Merge branch 'main' into animated-webp-encoder

src/ImageSharp/Compression/Zlib/ZlibInflateStream.cs

@@ -123,12 +123,12 @@ internal sealed class ZlibInflateStream : Stream
     /// <inheritdoc/>
     public override int Read(byte[] buffer, int offset, int count)
     {
-        if (this.currentDataRemaining == 0)
+        if (this.currentDataRemaining is 0)
         {
             // Last buffer was read in its entirety, let's make sure we don't actually have more in additional IDAT chunks.
             this.currentDataRemaining = this.getData();
 
-            if (this.currentDataRemaining == 0)
+            if (this.currentDataRemaining is 0)
             {
                 return 0;
             }
@@ -142,11 +142,11 @@ internal sealed class ZlibInflateStream : Stream
         // Keep reading data until we've reached the end of the stream or filled the buffer.
         int bytesRead = 0;
         offset += totalBytesRead;
-        while (this.currentDataRemaining == 0 && totalBytesRead < count)
+        while (this.currentDataRemaining is 0 && totalBytesRead < count)
         {
             this.currentDataRemaining = this.getData();
 
-            if (this.currentDataRemaining == 0)
+            if (this.currentDataRemaining is 0)
             {
                 return totalBytesRead;
             }

src/ImageSharp/Formats/Png/Chunks/AnimationControl.cs

@@ -0,0 +1,47 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers.Binary;
+
+namespace SixLabors.ImageSharp.Formats.Png.Chunks;
+
+internal readonly struct AnimationControl
+{
+    public const int Size = 8;
+
+    public AnimationControl(int numberFrames, int numberPlays)
+    {
+        this.NumberFrames = numberFrames;
+        this.NumberPlays = numberPlays;
+    }
+
+    /// <summary>
+    /// Gets the number of frames
+    /// </summary>
+    public int NumberFrames { get; }
+
+    /// <summary>
+    /// Gets the number of times to loop this APNG.  0 indicates infinite looping.
+    /// </summary>
+    public int NumberPlays { get; }
+
+    /// <summary>
+    /// Writes the acTL to the given buffer.
+    /// </summary>
+    /// <param name="buffer">The buffer to write to.</param>
+    public void WriteTo(Span<byte> buffer)
+    {
+        BinaryPrimitives.WriteInt32BigEndian(buffer[..4], this.NumberFrames);
+        BinaryPrimitives.WriteInt32BigEndian(buffer[4..8], this.NumberPlays);
+    }
+
+    /// <summary>
+    /// Parses the APngAnimationControl from the given data buffer.
+    /// </summary>
+    /// <param name="data">The data to parse.</param>
+    /// <returns>The parsed acTL.</returns>
+    public static AnimationControl Parse(ReadOnlySpan<byte> data)
+        => new(
+            numberFrames: BinaryPrimitives.ReadInt32BigEndian(data[..4]),
+            numberPlays: BinaryPrimitives.ReadInt32BigEndian(data[4..8]));
+}

src/ImageSharp/Formats/Png/Chunks/FrameControl.cs

@@ -0,0 +1,160 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers.Binary;
+
+namespace SixLabors.ImageSharp.Formats.Png.Chunks;
+
+internal readonly struct FrameControl
+{
+    public const int Size = 26;
+
+    public FrameControl(uint width, uint height)
+        : this(0, width, height, 0, 0, 0, 0, default, default)
+    {
+    }
+
+    public FrameControl(
+        uint sequenceNumber,
+        uint width,
+        uint height,
+        uint xOffset,
+        uint yOffset,
+        ushort delayNumerator,
+        ushort delayDenominator,
+        PngDisposalMethod disposeOperation,
+        PngBlendMethod blendOperation)
+    {
+        this.SequenceNumber = sequenceNumber;
+        this.Width = width;
+        this.Height = height;
+        this.XOffset = xOffset;
+        this.YOffset = yOffset;
+        this.DelayNumerator = delayNumerator;
+        this.DelayDenominator = delayDenominator;
+        this.DisposeOperation = disposeOperation;
+        this.BlendOperation = blendOperation;
+    }
+
+    /// <summary>
+    /// Gets the sequence number of the animation chunk, starting from 0
+    /// </summary>
+    public uint SequenceNumber { get; }
+
+    /// <summary>
+    /// Gets the width of the following frame
+    /// </summary>
+    public uint Width { get; }
+
+    /// <summary>
+    /// Gets the height of the following frame
+    /// </summary>
+    public uint Height { get; }
+
+    /// <summary>
+    /// Gets the X position at which to render the following frame
+    /// </summary>
+    public uint XOffset { get; }
+
+    /// <summary>
+    /// Gets the Y position at which to render the following frame
+    /// </summary>
+    public uint YOffset { get; }
+
+    /// <summary>
+    /// Gets the X limit at which to render the following frame
+    /// </summary>
+    public uint XMax => this.XOffset + this.Width;
+
+    /// <summary>
+    /// Gets the Y limit at which to render the following frame
+    /// </summary>
+    public uint YMax => this.YOffset + this.Height;
+
+    /// <summary>
+    /// Gets the frame delay fraction numerator
+    /// </summary>
+    public ushort DelayNumerator { get; }
+
+    /// <summary>
+    /// Gets the frame delay fraction denominator
+    /// </summary>
+    public ushort DelayDenominator { get; }
+
+    /// <summary>
+    /// Gets the type of frame area disposal to be done after rendering this frame
+    /// </summary>
+    public PngDisposalMethod DisposeOperation { get; }
+
+    /// <summary>
+    /// Gets the type of frame area rendering for this frame
+    /// </summary>
+    public PngBlendMethod BlendOperation { get; }
+
+    public Rectangle Bounds => new((int)this.XOffset, (int)this.YOffset, (int)this.Width, (int)this.Height);
+
+    /// <summary>
+    /// Validates the APng fcTL.
+    /// </summary>
+    /// <param name="header">The header.</param>
+    /// <exception cref="NotSupportedException">
+    /// Thrown if the image does pass validation.
+    /// </exception>
+    public void Validate(PngHeader header)
+    {
+        if (this.Width == 0)
+        {
+            PngThrowHelper.ThrowInvalidParameter(this.Width, "Expected > 0");
+        }
+
+        if (this.Height == 0)
+        {
+            PngThrowHelper.ThrowInvalidParameter(this.Height, "Expected > 0");
+        }
+
+        if (this.XMax > header.Width)
+        {
+            PngThrowHelper.ThrowInvalidParameter(this.XOffset, this.Width, $"The x-offset plus width > {nameof(PngHeader)}.{nameof(PngHeader.Width)}");
+        }
+
+        if (this.YMax > header.Height)
+        {
+            PngThrowHelper.ThrowInvalidParameter(this.YOffset, this.Height, $"The y-offset plus height > {nameof(PngHeader)}.{nameof(PngHeader.Height)}");
+        }
+    }
+
+    /// <summary>
+    /// Writes the fcTL to the given buffer.
+    /// </summary>
+    /// <param name="buffer">The buffer to write to.</param>
+    public void WriteTo(Span<byte> buffer)
+    {
+        BinaryPrimitives.WriteUInt32BigEndian(buffer[..4], this.SequenceNumber);
+        BinaryPrimitives.WriteUInt32BigEndian(buffer[4..8], this.Width);
+        BinaryPrimitives.WriteUInt32BigEndian(buffer[8..12], this.Height);
+        BinaryPrimitives.WriteUInt32BigEndian(buffer[12..16], this.XOffset);
+        BinaryPrimitives.WriteUInt32BigEndian(buffer[16..20], this.YOffset);
+        BinaryPrimitives.WriteUInt16BigEndian(buffer[20..22], this.DelayNumerator);
+        BinaryPrimitives.WriteUInt16BigEndian(buffer[22..24], this.DelayDenominator);
+
+        buffer[24] = (byte)this.DisposeOperation;
+        buffer[25] = (byte)this.BlendOperation;
+    }
+
+    /// <summary>
+    /// Parses the APngFrameControl from the given data buffer.
+    /// </summary>
+    /// <param name="data">The data to parse.</param>
+    /// <returns>The parsed fcTL.</returns>
+    public static FrameControl Parse(ReadOnlySpan<byte> data)
+        => new(
+            sequenceNumber: BinaryPrimitives.ReadUInt32BigEndian(data[..4]),
+            width: BinaryPrimitives.ReadUInt32BigEndian(data[4..8]),
+            height: BinaryPrimitives.ReadUInt32BigEndian(data[8..12]),
+            xOffset: BinaryPrimitives.ReadUInt32BigEndian(data[12..16]),
+            yOffset: BinaryPrimitives.ReadUInt32BigEndian(data[16..20]),
+            delayNumerator: BinaryPrimitives.ReadUInt16BigEndian(data[20..22]),
+            delayDenominator: BinaryPrimitives.ReadUInt16BigEndian(data[22..24]),
+            disposeOperation: (PngDisposalMethod)data[24],
+            blendOperation: (PngBlendMethod)data[25]);
+}

src/ImageSharp/Formats/Png/PngHeader.cs → src/ImageSharp/Formats/Png/Chunks/PngHeader.cs

@@ -4,7 +4,7 @@
 
 using System.Buffers.Binary;
 
-namespace SixLabors.ImageSharp.Formats.Png;
+namespace SixLabors.ImageSharp.Formats.Png.Chunks;
 
 /// <summary>
 /// Represents the png header chunk.

src/ImageSharp/Formats/Png/Chunks/PhysicalChunkData.cs → src/ImageSharp/Formats/Png/Chunks/PngPhysical.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
 using System.Buffers.Binary;
@@ -10,11 +10,11 @@ namespace SixLabors.ImageSharp.Formats.Png.Chunks;
 /// <summary>
 /// The pHYs chunk specifies the intended pixel size or aspect ratio for display of the image.
 /// </summary>
-internal readonly struct PhysicalChunkData
+internal readonly struct PngPhysical
 {
     public const int Size = 9;
 
-    public PhysicalChunkData(uint x, uint y, byte unitSpecifier)
+    public PngPhysical(uint x, uint y, byte unitSpecifier)
     {
         this.XAxisPixelsPerUnit = x;
         this.YAxisPixelsPerUnit = y;
@@ -44,13 +44,13 @@ internal readonly struct PhysicalChunkData
     /// </summary>
     /// <param name="data">The data buffer.</param>
     /// <returns>The parsed PhysicalChunkData.</returns>
-    public static PhysicalChunkData Parse(ReadOnlySpan<byte> data)
+    public static PngPhysical Parse(ReadOnlySpan<byte> data)
     {
         uint hResolution = BinaryPrimitives.ReadUInt32BigEndian(data[..4]);
         uint vResolution = BinaryPrimitives.ReadUInt32BigEndian(data.Slice(4, 4));
         byte unit = data[8];
 
-        return new PhysicalChunkData(hResolution, vResolution, unit);
+        return new PngPhysical(hResolution, vResolution, unit);
     }
 
     /// <summary>
@@ -59,7 +59,7 @@ internal readonly struct PhysicalChunkData
     /// </summary>
     /// <param name="meta">The metadata.</param>
     /// <returns>The constructed PngPhysicalChunkData instance.</returns>
-    public static PhysicalChunkData FromMetadata(ImageMetadata meta)
+    public static PngPhysical FromMetadata(ImageMetadata meta)
     {
         byte unitSpecifier = 0;
         uint x;
@@ -92,7 +92,7 @@ internal readonly struct PhysicalChunkData
                 break;
         }
 
-        return new PhysicalChunkData(x, y, unitSpecifier);
+        return new PngPhysical(x, y, unitSpecifier);
     }
 
     /// <summary>

src/ImageSharp/Formats/Png/PngTextData.cs → src/ImageSharp/Formats/Png/Chunks/PngTextData.cs

@@ -1,7 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-namespace SixLabors.ImageSharp.Formats.Png;
+namespace SixLabors.ImageSharp.Formats.Png.Chunks;
 
 /// <summary>
 /// Stores text data contained in the iTXt, tEXt, and zTXt chunks.

src/ImageSharp/Formats/Png/MetadataExtensions.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
 using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.Metadata;
 
@@ -14,7 +15,22 @@ public static partial class MetadataExtensions
     /// <summary>
     /// Gets the png format specific metadata for the image.
     /// </summary>
-    /// <param name="metadata">The metadata this method extends.</param>
+    /// <param name="source">The metadata this method extends.</param>
     /// <returns>The <see cref="PngMetadata"/>.</returns>
-    public static PngMetadata GetPngMetadata(this ImageMetadata metadata) => metadata.GetFormatMetadata(PngFormat.Instance);
+    public static PngMetadata GetPngMetadata(this ImageMetadata source) => source.GetFormatMetadata(PngFormat.Instance);
+
+    /// <summary>
+    /// Gets the aPng format specific metadata for the image frame.
+    /// </summary>
+    /// <param name="source">The metadata this method extends.</param>
+    /// <returns>The <see cref="PngFrameMetadata"/>.</returns>
+    public static PngFrameMetadata GetPngFrameMetadata(this ImageFrameMetadata source) => source.GetFormatMetadata(PngFormat.Instance);
+
+    /// <summary>
+    /// Gets the aPng format specific metadata for the image frame.
+    /// </summary>
+    /// <param name="source">The metadata this method extends.</param>
+    /// <param name="metadata">The metadata.</param>
+    /// <returns>The <see cref="PngFrameMetadata"/>.</returns>
+    public static bool TryGetPngFrameMetadata(this ImageFrameMetadata source, [NotNullWhen(true)] out PngFrameMetadata? metadata) => source.TryGetFormatMetadata(PngFormat.Instance, out metadata);
 }

src/ImageSharp/Formats/Png/PngBlendMethod.cs

@@ -0,0 +1,22 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Png;
+
+/// <summary>
+/// Specifies whether the frame is to be alpha blended into the current output buffer content,
+/// or whether it should completely replace its region in the output buffer.
+/// </summary>
+public enum PngBlendMethod
+{
+    /// <summary>
+    /// All color components of the frame, including alpha, overwrite the current contents of the frame's output buffer region.
+    /// </summary>
+    Source,
+
+    /// <summary>
+    /// The frame should be composited onto the output buffer based on its alpha, using a simple OVER operation as
+    /// described in the "Alpha Channel Processing" section of the PNG specification [PNG-1.2].
+    /// </summary>
+    Over
+}

src/ImageSharp/Formats/Png/PngChunk.cs

@@ -42,7 +42,8 @@ internal readonly struct PngChunk
     /// Gets a value indicating whether the given chunk is critical to decoding
     /// </summary>
     public bool IsCritical =>
-        this.Type == PngChunkType.Header ||
-        this.Type == PngChunkType.Palette ||
-        this.Type == PngChunkType.Data;
+        this.Type is PngChunkType.Header or
+        PngChunkType.Palette or
+        PngChunkType.Data or
+        PngChunkType.FrameData;
 }

src/ImageSharp/Formats/Png/PngChunkType.cs

@@ -9,15 +9,17 @@ namespace SixLabors.ImageSharp.Formats.Png;
 internal enum PngChunkType : uint
 {
     /// <summary>
-    /// The IDAT chunk contains the actual image data. The image can contains more
+    /// This chunk contains the actual image data. The image can contains more
     /// than one chunk of this type. All chunks together are the whole image.
     /// </summary>
+    /// <remarks>IDAT (Multiple)</remarks>
     Data = 0x49444154U,
 
     /// <summary>
     /// This chunk must appear last. It marks the end of the PNG data stream.
     /// The chunk's data field is empty.
     /// </summary>
+    /// <remarks>IEND (Single)</remarks>
     End = 0x49454E44U,
 
     /// <summary>
@@ -25,34 +27,40 @@ internal enum PngChunkType : uint
     /// common information like the width and the height of the image or
     /// the used compression method.
     /// </summary>
+    /// <remarks>IHDR (Single)</remarks>
     Header = 0x49484452U,
 
     /// <summary>
     /// The PLTE chunk contains from 1 to 256 palette entries, each a three byte
     /// series in the RGB format.
     /// </summary>
+    /// <remarks>PLTE (Single)</remarks>
     Palette = 0x504C5445U,
 
     /// <summary>
     /// The eXIf data chunk which contains the Exif profile.
     /// </summary>
+    /// <remarks>eXIF (Single)</remarks>
     Exif = 0x65584966U,
 
     /// <summary>
     /// This chunk specifies the relationship between the image samples and the desired
     /// display output intensity.
     /// </summary>
+    /// <remarks>gAMA (Single)</remarks>
     Gamma = 0x67414D41U,
 
     /// <summary>
-    /// The pHYs chunk specifies the intended pixel size or aspect ratio for display of the image.
+    /// This chunk specifies the intended pixel size or aspect ratio for display of the image.
     /// </summary>
+    /// <remarks>pHYs (Single)</remarks>
     Physical = 0x70485973U,
 
     /// <summary>
     /// Textual information that the encoder wishes to record with the image can be stored in
     /// tEXt chunks. Each tEXt chunk contains a keyword and a text string.
     /// </summary>
+    /// <remarks>tEXT (Multiple)</remarks>
     Text = 0x74455874U,
 
     /// <summary>
@@ -60,70 +68,103 @@ internal enum PngChunkType : uint
     /// but the zTXt chunk is recommended for storing large blocks of text. Each zTXt chunk contains a (uncompressed) keyword and
     /// a compressed text string.
     /// </summary>
+    /// <remarks>zTXt (Multiple)</remarks>
     CompressedText = 0x7A545874U,
 
     /// <summary>
-    /// The iTXt chunk contains International textual data. It contains a keyword, an optional language tag, an optional translated keyword
+    /// This chunk contains International textual data. It contains a keyword, an optional language tag, an optional translated keyword
     /// and the actual text string, which can be compressed or uncompressed.
     /// </summary>
+    /// <remarks>iTXt (Multiple)</remarks>
     InternationalText = 0x69545874U,
 
     /// <summary>
-    /// The tRNS chunk specifies that the image uses simple transparency:
+    /// This chunk specifies that the image uses simple transparency:
     /// either alpha values associated with palette entries (for indexed-color images)
     /// or a single transparent color (for grayscale and true color images).
     /// </summary>
+    /// <remarks>tRNS (Single)</remarks>
     Transparency = 0x74524E53U,
 
     /// <summary>
-    /// The tIME chunk gives the time of the last image modification (not the time of initial image creation).
+    /// This chunk gives the time of the last image modification (not the time of initial image creation).
     /// </summary>
+    /// <remarks>tIME (Single)</remarks>
     Time = 0x74494d45,
 
     /// <summary>
-    /// The bKGD chunk specifies a default background colour to present the image against.
+    /// This chunk specifies a default background colour to present the image against.
     /// If there is any other preferred background, either user-specified or part of a larger page (as in a browser),
     /// the bKGD chunk should be ignored.
     /// </summary>
+    /// <remarks>bKGD (Single)</remarks>
     Background = 0x624b4744,
 
     /// <summary>
-    /// The iCCP chunk contains a embedded color profile. If the iCCP chunk is present,
+    /// This chunk contains a embedded color profile. If the iCCP chunk is present,
     /// the image samples conform to the colour space represented by the embedded ICC profile as defined by the International Color Consortium.
     /// </summary>
+    /// <remarks>iCCP (Single)</remarks>
     EmbeddedColorProfile = 0x69434350,
 
     /// <summary>
-    /// The sBIT chunk defines the original number of significant bits (which can be less than or equal to the sample depth).
+    /// This chunk defines the original number of significant bits (which can be less than or equal to the sample depth).
     /// This allows PNG decoders to recover the original data losslessly even if the data had a sample depth not directly supported by PNG.
     /// </summary>
+    /// <remarks>sBIT (Single)</remarks>
     SignificantBits = 0x73424954,
 
     /// <summary>
-    /// If the sRGB chunk is present, the image samples conform to the sRGB colour space [IEC 61966-2-1] and should be displayed
+    /// If the this chunk is present, the image samples conform to the sRGB colour space [IEC 61966-2-1] and should be displayed
     /// using the specified rendering intent defined by the International Color Consortium.
     /// </summary>
+    /// <remarks>sRGB (Single)</remarks>
     StandardRgbColourSpace = 0x73524742,
 
     /// <summary>
-    /// The hIST chunk gives the approximate usage frequency of each colour in the palette.
+    /// This chunk gives the approximate usage frequency of each colour in the palette.
     /// </summary>
+    /// <remarks>hIST (Single)</remarks>
     Histogram = 0x68495354,
 
     /// <summary>
-    /// The sPLT chunk contains the suggested palette.
+    /// This chunk contains the suggested palette.
     /// </summary>
+    /// <remarks>sPLT (Single)</remarks>
     SuggestedPalette = 0x73504c54,
 
     /// <summary>
-    /// The cHRM chunk may be used to specify the 1931 CIE x,y chromaticities of the red,
+    /// This chunk may be used to specify the 1931 CIE x,y chromaticities of the red,
     /// green, and blue display primaries used in the image, and the referenced white point.
     /// </summary>
+    /// <remarks>cHRM (Single)</remarks>
     Chroma = 0x6348524d,
 
+    /// <summary>
+    /// This chunk is an ancillary chunk as defined in the PNG Specification.
+    /// It must appear before the first IDAT chunk within a valid PNG stream.
+    /// </summary>
+    /// <remarks>acTL (Single, APNG)</remarks>
+    AnimationControl = 0x6163544cU,
+
+    /// <summary>
+    /// This chunk is an ancillary chunk as defined in the PNG Specification.
+    /// It must appear before the IDAT or fdAT chunks of the frame to which it applies.
+    /// </summary>
+    /// <remarks>fcTL (Multiple, APNG)</remarks>
+    FrameControl = 0x6663544cU,
+
+    /// <summary>
+    /// This chunk has the same purpose as an IDAT chunk.
+    /// It has the same structure as an IDAT chunk, except preceded by a sequence number.
+    /// </summary>
+    /// <remarks>fdAT (Multiple, APNG)</remarks>
+    FrameData = 0x66644154U,
+
     /// <summary>
     /// Malformed chunk named CgBI produced by apple, which is not conform to the specification.
     /// Related issue is here https://github.com/SixLabors/ImageSharp/issues/410
     /// </summary>
+    /// <remarks>CgBI</remarks>
     ProprietaryApple = 0x43674249
 }

src/ImageSharp/Formats/Png/PngConstants.cs

@@ -28,12 +28,12 @@ internal static class PngConstants
     /// <summary>
     /// The list of mimetypes that equate to a Png.
     /// </summary>
-    public static readonly IEnumerable<string> MimeTypes = new[] { "image/png" };
+    public static readonly IEnumerable<string> MimeTypes = new[] { "image/png", "image/apng" };
 
     /// <summary>
     /// The list of file extensions that equate to a Png.
     /// </summary>
-    public static readonly IEnumerable<string> FileExtensions = new[] { "png" };
+    public static readonly IEnumerable<string> FileExtensions = new[] { "png", "apng" };
 
     /// <summary>
     /// The header bytes as a big-endian coded ulong.
@@ -43,7 +43,7 @@ internal static class PngConstants
     /// <summary>
     /// The dictionary of available color types.
     /// </summary>
-    public static readonly Dictionary<PngColorType, byte[]> ColorTypes = new Dictionary<PngColorType, byte[]>
+    public static readonly Dictionary<PngColorType, byte[]> ColorTypes = new()
     {
         [PngColorType.Grayscale] = new byte[] { 1, 2, 4, 8, 16 },
         [PngColorType.Rgb] = new byte[] { 8, 16 },
@@ -80,7 +80,7 @@ internal static class PngConstants
     /// <summary>
     /// Gets the keyword of the XMP metadata, encoded in an iTXT chunk.
     /// </summary>
-    public static ReadOnlySpan<byte> XmpKeyword => new byte[]
+    public static ReadOnlySpan<byte> XmpKeyword => new[]
     {
         (byte)'X',
         (byte)'M',

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -1,9 +1,9 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
-#nullable disable
 
 using System.Buffers;
 using System.Buffers.Binary;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.IO.Compression;
 using System.Runtime.CompilerServices;
@@ -34,12 +34,17 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     private readonly Configuration configuration;
 
     /// <summary>
-    /// Gets or sets a value indicating whether the metadata should be ignored when the image is being decoded.
+    /// Whether the metadata should be ignored when the image is being decoded.
+    /// </summary>
+    private readonly uint maxFrames;
+
+    /// <summary>
+    /// Whether the metadata should be ignored when the image is being decoded.
     /// </summary>
     private readonly bool skipMetadata;
 
     /// <summary>
-    /// Gets or sets a value indicating whether to read the IHDR and tRNS chunks only.
+    /// Whether to read the IHDR and tRNS chunks only.
     /// </summary>
     private readonly bool colorMetadataOnly;
 
@@ -51,13 +56,18 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// <summary>
     /// The stream to decode from.
     /// </summary>
-    private BufferedReadStream currentStream;
+    private BufferedReadStream currentStream = null!;
 
     /// <summary>
     /// The png header.
     /// </summary>
     private PngHeader header;
 
+    /// <summary>
+    /// The png animation control.
+    /// </summary>
+    private AnimationControl animationControl;
+
     /// <summary>
     /// The number of bytes per pixel.
     /// </summary>
@@ -76,32 +86,22 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// <summary>
     /// The palette containing color information for indexed png's.
     /// </summary>
-    private byte[] palette;
+    private byte[] palette = null!;
 
     /// <summary>
     /// The palette containing alpha channel color information for indexed png's.
     /// </summary>
-    private byte[] paletteAlpha;
+    private byte[] paletteAlpha = null!;
 
     /// <summary>
     /// Previous scanline processed.
     /// </summary>
-    private IMemoryOwner<byte> previousScanline;
+    private IMemoryOwner<byte> previousScanline = null!;
 
     /// <summary>
     /// The current scanline that is being processed.
     /// </summary>
-    private IMemoryOwner<byte> scanline;
-
-    /// <summary>
-    /// The index of the current scanline being processed.
-    /// </summary>
-    private int currentRow = Adam7.FirstRow[0];
-
-    /// <summary>
-    /// The current number of bytes read in the current scanline.
-    /// </summary>
-    private int currentRowBytesRead;
+    private IMemoryOwner<byte> scanline = null!;
 
     /// <summary>
     /// Gets or sets the png color type.
@@ -121,6 +121,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     {
         this.Options = options;
         this.configuration = options.Configuration;
+        this.maxFrames = options.MaxFrames;
         this.skipMetadata = options.SkipMetadata;
         this.memoryAllocator = this.configuration.MemoryAllocator;
     }
@@ -129,6 +130,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     {
         this.Options = options;
         this.colorMetadataOnly = colorMetadataOnly;
+        this.maxFrames = options.MaxFrames;
         this.skipMetadata = true;
         this.configuration = options.Configuration;
         this.memoryAllocator = this.configuration.MemoryAllocator;
@@ -144,11 +146,16 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     public Image<TPixel> Decode<TPixel>(BufferedReadStream stream, CancellationToken cancellationToken)
         where TPixel : unmanaged, IPixel<TPixel>
     {
+        uint frameCount = 0;
         ImageMetadata metadata = new();
         PngMetadata pngMetadata = metadata.GetPngMetadata();
         this.currentStream = stream;
         this.currentStream.Skip(8);
-        Image<TPixel> image = null;
+        Image<TPixel>? image = null;
+        FrameControl? previousFrameControl = null;
+        FrameControl? currentFrameControl = null;
+        ImageFrame<TPixel>? previousFrame = null;
+        ImageFrame<TPixel>? currentFrame = null;
         Span<byte> buffer = stackalloc byte[20];
 
         try
@@ -160,25 +167,84 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
                     switch (chunk.Type)
                     {
                         case PngChunkType.Header:
+                            if (!Equals(this.header, default(PngHeader)))
+                            {
+                                PngThrowHelper.ThrowInvalidHeader();
+                            }
+
                             this.ReadHeaderChunk(pngMetadata, chunk.Data.GetSpan());
                             break;
+                        case PngChunkType.AnimationControl:
+                            this.ReadAnimationControlChunk(pngMetadata, chunk.Data.GetSpan());
+                            break;
                         case PngChunkType.Physical:
                             ReadPhysicalChunk(metadata, chunk.Data.GetSpan());
                             break;
                         case PngChunkType.Gamma:
                             ReadGammaChunk(pngMetadata, chunk.Data.GetSpan());
                             break;
+                        case PngChunkType.FrameControl:
+                            frameCount++;
+                            if (frameCount == this.maxFrames)
+                            {
+                                break;
+                            }
+
+                            currentFrame = null;
+                            currentFrameControl = this.ReadFrameControlChunk(chunk.Data.GetSpan());
+                            break;
+                        case PngChunkType.FrameData:
+                            if (frameCount == this.maxFrames)
+                            {
+                                break;
+                            }
+
+                            if (image is null)
+                            {
+                                PngThrowHelper.ThrowMissingDefaultData();
+                            }
+
+                            if (currentFrameControl is null)
+                            {
+                                PngThrowHelper.ThrowMissingFrameControl();
+                            }
+
+                            previousFrameControl ??= new((uint)this.header.Width, (uint)this.header.Height);
+                            this.InitializeFrame(previousFrameControl.Value, currentFrameControl.Value, image, previousFrame, out currentFrame);
+
+                            this.currentStream.Position += 4;
+                            this.ReadScanlines(
+                                chunk.Length - 4,
+                                currentFrame,
+                                pngMetadata,
+                                this.ReadNextDataChunkAndSkipSeq,
+                                currentFrameControl.Value,
+                                cancellationToken);
+
+                            previousFrame = currentFrame;
+                            previousFrameControl = currentFrameControl;
+                            break;
                         case PngChunkType.Data:
+
+                            currentFrameControl ??= new((uint)this.header.Width, (uint)this.header.Height);
                             if (image is null)
                             {
-                                this.InitializeImage(metadata, out image);
+                                this.InitializeImage(metadata, currentFrameControl.Value, out image);
 
                                 // Both PLTE and tRNS chunks, if present, have been read at this point as per spec.
                                 AssignColorPalette(this.palette, this.paletteAlpha, pngMetadata);
                             }
 
-                            this.ReadScanlines(chunk, image.Frames.RootFrame, pngMetadata, cancellationToken);
+                            this.ReadScanlines(
+                                chunk.Length,
+                                image.Frames.RootFrame,
+                                pngMetadata,
+                                this.ReadNextDataChunk,
+                                currentFrameControl.Value,
+                                cancellationToken);
 
+                            previousFrame = currentFrame;
+                            previousFrameControl = currentFrameControl;
                             break;
                         case PngChunkType.Palette:
                             this.palette = chunk.Data.GetSpan().ToArray();
@@ -245,9 +311,11 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// <inheritdoc/>
     public ImageInfo Identify(BufferedReadStream stream, CancellationToken cancellationToken)
     {
+        uint frameCount = 0;
         ImageMetadata metadata = new();
         PngMetadata pngMetadata = metadata.GetPngMetadata();
         this.currentStream = stream;
+        FrameControl? lastFrameControl = null;
         Span<byte> buffer = stackalloc byte[20];
 
         this.currentStream.Skip(8);
@@ -263,6 +331,9 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
                         case PngChunkType.Header:
                             this.ReadHeaderChunk(pngMetadata, chunk.Data.GetSpan());
                             break;
+                        case PngChunkType.AnimationControl:
+                            this.ReadAnimationControlChunk(pngMetadata, chunk.Data.GetSpan());
+                            break;
                         case PngChunkType.Physical:
                             if (this.colorMetadataOnly)
                             {
@@ -281,8 +352,36 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
                             ReadGammaChunk(pngMetadata, chunk.Data.GetSpan());
                             break;
-                        case PngChunkType.Data:
+                        case PngChunkType.FrameControl:
+                            ++frameCount;
+                            if (frameCount == this.maxFrames)
+                            {
+                                break;
+                            }
+
+                            lastFrameControl = this.ReadFrameControlChunk(chunk.Data.GetSpan());
+                            break;
+                        case PngChunkType.FrameData:
+                            if (frameCount == this.maxFrames)
+                            {
+                                break;
+                            }
 
+                            if (this.colorMetadataOnly)
+                            {
+                                goto EOF;
+                            }
+
+                            if (lastFrameControl is null)
+                            {
+                                PngThrowHelper.ThrowMissingFrameControl();
+                            }
+
+                            // Skip sequence number
+                            this.currentStream.Skip(4);
+                            this.SkipChunkDataAndCrc(chunk);
+                            break;
+                        case PngChunkType.Data:
                             // Spec says tRNS must be before IDAT so safe to exit.
                             if (this.colorMetadataOnly)
                             {
@@ -369,7 +468,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
             EOF:
             if (this.header.Width == 0 && this.header.Height == 0)
             {
-                PngThrowHelper.ThrowNoHeader();
+                PngThrowHelper.ThrowInvalidHeader();
             }
 
             // Both PLTE and tRNS chunks, if present, have been read at this point as per spec.
@@ -403,7 +502,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// <param name="bits">The number of bits per value.</param>
     /// <param name="buffer">The new array.</param>
     /// <returns>The resulting <see cref="ReadOnlySpan{Byte}"/> array.</returns>
-    private bool TryScaleUpTo8BitArray(ReadOnlySpan<byte> source, int bytesPerScanline, int bits, out IMemoryOwner<byte> buffer)
+    private bool TryScaleUpTo8BitArray(ReadOnlySpan<byte> source, int bytesPerScanline, int bits, [NotNullWhen(true)] out IMemoryOwner<byte>? buffer)
     {
         if (bits >= 8)
         {
@@ -438,7 +537,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// <param name="data">The data containing physical data.</param>
     private static void ReadPhysicalChunk(ImageMetadata metadata, ReadOnlySpan<byte> data)
     {
-        PhysicalChunkData physicalChunk = PhysicalChunkData.Parse(data);
+        PngPhysical physicalChunk = PngPhysical.Parse(data);
 
         metadata.ResolutionUnits = physicalChunk.UnitSpecifier == byte.MinValue
             ? PixelResolutionUnit.AspectRatio
@@ -471,8 +570,9 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// </summary>
     /// <typeparam name="TPixel">The type the pixels will be</typeparam>
     /// <param name="metadata">The metadata information for the image</param>
+    /// <param name="frameControl">The frame control information for the frame</param>
     /// <param name="image">The image that we will populate</param>
-    private void InitializeImage<TPixel>(ImageMetadata metadata, out Image<TPixel> image)
+    private void InitializeImage<TPixel>(ImageMetadata metadata, FrameControl frameControl, out Image<TPixel> image)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         image = Image.CreateUninitialized<TPixel>(
@@ -481,6 +581,9 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
             this.header.Height,
             metadata);
 
+        PngFrameMetadata frameMetadata = image.Frames.RootFrame.Metadata.GetPngFrameMetadata();
+        frameMetadata.FromChunk(in frameControl);
+
         this.bytesPerPixel = this.CalculateBytesPerPixel();
         this.bytesPerScanline = this.CalculateScanlineLength(this.header.Width) + 1;
         this.bytesPerSample = 1;
@@ -495,6 +598,47 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
         this.scanline = this.configuration.MemoryAllocator.Allocate<byte>(this.bytesPerScanline, AllocationOptions.Clean);
     }
 
+    /// <summary>
+    /// Initializes the image and various buffers needed for processing
+    /// </summary>
+    /// <typeparam name="TPixel">The type the pixels will be</typeparam>
+    /// <param name="previousFrameControl">The frame control information for the previous frame.</param>
+    /// <param name="currentFrameControl">The frame control information for the current frame.</param>
+    /// <param name="image">The image that we will populate</param>
+    /// <param name="previousFrame">The previous frame.</param>
+    /// <param name="frame">The created frame</param>
+    private void InitializeFrame<TPixel>(
+        FrameControl previousFrameControl,
+        FrameControl currentFrameControl,
+        Image<TPixel> image,
+        ImageFrame<TPixel>? previousFrame,
+        out ImageFrame<TPixel> frame)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        // We create a clone of the previous frame and add it.
+        // We will overpaint the difference of pixels on the current frame to create a complete image.
+        // This ensures that we have enough pixel data to process without distortion. #2450
+        frame = image.Frames.AddFrame(previousFrame ?? image.Frames.RootFrame);
+
+        // If the first `fcTL` chunk uses a `dispose_op` of APNG_DISPOSE_OP_PREVIOUS it should be treated as APNG_DISPOSE_OP_BACKGROUND.
+        if (previousFrameControl.DisposeOperation == PngDisposalMethod.Background
+            || (previousFrame is null && previousFrameControl.DisposeOperation == PngDisposalMethod.Previous))
+        {
+            Rectangle restoreArea = previousFrameControl.Bounds;
+            Rectangle interest = Rectangle.Intersect(frame.Bounds(), restoreArea);
+            Buffer2DRegion<TPixel> pixelRegion = frame.PixelBuffer.GetRegion(interest);
+            pixelRegion.Clear();
+        }
+
+        PngFrameMetadata frameMetadata = frame.Metadata.GetPngFrameMetadata();
+        frameMetadata.FromChunk(currentFrameControl);
+
+        this.previousScanline?.Dispose();
+        this.scanline?.Dispose();
+        this.previousScanline = this.memoryAllocator.Allocate<byte>(this.bytesPerScanline, AllocationOptions.Clean);
+        this.scanline = this.configuration.MemoryAllocator.Allocate<byte>(this.bytesPerScanline, AllocationOptions.Clean);
+    }
+
     /// <summary>
     /// Calculates the correct number of bits per pixel for the given color type.
     /// </summary>
@@ -558,24 +702,32 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// Reads the scanlines within the image.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    /// <param name="chunk">The png chunk containing the compressed scanline data.</param>
+    /// <param name="chunkLength">The length of the chunk that containing the compressed scanline data.</param>
     /// <param name="image"> The pixel data.</param>
     /// <param name="pngMetadata">The png metadata</param>
+    /// <param name="getData">A delegate to get more data from the inner stream for <see cref="ZlibInflateStream"/>.</param>
+    /// <param name="frameControl">The frame control</param>
     /// <param name="cancellationToken">The cancellation token.</param>
-    private void ReadScanlines<TPixel>(PngChunk chunk, ImageFrame<TPixel> image, PngMetadata pngMetadata, CancellationToken cancellationToken)
+    private void ReadScanlines<TPixel>(
+        int chunkLength,
+        ImageFrame<TPixel> image,
+        PngMetadata pngMetadata,
+        Func<int> getData,
+        in FrameControl frameControl,
+        CancellationToken cancellationToken)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        using ZlibInflateStream deframeStream = new(this.currentStream, this.ReadNextDataChunk);
-        deframeStream.AllocateNewBytes(chunk.Length, true);
-        DeflateStream dataStream = deframeStream.CompressedStream;
+        using ZlibInflateStream inflateStream = new(this.currentStream, getData);
+        inflateStream.AllocateNewBytes(chunkLength, true);
+        DeflateStream dataStream = inflateStream.CompressedStream!;
 
-        if (this.header.InterlaceMethod == PngInterlaceMode.Adam7)
+        if (this.header.InterlaceMethod is PngInterlaceMode.Adam7)
         {
-            this.DecodeInterlacedPixelData(dataStream, image, pngMetadata, cancellationToken);
+            this.DecodeInterlacedPixelData(frameControl, dataStream, image, pngMetadata, cancellationToken);
         }
         else
         {
-            this.DecodePixelData(dataStream, image, pngMetadata, cancellationToken);
+            this.DecodePixelData(frameControl, dataStream, image, pngMetadata, cancellationToken);
         }
     }
 
@@ -583,29 +735,48 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// Decodes the raw pixel data row by row
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
+    /// <param name="frameControl">The frame control</param>
     /// <param name="compressedStream">The compressed pixel data stream.</param>
-    /// <param name="image">The image to decode to.</param>
+    /// <param name="imageFrame">The image frame to decode to.</param>
     /// <param name="pngMetadata">The png metadata</param>
     /// <param name="cancellationToken">The CancellationToken</param>
-    private void DecodePixelData<TPixel>(DeflateStream compressedStream, ImageFrame<TPixel> image, PngMetadata pngMetadata, CancellationToken cancellationToken)
+    private void DecodePixelData<TPixel>(
+        FrameControl frameControl,
+        DeflateStream compressedStream,
+        ImageFrame<TPixel> imageFrame,
+        PngMetadata pngMetadata,
+        CancellationToken cancellationToken)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        while (this.currentRow < this.header.Height)
+        int currentRow = (int)frameControl.YOffset;
+        int currentRowBytesRead = 0;
+        int height = (int)frameControl.YMax;
+
+        IMemoryOwner<TPixel>? blendMemory = null;
+        Span<TPixel> blendRowBuffer = Span<TPixel>.Empty;
+        if (frameControl.BlendOperation == PngBlendMethod.Over)
+        {
+            blendMemory = this.memoryAllocator.Allocate<TPixel>(imageFrame.Width, AllocationOptions.Clean);
+            blendRowBuffer = blendMemory.Memory.Span;
+        }
+
+        while (currentRow < height)
         {
             cancellationToken.ThrowIfCancellationRequested();
-            Span<byte> scanlineSpan = this.scanline.GetSpan();
-            while (this.currentRowBytesRead < this.bytesPerScanline)
+            int bytesPerFrameScanline = this.CalculateScanlineLength((int)frameControl.Width) + 1;
+            Span<byte> scanlineSpan = this.scanline.GetSpan()[..bytesPerFrameScanline];
+            while (currentRowBytesRead < bytesPerFrameScanline)
             {
-                int bytesRead = compressedStream.Read(scanlineSpan, this.currentRowBytesRead, this.bytesPerScanline - this.currentRowBytesRead);
+                int bytesRead = compressedStream.Read(scanlineSpan, currentRowBytesRead, bytesPerFrameScanline - currentRowBytesRead);
                 if (bytesRead <= 0)
                 {
                     return;
                 }
 
-                this.currentRowBytesRead += bytesRead;
+                currentRowBytesRead += bytesRead;
             }
 
-            this.currentRowBytesRead = 0;
+            currentRowBytesRead = 0;
 
             switch ((FilterType)scanlineSpan[0])
             {
@@ -633,28 +804,47 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
                     break;
             }
 
-            this.ProcessDefilteredScanline(scanlineSpan, image, pngMetadata);
-
+            this.ProcessDefilteredScanline(frameControl, currentRow, scanlineSpan, imageFrame, pngMetadata, blendRowBuffer);
             this.SwapScanlineBuffers();
-            this.currentRow++;
+            currentRow++;
         }
+
+        blendMemory?.Dispose();
     }
 
     /// <summary>
     /// Decodes the raw interlaced pixel data row by row
-    /// <see href="https://github.com/juehv/DentalImageViewer/blob/8a1a4424b15d6cc453b5de3f273daf3ff5e3a90d/DentalImageViewer/lib/jiu-0.14.3/net/sourceforge/jiu/codecs/PNGCodec.java"/>
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
+    /// <param name="frameControl">The frame control</param>
     /// <param name="compressedStream">The compressed pixel data stream.</param>
-    /// <param name="image">The current image.</param>
+    /// <param name="imageFrame">The current image frame.</param>
     /// <param name="pngMetadata">The png metadata.</param>
     /// <param name="cancellationToken">The cancellation token.</param>
-    private void DecodeInterlacedPixelData<TPixel>(DeflateStream compressedStream, ImageFrame<TPixel> image, PngMetadata pngMetadata, CancellationToken cancellationToken)
+    private void DecodeInterlacedPixelData<TPixel>(
+        in FrameControl frameControl,
+        DeflateStream compressedStream,
+        ImageFrame<TPixel> imageFrame,
+        PngMetadata pngMetadata,
+        CancellationToken cancellationToken)
         where TPixel : unmanaged, IPixel<TPixel>
     {
+        int currentRow = Adam7.FirstRow[0] + (int)frameControl.YOffset;
+        int currentRowBytesRead = 0;
         int pass = 0;
-        int width = this.header.Width;
-        Buffer2D<TPixel> imageBuffer = image.PixelBuffer;
+        int width = (int)frameControl.Width;
+        int endRow = (int)frameControl.YMax;
+
+        Buffer2D<TPixel> imageBuffer = imageFrame.PixelBuffer;
+
+        IMemoryOwner<TPixel>? blendMemory = null;
+        Span<TPixel> blendRowBuffer = Span<TPixel>.Empty;
+        if (frameControl.BlendOperation == PngBlendMethod.Over)
+        {
+            blendMemory = this.memoryAllocator.Allocate<TPixel>(imageFrame.Width, AllocationOptions.Clean);
+            blendRowBuffer = blendMemory.Memory.Span;
+        }
+
         while (true)
         {
             int numColumns = Adam7.ComputeColumns(width, pass);
@@ -669,21 +859,21 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
             int bytesPerInterlaceScanline = this.CalculateScanlineLength(numColumns) + 1;
 
-            while (this.currentRow < this.header.Height)
+            while (currentRow < endRow)
             {
                 cancellationToken.ThrowIfCancellationRequested();
-                while (this.currentRowBytesRead < bytesPerInterlaceScanline)
+                while (currentRowBytesRead < bytesPerInterlaceScanline)
                 {
-                    int bytesRead = compressedStream.Read(this.scanline.GetSpan(), this.currentRowBytesRead, bytesPerInterlaceScanline - this.currentRowBytesRead);
+                    int bytesRead = compressedStream.Read(this.scanline.GetSpan(), currentRowBytesRead, bytesPerInterlaceScanline - currentRowBytesRead);
                     if (bytesRead <= 0)
                     {
                         return;
                     }
 
-                    this.currentRowBytesRead += bytesRead;
+                    currentRowBytesRead += bytesRead;
                 }
 
-                this.currentRowBytesRead = 0;
+                currentRowBytesRead = 0;
 
                 Span<byte> scanSpan = this.scanline.Slice(0, bytesPerInterlaceScanline);
                 Span<byte> prevSpan = this.previousScanline.Slice(0, bytesPerInterlaceScanline);
@@ -714,12 +904,20 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
                         break;
                 }
 
-                Span<TPixel> rowSpan = imageBuffer.DangerousGetRowSpan(this.currentRow);
-                this.ProcessInterlacedDefilteredScanline(this.scanline.GetSpan(), rowSpan, pngMetadata, Adam7.FirstColumn[pass], Adam7.ColumnIncrement[pass]);
-
+                Span<TPixel> rowSpan = imageBuffer.DangerousGetRowSpan(currentRow);
+                this.ProcessInterlacedDefilteredScanline(
+                    frameControl,
+                    this.scanline.GetSpan(),
+                    rowSpan,
+                    pngMetadata,
+                    blendRowBuffer,
+                    pixelOffset: Adam7.FirstColumn[pass],
+                    increment: Adam7.ColumnIncrement[pass]);
+
+                blendRowBuffer.Clear();
                 this.SwapScanlineBuffers();
 
-                this.currentRow += Adam7.RowIncrement[pass];
+                currentRow += Adam7.RowIncrement[pass];
             }
 
             pass++;
@@ -727,7 +925,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
             if (pass < 7)
             {
-                this.currentRow = Adam7.FirstRow[pass];
+                currentRow = Adam7.FirstRow[pass];
             }
             else
             {
@@ -735,27 +933,44 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
                 break;
             }
         }
+
+        blendMemory?.Dispose();
     }
 
     /// <summary>
     /// Processes the de-filtered scanline filling the image pixel data
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    /// <param name="defilteredScanline">The de-filtered scanline</param>
+    /// <param name="frameControl">The frame control</param>
+    /// <param name="currentRow">The index of the current scanline being processed.</param>
+    /// <param name="scanline">The de-filtered scanline</param>
     /// <param name="pixels">The image</param>
     /// <param name="pngMetadata">The png metadata.</param>
-    private void ProcessDefilteredScanline<TPixel>(ReadOnlySpan<byte> defilteredScanline, ImageFrame<TPixel> pixels, PngMetadata pngMetadata)
+    /// <param name="blendRowBuffer">A span used to temporarily hold the decoded row pixel data for alpha blending.</param>
+    private void ProcessDefilteredScanline<TPixel>(
+        in FrameControl frameControl,
+        int currentRow,
+        ReadOnlySpan<byte> scanline,
+        ImageFrame<TPixel> pixels,
+        PngMetadata pngMetadata,
+        Span<TPixel> blendRowBuffer)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        Span<TPixel> rowSpan = pixels.PixelBuffer.DangerousGetRowSpan(this.currentRow);
+        Span<TPixel> destination = pixels.PixelBuffer.DangerousGetRowSpan(currentRow);
+
+        bool blend = frameControl.BlendOperation == PngBlendMethod.Over;
+        Span<TPixel> rowSpan = blend
+            ? blendRowBuffer
+            : destination;
 
         // Trim the first marker byte from the buffer
-        ReadOnlySpan<byte> trimmed = defilteredScanline[1..];
+        ReadOnlySpan<byte> trimmed = scanline[1..];
 
         // Convert 1, 2, and 4 bit pixel data into the 8 bit equivalent.
-        IMemoryOwner<byte> buffer = null;
+        IMemoryOwner<byte>? buffer = null;
         try
         {
+            // TODO: The allocation here could be per frame, not per scanline.
             ReadOnlySpan<byte> scanlineSpan = this.TryScaleUpTo8BitArray(
                 trimmed,
                 this.bytesPerScanline - 1,
@@ -768,7 +983,8 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
             {
                 case PngColorType.Grayscale:
                     PngScanlineProcessor.ProcessGrayscaleScanline(
-                        this.header,
+                        this.header.BitDepth,
+                        in frameControl,
                         scanlineSpan,
                         rowSpan,
                         pngMetadata.TransparentColor);
@@ -777,7 +993,8 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
                 case PngColorType.GrayscaleWithAlpha:
                     PngScanlineProcessor.ProcessGrayscaleWithAlphaScanline(
-                        this.header,
+                        this.header.BitDepth,
+                        in frameControl,
                         scanlineSpan,
                         rowSpan,
                         (uint)this.bytesPerPixel,
@@ -787,7 +1004,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
                 case PngColorType.Palette:
                     PngScanlineProcessor.ProcessPaletteScanline(
-                        this.header,
+                        in frameControl,
                         scanlineSpan,
                         rowSpan,
                         pngMetadata.ColorTable);
@@ -797,7 +1014,8 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
                 case PngColorType.Rgb:
                     PngScanlineProcessor.ProcessRgbScanline(
                         this.configuration,
-                        this.header,
+                        this.header.BitDepth,
+                        frameControl,
                         scanlineSpan,
                         rowSpan,
                         this.bytesPerPixel,
@@ -809,7 +1027,8 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
                 case PngColorType.RgbWithAlpha:
                     PngScanlineProcessor.ProcessRgbaScanline(
                         this.configuration,
-                        this.header,
+                        this.header.BitDepth,
+                        in frameControl,
                         scanlineSpan,
                         rowSpan,
                         this.bytesPerPixel,
@@ -817,6 +1036,13 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
                     break;
             }
+
+            if (blend)
+            {
+                PixelBlender<TPixel> blender =
+                    PixelOperations<TPixel>.Instance.GetPixelBlender(PixelColorBlendingMode.Normal, PixelAlphaCompositionMode.SrcOver);
+                blender.Blend<TPixel>(this.configuration, destination, destination, rowSpan, 1f);
+            }
         }
         finally
         {
@@ -828,19 +1054,33 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// Processes the interlaced de-filtered scanline filling the image pixel data
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    /// <param name="defilteredScanline">The de-filtered scanline</param>
-    /// <param name="rowSpan">The current image row.</param>
+    /// <param name="frameControl">The frame control</param>
+    /// <param name="scanline">The de-filtered scanline</param>
+    /// <param name="destination">The current image row.</param>
     /// <param name="pngMetadata">The png metadata.</param>
+    /// <param name="blendRowBuffer">A span used to temporarily hold the decoded row pixel data for alpha blending.</param>
     /// <param name="pixelOffset">The column start index. Always 0 for none interlaced images.</param>
     /// <param name="increment">The column increment. Always 1 for none interlaced images.</param>
-    private void ProcessInterlacedDefilteredScanline<TPixel>(ReadOnlySpan<byte> defilteredScanline, Span<TPixel> rowSpan, PngMetadata pngMetadata, int pixelOffset = 0, int increment = 1)
+    private void ProcessInterlacedDefilteredScanline<TPixel>(
+        in FrameControl frameControl,
+        ReadOnlySpan<byte> scanline,
+        Span<TPixel> destination,
+        PngMetadata pngMetadata,
+        Span<TPixel> blendRowBuffer,
+        int pixelOffset = 0,
+        int increment = 1)
         where TPixel : unmanaged, IPixel<TPixel>
     {
+        bool blend = frameControl.BlendOperation == PngBlendMethod.Over;
+        Span<TPixel> rowSpan = blend
+            ? blendRowBuffer
+            : destination;
+
         // Trim the first marker byte from the buffer
-        ReadOnlySpan<byte> trimmed = defilteredScanline[1..];
+        ReadOnlySpan<byte> trimmed = scanline[1..];
 
         // Convert 1, 2, and 4 bit pixel data into the 8 bit equivalent.
-        IMemoryOwner<byte> buffer = null;
+        IMemoryOwner<byte>? buffer = null;
         try
         {
             ReadOnlySpan<byte> scanlineSpan = this.TryScaleUpTo8BitArray(
@@ -855,7 +1095,8 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
             {
                 case PngColorType.Grayscale:
                     PngScanlineProcessor.ProcessInterlacedGrayscaleScanline(
-                        this.header,
+                        this.header.BitDepth,
+                        in frameControl,
                         scanlineSpan,
                         rowSpan,
                         (uint)pixelOffset,
@@ -866,7 +1107,8 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
                 case PngColorType.GrayscaleWithAlpha:
                     PngScanlineProcessor.ProcessInterlacedGrayscaleWithAlphaScanline(
-                        this.header,
+                        this.header.BitDepth,
+                        in frameControl,
                         scanlineSpan,
                         rowSpan,
                         (uint)pixelOffset,
@@ -878,7 +1120,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
                 case PngColorType.Palette:
                     PngScanlineProcessor.ProcessInterlacedPaletteScanline(
-                        this.header,
+                        in frameControl,
                         scanlineSpan,
                         rowSpan,
                         (uint)pixelOffset,
@@ -889,7 +1131,9 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
                 case PngColorType.Rgb:
                     PngScanlineProcessor.ProcessInterlacedRgbScanline(
-                        this.header,
+                        this.configuration,
+                        this.header.BitDepth,
+                        in frameControl,
                         scanlineSpan,
                         rowSpan,
                         (uint)pixelOffset,
@@ -902,7 +1146,9 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
                 case PngColorType.RgbWithAlpha:
                     PngScanlineProcessor.ProcessInterlacedRgbaScanline(
-                        this.header,
+                        this.configuration,
+                        this.header.BitDepth,
+                        in frameControl,
                         scanlineSpan,
                         rowSpan,
                         (uint)pixelOffset,
@@ -912,6 +1158,13 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
                     break;
             }
+
+            if (blend)
+            {
+                PixelBlender<TPixel> blender =
+                    PixelOperations<TPixel>.Instance.GetPixelBlender(PixelColorBlendingMode.Normal, PixelAlphaCompositionMode.SrcOver);
+                blender.Blend<TPixel>(this.configuration, destination, destination, rowSpan, 1f);
+            }
         }
         finally
         {
@@ -996,6 +1249,31 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
         }
     }
 
+    /// <summary>
+    /// Reads a animation control chunk from the data.
+    /// </summary>
+    /// <param name="pngMetadata">The png metadata.</param>
+    /// <param name="data">The <see cref="T:ReadOnlySpan{byte}"/> containing data.</param>
+    private void ReadAnimationControlChunk(PngMetadata pngMetadata, ReadOnlySpan<byte> data)
+    {
+        this.animationControl = AnimationControl.Parse(data);
+
+        pngMetadata.RepeatCount = this.animationControl.NumberPlays;
+    }
+
+    /// <summary>
+    /// Reads a header chunk from the data.
+    /// </summary>
+    /// <param name="data">The <see cref="T:ReadOnlySpan{byte}"/> containing data.</param>
+    private FrameControl ReadFrameControlChunk(ReadOnlySpan<byte> data)
+    {
+        FrameControl fcTL = FrameControl.Parse(data);
+
+        fcTL.Validate(this.header);
+
+        return fcTL;
+    }
+
     /// <summary>
     /// Reads a header chunk from the data.
     /// </summary>
@@ -1083,7 +1361,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
         ReadOnlySpan<byte> compressedData = data[(zeroIndex + 2)..];
 
-        if (this.TryUncompressTextData(compressedData, PngConstants.Encoding, out string uncompressed)
+        if (this.TryUncompressTextData(compressedData, PngConstants.Encoding, out string? uncompressed)
             && !TryReadTextChunkMetadata(baseMetadata, name, uncompressed))
         {
             metadata.TextData.Add(new PngTextData(name, uncompressed, string.Empty, string.Empty));
@@ -1376,7 +1654,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
         {
             ReadOnlySpan<byte> compressedData = data[dataStartIdx..];
 
-            if (this.TryUncompressTextData(compressedData, PngConstants.TranslatedEncoding, out string uncompressed))
+            if (this.TryUncompressTextData(compressedData, PngConstants.TranslatedEncoding, out string? uncompressed))
             {
                 pngMetadata.TextData.Add(new PngTextData(keyword, uncompressed, language, translatedKeyword));
             }
@@ -1399,7 +1677,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// <param name="encoding">The string encoding to use.</param>
     /// <param name="value">The uncompressed value.</param>
     /// <returns>The <see cref="bool"/>.</returns>
-    private bool TryUncompressTextData(ReadOnlySpan<byte> compressedData, Encoding encoding, out string value)
+    private bool TryUncompressTextData(ReadOnlySpan<byte> compressedData, Encoding encoding, [NotNullWhen(true)] out string? value)
     {
         if (this.TryUncompressZlibData(compressedData, out byte[] uncompressedData))
         {
@@ -1424,11 +1702,11 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
         Span<byte> buffer = stackalloc byte[20];
 
-        this.currentStream.Read(buffer, 0, 4);
+        _ = this.currentStream.Read(buffer, 0, 4);
 
         if (this.TryReadChunk(buffer, out PngChunk chunk))
         {
-            if (chunk.Type == PngChunkType.Data)
+            if (chunk.Type is PngChunkType.Data or PngChunkType.FrameData)
             {
                 chunk.Data?.Dispose();
                 return chunk.Length;
@@ -1440,6 +1718,22 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
         return 0;
     }
 
+    /// <summary>
+    /// Reads the next data chunk and skip sequence number.
+    /// </summary>
+    /// <returns>Count of bytes in the next data chunk, or 0 if there are no more data chunks left.</returns>
+    private int ReadNextDataChunkAndSkipSeq()
+    {
+        int length = this.ReadNextDataChunk();
+        if (this.ReadNextDataChunk() is 0)
+        {
+            return length;
+        }
+
+        this.currentStream.Position += 4; // Skip sequence number
+        return length - 4;
+    }
+
     /// <summary>
     /// Reads a chunk from the stream.
     /// </summary>
@@ -1497,9 +1791,9 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
 
         this.ValidateChunk(chunk, buffer);
 
-        // Restore the stream position for IDAT chunks, because it will be decoded later and
+        // Restore the stream position for IDAT and fdAT chunks, because it will be decoded later and
         // was only read to verifying the CRC is correct.
-        if (type == PngChunkType.Data)
+        if (type is PngChunkType.Data or PngChunkType.FrameData)
         {
             this.currentStream.Position = pos;
         }

src/ImageSharp/Formats/Png/PngDisposalMethod.cs

@@ -0,0 +1,25 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Png;
+
+/// <summary>
+/// Specifies how the output buffer should be changed at the end of the delay (before rendering the next frame).
+/// </summary>
+public enum PngDisposalMethod
+{
+    /// <summary>
+    /// No disposal is done on this frame before rendering the next; the contents of the output buffer are left as is.
+    /// </summary>
+    None,
+
+    /// <summary>
+    /// The frame's region of the output buffer is to be cleared to fully transparent black before rendering the next frame.
+    /// </summary>
+    Background,
+
+    /// <summary>
+    /// The frame's region of the output buffer is to be reverted to the previous contents before rendering the next frame.
+    /// </summary>
+    Previous
+}

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -1,6 +1,5 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
-#nullable disable
 
 using System.Buffers;
 using System.Buffers.Binary;
@@ -100,18 +99,23 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// <summary>
     /// The raw data of previous scanline.
     /// </summary>
-    private IMemoryOwner<byte> previousScanline;
+    private IMemoryOwner<byte> previousScanline = null!;
 
     /// <summary>
     /// The raw data of current scanline.
     /// </summary>
-    private IMemoryOwner<byte> currentScanline;
+    private IMemoryOwner<byte> currentScanline = null!;
 
     /// <summary>
     /// The color profile name.
     /// </summary>
     private const string ColorProfileName = "ICC Profile";
 
+    /// <summary>
+    /// The encoder quantizer, if present.
+    /// </summary>
+    private IQuantizer? quantizer;
+
     /// <summary>
     /// Initializes a new instance of the <see cref="PngEncoderCore" /> class.
     /// </summary>
@@ -122,6 +126,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         this.configuration = configuration;
         this.memoryAllocator = configuration.MemoryAllocator;
         this.encoder = encoder;
+        this.quantizer = encoder.Quantizer;
     }
 
     /// <summary>
@@ -141,20 +146,23 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         this.height = image.Height;
 
         ImageMetadata metadata = image.Metadata;
-
         PngMetadata pngMetadata = metadata.GetFormatMetadata(PngFormat.Instance);
         this.SanitizeAndSetEncoderOptions<TPixel>(this.encoder, pngMetadata, out this.use16Bit, out this.bytesPerPixel);
-        Image<TPixel> clonedImage = null;
-        bool clearTransparency = this.encoder.TransparentColorMode == PngTransparentColorMode.Clear;
+
+        stream.Write(PngConstants.HeaderBytes);
+
+        ImageFrame<TPixel>? clonedFrame = null;
+        ImageFrame<TPixel> currentFrame = image.Frames.RootFrame;
+
+        bool clearTransparency = this.encoder.TransparentColorMode is PngTransparentColorMode.Clear;
         if (clearTransparency)
         {
-            clonedImage = image.Clone();
-            ClearTransparentPixels(clonedImage);
+            currentFrame = clonedFrame = currentFrame.Clone();
+            ClearTransparentPixels(currentFrame);
         }
 
-        IndexedImageFrame<TPixel> quantized = this.CreateQuantizedImageAndUpdateBitDepth(image, clonedImage);
-
-        stream.Write(PngConstants.HeaderBytes);
+        // Do not move this. We require an accurate bit depth for the header chunk.
+        IndexedImageFrame<TPixel>? quantized = this.CreateQuantizedImageAndUpdateBitDepth(pngMetadata, currentFrame, null);
 
         this.WriteHeaderChunk(stream);
         this.WriteGammaChunk(stream);
@@ -165,13 +173,58 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         this.WriteExifChunk(stream, metadata);
         this.WriteXmpChunk(stream, metadata);
         this.WriteTextChunks(stream, pngMetadata);
-        this.WriteDataChunks(clearTransparency ? clonedImage : image, quantized, stream);
+
+        if (image.Frames.Count > 1)
+        {
+            this.WriteAnimationControlChunk(stream, image.Frames.Count, pngMetadata.RepeatCount);
+
+            // TODO: We should attempt to optimize the output by clipping the indexed result to
+            // non-transparent bounds. That way we can assign frame control bounds and encode
+            // less data. See GifEncoder for the implementation there.
+
+            // Write the first frame.
+            FrameControl frameControl = this.WriteFrameControlChunk(stream, currentFrame, 0);
+            this.WriteDataChunks(frameControl, currentFrame, quantized, stream, false);
+
+            // Capture the global palette for reuse on subsequent frames.
+            ReadOnlyMemory<TPixel>? previousPalette = quantized?.Palette.ToArray();
+
+            // Write following frames.
+            uint increment = 0;
+            for (int i = 1; i < image.Frames.Count; i++)
+            {
+                currentFrame = image.Frames[i];
+                if (clearTransparency)
+                {
+                    // Dispose of previous clone and reassign.
+                    clonedFrame?.Dispose();
+                    currentFrame = clonedFrame = currentFrame.Clone();
+                    ClearTransparentPixels(currentFrame);
+                }
+
+                // Each frame control sequence number must be incremented by the
+                // number of frame data chunks that follow.
+                frameControl = this.WriteFrameControlChunk(stream, currentFrame, (uint)i + increment);
+
+                // Dispose of previous quantized frame and reassign.
+                quantized?.Dispose();
+                quantized = this.CreateQuantizedImageAndUpdateBitDepth(pngMetadata, currentFrame, previousPalette);
+                increment += this.WriteDataChunks(frameControl, currentFrame, quantized, stream, true);
+            }
+        }
+        else
+        {
+            FrameControl frameControl = new((uint)this.width, (uint)this.height);
+            this.WriteDataChunks(frameControl, currentFrame, quantized, stream, false);
+        }
+
         this.WriteEndChunk(stream);
 
         stream.Flush();
 
+        // Dispose of allocations from final frame.
+        clonedFrame?.Dispose();
         quantized?.Dispose();
-        clonedImage?.Dispose();
     }
 
     /// <inheritdoc />
@@ -179,18 +232,16 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     {
         this.previousScanline?.Dispose();
         this.currentScanline?.Dispose();
-        this.previousScanline = null;
-        this.currentScanline = null;
     }
 
     /// <summary>
     /// Convert transparent pixels, to transparent black pixels, which can yield to better compression in some cases.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
-    /// <param name="image">The cloned image where the transparent pixels will be changed.</param>
-    private static void ClearTransparentPixels<TPixel>(Image<TPixel> image)
-        where TPixel : unmanaged, IPixel<TPixel> =>
-        image.ProcessPixelRows(accessor =>
+    /// <param name="clone">The cloned image frame where the transparent pixels will be changed.</param>
+    private static void ClearTransparentPixels<TPixel>(ImageFrame<TPixel> clone)
+        where TPixel : unmanaged, IPixel<TPixel>
+        => clone.ProcessPixelRows(accessor =>
         {
             // TODO: We should be able to speed this up with SIMD and masking.
             Rgba32 rgba32 = default;
@@ -202,7 +253,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
                 {
                     span[x].ToRgba32(ref rgba32);
 
-                    if (rgba32.A == 0)
+                    if (rgba32.A is 0)
                     {
                         span[x].FromRgba32(transparent);
                     }
@@ -214,24 +265,17 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// Creates the quantized image and calculates and sets the bit depth.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
-    /// <param name="image">The image to quantize.</param>
-    /// <param name="clonedImage">Cloned image with transparent pixels are changed to black.</param>
+    /// <param name="metadata">The image metadata.</param>
+    /// <param name="frame">The frame to quantize.</param>
+    /// <param name="previousPalette">Any previously derived palette.</param>
     /// <returns>The quantized image.</returns>
-    private IndexedImageFrame<TPixel> CreateQuantizedImageAndUpdateBitDepth<TPixel>(
-        Image<TPixel> image,
-        Image<TPixel> clonedImage)
+    private IndexedImageFrame<TPixel>? CreateQuantizedImageAndUpdateBitDepth<TPixel>(
+        PngMetadata metadata,
+        ImageFrame<TPixel> frame,
+        ReadOnlyMemory<TPixel>? previousPalette)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        IndexedImageFrame<TPixel> quantized;
-        if (this.encoder.TransparentColorMode == PngTransparentColorMode.Clear)
-        {
-            quantized = CreateQuantizedFrame(this.encoder, this.colorType, this.bitDepth, clonedImage);
-        }
-        else
-        {
-            quantized = CreateQuantizedFrame(this.encoder, this.colorType, this.bitDepth, image);
-        }
-
+        IndexedImageFrame<TPixel>? quantized = this.CreateQuantizedFrame(this.encoder, this.colorType, this.bitDepth, metadata, frame, previousPalette);
         this.bitDepth = CalculateBitDepth(this.colorType, this.bitDepth, quantized);
         return quantized;
     }
@@ -242,9 +286,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     private void CollectGrayscaleBytes<TPixel>(ReadOnlySpan<TPixel> rowSpan)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
         Span<byte> rawScanlineSpan = this.currentScanline.GetSpan();
-        ref byte rawScanlineSpanRef = ref MemoryMarshal.GetReference(rawScanlineSpan);
 
         if (this.colorType == PngColorType.Grayscale)
         {
@@ -400,20 +442,19 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// <param name="rowSpan">The row span.</param>
     /// <param name="quantized">The quantized pixels. Can be null.</param>
     /// <param name="row">The row.</param>
-    private void CollectPixelBytes<TPixel>(ReadOnlySpan<TPixel> rowSpan, IndexedImageFrame<TPixel> quantized, int row)
+    private void CollectPixelBytes<TPixel>(ReadOnlySpan<TPixel> rowSpan, IndexedImageFrame<TPixel>? quantized, int row)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         switch (this.colorType)
         {
             case PngColorType.Palette:
-
                 if (this.bitDepth < 8)
                 {
-                    PngEncoderHelpers.ScaleDownFrom8BitArray(quantized.DangerousGetRowSpan(row), this.currentScanline.GetSpan(), this.bitDepth);
+                    PngEncoderHelpers.ScaleDownFrom8BitArray(quantized!.DangerousGetRowSpan(row), this.currentScanline.GetSpan(), this.bitDepth);
                 }
                 else
                 {
-                    quantized.DangerousGetRowSpan(row).CopyTo(this.currentScanline.GetSpan());
+                    quantized?.DangerousGetRowSpan(row).CopyTo(this.currentScanline.GetSpan());
                 }
 
                 break;
@@ -474,7 +515,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         ReadOnlySpan<TPixel> rowSpan,
         ref Span<byte> filter,
         ref Span<byte> attempt,
-        IndexedImageFrame<TPixel> quantized,
+        IndexedImageFrame<TPixel>? quantized,
         int row)
         where TPixel : unmanaged, IPixel<TPixel>
     {
@@ -574,6 +615,21 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         this.WriteChunk(stream, PngChunkType.Header, this.chunkDataBuffer.Span, 0, PngHeader.Size);
     }
 
+    /// <summary>
+    /// Writes the animation control chunk to the stream.
+    /// </summary>
+    /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+    /// <param name="framesCount">The number of frames.</param>
+    /// <param name="playsCount">The number of times to loop this APNG.</param>
+    private void WriteAnimationControlChunk(Stream stream, int framesCount, int playsCount)
+    {
+        AnimationControl acTL = new(framesCount, playsCount);
+
+        acTL.WriteTo(this.chunkDataBuffer.Span);
+
+        this.WriteChunk(stream, PngChunkType.AnimationControl, this.chunkDataBuffer.Span, 0, AnimationControl.Size);
+    }
+
     /// <summary>
     /// Writes the palette chunk to the stream.
     /// Should be written before the first IDAT chunk.
@@ -581,7 +637,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// <typeparam name="TPixel">The pixel format.</typeparam>
     /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
     /// <param name="quantized">The quantized frame.</param>
-    private void WritePaletteChunk<TPixel>(Stream stream, IndexedImageFrame<TPixel> quantized)
+    private void WritePaletteChunk<TPixel>(Stream stream, IndexedImageFrame<TPixel>? quantized)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         if (quantized is null)
@@ -640,14 +696,14 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// <param name="meta">The image metadata.</param>
     private void WritePhysicalChunk(Stream stream, ImageMetadata meta)
     {
-        if ((this.chunkFilter & PngChunkFilter.ExcludePhysicalChunk) == PngChunkFilter.ExcludePhysicalChunk)
+        if (this.chunkFilter.HasFlag(PngChunkFilter.ExcludePhysicalChunk))
         {
             return;
         }
 
-        PhysicalChunkData.FromMetadata(meta).WriteTo(this.chunkDataBuffer.Span);
+        PngPhysical.FromMetadata(meta).WriteTo(this.chunkDataBuffer.Span);
 
-        this.WriteChunk(stream, PngChunkType.Physical, this.chunkDataBuffer.Span, 0, PhysicalChunkData.Size);
+        this.WriteChunk(stream, PngChunkType.Physical, this.chunkDataBuffer.Span, 0, PngPhysical.Size);
     }
 
     /// <summary>
@@ -689,9 +745,9 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
             return;
         }
 
-        byte[] xmpData = meta.XmpProfile.Data;
+        byte[]? xmpData = meta.XmpProfile.Data;
 
-        if (xmpData.Length == 0)
+        if (xmpData?.Length is 0 or null)
         {
             return;
         }
@@ -758,18 +814,9 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         }
 
         const int maxLatinCode = 255;
-        for (int i = 0; i < meta.TextData.Count; i++)
+        foreach (PngTextData textData in meta.TextData)
         {
-            PngTextData textData = meta.TextData[i];
-            bool hasUnicodeCharacters = false;
-            foreach (char c in textData.Value)
-            {
-                if (c > maxLatinCode)
-                {
-                    hasUnicodeCharacters = true;
-                    break;
-                }
-            }
+            bool hasUnicodeCharacters = textData.Value.Any(c => c > maxLatinCode);
 
             if (hasUnicodeCharacters || !string.IsNullOrWhiteSpace(textData.LanguageTag) || !string.IsNullOrWhiteSpace(textData.TranslatedKeyword))
             {
@@ -932,14 +979,45 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         }
     }
 
+    /// <summary>
+    /// Writes the animation control chunk to the stream.
+    /// </summary>
+    /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+    /// <param name="imageFrame">The image frame.</param>
+    /// <param name="sequenceNumber">The frame sequence number.</param>
+    private FrameControl WriteFrameControlChunk(Stream stream, ImageFrame imageFrame, uint sequenceNumber)
+    {
+        PngFrameMetadata frameMetadata = imageFrame.Metadata.GetPngFrameMetadata();
+
+        // TODO: If we can clip the indexed frame for transparent bounds we can set properties here.
+        FrameControl fcTL = new(
+            sequenceNumber: sequenceNumber,
+            width: (uint)imageFrame.Width,
+            height: (uint)imageFrame.Height,
+            xOffset: 0,
+            yOffset: 0,
+            delayNumerator: (ushort)frameMetadata.FrameDelay.Numerator,
+            delayDenominator: (ushort)frameMetadata.FrameDelay.Denominator,
+            disposeOperation: frameMetadata.DisposalMethod,
+            blendOperation: frameMetadata.BlendMethod);
+
+        fcTL.WriteTo(this.chunkDataBuffer.Span);
+
+        this.WriteChunk(stream, PngChunkType.FrameControl, this.chunkDataBuffer.Span, 0, FrameControl.Size);
+
+        return fcTL;
+    }
+
     /// <summary>
     /// Writes the pixel information to the stream.
     /// </summary>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
-    /// <param name="pixels">The image.</param>
+    /// <param name="frameControl">The frame control</param>
+    /// <param name="pixels">The frame.</param>
     /// <param name="quantized">The quantized pixel data. Can be null.</param>
     /// <param name="stream">The stream.</param>
-    private void WriteDataChunks<TPixel>(Image<TPixel> pixels, IndexedImageFrame<TPixel> quantized, Stream stream)
+    /// <param name="isFrame">Is writing fdAT or IDAT.</param>
+    private uint WriteDataChunks<TPixel>(FrameControl frameControl, ImageFrame<TPixel> pixels, IndexedImageFrame<TPixel>? quantized, Stream stream, bool isFrame)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         byte[] buffer;
@@ -949,20 +1027,20 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         {
             using (ZlibDeflateStream deflateStream = new(this.memoryAllocator, memoryStream, this.encoder.CompressionLevel))
             {
-                if (this.interlaceMode == PngInterlaceMode.Adam7)
+                if (this.interlaceMode is PngInterlaceMode.Adam7)
                 {
-                    if (quantized != null)
+                    if (quantized is not null)
                     {
-                        this.EncodeAdam7IndexedPixels(quantized, deflateStream);
+                        this.EncodeAdam7IndexedPixels(frameControl, quantized, deflateStream);
                     }
                     else
                     {
-                        this.EncodeAdam7Pixels(pixels, deflateStream);
+                        this.EncodeAdam7Pixels(frameControl, pixels, deflateStream);
                     }
                 }
                 else
                 {
-                    this.EncodePixels(pixels, quantized, deflateStream);
+                    this.EncodePixels(frameControl, pixels, quantized, deflateStream);
                 }
             }
 
@@ -972,24 +1050,42 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
 
         // Store the chunks in repeated 64k blocks.
         // This reduces the memory load for decoding the image for many decoders.
-        int numChunks = bufferLength / MaxBlockSize;
+        int maxBlockSize = MaxBlockSize;
+        if (isFrame)
+        {
+            maxBlockSize -= 4;
+        }
 
-        if (bufferLength % MaxBlockSize != 0)
+        int numChunks = bufferLength / maxBlockSize;
+
+        if (bufferLength % maxBlockSize != 0)
         {
             numChunks++;
         }
 
         for (int i = 0; i < numChunks; i++)
         {
-            int length = bufferLength - (i * MaxBlockSize);
+            int length = bufferLength - (i * maxBlockSize);
 
-            if (length > MaxBlockSize)
+            if (length > maxBlockSize)
             {
-                length = MaxBlockSize;
+                length = maxBlockSize;
             }
 
-            this.WriteChunk(stream, PngChunkType.Data, buffer, i * MaxBlockSize, length);
+            if (isFrame)
+            {
+                // We increment the sequence number for each frame chunk.
+                // '1' is added to the sequence number to account for the preceding frame control chunk.
+                uint sequenceNumber = (uint)(frameControl.SequenceNumber + 1 + i);
+                this.WriteFrameDataChunk(stream, sequenceNumber, buffer, i * maxBlockSize, length);
+            }
+            else
+            {
+                this.WriteChunk(stream, PngChunkType.Data, buffer, i * maxBlockSize, length);
+            }
         }
+
+        return (uint)numChunks;
     }
 
     /// <summary>
@@ -1009,13 +1105,17 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// Encodes the pixels.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
+    /// <param name="frameControl">The frame control</param>
     /// <param name="pixels">The pixels.</param>
     /// <param name="quantized">The quantized pixels span.</param>
     /// <param name="deflateStream">The deflate stream.</param>
-    private void EncodePixels<TPixel>(Image<TPixel> pixels, IndexedImageFrame<TPixel> quantized, ZlibDeflateStream deflateStream)
+    private void EncodePixels<TPixel>(FrameControl frameControl, ImageFrame<TPixel> pixels, IndexedImageFrame<TPixel>? quantized, ZlibDeflateStream deflateStream)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        int bytesPerScanline = this.CalculateScanlineLength(this.width);
+        int width = (int)frameControl.Width;
+        int height = (int)frameControl.Height;
+
+        int bytesPerScanline = this.CalculateScanlineLength(width);
         int filterLength = bytesPerScanline + 1;
         this.AllocateScanlineBuffers(bytesPerScanline);
 
@@ -1026,7 +1126,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         {
             Span<byte> filter = filterBuffer.GetSpan();
             Span<byte> attempt = attemptBuffer.GetSpan();
-            for (int y = 0; y < this.height; y++)
+            for (int y = (int)frameControl.YOffset; y < frameControl.YMax; y++)
             {
                 this.CollectAndFilterPixelRow(accessor.GetRowSpan(y), ref filter, ref attempt, quantized, y);
                 deflateStream.Write(filter);
@@ -1039,18 +1139,19 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// Interlaced encoding the pixels.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
-    /// <param name="image">The image.</param>
+    /// <param name="frameControl">The frame control</param>
+    /// <param name="frame">The image frame.</param>
     /// <param name="deflateStream">The deflate stream.</param>
-    private void EncodeAdam7Pixels<TPixel>(Image<TPixel> image, ZlibDeflateStream deflateStream)
+    private void EncodeAdam7Pixels<TPixel>(FrameControl frameControl, ImageFrame<TPixel> frame, ZlibDeflateStream deflateStream)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        int width = image.Width;
-        int height = image.Height;
-        Buffer2D<TPixel> pixelBuffer = image.Frames.RootFrame.PixelBuffer;
+        int width = (int)frameControl.XMax;
+        int height = (int)frameControl.YMax;
+        Buffer2D<TPixel> pixelBuffer = frame.PixelBuffer;
         for (int pass = 0; pass < 7; pass++)
         {
-            int startRow = Adam7.FirstRow[pass];
-            int startCol = Adam7.FirstColumn[pass];
+            int startRow = Adam7.FirstRow[pass] + (int)frameControl.YOffset;
+            int startCol = Adam7.FirstColumn[pass] + (int)frameControl.XOffset;
             int blockWidth = Adam7.ComputeBlockWidth(width, pass);
 
             int bytesPerScanline = this.bytesPerPixel <= 1
@@ -1072,7 +1173,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
             {
                 // Collect pixel data
                 Span<TPixel> srcRow = pixelBuffer.DangerousGetRowSpan(row);
-                for (int col = startCol, i = 0; col < width; col += Adam7.ColumnIncrement[pass])
+                for (int col = startCol, i = 0; col < frameControl.XMax; col += Adam7.ColumnIncrement[pass])
                 {
                     block[i++] = srcRow[col];
                 }
@@ -1092,17 +1193,18 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// Interlaced encoding the quantized (indexed, with palette) pixels.
     /// </summary>
     /// <typeparam name="TPixel">The type of the pixel.</typeparam>
+    /// <param name="frameControl">The frame control</param>
     /// <param name="quantized">The quantized.</param>
     /// <param name="deflateStream">The deflate stream.</param>
-    private void EncodeAdam7IndexedPixels<TPixel>(IndexedImageFrame<TPixel> quantized, ZlibDeflateStream deflateStream)
+    private void EncodeAdam7IndexedPixels<TPixel>(FrameControl frameControl, IndexedImageFrame<TPixel> quantized, ZlibDeflateStream deflateStream)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        int width = quantized.Width;
-        int height = quantized.Height;
+        int width = (int)frameControl.Width;
+        int endRow = (int)frameControl.YMax;
         for (int pass = 0; pass < 7; pass++)
         {
-            int startRow = Adam7.FirstRow[pass];
-            int startCol = Adam7.FirstColumn[pass];
+            int startRow = Adam7.FirstRow[pass] + (int)frameControl.YOffset;
+            int startCol = Adam7.FirstColumn[pass] + (int)frameControl.XOffset;
             int blockWidth = Adam7.ComputeBlockWidth(width, pass);
 
             int bytesPerScanline = this.bytesPerPixel <= 1
@@ -1121,17 +1223,16 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
             Span<byte> filter = filterBuffer.GetSpan();
             Span<byte> attempt = attemptBuffer.GetSpan();
 
-            for (int row = startRow;
-                row < height;
-                row += Adam7.RowIncrement[pass])
+            for (int row = startRow; row < endRow; row += Adam7.RowIncrement[pass])
             {
                 // Collect data
                 ReadOnlySpan<byte> srcRow = quantized.DangerousGetRowSpan(row);
                 for (int col = startCol, i = 0;
-                    col < width;
+                    col < frameControl.XMax;
                     col += Adam7.ColumnIncrement[pass])
                 {
-                    block[i++] = srcRow[col];
+                    block[i] = srcRow[col];
+                    i++;
                 }
 
                 // Encode data
@@ -1163,7 +1264,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// </summary>
     /// <param name="stream">The <see cref="Stream"/> to write to.</param>
     /// <param name="type">The type of chunk to write.</param>
-    /// <param name="data">The <see cref="T:byte[]"/> containing data.</param>
+    /// <param name="data">The <see cref="Span{Byte}"/> containing data.</param>
     /// <param name="offset">The position to offset the data at.</param>
     /// <param name="length">The of the data to write.</param>
     private void WriteChunk(Stream stream, PngChunkType type, Span<byte> data, int offset, int length)
@@ -1189,6 +1290,38 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         stream.Write(buffer, 0, 4); // write the crc
     }
 
+    /// <summary>
+    /// Writes a frame data chunk of a specified length to the stream at the given offset.
+    /// </summary>
+    /// <param name="stream">The <see cref="Stream"/> to write to.</param>
+    /// <param name="sequenceNumber">The frame sequence number.</param>
+    /// <param name="data">The <see cref="Span{Byte}"/> containing data.</param>
+    /// <param name="offset">The position to offset the data at.</param>
+    /// <param name="length">The of the data to write.</param>
+    private void WriteFrameDataChunk(Stream stream, uint sequenceNumber, Span<byte> data, int offset, int length)
+    {
+        Span<byte> buffer = stackalloc byte[12];
+
+        BinaryPrimitives.WriteInt32BigEndian(buffer, length + 4);
+        BinaryPrimitives.WriteUInt32BigEndian(buffer.Slice(4, 4), (uint)PngChunkType.FrameData);
+        BinaryPrimitives.WriteUInt32BigEndian(buffer.Slice(8, 4), sequenceNumber);
+
+        stream.Write(buffer);
+
+        uint crc = Crc32.Calculate(buffer[4..]); // Write the type buffer
+
+        if (data.Length > 0 && length > 0)
+        {
+            stream.Write(data, offset, length);
+
+            crc = Crc32.Calculate(crc, data.Slice(offset, length));
+        }
+
+        BinaryPrimitives.WriteUInt32BigEndian(buffer, crc);
+
+        stream.Write(buffer, 0, 4); // write the crc
+    }
+
     /// <summary>
     /// Calculates the scanline length.
     /// </summary>
@@ -1198,7 +1331,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// </returns>
     private int CalculateScanlineLength(int width)
     {
-        int mod = this.bitDepth == 16 ? 16 : 8;
+        int mod = this.bitDepth is 16 ? 16 : 8;
         int scanlineLength = width * this.bitDepth * this.bytesPerPixel;
 
         int amount = scanlineLength % mod;
@@ -1242,14 +1375,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         if (!encoder.FilterMethod.HasValue)
         {
             // Specification recommends default filter method None for paletted images and Paeth for others.
-            if (this.colorType == PngColorType.Palette)
-            {
-                this.filterMethod = PngFilterMethod.None;
-            }
-            else
-            {
-                this.filterMethod = PngFilterMethod.Paeth;
-            }
+            this.filterMethod = this.colorType is PngColorType.Palette ? PngFilterMethod.None : PngFilterMethod.Paeth;
         }
 
         // Ensure bit depth and color type are a supported combination.
@@ -1265,7 +1391,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         use16Bit = bits == (byte)PngBitDepth.Bit16;
         bytesPerPixel = CalculateBytesPerPixel(this.colorType, use16Bit);
 
-        this.interlaceMode = (encoder.InterlaceMethod ?? pngMetadata.InterlaceMethod).Value;
+        this.interlaceMode = (encoder.InterlaceMethod ?? pngMetadata.InterlaceMethod)!.Value;
         this.chunkFilter = encoder.SkipMetadata ? PngChunkFilter.ExcludeAll : encoder.ChunkFilter ?? PngChunkFilter.None;
     }
 
@@ -1276,40 +1402,50 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// <param name="encoder">The png encoder.</param>
     /// <param name="colorType">The color type.</param>
     /// <param name="bitDepth">The bits per component.</param>
-    /// <param name="image">The image.</param>
-    private static IndexedImageFrame<TPixel> CreateQuantizedFrame<TPixel>(
+    /// <param name="metadata">The image metadata.</param>
+    /// <param name="frame">The frame to quantize.</param>
+    /// <param name="previousPalette">Any previously derived palette.</param>
+    private IndexedImageFrame<TPixel>? CreateQuantizedFrame<TPixel>(
         QuantizingImageEncoder encoder,
         PngColorType colorType,
         byte bitDepth,
-        Image<TPixel> image)
+        PngMetadata metadata,
+        ImageFrame<TPixel> frame,
+        ReadOnlyMemory<TPixel>? previousPalette)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        if (colorType != PngColorType.Palette)
+        if (colorType is not PngColorType.Palette)
         {
             return null;
         }
 
+        if (previousPalette is not null)
+        {
+            // Use the previously derived palette created by quantizing the root frame to quantize the current frame.
+            using PaletteQuantizer<TPixel> paletteQuantizer = new(this.configuration, this.quantizer!.Options, previousPalette.Value, -1);
+            paletteQuantizer.BuildPalette(encoder.PixelSamplingStrategy, frame);
+            return paletteQuantizer.QuantizeFrame(frame, frame.Bounds());
+        }
+
         // Use the metadata to determine what quantization depth to use if no quantizer has been set.
-        IQuantizer quantizer = encoder.Quantizer;
-        if (quantizer is null)
+        if (this.quantizer is null)
         {
-            PngMetadata metadata = image.Metadata.GetPngMetadata();
             if (metadata.ColorTable is not null)
             {
-                // Use the provided palette in total. The caller is responsible for setting values.
-                quantizer = new PaletteQuantizer(metadata.ColorTable.Value);
+                // Use the provided palette. The caller is responsible for setting values.
+                this.quantizer = new PaletteQuantizer(metadata.ColorTable.Value);
             }
             else
             {
-                quantizer = new WuQuantizer(new QuantizerOptions { MaxColors = ColorNumerics.GetColorCountForBitDepth(bitDepth) });
+                this.quantizer = new WuQuantizer(new QuantizerOptions { MaxColors = ColorNumerics.GetColorCountForBitDepth(bitDepth) });
             }
         }
 
         // Create quantized frame returning the palette and set the bit depth.
-        using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(image.Configuration);
+        using IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(frame.Configuration);
 
-        frameQuantizer.BuildPalette(encoder.PixelSamplingStrategy, image);
-        return frameQuantizer.QuantizeFrame(image.Frames.RootFrame, image.Bounds);
+        frameQuantizer.BuildPalette(encoder.PixelSamplingStrategy, frame);
+        return frameQuantizer.QuantizeFrame(frame, frame.Bounds());
     }
 
     /// <summary>
@@ -1323,25 +1459,23 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     private static byte CalculateBitDepth<TPixel>(
         PngColorType colorType,
         byte bitDepth,
-        IndexedImageFrame<TPixel> quantizedFrame)
+        IndexedImageFrame<TPixel>? quantizedFrame)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        if (colorType == PngColorType.Palette)
+        if (colorType is PngColorType.Palette)
         {
-            byte quantizedBits = (byte)Numerics.Clamp(ColorNumerics.GetBitsNeededForColorDepth(quantizedFrame.Palette.Length), 1, 8);
+            byte quantizedBits = (byte)Numerics.Clamp(ColorNumerics.GetBitsNeededForColorDepth(quantizedFrame!.Palette.Length), 1, 8);
             byte bits = Math.Max(bitDepth, quantizedBits);
 
             // Png only supports in four pixel depths: 1, 2, 4, and 8 bits when using the PLTE chunk
             // We check again for the bit depth as the bit depth of the color palette from a given quantizer might not
             // be within the acceptable range.
-            if (bits == 3)
+            bits = bits switch
             {
-                bits = 4;
-            }
-            else if (bits is >= 5 and <= 7)
-            {
-                bits = 8;
-            }
+                3 => 4,
+                >= 5 and <= 7 => 8,
+                _ => bits
+            };
 
             bitDepth = bits;
         }
@@ -1379,21 +1513,21 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// <typeparam name="TPixel">The type of pixel format.</typeparam>
     private static PngColorType SuggestColorType<TPixel>()
         where TPixel : unmanaged, IPixel<TPixel>
-        => typeof(TPixel) switch
+        => default(TPixel) switch
         {
-            Type t when t == typeof(A8) => PngColorType.GrayscaleWithAlpha,
-            Type t when t == typeof(Argb32) => PngColorType.RgbWithAlpha,
-            Type t when t == typeof(Bgr24) => PngColorType.Rgb,
-            Type t when t == typeof(Bgra32) => PngColorType.RgbWithAlpha,
-            Type t when t == typeof(L8) => PngColorType.Grayscale,
-            Type t when t == typeof(L16) => PngColorType.Grayscale,
-            Type t when t == typeof(La16) => PngColorType.GrayscaleWithAlpha,
-            Type t when t == typeof(La32) => PngColorType.GrayscaleWithAlpha,
-            Type t when t == typeof(Rgb24) => PngColorType.Rgb,
-            Type t when t == typeof(Rgba32) => PngColorType.RgbWithAlpha,
-            Type t when t == typeof(Rgb48) => PngColorType.Rgb,
-            Type t when t == typeof(Rgba64) => PngColorType.RgbWithAlpha,
-            Type t when t == typeof(RgbaVector) => PngColorType.RgbWithAlpha,
+            A8 => PngColorType.GrayscaleWithAlpha,
+            Argb32 => PngColorType.RgbWithAlpha,
+            Bgr24 => PngColorType.Rgb,
+            Bgra32 => PngColorType.RgbWithAlpha,
+            L8 => PngColorType.Grayscale,
+            L16 => PngColorType.Grayscale,
+            La16 => PngColorType.GrayscaleWithAlpha,
+            La32 => PngColorType.GrayscaleWithAlpha,
+            Rgb24 => PngColorType.Rgb,
+            Rgba32 => PngColorType.RgbWithAlpha,
+            Rgb48 => PngColorType.Rgb,
+            Rgba64 => PngColorType.RgbWithAlpha,
+            RgbaVector => PngColorType.RgbWithAlpha,
             _ => PngColorType.RgbWithAlpha
         };
 
@@ -1404,27 +1538,27 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// <typeparam name="TPixel">The type of pixel format.</typeparam>
     private static PngBitDepth SuggestBitDepth<TPixel>()
         where TPixel : unmanaged, IPixel<TPixel>
-        => typeof(TPixel) switch
+        => default(TPixel) switch
         {
-            Type t when t == typeof(A8) => PngBitDepth.Bit8,
-            Type t when t == typeof(Argb32) => PngBitDepth.Bit8,
-            Type t when t == typeof(Bgr24) => PngBitDepth.Bit8,
-            Type t when t == typeof(Bgra32) => PngBitDepth.Bit8,
-            Type t when t == typeof(L8) => PngBitDepth.Bit8,
-            Type t when t == typeof(L16) => PngBitDepth.Bit16,
-            Type t when t == typeof(La16) => PngBitDepth.Bit8,
-            Type t when t == typeof(La32) => PngBitDepth.Bit16,
-            Type t when t == typeof(Rgb24) => PngBitDepth.Bit8,
-            Type t when t == typeof(Rgba32) => PngBitDepth.Bit8,
-            Type t when t == typeof(Rgb48) => PngBitDepth.Bit16,
-            Type t when t == typeof(Rgba64) => PngBitDepth.Bit16,
-            Type t when t == typeof(RgbaVector) => PngBitDepth.Bit16,
+            A8 => PngBitDepth.Bit8,
+            Argb32 => PngBitDepth.Bit8,
+            Bgr24 => PngBitDepth.Bit8,
+            Bgra32 => PngBitDepth.Bit8,
+            L8 => PngBitDepth.Bit8,
+            L16 => PngBitDepth.Bit16,
+            La16 => PngBitDepth.Bit8,
+            La32 => PngBitDepth.Bit16,
+            Rgb24 => PngBitDepth.Bit8,
+            Rgba32 => PngBitDepth.Bit8,
+            Rgb48 => PngBitDepth.Bit16,
+            Rgba64 => PngBitDepth.Bit16,
+            RgbaVector => PngBitDepth.Bit16,
             _ => PngBitDepth.Bit8
         };
 
     private unsafe struct ScratchBuffer
     {
-        private const int Size = 16;
+        private const int Size = 26;
         private fixed byte scratch[Size];
 
         public Span<byte> Span => MemoryMarshal.CreateSpan(ref this.scratch[0], Size);

src/ImageSharp/Formats/Png/PngFormat.cs

@@ -6,7 +6,7 @@ namespace SixLabors.ImageSharp.Formats.Png;
 /// <summary>
 /// Registers the image encoders, decoders and mime type detectors for the png format.
 /// </summary>
-public sealed class PngFormat : IImageFormat<PngMetadata>
+public sealed class PngFormat : IImageFormat<PngMetadata, PngFrameMetadata>
 {
     private PngFormat()
     {
@@ -31,4 +31,7 @@ public sealed class PngFormat : IImageFormat<PngMetadata>
 
     /// <inheritdoc/>
     public PngMetadata CreateDefaultFormatMetadata() => new();
+
+    /// <inheritdoc/>
+    public PngFrameMetadata CreateDefaultFormatFrameMetadata() => new();
 }

src/ImageSharp/Formats/Png/PngFrameMetadata.cs

@@ -0,0 +1,62 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Png.Chunks;
+
+namespace SixLabors.ImageSharp.Formats.Png;
+
+/// <summary>
+/// Provides APng specific metadata information for the image frame.
+/// </summary>
+public class PngFrameMetadata : IDeepCloneable
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="PngFrameMetadata"/> class.
+    /// </summary>
+    public PngFrameMetadata()
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="PngFrameMetadata"/> class.
+    /// </summary>
+    /// <param name="other">The metadata to create an instance from.</param>
+    private PngFrameMetadata(PngFrameMetadata other)
+    {
+        this.FrameDelay = other.FrameDelay;
+        this.DisposalMethod = other.DisposalMethod;
+        this.BlendMethod = other.BlendMethod;
+    }
+
+    /// <summary>
+    /// Gets or sets the frame delay for animated images.
+    /// If not 0, when utilized in Png animation, this field specifies the number of hundredths (1/100) of a second to
+    /// wait before continuing with the processing of the Data Stream.
+    /// The clock starts ticking immediately after the graphic is rendered.
+    /// </summary>
+    public Rational FrameDelay { get; set; }
+
+    /// <summary>
+    /// Gets or sets the type of frame area disposal to be done after rendering this frame
+    /// </summary>
+    public PngDisposalMethod DisposalMethod { get; set; }
+
+    /// <summary>
+    /// Gets or sets the type of frame area rendering for this frame
+    /// </summary>
+    public PngBlendMethod BlendMethod { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="PngFrameMetadata"/> class.
+    /// </summary>
+    /// <param name="frameControl">The chunk to create an instance from.</param>
+    internal void FromChunk(in FrameControl frameControl)
+    {
+        this.FrameDelay = new Rational(frameControl.DelayNumerator, frameControl.DelayDenominator);
+        this.DisposalMethod = frameControl.DisposeOperation;
+        this.BlendMethod = frameControl.BlendOperation;
+    }
+
+    /// <inheritdoc/>
+    public IDeepCloneable DeepClone() => new PngFrameMetadata(this);
+}

src/ImageSharp/Formats/Png/PngMetadata.cs

@@ -1,6 +1,9 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using SixLabors.ImageSharp.Formats.Png.Chunks;
+using SixLabors.ImageSharp.PixelFormats;
+
 namespace SixLabors.ImageSharp.Formats.Png;
 
 /// <summary>
@@ -26,6 +29,7 @@ public class PngMetadata : IDeepCloneable
         this.Gamma = other.Gamma;
         this.InterlaceMethod = other.InterlaceMethod;
         this.TransparentColor = other.TransparentColor;
+        this.RepeatCount = other.RepeatCount;
 
         if (other.ColorTable?.Length > 0)
         {
@@ -75,6 +79,11 @@ public class PngMetadata : IDeepCloneable
     /// </summary>
     public IList<PngTextData> TextData { get; set; } = new List<PngTextData>();
 
+    /// <summary>
+    /// Gets or sets the number of times to loop this APNG.  0 indicates infinite looping.
+    /// </summary>
+    public int RepeatCount { get; set; }
+
     /// <inheritdoc/>
     public IDeepCloneable DeepClone() => new PngMetadata(this);
 }

src/ImageSharp/Formats/Png/PngScanlineProcessor.cs

@@ -4,6 +4,7 @@
 using System.Buffers.Binary;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.Formats.Png.Chunks;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Png;
@@ -15,75 +16,24 @@ namespace SixLabors.ImageSharp.Formats.Png;
 internal static class PngScanlineProcessor
 {
     public static void ProcessGrayscaleScanline<TPixel>(
-        in PngHeader header,
+        int bitDepth,
+        in FrameControl frameControl,
         ReadOnlySpan<byte> scanlineSpan,
         Span<TPixel> rowSpan,
         Color? transparentColor)
-        where TPixel : unmanaged, IPixel<TPixel>
-    {
-        TPixel pixel = default;
-        ref byte scanlineSpanRef = ref MemoryMarshal.GetReference(scanlineSpan);
-        ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
-        int scaleFactor = 255 / (ColorNumerics.GetColorCountForBitDepth(header.BitDepth) - 1);
-
-        if (transparentColor is null)
-        {
-            if (header.BitDepth == 16)
-            {
-                int o = 0;
-                for (nuint x = 0; x < (uint)header.Width; x++, o += 2)
-                {
-                    ushort luminance = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, 2));
-                    pixel.FromL16(Unsafe.As<ushort, L16>(ref luminance));
-                    Unsafe.Add(ref rowSpanRef, x) = pixel;
-                }
-            }
-            else
-            {
-                for (nuint x = 0; x < (uint)header.Width; x++)
-                {
-                    byte luminance = (byte)(Unsafe.Add(ref scanlineSpanRef, x) * scaleFactor);
-                    pixel.FromL8(Unsafe.As<byte, L8>(ref luminance));
-                    Unsafe.Add(ref rowSpanRef, x) = pixel;
-                }
-            }
-
-            return;
-        }
-
-        if (header.BitDepth == 16)
-        {
-            L16 transparent = transparentColor.Value.ToPixel<L16>();
-            La32 source = default;
-            int o = 0;
-            for (nuint x = 0; x < (uint)header.Width; x++, o += 2)
-            {
-                ushort luminance = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, 2));
-                source.L = luminance;
-                source.A = luminance.Equals(transparent.PackedValue) ? ushort.MinValue : ushort.MaxValue;
-
-                pixel.FromLa32(source);
-                Unsafe.Add(ref rowSpanRef, x) = pixel;
-            }
-        }
-        else
-        {
-            byte transparent = (byte)(transparentColor.Value.ToPixel<L8>().PackedValue * scaleFactor);
-            La16 source = default;
-            for (nuint x = 0; x < (uint)header.Width; x++)
-            {
-                byte luminance = (byte)(Unsafe.Add(ref scanlineSpanRef, x) * scaleFactor);
-                source.L = luminance;
-                source.A = luminance.Equals(transparent) ? byte.MinValue : byte.MaxValue;
-
-                pixel.FromLa16(source);
-                Unsafe.Add(ref rowSpanRef, x) = pixel;
-            }
-        }
-    }
+        where TPixel : unmanaged, IPixel<TPixel> =>
+        ProcessInterlacedGrayscaleScanline(
+            bitDepth,
+            frameControl,
+            scanlineSpan,
+            rowSpan,
+            0,
+            1,
+            transparentColor);
 
     public static void ProcessInterlacedGrayscaleScanline<TPixel>(
-        in PngHeader header,
+        int bitDepth,
+        in FrameControl frameControl,
         ReadOnlySpan<byte> scanlineSpan,
         Span<TPixel> rowSpan,
         uint pixelOffset,
@@ -91,17 +41,18 @@ internal static class PngScanlineProcessor
         Color? transparentColor)
         where TPixel : unmanaged, IPixel<TPixel>
     {
+        uint offset = pixelOffset + frameControl.XOffset;
         TPixel pixel = default;
         ref byte scanlineSpanRef = ref MemoryMarshal.GetReference(scanlineSpan);
         ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
-        int scaleFactor = 255 / (ColorNumerics.GetColorCountForBitDepth(header.BitDepth) - 1);
+        int scaleFactor = 255 / (ColorNumerics.GetColorCountForBitDepth(bitDepth) - 1);
 
         if (transparentColor is null)
         {
-            if (header.BitDepth == 16)
+            if (bitDepth == 16)
             {
                 int o = 0;
-                for (nuint x = pixelOffset; x < (uint)header.Width; x += increment, o += 2)
+                for (nuint x = offset; x < frameControl.XMax; x += increment, o += 2)
                 {
                     ushort luminance = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, 2));
                     pixel.FromL16(Unsafe.As<ushort, L16>(ref luminance));
@@ -110,7 +61,7 @@ internal static class PngScanlineProcessor
             }
             else
             {
-                for (nuint x = pixelOffset, o = 0; x < (uint)header.Width; x += increment, o++)
+                for (nuint x = offset, o = 0; x < frameControl.XMax; x += increment, o++)
                 {
                     byte luminance = (byte)(Unsafe.Add(ref scanlineSpanRef, o) * scaleFactor);
                     pixel.FromL8(Unsafe.As<byte, L8>(ref luminance));
@@ -121,12 +72,12 @@ internal static class PngScanlineProcessor
             return;
         }
 
-        if (header.BitDepth == 16)
+        if (bitDepth == 16)
         {
             L16 transparent = transparentColor.Value.ToPixel<L16>();
             La32 source = default;
             int o = 0;
-            for (nuint x = pixelOffset; x < (uint)header.Width; x += increment, o += 2)
+            for (nuint x = offset; x < frameControl.XMax; x += increment, o += 2)
             {
                 ushort luminance = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, 2));
                 source.L = luminance;
@@ -140,7 +91,7 @@ internal static class PngScanlineProcessor
         {
             byte transparent = (byte)(transparentColor.Value.ToPixel<L8>().PackedValue * scaleFactor);
             La16 source = default;
-            for (nuint x = pixelOffset, o = 0; x < (uint)header.Width; x += increment, o++)
+            for (nuint x = offset, o = 0; x < frameControl.XMax; x += increment, o++)
             {
                 byte luminance = (byte)(Unsafe.Add(ref scanlineSpanRef, o) * scaleFactor);
                 source.L = luminance;
@@ -153,47 +104,26 @@ internal static class PngScanlineProcessor
     }
 
     public static void ProcessGrayscaleWithAlphaScanline<TPixel>(
-        in PngHeader header,
+        int bitDepth,
+        in FrameControl frameControl,
         ReadOnlySpan<byte> scanlineSpan,
         Span<TPixel> rowSpan,
         uint bytesPerPixel,
         uint bytesPerSample)
-        where TPixel : unmanaged, IPixel<TPixel>
-    {
-        TPixel pixel = default;
-        ref byte scanlineSpanRef = ref MemoryMarshal.GetReference(scanlineSpan);
-        ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
-
-        if (header.BitDepth == 16)
-        {
-            La32 source = default;
-            int o = 0;
-            for (nuint x = 0; x < (uint)header.Width; x++, o += 4)
-            {
-                source.L = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, 2));
-                source.A = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + 2, 2));
-
-                pixel.FromLa32(source);
-                Unsafe.Add(ref rowSpanRef, x) = pixel;
-            }
-        }
-        else
-        {
-            La16 source = default;
-            for (nuint x = 0; x < (uint)header.Width; x++)
-            {
-                nuint offset = x * bytesPerPixel;
-                source.L = Unsafe.Add(ref scanlineSpanRef, offset);
-                source.A = Unsafe.Add(ref scanlineSpanRef, offset + bytesPerSample);
-
-                pixel.FromLa16(source);
-                Unsafe.Add(ref rowSpanRef, x) = pixel;
-            }
-        }
-    }
+        where TPixel : unmanaged, IPixel<TPixel> =>
+        ProcessInterlacedGrayscaleWithAlphaScanline(
+            bitDepth,
+            frameControl,
+            scanlineSpan,
+            rowSpan,
+            0,
+            1,
+            bytesPerPixel,
+            bytesPerSample);
 
     public static void ProcessInterlacedGrayscaleWithAlphaScanline<TPixel>(
-        in PngHeader header,
+        int bitDepth,
+        in FrameControl frameControl,
         ReadOnlySpan<byte> scanlineSpan,
         Span<TPixel> rowSpan,
         uint pixelOffset,
@@ -202,15 +132,16 @@ internal static class PngScanlineProcessor
         uint bytesPerSample)
         where TPixel : unmanaged, IPixel<TPixel>
     {
+        uint offset = pixelOffset + frameControl.XOffset;
         TPixel pixel = default;
         ref byte scanlineSpanRef = ref MemoryMarshal.GetReference(scanlineSpan);
         ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
 
-        if (header.BitDepth == 16)
+        if (bitDepth == 16)
         {
             La32 source = default;
             int o = 0;
-            for (nuint x = pixelOffset; x < (uint)header.Width; x += increment, o += 4)
+            for (nuint x = offset; x < frameControl.XMax; x += increment, o += 4)
             {
                 source.L = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, 2));
                 source.A = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + 2, 2));
@@ -222,46 +153,35 @@ internal static class PngScanlineProcessor
         else
         {
             La16 source = default;
-            nuint offset = 0;
-            for (nuint x = pixelOffset; x < (uint)header.Width; x += increment)
+            nuint offset2 = 0;
+            for (nuint x = offset; x < frameControl.XMax; x += increment)
             {
-                source.L = Unsafe.Add(ref scanlineSpanRef, offset);
-                source.A = Unsafe.Add(ref scanlineSpanRef, offset + bytesPerSample);
+                source.L = Unsafe.Add(ref scanlineSpanRef, offset2);
+                source.A = Unsafe.Add(ref scanlineSpanRef, offset2 + bytesPerSample);
 
                 pixel.FromLa16(source);
                 Unsafe.Add(ref rowSpanRef, x) = pixel;
-                offset += bytesPerPixel;
+                offset2 += bytesPerPixel;
             }
         }
     }
 
     public static void ProcessPaletteScanline<TPixel>(
-        in PngHeader header,
+        in FrameControl frameControl,
         ReadOnlySpan<byte> scanlineSpan,
         Span<TPixel> rowSpan,
         ReadOnlyMemory<Color>? palette)
-        where TPixel : unmanaged, IPixel<TPixel>
-    {
-        if (palette is null)
-        {
-            PngThrowHelper.ThrowMissingPalette();
-        }
-
-        TPixel pixel = default;
-        ref byte scanlineSpanRef = ref MemoryMarshal.GetReference(scanlineSpan);
-        ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
-        ref Color paletteBase = ref MemoryMarshal.GetReference(palette.Value.Span);
-
-        for (nuint x = 0; x < (uint)header.Width; x++)
-        {
-            uint index = Unsafe.Add(ref scanlineSpanRef, x);
-            pixel.FromRgba32(Unsafe.Add(ref paletteBase, index).ToRgba32());
-            Unsafe.Add(ref rowSpanRef, x) = pixel;
-        }
-    }
+        where TPixel : unmanaged, IPixel<TPixel> =>
+        ProcessInterlacedPaletteScanline(
+            frameControl,
+            scanlineSpan,
+            rowSpan,
+            0,
+            1,
+            palette);
 
     public static void ProcessInterlacedPaletteScanline<TPixel>(
-        in PngHeader header,
+        in FrameControl frameControl,
         ReadOnlySpan<byte> scanlineSpan,
         Span<TPixel> rowSpan,
         uint pixelOffset,
@@ -279,7 +199,7 @@ internal static class PngScanlineProcessor
         ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
         ref Color paletteBase = ref MemoryMarshal.GetReference(palette.Value.Span);
 
-        for (nuint x = pixelOffset, o = 0; x < (uint)header.Width; x += increment, o++)
+        for (nuint x = pixelOffset, o = 0; x < frameControl.XMax; x += increment, o++)
         {
             uint index = Unsafe.Add(ref scanlineSpanRef, o);
             pixel.FromRgba32(Unsafe.Add(ref paletteBase, index).ToRgba32());
@@ -289,82 +209,30 @@ internal static class PngScanlineProcessor
 
     public static void ProcessRgbScanline<TPixel>(
         Configuration configuration,
-        in PngHeader header,
+        int bitDepth,
+        in FrameControl frameControl,
         ReadOnlySpan<byte> scanlineSpan,
         Span<TPixel> rowSpan,
         int bytesPerPixel,
         int bytesPerSample,
         Color? transparentColor)
-        where TPixel : unmanaged, IPixel<TPixel>
-    {
-        TPixel pixel = default;
-        ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
-
-        if (transparentColor is null)
-        {
-            if (header.BitDepth == 16)
-            {
-                Rgb48 rgb48 = default;
-                int o = 0;
-                for (nuint x = 0; x < (uint)header.Width; x++, o += bytesPerPixel)
-                {
-                    rgb48.R = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, bytesPerSample));
-                    rgb48.G = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + bytesPerSample, bytesPerSample));
-                    rgb48.B = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + (2 * bytesPerSample), bytesPerSample));
-
-                    pixel.FromRgb48(rgb48);
-                    Unsafe.Add(ref rowSpanRef, x) = pixel;
-                }
-            }
-            else
-            {
-                PixelOperations<TPixel>.Instance.FromRgb24Bytes(configuration, scanlineSpan, rowSpan, header.Width);
-            }
-
-            return;
-        }
-
-        if (header.BitDepth == 16)
-        {
-            Rgb48 transparent = transparentColor.Value.ToPixel<Rgb48>();
-
-            Rgb48 rgb48 = default;
-            Rgba64 rgba64 = default;
-            int o = 0;
-            for (nuint x = 0; x < (uint)header.Width; x++, o += bytesPerPixel)
-            {
-                rgb48.R = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, bytesPerSample));
-                rgb48.G = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + bytesPerSample, bytesPerSample));
-                rgb48.B = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + (2 * bytesPerSample), bytesPerSample));
-
-                rgba64.Rgb = rgb48;
-                rgba64.A = rgb48.Equals(transparent) ? ushort.MinValue : ushort.MaxValue;
-
-                pixel.FromRgba64(rgba64);
-                Unsafe.Add(ref rowSpanRef, x) = pixel;
-            }
-        }
-        else
-        {
-            Rgb24 transparent = transparentColor.Value.ToPixel<Rgb24>();
-
-            Rgba32 rgba32 = default;
-            ReadOnlySpan<Rgb24> rgb24Span = MemoryMarshal.Cast<byte, Rgb24>(scanlineSpan);
-            ref Rgb24 rgb24SpanRef = ref MemoryMarshal.GetReference(rgb24Span);
-            for (nuint x = 0; x < (uint)header.Width; x++)
-            {
-                ref readonly Rgb24 rgb24 = ref Unsafe.Add(ref rgb24SpanRef, x);
-                rgba32.Rgb = rgb24;
-                rgba32.A = rgb24.Equals(transparent) ? byte.MinValue : byte.MaxValue;
-
-                pixel.FromRgba32(rgba32);
-                Unsafe.Add(ref rowSpanRef, x) = pixel;
-            }
-        }
-    }
+       where TPixel : unmanaged, IPixel<TPixel> =>
+       ProcessInterlacedRgbScanline(
+           configuration,
+           bitDepth,
+           frameControl,
+           scanlineSpan,
+           rowSpan,
+           0,
+           1,
+           bytesPerPixel,
+           bytesPerSample,
+           transparentColor);
 
     public static void ProcessInterlacedRgbScanline<TPixel>(
-        in PngHeader header,
+        Configuration configuration,
+        int bitDepth,
+        in FrameControl frameControl,
         ReadOnlySpan<byte> scanlineSpan,
         Span<TPixel> rowSpan,
         uint pixelOffset,
@@ -374,18 +242,19 @@ internal static class PngScanlineProcessor
         Color? transparentColor)
         where TPixel : unmanaged, IPixel<TPixel>
     {
+        uint offset = pixelOffset + frameControl.XOffset;
+
         TPixel pixel = default;
         ref byte scanlineSpanRef = ref MemoryMarshal.GetReference(scanlineSpan);
         ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
-        bool hasTransparency = transparentColor is not null;
 
         if (transparentColor is null)
         {
-            if (header.BitDepth == 16)
+            if (bitDepth == 16)
             {
                 Rgb48 rgb48 = default;
                 int o = 0;
-                for (nuint x = pixelOffset; x < (uint)header.Width; x += increment, o += bytesPerPixel)
+                for (nuint x = offset; x < frameControl.XMax; x += increment, o += bytesPerPixel)
                 {
                     rgb48.R = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, bytesPerSample));
                     rgb48.G = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + bytesPerSample, bytesPerSample));
@@ -395,11 +264,19 @@ internal static class PngScanlineProcessor
                     Unsafe.Add(ref rowSpanRef, x) = pixel;
                 }
             }
+            else if (pixelOffset == 0 && increment == 1)
+            {
+                PixelOperations<TPixel>.Instance.FromRgb24Bytes(
+                    configuration,
+                    scanlineSpan[..(int)(frameControl.Width * bytesPerPixel)],
+                    rowSpan.Slice((int)frameControl.XOffset, (int)frameControl.Width),
+                    (int)frameControl.Width);
+            }
             else
             {
                 Rgb24 rgb = default;
                 int o = 0;
-                for (nuint x = pixelOffset; x < (uint)header.Width; x += increment, o += bytesPerPixel)
+                for (nuint x = offset; x < frameControl.XMax; x += increment, o += bytesPerPixel)
                 {
                     rgb.R = Unsafe.Add(ref scanlineSpanRef, (uint)o);
                     rgb.G = Unsafe.Add(ref scanlineSpanRef, (uint)(o + bytesPerSample));
@@ -413,14 +290,14 @@ internal static class PngScanlineProcessor
             return;
         }
 
-        if (header.BitDepth == 16)
+        if (bitDepth == 16)
         {
             Rgb48 transparent = transparentColor.Value.ToPixel<Rgb48>();
 
             Rgb48 rgb48 = default;
             Rgba64 rgba64 = default;
             int o = 0;
-            for (nuint x = pixelOffset; x < (uint)header.Width; x += increment, o += bytesPerPixel)
+            for (nuint x = offset; x < frameControl.XMax; x += increment, o += bytesPerPixel)
             {
                 rgb48.R = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, bytesPerSample));
                 rgb48.G = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + bytesPerSample, bytesPerSample));
@@ -439,7 +316,7 @@ internal static class PngScanlineProcessor
 
             Rgba32 rgba = default;
             int o = 0;
-            for (nuint x = pixelOffset; x < (uint)header.Width; x += increment, o += bytesPerPixel)
+            for (nuint x = offset; x < frameControl.XMax; x += increment, o += bytesPerPixel)
             {
                 rgba.R = Unsafe.Add(ref scanlineSpanRef, (uint)o);
                 rgba.G = Unsafe.Add(ref scanlineSpanRef, (uint)(o + bytesPerSample));
@@ -454,39 +331,28 @@ internal static class PngScanlineProcessor
 
     public static void ProcessRgbaScanline<TPixel>(
         Configuration configuration,
-        in PngHeader header,
+        int bitDepth,
+        in FrameControl frameControl,
         ReadOnlySpan<byte> scanlineSpan,
         Span<TPixel> rowSpan,
         int bytesPerPixel,
         int bytesPerSample)
-        where TPixel : unmanaged, IPixel<TPixel>
-    {
-        TPixel pixel = default;
-        ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
-
-        if (header.BitDepth == 16)
-        {
-            Rgba64 rgba64 = default;
-            int o = 0;
-            for (nuint x = 0; x < (uint)header.Width; x++, o += bytesPerPixel)
-            {
-                rgba64.R = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, bytesPerSample));
-                rgba64.G = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + bytesPerSample, bytesPerSample));
-                rgba64.B = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + (2 * bytesPerSample), bytesPerSample));
-                rgba64.A = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + (3 * bytesPerSample), bytesPerSample));
-
-                pixel.FromRgba64(rgba64);
-                Unsafe.Add(ref rowSpanRef, x) = pixel;
-            }
-        }
-        else
-        {
-            PixelOperations<TPixel>.Instance.FromRgba32Bytes(configuration, scanlineSpan, rowSpan, header.Width);
-        }
-    }
+       where TPixel : unmanaged, IPixel<TPixel> =>
+       ProcessInterlacedRgbaScanline(
+           configuration,
+           bitDepth,
+           frameControl,
+           scanlineSpan,
+           rowSpan,
+           0,
+           1,
+           bytesPerPixel,
+           bytesPerSample);
 
     public static void ProcessInterlacedRgbaScanline<TPixel>(
-        in PngHeader header,
+        Configuration configuration,
+        int bitDepth,
+        in FrameControl frameControl,
         ReadOnlySpan<byte> scanlineSpan,
         Span<TPixel> rowSpan,
         uint pixelOffset,
@@ -495,15 +361,15 @@ internal static class PngScanlineProcessor
         int bytesPerSample)
         where TPixel : unmanaged, IPixel<TPixel>
     {
+        uint offset = pixelOffset + frameControl.XOffset;
         TPixel pixel = default;
-        ref byte scanlineSpanRef = ref MemoryMarshal.GetReference(scanlineSpan);
         ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
 
-        if (header.BitDepth == 16)
+        if (bitDepth == 16)
         {
             Rgba64 rgba64 = default;
             int o = 0;
-            for (nuint x = pixelOffset; x < (uint)header.Width; x += increment, o += bytesPerPixel)
+            for (nuint x = offset; x < frameControl.XMax; x += increment, o += bytesPerPixel)
             {
                 rgba64.R = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o, bytesPerSample));
                 rgba64.G = BinaryPrimitives.ReadUInt16BigEndian(scanlineSpan.Slice(o + bytesPerSample, bytesPerSample));
@@ -514,11 +380,20 @@ internal static class PngScanlineProcessor
                 Unsafe.Add(ref rowSpanRef, x) = pixel;
             }
         }
+        else if (pixelOffset == 0 && increment == 1)
+        {
+            PixelOperations<TPixel>.Instance.FromRgba32Bytes(
+                configuration,
+                scanlineSpan[..(int)(frameControl.Width * bytesPerPixel)],
+                rowSpan.Slice((int)frameControl.XOffset, (int)frameControl.Width),
+                (int)frameControl.Width);
+        }
         else
         {
+            ref byte scanlineSpanRef = ref MemoryMarshal.GetReference(scanlineSpan);
             Rgba32 rgba = default;
             int o = 0;
-            for (nuint x = pixelOffset; x < (uint)header.Width; x += increment, o += bytesPerPixel)
+            for (nuint x = offset; x < frameControl.XMax; x += increment, o += bytesPerPixel)
             {
                 rgba.R = Unsafe.Add(ref scanlineSpanRef, (uint)o);
                 rgba.G = Unsafe.Add(ref scanlineSpanRef, (uint)(o + bytesPerSample));

src/ImageSharp/Formats/Png/PngThrowHelper.cs

@@ -2,6 +2,7 @@
 // Licensed under the Six Labors Split License.
 
 using System.Diagnostics.CodeAnalysis;
+using System.Runtime.CompilerServices;
 
 namespace SixLabors.ImageSharp.Formats.Png;
 
@@ -12,13 +13,22 @@ internal static class PngThrowHelper
         => throw new InvalidImageContentException(errorMessage, innerException);
 
     [DoesNotReturn]
-    public static void ThrowNoHeader() => throw new InvalidImageContentException("PNG Image does not contain a header chunk");
+    public static void ThrowInvalidHeader() => throw new InvalidImageContentException("PNG Image must contain a header chunk and it must be located before any other chunks.");
 
     [DoesNotReturn]
-    public static void ThrowNoData() => throw new InvalidImageContentException("PNG Image does not contain a data chunk");
+    public static void ThrowNoData() => throw new InvalidImageContentException("PNG Image does not contain a data chunk.");
 
     [DoesNotReturn]
-    public static void ThrowMissingPalette() => throw new InvalidImageContentException("PNG Image does not contain a palette chunk");
+    public static void ThrowMissingDefaultData() => throw new InvalidImageContentException("APNG Image does not contain a default data chunk.");
+
+    [DoesNotReturn]
+    public static void ThrowInvalidAnimationControl() => throw new InvalidImageContentException("APNG Image must contain a acTL chunk and it must be located before any IDAT and fdAT chunks.");
+
+    [DoesNotReturn]
+    public static void ThrowMissingFrameControl() => throw new InvalidImageContentException("One of APNG Image's frames do not have a frame control chunk.");
+
+    [DoesNotReturn]
+    public static void ThrowMissingPalette() => throw new InvalidImageContentException("PNG Image does not contain a palette chunk.");
 
     [DoesNotReturn]
     public static void ThrowInvalidChunkType() => throw new InvalidImageContentException("Invalid PNG data.");
@@ -30,7 +40,15 @@ internal static class PngThrowHelper
     public static void ThrowInvalidChunkCrc(string chunkTypeName) => throw new InvalidImageContentException($"CRC Error. PNG {chunkTypeName} chunk is corrupt!");
 
     [DoesNotReturn]
-    public static void ThrowNotSupportedColor() => throw new NotSupportedException("Unsupported PNG color type");
+    public static void ThrowInvalidParameter(object value, string message, [CallerArgumentExpression(nameof(value))] string name = "")
+        => throw new NotSupportedException($"Invalid {name}. {message}. Was '{value}'.");
+
+    [DoesNotReturn]
+    public static void ThrowInvalidParameter(object value1, object value2, string message, [CallerArgumentExpression(nameof(value1))] string name1 = "", [CallerArgumentExpression(nameof(value1))] string name2 = "")
+        => throw new NotSupportedException($"Invalid {name1} or {name2}. {message}. Was '{value1}' and '{value2}'.");
+
+    [DoesNotReturn]
+    public static void ThrowNotSupportedColor() => throw new NotSupportedException("Unsupported PNG color type.");
 
     [DoesNotReturn]
     public static void ThrowUnknownFilter() => throw new InvalidImageContentException("Unknown filter type.");

src/ImageSharp/ImageFrameCollection{TPixel}.cs

@@ -2,7 +2,6 @@
 // Licensed under the Six Labors Split License.
 
 using System.Collections;
-using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 

src/ImageSharp/Primitives/Rational.cs

@@ -70,7 +70,7 @@ public readonly struct Rational : IEquatable<Rational>
     /// <param name="bestPrecision">Whether to use the best possible precision when parsing the value.</param>
     public Rational(double value, bool bestPrecision)
     {
-        var rational = LongRational.FromDouble(Math.Abs(value), bestPrecision);
+        LongRational rational = LongRational.FromDouble(Math.Abs(value), bestPrecision);
 
         this.Numerator = (uint)rational.Numerator;
         this.Denominator = (uint)rational.Denominator;
@@ -109,7 +109,7 @@ public readonly struct Rational : IEquatable<Rational>
     /// <returns>
     /// The <see cref="Rational"/>.
     /// </returns>
-    public static Rational FromDouble(double value) => new Rational(value, false);
+    public static Rational FromDouble(double value) => new(value, false);
 
     /// <summary>
     /// Converts the specified <see cref="double"/> to an instance of this type.
@@ -119,24 +119,19 @@ public readonly struct Rational : IEquatable<Rational>
     /// <returns>
     /// The <see cref="Rational"/>.
     /// </returns>
-    public static Rational FromDouble(double value, bool bestPrecision) => new Rational(value, bestPrecision);
+    public static Rational FromDouble(double value, bool bestPrecision) => new(value, bestPrecision);
 
     /// <inheritdoc/>
     public override bool Equals(object? obj) => obj is Rational other && this.Equals(other);
 
     /// <inheritdoc/>
     public bool Equals(Rational other)
-    {
-        var left = new LongRational(this.Numerator, this.Denominator);
-        var right = new LongRational(other.Numerator, other.Denominator);
-
-        return left.Equals(right);
-    }
+        => this.Numerator == other.Numerator && this.Denominator == other.Denominator;
 
     /// <inheritdoc/>
     public override int GetHashCode()
     {
-        var self = new LongRational(this.Numerator, this.Denominator);
+        LongRational self = new(this.Numerator, this.Denominator);
         return self.GetHashCode();
     }
 
@@ -169,7 +164,7 @@ public readonly struct Rational : IEquatable<Rational>
     /// <returns>The <see cref="string"/></returns>
     public string ToString(IFormatProvider provider)
     {
-        var rational = new LongRational(this.Numerator, this.Denominator);
+        LongRational rational = new(this.Numerator, this.Denominator);
         return rational.ToString(provider);
     }
 }

tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs

@@ -7,7 +7,6 @@ using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
-using SixLabors.ImageSharp.Processing.Processors.Quantization;
 using SixLabors.ImageSharp.Tests.TestUtilities;
 using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
 using SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs;
@@ -79,6 +78,18 @@ public partial class PngDecoderTests
         { TestImages.Png.Rgba64Bpp, typeof(Image<Rgba64>) },
     };
 
+    public static readonly string[] MultiFrameTestFiles =
+    {
+        TestImages.Png.APng,
+        TestImages.Png.SplitIDatZeroLength,
+        TestImages.Png.DisposeNone,
+        TestImages.Png.DisposeBackground,
+        TestImages.Png.DisposeBackgroundRegion,
+        TestImages.Png.DisposePreviousFirst,
+        TestImages.Png.DisposeBackgroundBeforeRegion,
+        TestImages.Png.BlendOverMultiple
+    };
+
     [Theory]
     [MemberData(nameof(PixelFormatRange))]
     public void Decode_NonGeneric_CreatesCorrectImageType(string path, Type type)
@@ -107,6 +118,19 @@ public partial class PngDecoderTests
         image.CompareToOriginal(provider, ImageComparer.Exact);
     }
 
+    [Theory]
+    [WithFileCollection(nameof(MultiFrameTestFiles), PixelTypes.Rgba32)]
+    public void Decode_VerifyAllFrames<TPixel>(TestImageProvider<TPixel> provider)
+    where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(PngDecoder.Instance);
+
+        // Some images have many frames, only compare a selection of them.
+        static bool Predicate(int i, int _) => i <= 8 || i % 8 == 0;
+        image.DebugSaveMultiFrame(provider, predicate: Predicate);
+        image.CompareToReferenceOutputMultiFrame(provider, ImageComparer.Exact, predicate: Predicate);
+    }
+
     [Theory]
     [WithFile(TestImages.Png.Splash, PixelTypes.Rgba32)]
     public void PngDecoder_Decode_Resize<TPixel>(TestImageProvider<TPixel> provider)

tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs

@@ -442,6 +442,40 @@ public partial class PngEncoderTests
         });
     }
 
+    [Theory]
+    [WithFile(TestImages.Png.APng, PixelTypes.Rgba32)]
+    public void Encode_APng<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(PngDecoder.Instance);
+        using MemoryStream memStream = new();
+        image.Save(memStream, PngEncoder);
+        memStream.Position = 0;
+
+        image.DebugSave(provider: provider, encoder: PngEncoder, null, false);
+
+        using Image<Rgba32> output = Image.Load<Rgba32>(memStream);
+        ImageComparer.Exact.VerifySimilarity(output, image);
+
+        Assert.Equal(5, image.Frames.Count);
+        Assert.Equal(image.Frames.Count, output.Frames.Count);
+
+        PngMetadata originalMetadata = image.Metadata.GetPngMetadata();
+        PngMetadata outputMetadata = output.Metadata.GetPngMetadata();
+
+        Assert.Equal(originalMetadata.RepeatCount, outputMetadata.RepeatCount);
+
+        for (int i = 0; i < image.Frames.Count; i++)
+        {
+            PngFrameMetadata originalFrameMetadata = image.Frames[i].Metadata.GetPngFrameMetadata();
+            PngFrameMetadata outputFrameMetadata = output.Frames[i].Metadata.GetPngFrameMetadata();
+
+            Assert.Equal(originalFrameMetadata.FrameDelay, outputFrameMetadata.FrameDelay);
+            Assert.Equal(originalFrameMetadata.BlendMethod, outputFrameMetadata.BlendMethod);
+            Assert.Equal(originalFrameMetadata.DisposalMethod, outputFrameMetadata.DisposalMethod);
+        }
+    }
+
     [Theory]
     [MemberData(nameof(PngTrnsFiles))]
     public void Encode_PreserveTrns(string imagePath, PngBitDepth pngBitDepth, PngColorType pngColorType)

tests/ImageSharp.Tests/Formats/Png/PngFrameMetadataTests.cs

@@ -0,0 +1,35 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Png;
+
+namespace SixLabors.ImageSharp.Tests.Formats.Png;
+
+[Trait("Format", "Png")]
+public class PngFrameMetadataTests
+{
+    [Fact]
+    public void CloneIsDeep()
+    {
+        PngFrameMetadata meta = new()
+        {
+            FrameDelay = new(1, 0),
+            DisposalMethod = PngDisposalMethod.Background,
+            BlendMethod = PngBlendMethod.Over,
+        };
+
+        PngFrameMetadata clone = (PngFrameMetadata)meta.DeepClone();
+
+        Assert.True(meta.FrameDelay.Equals(clone.FrameDelay));
+        Assert.True(meta.DisposalMethod.Equals(clone.DisposalMethod));
+        Assert.True(meta.BlendMethod.Equals(clone.BlendMethod));
+
+        clone.FrameDelay = new(2, 1);
+        clone.DisposalMethod = PngDisposalMethod.Previous;
+        clone.BlendMethod = PngBlendMethod.Source;
+
+        Assert.False(meta.FrameDelay.Equals(clone.FrameDelay));
+        Assert.False(meta.DisposalMethod.Equals(clone.DisposalMethod));
+        Assert.False(meta.BlendMethod.Equals(clone.BlendMethod));
+    }
+}

tests/ImageSharp.Tests/Formats/Png/PngMetadataTests.cs

@@ -3,6 +3,7 @@
 
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Png;
+using SixLabors.ImageSharp.Formats.Png.Chunks;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.PixelFormats;
@@ -30,15 +31,25 @@ public class PngMetadataTests
             ColorType = PngColorType.GrayscaleWithAlpha,
             InterlaceMethod = PngInterlaceMode.Adam7,
             Gamma = 2,
-            TextData = new List<PngTextData> { new PngTextData("name", "value", "foo", "bar") }
+            TextData = new List<PngTextData> { new PngTextData("name", "value", "foo", "bar") },
+            RepeatCount = 123
         };
 
         PngMetadata clone = (PngMetadata)meta.DeepClone();
 
+        Assert.True(meta.BitDepth == clone.BitDepth);
+        Assert.True(meta.ColorType == clone.ColorType);
+        Assert.True(meta.InterlaceMethod == clone.InterlaceMethod);
+        Assert.True(meta.Gamma.Equals(clone.Gamma));
+        Assert.False(meta.TextData.Equals(clone.TextData));
+        Assert.True(meta.TextData.SequenceEqual(clone.TextData));
+        Assert.True(meta.RepeatCount == clone.RepeatCount);
+
         clone.BitDepth = PngBitDepth.Bit2;
         clone.ColorType = PngColorType.Palette;
         clone.InterlaceMethod = PngInterlaceMode.None;
         clone.Gamma = 1;
+        clone.RepeatCount = 321;
 
         Assert.False(meta.BitDepth == clone.BitDepth);
         Assert.False(meta.ColorType == clone.ColorType);
@@ -46,6 +57,7 @@ public class PngMetadataTests
         Assert.False(meta.Gamma.Equals(clone.Gamma));
         Assert.False(meta.TextData.Equals(clone.TextData));
         Assert.True(meta.TextData.SequenceEqual(clone.TextData));
+        Assert.False(meta.RepeatCount == clone.RepeatCount);
     }
 
     [Theory]

tests/ImageSharp.Tests/Formats/Png/PngTextDataTests.cs

@@ -1,7 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-using SixLabors.ImageSharp.Formats.Png;
+using SixLabors.ImageSharp.Formats.Png.Chunks;
 
 namespace SixLabors.ImageSharp.Tests.Formats.Png;
 

tests/ImageSharp.Tests/TestImages.cs

@@ -62,6 +62,17 @@ public static class TestImages
         public const string TestPattern31x31HalfTransparent = "Png/testpattern31x31-halftransparent.png";
         public const string XmpColorPalette = "Png/xmp-colorpalette.png";
 
+        // Animated
+        // https://philip.html5.org/tests/apng/tests.html
+        public const string APng = "Png/animated/apng.png";
+        public const string SplitIDatZeroLength = "Png/animated/4-split-idat-zero-length.png";
+        public const string DisposeNone = "Png/animated/7-dispose-none.png";
+        public const string DisposeBackground = "Png/animated/8-dispose-background.png";
+        public const string DisposeBackgroundBeforeRegion = "Png/animated/14-dispose-background-before-region.png";
+        public const string DisposeBackgroundRegion = "Png/animated/15-dispose-background-region.png";
+        public const string DisposePreviousFirst = "Png/animated/12-dispose-prev-first.png";
+        public const string BlendOverMultiple = "Png/animated/21-blend-over-multiple.png";
+
         // Filtered test images from http://www.schaik.com/pngsuite/pngsuite_fil_png.html
         public const string Filter0 = "Png/filter0.png";
         public const string SubFilter3BytesPerPixel = "Png/filter1.png";

tests/ImageSharp.Tests/TestUtilities/ImagingTestCaseUtility.cs

@@ -179,7 +179,7 @@ public class ImagingTestCaseUtility
         return path;
     }
 
-    public IEnumerable<string> GetTestOutputFileNamesMultiFrame(
+    public IEnumerable<(int Index, string FileName)> GetTestOutputFileNamesMultiFrame(
         int frameCount,
         string extension = null,
         object testOutputDetails = null,
@@ -201,11 +201,11 @@ public class ImagingTestCaseUtility
                 continue;
             }
 
-            yield return $"{baseDir}/{i:D2}.{extension}";
+            yield return (i, $"{baseDir}/{i:D2}.{extension}");
         }
     }
 
-    public string[] SaveTestOutputFileMultiFrame<TPixel>(
+    public (int Index, string FileName)[] SaveTestOutputFileMultiFrame<TPixel>(
         Image<TPixel> image,
         string extension = "png",
         IImageEncoder encoder = null,
@@ -216,27 +216,17 @@ public class ImagingTestCaseUtility
     {
         encoder ??= TestEnvironment.GetReferenceEncoder($"foo.{extension}");
 
-        string[] files = this.GetTestOutputFileNamesMultiFrame(
+        (int Index, string FileName)[] files = this.GetTestOutputFileNamesMultiFrame(
             image.Frames.Count,
             extension,
             testOutputDetails,
             appendPixelTypeToFileName,
             predicate: predicate).ToArray();
 
-        for (int i = 0; i < image.Frames.Count; i++)
+        foreach ((int Index, string FileName) file in files)
         {
-            if (predicate != null && !predicate(i, image.Frames.Count))
-            {
-                continue;
-            }
-
-            if (i >= files.Length)
-            {
-                break;
-            }
-
-            using Image<TPixel> frameImage = image.Frames.CloneFrame(i);
-            string filePath = files[i];
+            using Image<TPixel> frameImage = image.Frames.CloneFrame(file.Index);
+            string filePath = file.FileName;
             using FileStream stream = File.OpenWrite(filePath);
             frameImage.Save(stream, encoder);
         }
@@ -252,14 +242,14 @@ public class ImagingTestCaseUtility
         => TestEnvironment.GetReferenceOutputFileName(
             this.GetTestOutputFileName(extension, testOutputDetails, appendPixelTypeToFileName, appendSourceFileOrDescription));
 
-    public string[] GetReferenceOutputFileNamesMultiFrame(
+    public (int Index, string FileName)[] GetReferenceOutputFileNamesMultiFrame(
         int frameCount,
         string extension,
         object testOutputDetails,
         bool appendPixelTypeToFileName = true,
         Func<int, int, bool> predicate = null)
         => this.GetTestOutputFileNamesMultiFrame(frameCount, extension, testOutputDetails, appendPixelTypeToFileName, predicate: predicate)
-        .Select(TestEnvironment.GetReferenceOutputFileName).ToArray();
+        .Select(x => (x.Index, TestEnvironment.GetReferenceOutputFileName(x.FileName))).ToArray();
 
     internal void Init(string typeName, string methodName, string outputSubfolderName)
     {

tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs

@@ -336,7 +336,7 @@ public static class TestImageExtensions
         Func<int, int, bool> predicate = null)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        string[] frameFiles = provider.Utility.GetReferenceOutputFileNamesMultiFrame(
+        (int Index, string FileName)[] frameFiles = provider.Utility.GetReferenceOutputFileNamesMultiFrame(
             frameCount,
             extension,
             testOutputDetails,
@@ -345,10 +345,11 @@ public static class TestImageExtensions
 
         List<Image<TPixel>> temporaryFrameImages = new();
 
-        IImageDecoder decoder = TestEnvironment.GetReferenceDecoder(frameFiles[0]);
+        IImageDecoder decoder = TestEnvironment.GetReferenceDecoder(frameFiles[0].FileName);
 
-        foreach (string path in frameFiles)
+        for (int i = 0; i < frameFiles.Length; i++)
         {
+            string path = frameFiles[i].FileName;
             if (!File.Exists(path))
             {
                 throw new FileNotFoundException("Reference output file missing: " + path);
@@ -536,10 +537,8 @@ public static class TestImageExtensions
         referenceDecoder ??= TestEnvironment.GetReferenceDecoder(path);
 
         using MemoryStream stream = new(testFile.Bytes);
-        using (Image<TPixel> original = referenceDecoder.Decode<TPixel>(referenceDecoderOptions ?? DecoderOptions.Default, stream))
-        {
-            comparer.VerifySimilarity(original, image);
-        }
+        using Image<TPixel> original = referenceDecoder.Decode<TPixel>(referenceDecoderOptions ?? DecoderOptions.Default, stream);
+        comparer.VerifySimilarity(original, image);
 
         return image;
     }
@@ -562,10 +561,8 @@ public static class TestImageExtensions
         referenceDecoder ??= TestEnvironment.GetReferenceDecoder(path);
 
         using MemoryStream stream = new(testFile.Bytes);
-        using (Image<TPixel> original = referenceDecoder.Decode<TPixel>(DecoderOptions.Default, stream))
-        {
-            comparer.VerifySimilarity(original, image);
-        }
+        using Image<TPixel> original = referenceDecoder.Decode<TPixel>(DecoderOptions.Default, stream);
+        comparer.VerifySimilarity(original, image);
 
         return image;
     }

tests/ImageSharp.Tests/TestUtilities/Tests/TestImageProviderTests.cs

@@ -200,13 +200,13 @@ public class TestImageProviderTests
         where TPixel : unmanaged, IPixel<TPixel>
     {
         using Image<TPixel> image = provider.GetImage();
-        string[] files = provider.Utility.SaveTestOutputFileMultiFrame(image);
+        (int Index, string FileName)[] files = provider.Utility.SaveTestOutputFileMultiFrame(image);
 
         Assert.True(files.Length > 2);
-        foreach (string path in files)
+        foreach ((int Index, string FileName) file in files)
         {
-            this.Output.WriteLine(path);
-            Assert.True(File.Exists(path));
+            this.Output.WriteLine(file.FileName);
+            Assert.True(File.Exists(file.FileName));
         }
     }
 

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_12-dispose-prev-first.png/00.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:cb2d35aad4996610f754a166ae30906b49f98979c14a71143f99911e465755a8
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_12-dispose-prev-first.png/01.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6ea3f66d081c07c2eeefccae69084dbd0eabb824ace03280cb58a39b818de556
+size 102

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_14-dispose-background-before-region.png/00.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:cb2d35aad4996610f754a166ae30906b49f98979c14a71143f99911e465755a8
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_14-dispose-background-before-region.png/01.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6ea3f66d081c07c2eeefccae69084dbd0eabb824ace03280cb58a39b818de556
+size 102

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_15-dispose-background-region.png/00.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:02c81691db45508be3fe8c6051e8b09937eaa347f332f1097026e00a0e084b38
+size 99

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_15-dispose-background-region.png/01.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:02c81691db45508be3fe8c6051e8b09937eaa347f332f1097026e00a0e084b38
+size 99

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_15-dispose-background-region.png/02.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:e1322aa335ad845cacfa20266bc0ffc31db117376373c15bcdb222abcf4b8f83
+size 113

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/00.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:cb2d35aad4996610f754a166ae30906b49f98979c14a71143f99911e465755a8
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/01.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/02.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/03.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/04.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/05.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/06.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/07.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/08.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/104.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/112.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/120.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/128.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/16.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/24.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/32.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:11558f68c1a1c3ad32832c7fc91ae093b7351bef68222e4d28ea44f6f2d6511a
+size 89

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_21-blend-over-multiple.png/40.png

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