Allow encoding 4bit color palette images

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

@@ -3,13 +3,14 @@
 
 using System;
 using System.IO;
+using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Compressors
 {
     internal class NoCompressor : TiffBaseCompressor
     {
-        public NoCompressor(Stream output)
-            : base(output, default, default, default)
+        public NoCompressor(Stream output, MemoryAllocator memoryAllocator, int width, int bitsPerPixel)
+            : base(output, memoryAllocator, width, bitsPerPixel)
         {
         }
 

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

@@ -201,8 +201,10 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Compressors
             this.useModifiedHuffman = useModifiedHuffman;
         }
 
+        /// <inheritdoc/>
         public override TiffEncoderCompression Method => this.useModifiedHuffman ? TiffEncoderCompression.ModifiedHuffman : TiffEncoderCompression.CcittGroup3Fax;
 
+        /// <inheritdoc/>
         public override void Initialize(int rowsPerStrip)
         {
             // This is too much memory allocated, but just 1 bit per pixel will not do, if the compression rate is not good.

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

@@ -17,7 +17,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Decompresso
     /// <remarks>
     /// Note that the 'OldDeflate' compression type is identical to the 'Deflate' compression type.
     /// </remarks>
-    internal class DeflateTiffCompression : TiffBaseDecompresor
+    internal class DeflateTiffCompression : TiffBaseDecompressor
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="DeflateTiffCompression" /> class.

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

@@ -12,7 +12,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Decompresso
     /// <summary>
     /// Class to handle cases where TIFF image data is compressed using LZW compression.
     /// </summary>
-    internal class LzwTiffCompression : TiffBaseDecompresor
+    internal class LzwTiffCompression : TiffBaseDecompressor
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="LzwTiffCompression" /> class.

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

@@ -22,10 +22,11 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Decompresso
         /// Initializes a new instance of the <see cref="ModifiedHuffmanTiffCompression" /> class.
         /// </summary>
         /// <param name="allocator">The memory allocator.</param>
-        /// <param name="photometricInterpretation">The photometric interpretation.</param>
         /// <param name="width">The image width.</param>
-        public ModifiedHuffmanTiffCompression(MemoryAllocator allocator, TiffPhotometricInterpretation photometricInterpretation, int width)
-            : base(allocator, FaxCompressionOptions.None, photometricInterpretation, width)
+        /// <param name="bitsPerPixel">The number of bits per pixel.</param>
+        /// <param name="photometricInterpretation">The photometric interpretation.</param>
+        public ModifiedHuffmanTiffCompression(MemoryAllocator allocator, int width, int bitsPerPixel, TiffPhotometricInterpretation photometricInterpretation)
+            : base(allocator, width, bitsPerPixel, FaxCompressionOptions.None, photometricInterpretation)
         {
             bool isWhiteZero = photometricInterpretation == TiffPhotometricInterpretation.WhiteIsZero;
             this.whiteValue = (byte)(isWhiteZero ? 0 : 1);

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

@@ -4,19 +4,23 @@
 using System;
 
 using SixLabors.ImageSharp.IO;
+using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Decompressors
 {
     /// <summary>
     /// Class to handle cases where TIFF image data is not compressed.
     /// </summary>
-    internal class NoneTiffCompression : TiffBaseDecompresor
+    internal class NoneTiffCompression : TiffBaseDecompressor
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="NoneTiffCompression" /> class.
         /// </summary>
-        public NoneTiffCompression()
-            : base(default, default, default)
+        /// <param name="memoryAllocator">The memory allocator.</param>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="bitsPerPixel">The bits per pixel.</param>
+        public NoneTiffCompression(MemoryAllocator memoryAllocator, int width, int bitsPerPixel)
+            : base(memoryAllocator, width, bitsPerPixel)
         {
         }
 

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

@@ -12,7 +12,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Decompresso
     /// <summary>
     /// Class to handle cases where TIFF image data is compressed using PackBits compression.
     /// </summary>
-    internal class PackBitsTiffCompression : TiffBaseDecompresor
+    internal class PackBitsTiffCompression : TiffBaseDecompressor
     {
         private IMemoryOwner<byte> compressedDataMemory;
 
@@ -20,8 +20,10 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Decompresso
         /// Initializes a new instance of the <see cref="PackBitsTiffCompression" /> class.
         /// </summary>
         /// <param name="memoryAllocator">The memoryAllocator to use for buffer allocations.</param>
-        public PackBitsTiffCompression(MemoryAllocator memoryAllocator)
-                : base(memoryAllocator, default, default)
+        /// <param name="width">The width of the image.</param>
+        /// <param name="bitsPerPixel">The number of bits per pixel.</param>
+        public PackBitsTiffCompression(MemoryAllocator memoryAllocator, int width, int bitsPerPixel)
+                : base(memoryAllocator, width, bitsPerPixel)
         {
         }
 

src/ImageSharp/Formats/Tiff/Compression/Decompressors/T4TiffCompression.cs

@@ -12,7 +12,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Decompresso
     /// <summary>
     /// Class to handle cases where TIFF image data is compressed using CCITT T4 compression.
     /// </summary>
-    internal class T4TiffCompression : TiffBaseDecompresor
+    internal class T4TiffCompression : TiffBaseDecompressor
     {
         private readonly FaxCompressionOptions faxCompressionOptions;
 
@@ -24,11 +24,12 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Decompresso
         /// Initializes a new instance of the <see cref="T4TiffCompression" /> class.
         /// </summary>
         /// <param name="allocator">The memory allocator.</param>
+        /// <param name="width">The image width.</param>
+        /// <param name="bitsPerPixel">The number of bits per pixel.</param>
         /// <param name="faxOptions">Fax compression options.</param>
         /// <param name="photometricInterpretation">The photometric interpretation.</param>
-        /// <param name="width">The image width.</param>
-        public T4TiffCompression(MemoryAllocator allocator, FaxCompressionOptions faxOptions, TiffPhotometricInterpretation photometricInterpretation, int width)
-            : base(allocator, width, default)
+        public T4TiffCompression(MemoryAllocator allocator, int width, int bitsPerPixel, FaxCompressionOptions faxOptions, TiffPhotometricInterpretation photometricInterpretation)
+            : base(allocator, width, bitsPerPixel)
         {
             this.faxCompressionOptions = faxOptions;
 

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

@@ -13,9 +13,9 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression
     /// <summary>
     /// The base tiff decompressor class.
     /// </summary>
-    internal abstract class TiffBaseDecompresor : TiffBaseCompression
+    internal abstract class TiffBaseDecompressor : TiffBaseCompression
     {
-        protected TiffBaseDecompresor(MemoryAllocator allocator, int width, int bitsPerPixel, TiffPredictor predictor = TiffPredictor.None)
+        protected TiffBaseDecompressor(MemoryAllocator allocator, int width, int bitsPerPixel, TiffPredictor predictor = TiffPredictor.None)
          : base(allocator, width, bitsPerPixel, predictor)
         {
         }

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

@@ -26,7 +26,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression
                     DebugGuard.IsTrue(compressionLevel == DeflateCompressionLevel.DefaultCompression, "No deflate compression level is expected to be set");
                     DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
 
-                    return new NoCompressor(output);
+                    return new NoCompressor(output, allocator, width, bitsPerPixel);
 
                 case TiffEncoderCompression.PackBits:
                     DebugGuard.IsTrue(compressionLevel == DeflateCompressionLevel.DefaultCompression, "No deflate compression level is expected to be set");

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

@@ -9,7 +9,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression
 {
     internal static class TiffDecompressorsFactory
     {
-        public static TiffBaseDecompresor Create(
+        public static TiffBaseDecompressor Create(
             TiffDecoderCompressionType method,
             MemoryAllocator allocator,
             TiffPhotometricInterpretation photometricInterpretation,
@@ -23,12 +23,12 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression
                 case TiffDecoderCompressionType.None:
                     DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
                     DebugGuard.IsTrue(faxOptions == FaxCompressionOptions.None, "No fax compression options are expected");
-                    return new NoneTiffCompression();
+                    return new NoneTiffCompression(allocator, width, bitsPerPixel);
 
                 case TiffDecoderCompressionType.PackBits:
                     DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
                     DebugGuard.IsTrue(faxOptions == FaxCompressionOptions.None, "No fax compression options are expected");
-                    return new PackBitsTiffCompression(allocator);
+                    return new PackBitsTiffCompression(allocator, width, bitsPerPixel);
 
                 case TiffDecoderCompressionType.Deflate:
                     DebugGuard.IsTrue(faxOptions == FaxCompressionOptions.None, "No fax compression options are expected");
@@ -40,11 +40,11 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression
 
                 case TiffDecoderCompressionType.T4:
                     DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
-                    return new T4TiffCompression(allocator, faxOptions, photometricInterpretation, width);
+                    return new T4TiffCompression(allocator, width, bitsPerPixel, faxOptions, photometricInterpretation);
 
                 case TiffDecoderCompressionType.HuffmanRle:
                     DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
-                    return new ModifiedHuffmanTiffCompression(allocator, photometricInterpretation, width);
+                    return new ModifiedHuffmanTiffCompression(allocator, width, bitsPerPixel, photometricInterpretation);
 
                 default:
                     throw TiffThrowHelper.NotSupportedDecompressor(nameof(method));

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

@@ -75,6 +75,26 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Constants
         /// </summary>
         public const int SizeOfDouble = 8;
 
+        /// <summary>
+        /// The bits per sample for 1 bit bicolor images.
+        /// </summary>
+        public static readonly ushort[] BitsPerSample1Bit = { 1 };
+
+        /// <summary>
+        /// The bits per sample for images with a 4 color palette.
+        /// </summary>
+        public static readonly ushort[] BitsPerSample4Bit = { 4 };
+
+        /// <summary>
+        /// The bits per sample for 8 bit images.
+        /// </summary>
+        public static readonly ushort[] BitsPerSample8Bit = { 8 };
+
+        /// <summary>
+        /// The bits per sample for images with 8 bits for each color channel.
+        /// </summary>
+        public static readonly ushort[] BitsPerSampleRgb8Bit = { 8, 8, 8 };
+
         /// <summary>
         /// The list of mimetypes that equate to a tiff.
         /// </summary>

src/ImageSharp/Formats/Tiff/ITiffEncoderOptions.cs

@@ -11,6 +11,11 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
     /// </summary>
     internal interface ITiffEncoderOptions
     {
+        /// <summary>
+        /// Gets or sets the number of bits per pixel.
+        /// </summary>
+        TiffBitsPerPixel? BitsPerPixel { get; set; }
+
         /// <summary>
         /// Gets the compression type to use.
         /// </summary>

src/ImageSharp/Formats/Tiff/TiffBitsPerSampleExtensions.cs

@@ -3,19 +3,12 @@
 
 using System;
 using SixLabors.ImageSharp.Formats.Experimental.Tiff;
+using SixLabors.ImageSharp.Formats.Experimental.Tiff.Constants;
 
 namespace SixLabors.ImageSharp.Formats.Tiff
 {
     internal static class TiffBitsPerSampleExtensions
     {
-        private static readonly ushort[] One = { 1 };
-
-        private static readonly ushort[] Four = { 4 };
-
-        private static readonly ushort[] Eight = { 8 };
-
-        private static readonly ushort[] Rgb888 = { 8, 8, 8 };
-
         /// <summary>
         /// Gets the bits per channel array for a given BitsPerSample value, e,g, for RGB888: [8, 8, 8]
         /// </summary>
@@ -26,13 +19,13 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             switch (tiffBitsPerSample)
             {
                 case TiffBitsPerSample.One:
-                    return One;
+                    return TiffConstants.BitsPerSample1Bit;
                 case TiffBitsPerSample.Four:
-                    return Four;
+                    return TiffConstants.BitsPerSample4Bit;
                 case TiffBitsPerSample.Eight:
-                    return Eight;
+                    return TiffConstants.BitsPerSample8Bit;
                 case TiffBitsPerSample.Rgb888:
-                    return Rgb888;
+                    return TiffConstants.BitsPerSampleRgb8Bit;
 
                 default:
                     TiffThrowHelper.ThrowNotSupported("The bits per pixels are not supported");
@@ -50,7 +43,9 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             switch (bitsPerSample.Length)
             {
                 case 3:
-                    if (bitsPerSample[0] == Rgb888[0] && bitsPerSample[1] == Rgb888[1] && bitsPerSample[2] == Rgb888[2])
+                    if (bitsPerSample[0] == TiffConstants.BitsPerSampleRgb8Bit[0] &&
+                        bitsPerSample[1] == TiffConstants.BitsPerSampleRgb8Bit[1] &&
+                        bitsPerSample[2] == TiffConstants.BitsPerSampleRgb8Bit[2])
                     {
                         return TiffBitsPerSample.Rgb888;
                     }
@@ -58,17 +53,17 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     break;
 
                 case 1:
-                    if (bitsPerSample[0] == One[0])
+                    if (bitsPerSample[0] == TiffConstants.BitsPerSample1Bit[0])
                     {
                         return TiffBitsPerSample.One;
                     }
 
-                    if (bitsPerSample[0] == Four[0])
+                    if (bitsPerSample[0] == TiffConstants.BitsPerSample4Bit[0])
                     {
                         return TiffBitsPerSample.Four;
                     }
 
-                    if (bitsPerSample[0] == Eight[0])
+                    if (bitsPerSample[0] == TiffConstants.BitsPerSample8Bit[0])
                     {
                         return TiffBitsPerSample.Eight;
                     }

src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs

@@ -250,7 +250,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
                     stripBuffers[stripIndex] = this.memoryAllocator.AllocateManagedByteBuffer(uncompressedStripSize);
                 }
 
-                using TiffBaseDecompresor decompressor = TiffDecompressorsFactory.Create(this.CompressionType, this.memoryAllocator, this.PhotometricInterpretation, frame.Width, bitsPerPixel, this.Predictor, this.FaxCompressionOptions);
+                using TiffBaseDecompressor decompressor = TiffDecompressorsFactory.Create(this.CompressionType, this.memoryAllocator, this.PhotometricInterpretation, frame.Width, bitsPerPixel, this.Predictor, this.FaxCompressionOptions);
 
                 RgbPlanarTiffColor<TPixel> colorDecoder = TiffColorDecoderFactory<TPixel>.CreatePlanar(this.ColorType, this.BitsPerSample.Bits(), this.ColorMap);
 
@@ -293,7 +293,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
 
             Buffer2D<TPixel> pixels = frame.PixelBuffer;
 
-            using TiffBaseDecompresor decompressor = TiffDecompressorsFactory.Create(this.CompressionType, this.memoryAllocator, this.PhotometricInterpretation, frame.Width, bitsPerPixel, this.Predictor, this.FaxCompressionOptions);
+            using TiffBaseDecompressor decompressor = TiffDecompressorsFactory.Create(this.CompressionType, this.memoryAllocator, this.PhotometricInterpretation, frame.Width, bitsPerPixel, this.Predictor, this.FaxCompressionOptions);
 
             TiffBaseColorDecoder<TPixel> colorDecoder = TiffColorDecoderFactory<TPixel>.Create(this.ColorType, this.BitsPerSample.Bits(), this.ColorMap);
 

src/ImageSharp/Formats/Tiff/TiffEncoder.cs

@@ -17,6 +17,9 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
     /// </summary>
     public class TiffEncoder : IImageEncoder, ITiffEncoderOptions
     {
+        /// <inheritdoc/>
+        public TiffBitsPerPixel? BitsPerPixel { get; set; }
+
         /// <inheritdoc/>
         public TiffEncoderCompression Compression { get; set; } = TiffEncoderCompression.None;
 

src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs

@@ -12,6 +12,7 @@ using SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression;
 using SixLabors.ImageSharp.Formats.Experimental.Tiff.Constants;
 using SixLabors.ImageSharp.Formats.Experimental.Tiff.Writers;
 using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing;
@@ -40,11 +41,6 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
         /// </summary>
         private Configuration configuration;
 
-        /// <summary>
-        /// The color depth, in number of bits per pixel.
-        /// </summary>
-        private TiffBitsPerPixel bitsPerPixel;
-
         /// <summary>
         /// The quantizer for creating color palette image.
         /// </summary>
@@ -70,6 +66,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
             this.memoryAllocator = memoryAllocator;
             this.Mode = options.Mode;
             this.quantizer = options.Quantizer ?? KnownQuantizers.Octree;
+            this.BitsPerPixel = options.BitsPerPixel;
             this.UseHorizontalPredictor = options.UseHorizontalPredictor;
             this.CompressionType = options.Compression;
             this.compressionLevel = options.CompressionLevel;
@@ -82,9 +79,9 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
         internal TiffPhotometricInterpretation PhotometricInterpretation { get; private set; }
 
         /// <summary>
-        /// Gets the compression implementation to use when encoding the image.
+        /// Gets or sets the compression implementation to use when encoding the image.
         /// </summary>
-        internal TiffEncoderCompression CompressionType { get; }
+        internal TiffEncoderCompression CompressionType { get; set; }
 
         /// <summary>
         /// Gets the encoding mode to use. RGB, RGB with color palette or gray.
@@ -97,6 +94,11 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
         /// </summary>
         internal bool UseHorizontalPredictor { get; }
 
+        /// <summary>
+        /// Gets the bits per pixel.
+        /// </summary>
+        internal TiffBitsPerPixel? BitsPerPixel { get; private set; }
+
         /// <summary>
         /// Encodes the image to the specified stream from the <see cref="Image{TPixel}"/>.
         /// </summary>
@@ -111,8 +113,12 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
             Guard.NotNull(stream, nameof(stream));
 
             this.configuration = image.GetConfiguration();
+            ImageMetadata metadata = image.Metadata;
+            TiffMetadata tiffMetadata = metadata.GetTiffMetadata();
+            this.BitsPerPixel ??= tiffMetadata.BitsPerPixel;
 
-            this.SetMode(image);
+            this.SetMode(tiffMetadata);
+            this.SetBitsPerPixel();
             this.SetPhotometricInterpretation();
 
             using (var writer = new TiffStreamWriter(stream))
@@ -155,20 +161,31 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
             // Write the image bytes to the steam.
             var imageDataStart = (uint)writer.Position;
 
-            using TiffBaseCompressor compressor = TiffCompressorFactory.Create(
-                     this.CompressionType,
-                     writer.BaseStream,
-                     this.memoryAllocator,
-                     image.Width,
-                     (int)this.bitsPerPixel,
-                     this.compressionLevel,
-                     this.UseHorizontalPredictor ? TiffPredictor.Horizontal : TiffPredictor.None);
-
-            using TiffBaseColorWriter<TPixel> colorWriter = TiffColorWriterFactory.Create(this.Mode, image.Frames.RootFrame, this.quantizer, this.memoryAllocator, this.configuration, entriesCollector);
-
-            int rowsPerStrip = this.CalcRowsPerStrip(image.Frames.RootFrame, colorWriter.BytesPerRow);
-
-            colorWriter.Write(compressor, rowsPerStrip);
+            TiffBitsPerPixel? tiffBitsPerPixel = this.BitsPerPixel;
+            if (tiffBitsPerPixel != null)
+            {
+                using TiffBaseCompressor compressor = TiffCompressorFactory.Create(
+                    this.CompressionType,
+                    writer.BaseStream,
+                    this.memoryAllocator,
+                    image.Width,
+                    (int)tiffBitsPerPixel,
+                    this.compressionLevel,
+                    this.UseHorizontalPredictor ? TiffPredictor.Horizontal : TiffPredictor.None);
+
+                using TiffBaseColorWriter<TPixel> colorWriter = TiffColorWriterFactory.Create(
+                    this.Mode,
+                    image.Frames.RootFrame,
+                    this.quantizer,
+                    this.memoryAllocator,
+                    this.configuration,
+                    entriesCollector,
+                    (int)tiffBitsPerPixel);
+
+                int rowsPerStrip = this.CalcRowsPerStrip(image.Frames.RootFrame.Height, colorWriter.BytesPerRow);
+
+                colorWriter.Write(compressor, rowsPerStrip);
+            }
 
             entriesCollector.ProcessImageFormat(this);
             entriesCollector.ProcessGeneral(image);
@@ -177,12 +194,21 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
             long nextIfdMarker = this.WriteIfd(writer, entriesCollector.Entries);
         }
 
-        private int CalcRowsPerStrip(ImageFrame image, int bytesPerRow)
+        /// <summary>
+        /// Calculates the number of rows written per strip.
+        /// </summary>
+        /// <param name="height">The height of the image.</param>
+        /// <param name="bytesPerRow">The number of bytes per row.</param>
+        /// <returns>Number of rows per strip.</returns>
+        private int CalcRowsPerStrip(int height, int bytesPerRow)
         {
-            int sz = this.maxStripBytes > 0 ? this.maxStripBytes : DefaultStripSize;
-            int height = sz / bytesPerRow;
+            DebugGuard.MustBeGreaterThan(height, 0, nameof(height));
+            DebugGuard.MustBeGreaterThan(bytesPerRow, 0, nameof(bytesPerRow));
+
+            int stripBytes = this.maxStripBytes > 0 ? this.maxStripBytes : DefaultStripSize;
+            int rowsPerStrip = stripBytes / bytesPerRow;
 
-            return height > 0 ? (height < image.Height ? height : image.Height) : 1;
+            return rowsPerStrip > 0 ? (rowsPerStrip < height ? rowsPerStrip : height) : 1;
         }
 
         /// <summary>
@@ -242,14 +268,15 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
             return nextIfdMarker;
         }
 
-        private void SetMode(Image image)
+        private void SetMode(TiffMetadata tiffMetadata)
         {
+            // Make sure, that the fax compressions are only used together with the BiColor mode.
             if (this.CompressionType == TiffEncoderCompression.CcittGroup3Fax || this.CompressionType == TiffEncoderCompression.ModifiedHuffman)
             {
+                // Default means the user has not specified a preferred encoding mode.
                 if (this.Mode == TiffEncodingMode.Default)
                 {
                     this.Mode = TiffEncodingMode.BiColor;
-                    this.bitsPerPixel = TiffBitsPerPixel.Pixel1;
                     return;
                 }
 
@@ -262,36 +289,48 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
             if (this.Mode == TiffEncodingMode.Default)
             {
                 // Preserve input bits per pixel, if no mode was specified.
-                TiffMetadata tiffMetadata = image.Metadata.GetTiffMetadata();
                 switch (tiffMetadata.BitsPerPixel)
                 {
                     case TiffBitsPerPixel.Pixel1:
                         this.Mode = TiffEncodingMode.BiColor;
                         break;
+                    case TiffBitsPerPixel.Pixel4:
+                        this.Mode = TiffEncodingMode.ColorPalette;
+                        break;
                     case TiffBitsPerPixel.Pixel8:
-                        this.Mode = tiffMetadata.PhotometricInterpretation != TiffPhotometricInterpretation.PaletteColor ? TiffEncodingMode.Gray : TiffEncodingMode.Rgb;
+                        this.Mode = tiffMetadata.PhotometricInterpretation == TiffPhotometricInterpretation.PaletteColor ? TiffEncodingMode.ColorPalette : TiffEncodingMode.Gray;
+
                         break;
                     default:
                         this.Mode = TiffEncodingMode.Rgb;
                         break;
                 }
             }
+        }
 
+        private void SetBitsPerPixel()
+        {
             switch (this.Mode)
             {
                 case TiffEncodingMode.BiColor:
-                    this.bitsPerPixel = TiffBitsPerPixel.Pixel1;
+                    this.BitsPerPixel = TiffBitsPerPixel.Pixel1;
                     break;
                 case TiffEncodingMode.ColorPalette:
+                    if (this.BitsPerPixel != TiffBitsPerPixel.Pixel8 && this.BitsPerPixel != TiffBitsPerPixel.Pixel4)
+                    {
+                        this.BitsPerPixel = TiffBitsPerPixel.Pixel8;
+                    }
+
+                    break;
                 case TiffEncodingMode.Gray:
-                    this.bitsPerPixel = TiffBitsPerPixel.Pixel8;
+                    this.BitsPerPixel = TiffBitsPerPixel.Pixel8;
                     break;
                 case TiffEncodingMode.Rgb:
-                    this.bitsPerPixel = TiffBitsPerPixel.Pixel24;
+                    this.BitsPerPixel = TiffBitsPerPixel.Pixel24;
                     break;
                 default:
                     this.Mode = TiffEncodingMode.Rgb;
-                    this.bitsPerPixel = TiffBitsPerPixel.Pixel24;
+                    this.BitsPerPixel = TiffBitsPerPixel.Pixel24;
                     break;
             }
         }

src/ImageSharp/Formats/Tiff/TiffEncoderEntriesCollector.cs

@@ -298,25 +298,33 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff
                 switch (encoder.PhotometricInterpretation)
                 {
                     case TiffPhotometricInterpretation.PaletteColor:
-                        return new ushort[] { 8 };
+                        if (encoder.BitsPerPixel == TiffBitsPerPixel.Pixel4)
+                        {
+                            return TiffConstants.BitsPerSample4Bit;
+                        }
+                        else
+                        {
+                            return TiffConstants.BitsPerSample8Bit;
+                        }
+
                     case TiffPhotometricInterpretation.Rgb:
-                        return new ushort[] { 8, 8, 8 };
+                        return TiffConstants.BitsPerSampleRgb8Bit;
                     case TiffPhotometricInterpretation.WhiteIsZero:
                         if (encoder.Mode == TiffEncodingMode.BiColor)
                         {
-                            return new ushort[] { 1 };
+                            return TiffConstants.BitsPerSample1Bit;
                         }
 
-                        return new ushort[] { 8 };
+                        return TiffConstants.BitsPerSample8Bit;
                     case TiffPhotometricInterpretation.BlackIsZero:
                         if (encoder.Mode == TiffEncodingMode.BiColor)
                         {
-                            return new ushort[] { 1 };
+                            return TiffConstants.BitsPerSample1Bit;
                         }
 
-                        return new ushort[] { 8 };
+                        return TiffConstants.BitsPerSample8Bit;
                     default:
-                        return new ushort[] { 8, 8, 8 };
+                        return TiffConstants.BitsPerSampleRgb8Bit;
                 }
             }
 

src/ImageSharp/Formats/Tiff/Writers/TiffBaseColorWriter.cs

@@ -20,13 +20,11 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Writers
             this.MemoryAllocator = memoryAllocator;
             this.Configuration = configuration;
             this.EntriesCollector = entriesCollector;
-
-            this.BytesPerRow = ((image.Width * this.BitsPerPixel) + 7) / 8;
         }
 
         public abstract int BitsPerPixel { get; }
 
-        public int BytesPerRow { get; }
+        public int BytesPerRow => ((this.Image.Width * this.BitsPerPixel) + 7) / 8;
 
         protected ImageFrame<TPixel> Image { get; }
 
@@ -38,7 +36,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Writers
 
         public virtual void Write(TiffBaseCompressor compressor, int rowsPerStrip)
         {
-            DebugGuard.IsTrue(this.BytesPerRow == compressor.BytesPerRow || compressor.BytesPerRow == 0, "Values must be equals");
+            DebugGuard.IsTrue(this.BytesPerRow == compressor.BytesPerRow, "bytes per row of the compressor does not match tiff color writer");
             int stripsCount = (this.Image.Height + rowsPerStrip - 1) / rowsPerStrip;
 
             uint[] stripOffsets = new uint[stripsCount];
@@ -59,7 +57,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Writers
                 stripIndex++;
             }
 
-            DebugGuard.IsTrue(stripIndex == stripsCount, "Values must be equals");
+            DebugGuard.IsTrue(stripIndex == stripsCount, "stripIndex and stripsCount should match");
             this.AddStripTags(rowsPerStrip, stripOffsets, stripByteCounts);
         }
 

src/ImageSharp/Formats/Tiff/Writers/TiffColorWriterFactory.cs

@@ -15,13 +15,14 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Writers
             IQuantizer quantizer,
             MemoryAllocator memoryAllocator,
             Configuration configuration,
-            TiffEncoderEntriesCollector entriesCollector)
+            TiffEncoderEntriesCollector entriesCollector,
+            int bitsPerPixel)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             switch (mode)
             {
                 case TiffEncodingMode.ColorPalette:
-                    return new TiffPaletteWriter<TPixel>(image, quantizer, memoryAllocator, configuration, entriesCollector);
+                    return new TiffPaletteWriter<TPixel>(image, quantizer, memoryAllocator, configuration, entriesCollector, bitsPerPixel);
                 case TiffEncodingMode.Gray:
                     return new TiffGrayWriter<TPixel>(image, memoryAllocator, configuration, entriesCollector);
                 case TiffEncodingMode.BiColor:

src/ImageSharp/Formats/Tiff/Writers/TiffPaletteWriter.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Buffers;
 using System.Runtime.InteropServices;
+
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression;
 using SixLabors.ImageSharp.Memory;
@@ -16,52 +17,85 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Writers
     internal sealed class TiffPaletteWriter<TPixel> : TiffBaseColorWriter<TPixel>
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        private const int ColorsPerChannel = 256;
-        private const int ColorPaletteSize = ColorsPerChannel * 3;
-        private const int ColorPaletteBytes = ColorPaletteSize * 2;
-
-        private readonly IndexedImageFrame<TPixel> quantized;
-
-        public TiffPaletteWriter(ImageFrame<TPixel> image, IQuantizer quantizer, MemoryAllocator memoryAllocator, Configuration configuration, TiffEncoderEntriesCollector entriesCollector)
+        private readonly int maxColors;
+        private readonly int colorPaletteSize;
+        private readonly int colorPaletteBytes;
+        private readonly IndexedImageFrame<TPixel> quantizedImage;
+
+        public TiffPaletteWriter(
+            ImageFrame<TPixel> image,
+            IQuantizer quantizer,
+            MemoryAllocator memoryAllocator,
+            Configuration configuration,
+            TiffEncoderEntriesCollector entriesCollector,
+            int bitsPerPixel)
              : base(image, memoryAllocator, configuration, entriesCollector)
         {
-            using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.Configuration);
-            this.quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(image, image.Bounds());
+            DebugGuard.NotNull(quantizer, nameof(quantizer));
+            DebugGuard.NotNull(configuration, nameof(configuration));
+            DebugGuard.NotNull(entriesCollector, nameof(entriesCollector));
+            DebugGuard.MustBeBetweenOrEqualTo(bitsPerPixel, 4, 8, nameof(bitsPerPixel));
+
+            this.BitsPerPixel = bitsPerPixel;
+            this.maxColors = this.BitsPerPixel == 4 ? 16 : 256;
+            this.colorPaletteSize = this.maxColors * 3;
+            this.colorPaletteBytes = this.colorPaletteSize * 2;
+            using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.Configuration, new QuantizerOptions()
+            {
+                MaxColors = this.maxColors
+            });
+            this.quantizedImage = frameQuantizer.BuildPaletteAndQuantizeFrame(image, image.Bounds());
 
-            this.AddTag(this.quantized);
+            this.AddColorMapTag();
         }
 
         /// <inheritdoc />
-        public override int BitsPerPixel => 8;
+        public override int BitsPerPixel { get; }
 
         /// <inheritdoc />
         protected override void EncodeStrip(int y, int height, TiffBaseCompressor compressor)
         {
-            Span<byte> pixels = GetStripPixels(((IPixelSource)this.quantized).PixelBuffer, y, height);
-            compressor.CompressStrip(pixels, height);
+            Span<byte> pixels = GetStripPixels(((IPixelSource)this.quantizedImage).PixelBuffer, y, height);
+            if (this.BitsPerPixel == 4)
+            {
+                using IMemoryOwner<byte> rows4bitBuffer = this.MemoryAllocator.Allocate<byte>(pixels.Length / 2);
+                Span<byte> rows4bit = rows4bitBuffer.GetSpan();
+                int idx = 0;
+                for (int i = 0; i < rows4bit.Length; i++)
+                {
+                    rows4bit[i] = (byte)((pixels[idx] << 4) | (pixels[idx + 1] & 0xF));
+                    idx += 2;
+                }
+
+                compressor.CompressStrip(rows4bit, height);
+            }
+            else
+            {
+                compressor.CompressStrip(pixels, height);
+            }
         }
 
         /// <inheritdoc />
-        protected override void Dispose(bool disposing) => this.quantized?.Dispose();
+        protected override void Dispose(bool disposing) => this.quantizedImage?.Dispose();
 
-        private void AddTag(IndexedImageFrame<TPixel> quantized)
+        private void AddColorMapTag()
         {
-            using IMemoryOwner<byte> colorPaletteBuffer = this.MemoryAllocator.AllocateManagedByteBuffer(ColorPaletteBytes);
+            using IMemoryOwner<byte> colorPaletteBuffer = this.MemoryAllocator.AllocateManagedByteBuffer(this.colorPaletteBytes);
             Span<byte> colorPalette = colorPaletteBuffer.GetSpan();
 
-            ReadOnlySpan<TPixel> quantizedColors = quantized.Palette.Span;
+            ReadOnlySpan<TPixel> quantizedColors = this.quantizedImage.Palette.Span;
             int quantizedColorBytes = quantizedColors.Length * 3 * 2;
 
-            // In the ColorMap, black is represented by 0,0,0 and white is represented by 65535, 65535, 65535.
+            // In the ColorMap, black is represented by 0, 0, 0 and white is represented by 65535, 65535, 65535.
             Span<Rgb48> quantizedColorRgb48 = MemoryMarshal.Cast<byte, Rgb48>(colorPalette.Slice(0, quantizedColorBytes));
             PixelOperations<TPixel>.Instance.ToRgb48(this.Configuration, quantizedColors, quantizedColorRgb48);
 
-            // It can happen that the quantized colors are less than the expected 256 per channel.
-            var diffToMaxColors = ColorsPerChannel - quantizedColors.Length;
+            // It can happen that the quantized colors are less than the expected maximum per channel.
+            var diffToMaxColors = this.maxColors - quantizedColors.Length;
 
             // In a TIFF ColorMap, all the Red values come first, followed by the Green values,
             // then the Blue values. Convert the quantized palette to this format.
-            var palette = new ushort[ColorPaletteSize];
+            var palette = new ushort[this.colorPaletteSize];
             int paletteIdx = 0;
             for (int i = 0; i < quantizedColors.Length; i++)
             {

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

@@ -20,7 +20,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff.Compression
             var stream = new BufferedReadStream(Configuration.Default, new MemoryStream(inputData));
             var buffer = new byte[expectedResult.Length];
 
-            new NoneTiffCompression().Decompress(stream, 0, byteCount, buffer);
+            new NoneTiffCompression(default, default, default).Decompress(stream, 0, byteCount, buffer);
 
             Assert.Equal(expectedResult, buffer);
         }

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

@@ -29,7 +29,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff.Compression
             var stream = new BufferedReadStream(Configuration.Default, new MemoryStream(inputData));
             var buffer = new byte[expectedResult.Length];
 
-            using var decompressor = new PackBitsTiffCompression(new ArrayPoolMemoryAllocator());
+            using var decompressor = new PackBitsTiffCompression(new ArrayPoolMemoryAllocator(), default, default);
             decompressor.Decompress(stream, 0, (uint)inputData.Length, buffer);
 
             Assert.Equal(expectedResult, buffer);

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

@@ -1,7 +1,6 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
-using System;
 using System.IO;
 
 using SixLabors.ImageSharp.Formats;
@@ -38,7 +37,6 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         [InlineData(TiffEncodingMode.BiColor, TiffEncoderCompression.None, TiffBitsPerPixel.Pixel1, TiffCompression.None)]
         [InlineData(TiffEncodingMode.Default, TiffEncoderCompression.Deflate, TiffBitsPerPixel.Pixel24, TiffCompression.Deflate)]
         [InlineData(TiffEncodingMode.Rgb, TiffEncoderCompression.Deflate, TiffBitsPerPixel.Pixel24, TiffCompression.Deflate)]
-        [InlineData(TiffEncodingMode.ColorPalette, TiffEncoderCompression.Deflate, TiffBitsPerPixel.Pixel8, TiffCompression.Deflate)]
         [InlineData(TiffEncodingMode.Gray, TiffEncoderCompression.Deflate, TiffBitsPerPixel.Pixel8, TiffCompression.Deflate)]
         [InlineData(TiffEncodingMode.BiColor, TiffEncoderCompression.Deflate, TiffBitsPerPixel.Pixel1, TiffCompression.Deflate)]
         [InlineData(TiffEncodingMode.Default, TiffEncoderCompression.PackBits, TiffBitsPerPixel.Pixel24, TiffCompression.PackBits)]
@@ -47,7 +45,6 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         [InlineData(TiffEncodingMode.Gray, TiffEncoderCompression.PackBits, TiffBitsPerPixel.Pixel8, TiffCompression.PackBits)]
         [InlineData(TiffEncodingMode.BiColor, TiffEncoderCompression.PackBits, TiffBitsPerPixel.Pixel1, TiffCompression.PackBits)]
         [InlineData(TiffEncodingMode.Rgb, TiffEncoderCompression.Lzw, TiffBitsPerPixel.Pixel24, TiffCompression.Lzw)]
-        [InlineData(TiffEncodingMode.ColorPalette, TiffEncoderCompression.Lzw, TiffBitsPerPixel.Pixel8, TiffCompression.Lzw)]
         [InlineData(TiffEncodingMode.Gray, TiffEncoderCompression.Lzw, TiffBitsPerPixel.Pixel8, TiffCompression.Lzw)]
         [InlineData(TiffEncodingMode.BiColor, TiffEncoderCompression.CcittGroup3Fax, TiffBitsPerPixel.Pixel1, TiffCompression.CcittGroup3Fax)]
         [InlineData(TiffEncodingMode.BiColor, TiffEncoderCompression.ModifiedHuffman, TiffBitsPerPixel.Pixel1, TiffCompression.Ccitt1D)]
@@ -73,7 +70,9 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         [WithFile(Calliphora_BiColorUncompressed, PixelTypes.Rgba32, TiffBitsPerPixel.Pixel1)]
         [WithFile(GrayscaleUncompressed, PixelTypes.Rgba32, TiffBitsPerPixel.Pixel8)]
         [WithFile(RgbUncompressed, PixelTypes.Rgba32, TiffBitsPerPixel.Pixel24)]
-        [WithFile(Calliphora_PaletteUncompressed, PixelTypes.Rgba32, TiffBitsPerPixel.Pixel24)]
+        [WithFile(Rgb4BitPalette, PixelTypes.Rgba32, TiffBitsPerPixel.Pixel4)]
+        [WithFile(RgbPalette, PixelTypes.Rgba32, TiffBitsPerPixel.Pixel8)]
+        [WithFile(Calliphora_PaletteUncompressed, PixelTypes.Rgba32, TiffBitsPerPixel.Pixel8)]
         public void TiffEncoder_PreserveBitsPerPixel<TPixel>(TestImageProvider<TPixel> provider, TiffBitsPerPixel expectedBitsPerPixel)
             where TPixel : unmanaged, IPixel<TPixel>
         {
@@ -97,7 +96,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         [WithFile(RgbUncompressed, PixelTypes.Rgba32, TiffEncoderCompression.ModifiedHuffman, TiffCompression.Ccitt1D)]
         [WithFile(GrayscaleUncompressed, PixelTypes.L8, TiffEncoderCompression.CcittGroup3Fax, TiffCompression.CcittGroup3Fax)]
         [WithFile(PaletteDeflateMultistrip, PixelTypes.L8, TiffEncoderCompression.ModifiedHuffman, TiffCompression.Ccitt1D)]
-        public void TiffEncoder_CorrectBiMode<TPixel>(TestImageProvider<TPixel> provider, TiffEncoderCompression compression, TiffCompression expectedCompression)
+        public void TiffEncoder_EncodesWithCorrectBiColorModeCompression<TPixel>(TestImageProvider<TPixel> provider, TiffEncoderCompression compression, TiffCompression expectedCompression)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             // arrange
@@ -197,37 +196,19 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         [WithFile(Calliphora_PaletteUncompressed, PixelTypes.Rgba32)]
         public void TiffEncoder_EncodeColorPalette_Works<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> =>
-            TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel24, TiffEncodingMode.ColorPalette, useExactComparer: false, compareTolerance: 0.001f);
+            TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel8, TiffEncodingMode.ColorPalette, useExactComparer: false, compareTolerance: 0.001f);
 
         [Theory]
-        [WithFile(Calliphora_PaletteUncompressed, PixelTypes.Rgba32)]
-        public void TiffEncoder_EncodeColorPalette_WithDeflateCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
-            where TPixel : unmanaged, IPixel<TPixel> =>
-            TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel24, TiffEncodingMode.ColorPalette, TiffEncoderCompression.Deflate, useExactComparer: false, compareTolerance: 0.001f);
-
-        [Theory]
-        [WithFile(Calliphora_PaletteUncompressed, PixelTypes.Rgba32)]
-        public void TiffEncoder_EncodeColorPalette_WithDeflateCompressionAndPredictor_Works<TPixel>(TestImageProvider<TPixel> provider)
-            where TPixel : unmanaged, IPixel<TPixel> =>
-            TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel24, TiffEncodingMode.ColorPalette, TiffEncoderCompression.Deflate, usePredictor: true, useExactComparer: false, compareTolerance: 0.001f);
-
-        [Theory]
-        [WithFile(Calliphora_PaletteUncompressed, PixelTypes.Rgba32)]
-        public void TiffEncoder_EncodeColorPalette_WithLzwCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
-            where TPixel : unmanaged, IPixel<TPixel> =>
-            TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel24, TiffEncodingMode.ColorPalette, TiffEncoderCompression.Lzw, useExactComparer: false, compareTolerance: 0.001f);
-
-        [Theory]
-        [WithFile(Calliphora_PaletteUncompressed, PixelTypes.Rgba32)]
-        public void TiffEncoder_EncodeColorPalette_WithLzwCompressionAndPredictor_Works<TPixel>(TestImageProvider<TPixel> provider)
+        [WithFile(Rgb4BitPalette, PixelTypes.Rgba32)]
+        public void TiffEncoder_EncodeColorPalette_With4Bit_Works<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> =>
-            TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel24, TiffEncodingMode.ColorPalette, TiffEncoderCompression.Lzw, usePredictor: true, useExactComparer: false, compareTolerance: 0.001f);
+            TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel8, TiffEncodingMode.ColorPalette, useExactComparer: false, compareTolerance: 0.001f);
 
         [Theory]
         [WithFile(Calliphora_PaletteUncompressed, PixelTypes.Rgba32)]
         public void TiffEncoder_EncodeColorPalette_WithPackBitsCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> =>
-            TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel24, TiffEncodingMode.ColorPalette, TiffEncoderCompression.PackBits, useExactComparer: false, compareTolerance: 0.001f);
+            TestTiffEncoderCore(provider, TiffBitsPerPixel.Pixel8, TiffEncodingMode.ColorPalette, TiffEncoderCompression.PackBits, useExactComparer: false, compareTolerance: 0.001f);
 
         [Theory]
         [WithFile(Calliphora_BiColorUncompressed, PixelTypes.Rgba32)]
@@ -335,6 +316,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
             var encoder = new TiffEncoder
             {
                 Mode = mode,
+                BitsPerPixel = bitsPerPixel,
                 Compression = compression,
                 UseHorizontalPredictor = usePredictor,
                 MaxStripBytes = maxStripSize

tests/ImageSharp.Tests/TestImages.cs

@@ -556,6 +556,7 @@ namespace SixLabors.ImageSharp.Tests
             public const string RgbPackbitsMultistrip = "Tiff/rgb_packbits_multistrip.tiff";
             public const string RgbUncompressed = "Tiff/rgb_uncompressed.tiff";
             public const string RgbPalette = "Tiff/rgb_palette.tiff";
+            public const string Rgb4BitPalette = "Tiff/bike_colorpalette_4bit.tiff";
             public const string RgbPaletteDeflate = "Tiff/rgb_palette_deflate.tiff";
 
             public const string SmallRgbDeflate = "Tiff/rgb_small_deflate.tiff";

tests/Images/Input/Tiff/bike_colorpalette_4bit.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:bc9047bc28ff5256530a7203bf73fa0a7ed1545736cd57fabdaff2d600cfa3f1
+size 132265