Add support for encoding packed bits compressed tiff's

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

@@ -4,6 +4,7 @@
 using System;
 using System.IO;
 using System.IO.Compression;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Tiff.Compression

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

@@ -3,6 +3,7 @@
 
 using System;
 using System.IO;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Tiff.Compression

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

@@ -3,6 +3,7 @@
 
 using System;
 using System.IO;
+
 using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Tiff.Compression

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

@@ -3,6 +3,8 @@
 
 using System;
 using System.IO;
+
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Tiff.Compression

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

@@ -4,6 +4,8 @@
 using System;
 using System.Buffers;
 using System.IO;
+
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Tiff.Compression

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

@@ -0,0 +1,128 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+
+namespace SixLabors.ImageSharp.Formats.Tiff.Compression
+{
+    /// <summary>
+    /// Pack Bits compression for tiff images. See Tiff Spec v6, section 9.
+    /// </summary>
+    internal static class PackBitsWriter
+    {
+        public static int PackBits(Span<byte> rowSpan, Span<byte> compressedRowSpan)
+        {
+            int maxRunLength = 127;
+            int posInRowSpan = 0;
+            int bytesWritten = 0;
+            int literalRunLength = 0;
+
+            while (posInRowSpan < rowSpan.Length)
+            {
+                var useReplicateRun = IsReplicateRun(rowSpan, posInRowSpan);
+                if (useReplicateRun)
+                {
+                    if (literalRunLength > 0)
+                    {
+                        WriteLiteralRun(rowSpan, posInRowSpan, literalRunLength, compressedRowSpan, bytesWritten);
+                        bytesWritten += literalRunLength + 1;
+                    }
+
+                    // Write a run with the same bytes.
+                    var runLength = FindRunLength(rowSpan, posInRowSpan, maxRunLength);
+                    WriteRun(rowSpan, posInRowSpan, runLength, compressedRowSpan, bytesWritten);
+
+                    bytesWritten += 2;
+                    literalRunLength = 0;
+                    posInRowSpan += runLength;
+                    continue;
+                }
+
+                literalRunLength++;
+                posInRowSpan++;
+
+                if (literalRunLength >= maxRunLength)
+                {
+                    WriteLiteralRun(rowSpan, posInRowSpan, literalRunLength, compressedRowSpan, bytesWritten);
+                    bytesWritten += literalRunLength + 1;
+                    literalRunLength = 0;
+                }
+            }
+
+            if (literalRunLength > 0)
+            {
+                WriteLiteralRun(rowSpan, posInRowSpan, literalRunLength, compressedRowSpan, bytesWritten);
+                bytesWritten += literalRunLength + 1;
+            }
+
+            return bytesWritten;
+        }
+
+        private static void WriteLiteralRun(Span<byte> rowSpan, int end, int literalRunLength, Span<byte> compressedRowSpan, int compressedRowPos)
+        {
+            DebugGuard.MustBeLessThanOrEqualTo(literalRunLength, 127, nameof(literalRunLength));
+
+            int literalRunStart = end - literalRunLength;
+            sbyte runLength = (sbyte)(literalRunLength - 1);
+            compressedRowSpan[compressedRowPos] = (byte)runLength;
+            rowSpan.Slice(literalRunStart, literalRunLength).CopyTo(compressedRowSpan.Slice(compressedRowPos + 1));
+        }
+
+        private static void WriteRun(Span<byte> rowSpan, int start, int runLength, Span<byte> compressedRowSpan, int compressedRowPos)
+        {
+            DebugGuard.MustBeLessThanOrEqualTo(runLength, 127, nameof(runLength));
+
+            sbyte headerByte = (sbyte)(-runLength + 1);
+            compressedRowSpan[compressedRowPos] = (byte)headerByte;
+            compressedRowSpan[compressedRowPos + 1] = rowSpan[start];
+        }
+
+        private static bool IsReplicateRun(Span<byte> rowSpan, int startPos)
+        {
+            // We consider run which has at least 3 same consecutive bytes a candidate for a run.
+            var startByte = rowSpan[startPos];
+            int count = 0;
+            for (int i = startPos + 1; i < rowSpan.Length; i++)
+            {
+                if (rowSpan[i] == startByte)
+                {
+                    count++;
+                    if (count >= 2)
+                    {
+                        return true;
+                    }
+                }
+                else
+                {
+                    break;
+                }
+            }
+
+            return false;
+        }
+
+        private static int FindRunLength(Span<byte> rowSpan, int startPos, int maxRunLength)
+        {
+            var startByte = rowSpan[startPos];
+            int count = 1;
+            for (int i = startPos + 1; i < rowSpan.Length; i++)
+            {
+                if (rowSpan[i] == startByte)
+                {
+                    count++;
+                }
+                else
+                {
+                    break;
+                }
+
+                if (count == maxRunLength)
+                {
+                    break;
+                }
+            }
+
+            return count;
+        }
+    }
+}

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/BlackIsZeroTiffColor.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Numerics;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/PaletteTiffColor.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Numerics;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/RgbPlanarTiffColor.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System.Numerics;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/RgbTiffColor.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Numerics;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/WhiteIsZeroTiffColor.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Numerics;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 

src/ImageSharp/Formats/Tiff/TiffEncoderCompression.cs

@@ -18,6 +18,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// </summary>
         Deflate,
 
+        /// <summary>
+        /// Use PackBits to compression the image data.
+        /// </summary>
+        PackBits,
+
         /// <summary>
         /// Use CCITT T4 1D compression. Note: This is only valid for bi-level images.
         /// </summary>

src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs

@@ -7,6 +7,7 @@ using System.IO;
 using System.Threading;
 
 using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
@@ -166,7 +167,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     imageDataBytes = writer.WriteBiColor(image, this.CompressionType);
                     break;
                 default:
-                    imageDataBytes = writer.WriteRgbImageData(image, this.padding, this.CompressionType);
+                    imageDataBytes = writer.WriteRgb(image, this.padding, this.CompressionType);
                     break;
             }
 
@@ -415,11 +416,21 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 return (ushort)TiffCompression.Deflate;
             }
 
+            if (this.CompressionType == TiffEncoderCompression.PackBits && this.Mode == TiffEncodingMode.Rgb)
+            {
+                return (ushort)TiffCompression.PackBits;
+            }
+
             if (this.CompressionType == TiffEncoderCompression.Deflate && this.Mode == TiffEncodingMode.Gray)
             {
                 return (ushort)TiffCompression.Deflate;
             }
 
+            if (this.CompressionType == TiffEncoderCompression.PackBits && this.Mode == TiffEncodingMode.Gray)
+            {
+                return (ushort)TiffCompression.PackBits;
+            }
+
             if (this.CompressionType == TiffEncoderCompression.Deflate && this.Mode == TiffEncodingMode.ColorPalette)
             {
                 return (ushort)TiffCompression.Deflate;
@@ -430,6 +441,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 return (ushort)TiffCompression.Deflate;
             }
 
+            if (this.CompressionType == TiffEncoderCompression.PackBits && this.Mode == TiffEncodingMode.BiColor)
+            {
+                return (ushort)TiffCompression.PackBits;
+            }
+
             if (this.CompressionType == TiffEncoderCompression.CcittGroup3Fax && this.Mode == TiffEncodingMode.BiColor)
             {
                 return (ushort)TiffCompression.CcittGroup3Fax;

src/ImageSharp/Formats/Tiff/Utils/BitReader.cs

@@ -3,7 +3,7 @@
 
 using System;
 
-namespace SixLabors.ImageSharp.Formats.Tiff
+namespace SixLabors.ImageSharp.Formats.Tiff.Utils
 {
     /// <summary>
     /// Utility class to read a sequence of bits from an array

src/ImageSharp/Formats/Tiff/Utils/SubStream.cs

@@ -4,7 +4,7 @@
 using System;
 using System.IO;
 
-namespace SixLabors.ImageSharp.Formats.Tiff
+namespace SixLabors.ImageSharp.Formats.Tiff.Utils
 {
     /// <summary>
     /// Utility class to encapsulate a sub-portion of another <see cref="Stream"/>.
@@ -173,4 +173,4 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             throw new NotSupportedException();
         }
     }
-}
+}

src/ImageSharp/Formats/Tiff/Utils/TiffLzwDecoder.cs

@@ -7,7 +7,7 @@ using System.IO;
 using SixLabors.ImageSharp.Formats.Gif;
 using SixLabors.ImageSharp.Memory;
 
-namespace SixLabors.ImageSharp.Formats.Tiff
+namespace SixLabors.ImageSharp.Formats.Tiff.Utils
 {
     /// <summary>
     /// Decompresses and decodes data using the dynamic LZW algorithms.

src/ImageSharp/Formats/Tiff/Utils/TiffLzwEncoder.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -6,7 +6,7 @@ using System.Buffers;
 using System.IO;
 using SixLabors.ImageSharp.Formats.Gif;
 
-namespace SixLabors.ImageSharp.Formats.Tiff
+namespace SixLabors.ImageSharp.Formats.Tiff.Utils
 {
     /// <summary>
     /// Encodes and compresses the image data using dynamic Lempel-Ziv compression.
@@ -492,4 +492,4 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             this.isDisposed = true;
         }
     }
-}
+}

src/ImageSharp/Formats/Tiff/Utils/TiffUtils.cs

@@ -4,7 +4,7 @@
 using System;
 using System.IO;
 
-namespace SixLabors.ImageSharp.Formats.Tiff
+namespace SixLabors.ImageSharp.Formats.Tiff.Utils
 {
     /// <summary>
     /// TIFF specific utilities and extension methods.

src/ImageSharp/Formats/Tiff/Utils/TiffWriter.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Buffers;
-using System.Collections.Generic;
 using System.IO;
 using System.Runtime.InteropServices;
 
@@ -17,7 +16,7 @@ using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Dithering;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
-namespace SixLabors.ImageSharp.Formats.Tiff
+namespace SixLabors.ImageSharp.Formats.Tiff.Utils
 {
     /// <summary>
     /// Utility class for writing TIFF data to a <see cref="Stream"/>.
@@ -32,8 +31,6 @@ namespace SixLabors.ImageSharp.Formats.Tiff
 
         private readonly byte[] paddingBytes = new byte[4];
 
-        private readonly List<long> references = new List<long>();
-
         /// <summary>
         /// Initializes a new instance of the <see cref="TiffWriter"/> class.
         /// </summary>
@@ -141,7 +138,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// <param name="padding">The padding bytes for each row.</param>
         /// <param name="compression">The compression to use.</param>
         /// <returns>The number of bytes written.</returns>
-        public int WriteRgbImageData<TPixel>(Image<TPixel> image, int padding, TiffEncoderCompression compression)
+        public int WriteRgb<TPixel>(Image<TPixel> image, int padding, TiffEncoderCompression compression)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             using IManagedByteBuffer row = this.AllocateRow(image.Width, 3, padding);
@@ -151,6 +148,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 return this.WriteDeflateCompressedRgb(image, rowSpan);
             }
 
+            if (compression == TiffEncoderCompression.PackBits)
+            {
+                return this.WriteRgbPackBitsCompressed(image, rowSpan);
+            }
+
             // No compression.
             int bytesWritten = 0;
             for (int y = 0; y < image.Height; y++)
@@ -195,6 +197,35 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             return bytesWritten;
         }
 
+        /// <summary>
+        /// Writes the image data as RGB with packed bits compression to the stream.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel data.</typeparam>
+        /// <param name="image">The image to write to the stream.</param>
+        /// <param name="rowSpan">A Span for a pixel row.</param>
+        /// <returns>The number of bytes written.</returns>
+        private int WriteRgbPackBitsCompressed<TPixel>(Image<TPixel> image, Span<byte> rowSpan)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            // Worst case is that the actual compressed data is larger then the input data. In this case we need 1 additional byte per 127 bytes.
+            int additionalBytes = ((image.Width * 3) / 127) + 1;
+            using IManagedByteBuffer compressedRow = this.memoryAllocator.AllocateManagedByteBuffer((image.Width * 3) + additionalBytes, AllocationOptions.Clean);
+            Span<byte> compressedRowSpan = compressedRow.GetSpan();
+            int bytesWritten = 0;
+
+            for (int y = 0; y < image.Height; y++)
+            {
+                Span<TPixel> pixelRow = image.GetPixelRowSpan(y);
+                PixelOperations<TPixel>.Instance.ToRgb24Bytes(this.configuration, pixelRow, rowSpan, pixelRow.Length);
+                int size = PackBitsWriter.PackBits(rowSpan, compressedRowSpan);
+                this.output.Write(compressedRow.Slice(0, size));
+                bytesWritten += size;
+                compressedRowSpan.Clear();
+            }
+
+            return bytesWritten;
+        }
+
         /// <summary>
         /// Writes the image data as indices into a color map to the stream.
         /// </summary>
@@ -316,6 +347,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 return this.WriteGrayDeflateCompressed(image, rowSpan);
             }
 
+            if (compression == TiffEncoderCompression.PackBits)
+            {
+                return this.WriteGrayPackBitsCompressed(image, rowSpan);
+            }
+
             int bytesWritten = 0;
             for (int y = 0; y < image.Height; y++)
             {
@@ -358,6 +394,35 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             return bytesWritten;
         }
 
+        /// <summary>
+        /// Writes the image data as 8 bit gray to the stream.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel data.</typeparam>
+        /// <param name="image">The image to write to the stream.</param>
+        /// <param name="rowSpan">A span of a row of pixels.</param>
+        /// <returns>The number of bytes written.</returns>
+        private int WriteGrayPackBitsCompressed<TPixel>(Image<TPixel> image, Span<byte> rowSpan)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            // Worst case is that the actual compressed data is larger then the input data. In this case we need 1 additional byte per 127 bytes.
+            int additionalBytes = (image.Width / 127) + 1;
+            using IManagedByteBuffer compressedRow = this.memoryAllocator.AllocateManagedByteBuffer(image.Width + additionalBytes, AllocationOptions.Clean);
+            Span<byte> compressedRowSpan = compressedRow.GetSpan();
+
+            int bytesWritten = 0;
+            for (int y = 0; y < image.Height; y++)
+            {
+                Span<TPixel> pixelRow = image.GetPixelRowSpan(y);
+                PixelOperations<TPixel>.Instance.ToL8Bytes(this.configuration, pixelRow, rowSpan, pixelRow.Length);
+                int size = PackBitsWriter.PackBits(rowSpan, compressedRowSpan);
+                this.output.Write(compressedRow.Slice(0, size));
+                bytesWritten += size;
+                compressedRowSpan.Clear();
+            }
+
+            return bytesWritten;
+        }
+
         /// <summary>
         /// Writes the image data as 1 bit black and white to the stream.
         /// </summary>
@@ -385,6 +450,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 return this.WriteBiColorDeflate(imageBlackWhite, pixelRowAsGraySpan, outputRow);
             }
 
+            if (compression == TiffEncoderCompression.PackBits)
+            {
+                return this.WriteBiColorPackBits(imageBlackWhite, pixelRowAsGraySpan, outputRow);
+            }
+
             if (compression == TiffEncoderCompression.CcittGroup3Fax)
             {
                 var bitWriter = new T4BitWriter(this.memoryAllocator, this.configuration);
@@ -397,6 +467,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 return bitWriter.CompressImage(imageBlackWhite, pixelRowAsGraySpan, this.output);
             }
 
+            // Write image uncompressed.
             int bytesWritten = 0;
             for (int y = 0; y < image.Height; y++)
             {
@@ -479,6 +550,56 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             return bytesWritten;
         }
 
+        /// <summary>
+        /// Writes the image data as 1 bit black and white with pack bits compression to the stream.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel data.</typeparam>
+        /// <param name="image">The image to write to the stream.</param>
+        /// <param name="pixelRowAsGraySpan">A span for converting a pixel row to gray.</param>
+        /// <param name="outputRow">A span which will be used to store the output pixels.</param>
+        /// <returns>The number of bytes written.</returns>
+        public int WriteBiColorPackBits<TPixel>(Image<TPixel> image, Span<L8> pixelRowAsGraySpan, Span<byte> outputRow)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            // Worst case is that the actual compressed data is larger then the input data. In this case we need 1 additional byte per 127 bits.
+            int additionalBytes = (image.Width / 127) + 1;
+            int compressedRowBytes = (image.Width / 8) + additionalBytes;
+            using IManagedByteBuffer compressedRow = this.memoryAllocator.AllocateManagedByteBuffer(compressedRowBytes, AllocationOptions.Clean);
+            Span<byte> compressedRowSpan = compressedRow.GetSpan();
+
+            int bytesWritten = 0;
+            for (int y = 0; y < image.Height; y++)
+            {
+                int bitIndex = 0;
+                int byteIndex = 0;
+                Span<TPixel> pixelRow = image.GetPixelRowSpan(y);
+                PixelOperations<TPixel>.Instance.ToL8(this.configuration, pixelRow, pixelRowAsGraySpan);
+                for (int x = 0; x < pixelRow.Length; x++)
+                {
+                    int shift = 7 - bitIndex;
+                    if (pixelRowAsGraySpan[x].PackedValue == 255)
+                    {
+                        outputRow[byteIndex] |= (byte)(1 << shift);
+                    }
+
+                    bitIndex++;
+                    if (bitIndex == 8)
+                    {
+                        byteIndex++;
+                        bitIndex = 0;
+                    }
+                }
+
+                var size = PackBitsWriter.PackBits(outputRow, compressedRowSpan);
+                this.output.Write(compressedRowSpan);
+                bytesWritten += size;
+
+                outputRow.Clear();
+            }
+
+            return bytesWritten;
+        }
+
         private IManagedByteBuffer AllocateRow(int width, int bytesPerPixel, int padding) => this.memoryAllocator.AllocatePaddedPixelRowBuffer(width, bytesPerPixel, padding);
 
         /// <summary>

tests/ImageSharp.Tests/Formats/Tiff/Compression/DeflateTiffCompressionTests.cs

@@ -6,7 +6,7 @@ using SixLabors.ImageSharp.Formats.Png.Zlib;
 using SixLabors.ImageSharp.Formats.Tiff.Compression;
 using Xunit;
 
-namespace SixLabors.ImageSharp.Tests.Formats.Tiff
+namespace SixLabors.ImageSharp.Tests.Formats.Tiff.Compression
 {
     [Trait("Category", "Tiff")]
     public class DeflateTiffCompressionTests

tests/ImageSharp.Tests/Formats/Tiff/Compression/LzwTiffCompressionTests.cs

@@ -2,11 +2,13 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System.IO;
-using SixLabors.ImageSharp.Formats.Tiff;
+
 using SixLabors.ImageSharp.Formats.Tiff.Compression;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
+
 using Xunit;
 
-namespace SixLabors.ImageSharp.Tests.Formats.Tiff
+namespace SixLabors.ImageSharp.Tests.Formats.Tiff.Compression
 {
     [Trait("Category", "Tiff")]
     public class LzwTiffCompressionTests
@@ -19,14 +21,12 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         [InlineData(new byte[] { 1, 2, 42, 53, 42, 53, 42, 53, 42, 53, 42, 53, 3, 4 })] // Repeated sequence
         public void Decompress_ReadsData(byte[] data)
         {
-            using (Stream stream = CreateCompressedStream(data))
-            {
-                var buffer = new byte[data.Length];
+            using Stream stream = CreateCompressedStream(data);
+            var buffer = new byte[data.Length];
 
-                new LzwTiffCompression(Configuration.Default.MemoryAllocator).Decompress(stream, (int)stream.Length, buffer);
+            new LzwTiffCompression(Configuration.Default.MemoryAllocator).Decompress(stream, (int)stream.Length, buffer);
 
-                Assert.Equal(data, buffer);
-            }
+            Assert.Equal(data, buffer);
         }
 
         private static Stream CreateCompressedStream(byte[] data)

tests/ImageSharp.Tests/Formats/Tiff/Compression/NoneTiffCompressionTests.cs

@@ -5,7 +5,7 @@ using System.IO;
 using SixLabors.ImageSharp.Formats.Tiff.Compression;
 using Xunit;
 
-namespace SixLabors.ImageSharp.Tests.Formats.Tiff
+namespace SixLabors.ImageSharp.Tests.Formats.Tiff.Compression
 {
     [Trait("Category", "Tiff")]
     public class NoneTiffCompressionTests

tests/ImageSharp.Tests/Formats/Tiff/Compression/PackBitsTiffCompressionTests.cs

@@ -1,13 +1,15 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.IO;
-using SixLabors.ImageSharp.Formats.Tiff;
+
 using SixLabors.ImageSharp.Formats.Tiff.Compression;
 using SixLabors.ImageSharp.Memory;
+
 using Xunit;
 
-namespace SixLabors.ImageSharp.Tests.Formats.Tiff.Formats.Tiff
+namespace SixLabors.ImageSharp.Tests.Formats.Tiff.Compression
 {
     [Trait("Category", "Tiff")]
     public class PackBitsTiffCompressionTests
@@ -20,16 +22,32 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff.Formats.Tiff
         [InlineData(new byte[] { 0xFE, 0x2A }, new byte[] { 0x2A, 0x2A, 0x2A })] // Repeat three bytes
         [InlineData(new byte[] { 0x80 }, new byte[] { })] // Read a 'No operation' byte
         [InlineData(new byte[] { 0x01, 0x15, 0x32, 0x80, 0xFF, 0xA2 }, new byte[] { 0x15, 0x32, 0xA2, 0xA2 })] // Read two bytes, nop, repeat two bytes
-        [InlineData(new byte[] { 0xFE, 0xAA, 0x02, 0x80, 0x00, 0x2A, 0xFD, 0xAA, 0x03, 0x80, 0x00, 0x2A, 0x22, 0xF7, 0xAA },
-                new byte[] { 0xAA, 0xAA, 0xAA, 0x80, 0x00, 0x2A, 0xAA, 0xAA, 0xAA, 0xAA, 0x80, 0x00, 0x2A, 0x22, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA })] // Apple PackBits sample
+        [InlineData(new byte[] { 0xFE, 0xAA, 0x02, 0x80, 0x00, 0x2A, 0xFD, 0xAA, 0x03, 0x80, 0x00, 0x2A, 0x22, 0xF7, 0xAA }, new byte[] { 0xAA, 0xAA, 0xAA, 0x80, 0x00, 0x2A, 0xAA, 0xAA, 0xAA, 0xAA, 0x80, 0x00, 0x2A, 0x22, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA })] // Apple PackBits sample
         public void Decompress_ReadsData(byte[] inputData, byte[] expectedResult)
         {
             Stream stream = new MemoryStream(inputData);
-            byte[] buffer = new byte[expectedResult.Length];
+            var buffer = new byte[expectedResult.Length];
 
             new PackBitsTiffCompression(new ArrayPoolMemoryAllocator()).Decompress(stream, inputData.Length, buffer);
 
             Assert.Equal(expectedResult, buffer);
         }
+
+        [Theory]
+        [InlineData(new byte[] { 0xAA, 0xAA, 0xAA, 0xCD, 0xBB, 0xBB, 0xBB, 0xBB }, new byte[] { 0xFE, 0xAA, 0x02, 0xCD, 0xFD, 0xBB })] // A run of 3, then one byte, followed by a run of 4.
+        [InlineData(new byte[] { 0xAB, 0xCD, 0xEF }, new byte[] { 0x04, 0xAB, 0xCD, 0xEF })] // all bytes are different.
+        [InlineData(new byte[] { 0xAA, 0xAA, 0xAA, 0x80, 0x00, 0x2A, 0xAA, 0xAA, 0xAA, 0xAA, 0x80, 0x00, 0x2A, 0x22, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA }, new byte[] { 0xFE, 0xAA, 0x02, 0x80, 0x00, 0x2A, 0xFD, 0xAA, 0x03, 0x80, 0x00, 0x2A, 0x22, 0xF7, 0xAA })] // Apple PackBits sample
+        public void Compress_Works(byte[] inputData, byte[] expectedResult)
+        {
+            // arrange
+            Span<byte> input = inputData.AsSpan();
+            var compressed = new byte[expectedResult.Length];
+
+            // act
+            PackBitsWriter.PackBits(input, compressed);
+
+            // assert
+            Assert.Equal(expectedResult, compressed);
+        }
     }
 }

tests/ImageSharp.Tests/Formats/Tiff/TiffEncoderHeaderTests.cs

@@ -2,8 +2,11 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System.IO;
+
 using SixLabors.ImageSharp.Formats.Tiff;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
+
 using Xunit;
 
 namespace SixLabors.ImageSharp.Tests.Formats.Tiff

tests/ImageSharp.Tests/Formats/Tiff/TiffEncoderTests.cs

@@ -47,25 +47,35 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         }
 
         [Theory]
-        [WithFile(TestImages.Tiff.RgbUncompressed, PixelTypes.Rgba32)]
+        [WithFile(TestImages.Tiff.Calliphora_RgbUncompressed, PixelTypes.Rgba32)]
         public void TiffEncoder_EncodeRgb_Works<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel24, TiffEncodingMode.Rgb);
 
         [Theory]
-        [WithFile(TestImages.Tiff.RgbUncompressed, PixelTypes.Rgba32)]
+        [WithFile(TestImages.Tiff.Calliphora_RgbUncompressed, PixelTypes.Rgba32)]
         public void TiffEncoder_EncodeRgb_WithDeflateCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel24, TiffEncodingMode.Rgb, TiffEncoderCompression.Deflate);
 
         [Theory]
-        [WithFile(TestImages.Tiff.GrayscaleUncompressed, PixelTypes.Rgba32)]
+        [WithFile(TestImages.Tiff.Calliphora_RgbUncompressed, PixelTypes.Rgba32)]
+        public void TiffEncoder_EncodeRgb_WithPackBitsCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel24, TiffEncodingMode.Rgb, TiffEncoderCompression.PackBits);
+
+        [Theory]
+        [WithFile(TestImages.Tiff.Calliphora_GrayscaleUncompressed, PixelTypes.Rgba32)]
         public void TiffEncoder_EncodeGray_Works<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel8, TiffEncodingMode.Gray);
 
         [Theory]
-        [WithFile(TestImages.Tiff.GrayscaleUncompressed, PixelTypes.Rgba32)]
+        [WithFile(TestImages.Tiff.Calliphora_GrayscaleUncompressed, PixelTypes.Rgba32)]
         public void TiffEncoder_EncodeGray_WithDeflateCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel8, TiffEncodingMode.Gray, TiffEncoderCompression.Deflate);
 
+        [Theory]
+        [WithFile(TestImages.Tiff.Calliphora_GrayscaleUncompressed, PixelTypes.Rgba32)]
+        public void TiffEncoder_EncodeGray_WithPackBitsCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel8, TiffEncodingMode.Gray, TiffEncoderCompression.PackBits);
+
         // TODO: this test fails, but the output looks correct. I thinks its due to the fact that a quantizer is used to create the palette.
         [Theory]
         [WithFile(TestImages.Tiff.Calliphora_PaletteUncompressed, PixelTypes.Rgba32)]
@@ -88,6 +98,11 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         public void TiffEncoder_EncodeBiColor_WithDeflateCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel1, TiffEncodingMode.BiColor, TiffEncoderCompression.Deflate);
 
+        [Theory]
+        [WithFile(TestImages.Tiff.Calliphora_BiColor, PixelTypes.Rgba32)]
+        public void TiffEncoder_EncodeBiColor_WithPackBitsCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel1, TiffEncodingMode.BiColor, TiffEncoderCompression.PackBits);
+
         [Theory]
         [WithFile(TestImages.Tiff.Calliphora_BiColor, PixelTypes.Rgba32)]
         public void TiffEncoder_EncodeBiColor_WithCcittGroup3FaxCompression_Works<TPixel>(TestImageProvider<TPixel> provider)

tests/ImageSharp.Tests/Formats/Tiff/Utils/SubStreamTests.cs

@@ -3,7 +3,9 @@
 
 using System;
 using System.IO;
-using SixLabors.ImageSharp.Formats.Tiff;
+
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
+
 using Xunit;
 
 namespace SixLabors.ImageSharp.Tests.Formats.Tiff

tests/ImageSharp.Tests/Formats/Tiff/Utils/TiffWriterTests.cs

@@ -2,8 +2,10 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System.IO;
-using SixLabors.ImageSharp.Formats.Tiff;
+
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
+
 using Xunit;
 
 namespace SixLabors.ImageSharp.Tests.Formats.Tiff