/Profiles/Exif/Values/EncodedString.cs

@@ -0,0 +1,94 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+
+namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
+{
+    /// <summary>
+    /// The EXIF encoded string structure.
+    /// </summary>
+    public readonly struct EncodedString : IEquatable<EncodedString>
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="EncodedString" /> struct.
+        /// Default use Unicode character code.
+        /// </summary>
+        /// <param name="text">The text value.</param>
+        public EncodedString(string text)
+          : this(CharacterCode.Unicode, text)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="EncodedString" /> struct.
+        /// </summary>
+        /// <param name="code">The character code.</param>
+        /// <param name="text">The text value.</param>
+        public EncodedString(CharacterCode code, string text)
+        {
+            this.Text = text;
+            this.Code = code;
+        }
+
+        /// <summary>
+        /// The 8-byte character code enum.
+        /// </summary>
+        public enum CharacterCode
+        {
+            /// <summary>
+            /// The ASCII (ITU-T T.50 IA5) character code.
+            /// </summary>
+            ASCII,
+
+            /// <summary>
+            /// The JIS (X208-1990) character code.
+            /// </summary>
+            JIS,
+
+            /// <summary>
+            /// The Unicode character code.
+            /// </summary>
+            Unicode,
+
+            /// <summary>
+            /// The undefined character code.
+            /// </summary>
+            Undefined
+        }
+
+        /// <summary>
+        /// Gets the character ode.
+        /// </summary>
+        public CharacterCode Code { get; }
+
+        /// <summary>
+        /// Gets the text.
+        /// </summary>
+        public string Text { get; }
+
+        /// <summary>
+        /// Converts the specified <see cref="string"/> to an instance of this type.
+        /// </summary>
+        /// <param name="text">The text value.</param>
+        public static implicit operator EncodedString(string text) => new(text);
+
+        /// <summary>
+        /// Converts the specified <see cref="EncodedString"/> to a <see cref="string"/>.
+        /// </summary>
+        /// <param name="encodedString">The <see cref="EncodedString"/> to convert.</param>
+        public static explicit operator string(EncodedString encodedString) => encodedString.Text;
+
+        /// <inheritdoc/>
+        public override bool Equals(object obj) => obj is EncodedString other && this.Equals(other);
+
+        /// <inheritdoc/>
+        public bool Equals(EncodedString other) => this.Text == other.Text && this.Code == other.Code;
+
+        /// <inheritdoc/>
+        public override int GetHashCode() => HashCode.Combine(this.Text, this.Code);
+
+        /// <inheritdoc/>
+        public override string ToString() => this.Text;
+    }
+}

src/ImageSharp/Metadata/Profiles/Exif/Values/ExifEncodedString.cs

@@ -0,0 +1,55 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Globalization;
+
+namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
+{
+    internal sealed class ExifEncodedString : ExifValue<EncodedString>
+    {
+        public ExifEncodedString(ExifTag<EncodedString> tag)
+            : base(tag)
+        {
+        }
+
+        public ExifEncodedString(ExifTagValue tag)
+            : base(tag)
+        {
+        }
+
+        private ExifEncodedString(ExifEncodedString value)
+            : base(value)
+        {
+        }
+
+        public override ExifDataType DataType => ExifDataType.Undefined;
+
+        protected override string StringValue => this.Value.Text;
+
+        public override bool TrySetValue(object value)
+        {
+            if (base.TrySetValue(value))
+            {
+                return true;
+            }
+
+            if (value is string stringValue)
+            {
+                this.Value = new EncodedString(stringValue);
+                return true;
+            }
+            else if (value is byte[] buffer)
+            {
+                if (ExifEncodedStringHelpers.TryParse(buffer, out EncodedString encodedString))
+                {
+                    this.Value = encodedString;
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        public override IExifValue DeepClone() => new ExifEncodedString(this);
+    }
+}

src/ImageSharp/Metadata/Profiles/Exif/Values/ExifLong8.cs

@@ -0,0 +1,66 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Globalization;
+
+namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
+{
+    internal sealed class ExifLong8 : ExifValue<ulong>
+    {
+        public ExifLong8(ExifTag<ulong> tag)
+            : base(tag)
+        {
+        }
+
+        public ExifLong8(ExifTagValue tag)
+            : base(tag)
+        {
+        }
+
+        private ExifLong8(ExifLong8 value)
+            : base(value)
+        {
+        }
+
+        public override ExifDataType DataType => ExifDataType.Long8;
+
+        protected override string StringValue => this.Value.ToString(CultureInfo.InvariantCulture);
+
+        public override bool TrySetValue(object value)
+        {
+            if (base.TrySetValue(value))
+            {
+                return true;
+            }
+
+            switch (value)
+            {
+                case int intValue:
+                    if (intValue >= uint.MinValue)
+                    {
+                        this.Value = (uint)intValue;
+                        return true;
+                    }
+
+                    return false;
+                case uint uintValue:
+                    this.Value = uintValue;
+
+                    return true;
+                case long intValue:
+                    if (intValue >= 0)
+                    {
+                        this.Value = (ulong)intValue;
+                        return true;
+                    }
+
+                    return false;
+                default:
+
+                    return false;
+            }
+        }
+
+        public override IExifValue DeepClone() => new ExifLong8(this);
+    }
+}

src/ImageSharp/Metadata/Profiles/Exif/Values/ExifLong8Array.cs

@@ -0,0 +1,171 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Runtime.CompilerServices;
+
+namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
+{
+    internal sealed class ExifLong8Array : ExifArrayValue<ulong>
+    {
+        public ExifLong8Array(ExifTagValue tag)
+            : base(tag)
+        {
+        }
+
+        private ExifLong8Array(ExifLong8Array value)
+            : base(value)
+        {
+        }
+
+        public override ExifDataType DataType
+        {
+            get
+            {
+                if (this.Value is not null)
+                {
+                    foreach (ulong value in this.Value)
+                    {
+                        if (value > uint.MaxValue)
+                        {
+                            return ExifDataType.Long8;
+                        }
+                    }
+                }
+
+                return ExifDataType.Long;
+            }
+        }
+
+        public override bool TrySetValue(object value)
+        {
+            if (base.TrySetValue(value))
+            {
+                return true;
+            }
+
+            switch (value)
+            {
+                case int val:
+                    return this.SetSingle((ulong)Numerics.Clamp(val, 0, int.MaxValue));
+
+                case uint val:
+                    return this.SetSingle((ulong)val);
+
+                case short val:
+                    return this.SetSingle((ulong)Numerics.Clamp(val, 0, short.MaxValue));
+
+                case ushort val:
+                    return this.SetSingle((ulong)val);
+
+                case long val:
+                    return this.SetSingle((ulong)Numerics.Clamp(val, 0, long.MaxValue));
+
+                case long[] array:
+                {
+                    if (value.GetType() == typeof(ulong[]))
+                    {
+                        return this.SetArray((ulong[])value);
+                    }
+
+                    return this.SetArray(array);
+                }
+
+                case int[] array:
+                {
+                    if (value.GetType() == typeof(uint[]))
+                    {
+                        return this.SetArray((uint[])value);
+                    }
+
+                    return this.SetArray(array);
+                }
+
+                case short[] array:
+                {
+                    if (value.GetType() == typeof(ushort[]))
+                    {
+                        return this.SetArray((ushort[])value);
+                    }
+
+                    return this.SetArray(array);
+                }
+            }
+
+            return false;
+        }
+
+        public override IExifValue DeepClone() => new ExifLong8Array(this);
+
+        private bool SetSingle(ulong value)
+        {
+            this.Value = new[] { value };
+            return true;
+        }
+
+        private bool SetArray(long[] values)
+        {
+            var numbers = new ulong[values.Length];
+            for (int i = 0; i < values.Length; i++)
+            {
+                numbers[i] = (ulong)(values[i] < 0 ? 0 : values[i]);
+            }
+
+            this.Value = numbers;
+            return true;
+        }
+
+        private bool SetArray(ulong[] values)
+        {
+            this.Value = values;
+            return true;
+        }
+
+        private bool SetArray(int[] values)
+        {
+            var numbers = new ulong[values.Length];
+            for (int i = 0; i < values.Length; i++)
+            {
+                numbers[i] = (ulong)Numerics.Clamp(values[i], 0, int.MaxValue);
+            }
+
+            this.Value = numbers;
+            return true;
+        }
+
+        private bool SetArray(uint[] values)
+        {
+            var numbers = new ulong[values.Length];
+            for (int i = 0; i < values.Length; i++)
+            {
+                numbers[i] = (ulong)values[i];
+            }
+
+            this.Value = numbers;
+            return true;
+        }
+
+        private bool SetArray(short[] values)
+        {
+            var numbers = new ulong[values.Length];
+            for (int i = 0; i < values.Length; i++)
+            {
+                numbers[i] = (ulong)Numerics.Clamp(values[i], 0, short.MaxValue);
+            }
+
+            this.Value = numbers;
+            return true;
+        }
+
+        private bool SetArray(ushort[] values)
+        {
+            var numbers = new ulong[values.Length];
+            for (int i = 0; i < values.Length; i++)
+            {
+                numbers[i] = (ulong)values[i];
+            }
+
+            this.Value = numbers;
+            return true;
+        }
+    }
+}