Preserve color palettes and deduplicate frame pixels.

src/ImageSharp/Common/Helpers/SimdUtils.HwIntrinsics.cs

@@ -629,6 +629,33 @@ internal static partial class SimdUtils
             return Avx.Subtract(c, Avx.Multiply(a, b));
         }
 
+        /// <summary>
+        /// Blend packed 8-bit integers from <paramref name="left"/> and <paramref name="right"/> using <paramref name="mask"/>.
+        /// The high bit of each corresponding <paramref name="mask"/> byte determines the selection.
+        /// If the high bit is set the element of <paramref name="left"/> is selected.
+        /// The element of <paramref name="right"/> is selected otherwise.
+        /// </summary>
+        /// <param name="left">The left vector.</param>
+        /// <param name="right">The right vector.</param>
+        /// <param name="mask">The mask vector.</param>
+        /// <returns>The <see cref="Vector256{T}"/>.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector128<byte> BlendVariable(in Vector128<byte> left, in Vector128<byte> right, in Vector128<byte> mask)
+        {
+            if (Sse41.IsSupported)
+            {
+                return Sse41.BlendVariable(left, right, mask);
+            }
+            else if (Sse2.IsSupported)
+            {
+                return Sse2.Or(Sse2.And(right, mask), Sse2.AndNot(mask, left));
+            }
+
+            // Use a signed shift right to create a mask with the sign bit.
+            Vector128<short> signedMask = AdvSimd.ShiftRightArithmetic(mask.AsInt16(), 7);
+            return AdvSimd.BitwiseSelect(signedMask, right.AsInt16(), left.AsInt16()).AsByte();
+        }
+
         /// <summary>
         /// <see cref="ByteToNormalizedFloat"/> as many elements as possible, slicing them down (keeping the remainder).
         /// </summary>

src/ImageSharp/Formats/Bmp/BmpEncoder.cs

@@ -2,6 +2,7 @@
 // Licensed under the Six Labors Split License.
 
 using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.Processing;
 
 namespace SixLabors.ImageSharp.Formats.Bmp;
 
@@ -10,6 +11,11 @@ namespace SixLabors.ImageSharp.Formats.Bmp;
 /// </summary>
 public sealed class BmpEncoder : QuantizingImageEncoder
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="BmpEncoder"/> class.
+    /// </summary>
+    public BmpEncoder() => this.Quantizer = KnownQuantizers.Octree;
+
     /// <summary>
     /// Gets the number of bits per pixel.
     /// </summary>

src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs

@@ -9,6 +9,7 @@ using SixLabors.ImageSharp.Common.Helpers;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
 namespace SixLabors.ImageSharp.Formats.Bmp;
@@ -100,7 +101,7 @@ internal sealed class BmpEncoderCore : IImageEncoderInternals
     {
         this.memoryAllocator = memoryAllocator;
         this.bitsPerPixel = encoder.BitsPerPixel;
-        this.quantizer = encoder.Quantizer;
+        this.quantizer = encoder.Quantizer ?? KnownQuantizers.Octree;
         this.pixelSamplingStrategy = encoder.PixelSamplingStrategy;
         this.infoHeaderType = encoder.SupportTransparency ? BmpInfoHeaderType.WinVersion4 : BmpInfoHeaderType.WinVersion3;
     }

src/ImageSharp/Formats/Gif/GifDecoderCore.cs

@@ -29,6 +29,16 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
     /// </summary>
     private IMemoryOwner<byte>? globalColorTable;
 
+    /// <summary>
+    /// The current local color table.
+    /// </summary>
+    private IMemoryOwner<byte>? currentLocalColorTable;
+
+    /// <summary>
+    /// Gets the size in bytes of the current local color table.
+    /// </summary>
+    private int currentLocalColorTableSize;
+
     /// <summary>
     /// The area to restore.
     /// </summary>
@@ -159,6 +169,7 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
         finally
         {
             this.globalColorTable?.Dispose();
+            this.currentLocalColorTable?.Dispose();
         }
 
         if (image is null)
@@ -229,6 +240,7 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
         finally
         {
             this.globalColorTable?.Dispose();
+            this.currentLocalColorTable?.Dispose();
         }
 
         if (this.logicalScreenDescriptor.Width == 0 && this.logicalScreenDescriptor.Height == 0)
@@ -332,7 +344,7 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
             if (subBlockSize == GifConstants.NetscapeLoopingSubBlockSize)
             {
                 stream.Read(this.buffer.Span, 0, GifConstants.NetscapeLoopingSubBlockSize);
-                this.gifMetadata!.RepeatCount = GifNetscapeLoopingApplicationExtension.Parse(this.buffer.Span.Slice(1)).RepeatCount;
+                this.gifMetadata!.RepeatCount = GifNetscapeLoopingApplicationExtension.Parse(this.buffer.Span[1..]).RepeatCount;
                 stream.Skip(1); // Skip the terminator.
                 return;
             }
@@ -415,25 +427,27 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
     {
         this.ReadImageDescriptor(stream);
 
-        IMemoryOwner<byte>? localColorTable = null;
         Buffer2D<byte>? indices = null;
         try
         {
             // Determine the color table for this frame. If there is a local one, use it otherwise use the global color table.
-            if (this.imageDescriptor.LocalColorTableFlag)
+            bool hasLocalColorTable = this.imageDescriptor.LocalColorTableFlag;
+
+            if (hasLocalColorTable)
             {
-                int length = this.imageDescriptor.LocalColorTableSize * 3;
+                // Read and store the local color table. We allocate the maximum possible size and slice to match.
-                localColorTable = this.configuration.MemoryAllocator.Allocate<byte>(length, AllocationOptions.Clean);
+                int length = this.currentLocalColorTableSize = this.imageDescriptor.LocalColorTableSize * 3;
-                stream.Read(localColorTable.GetSpan());
+                this.currentLocalColorTable ??= this.configuration.MemoryAllocator.Allocate<byte>(768, AllocationOptions.Clean);
+                stream.Read(this.currentLocalColorTable.GetSpan()[..length]);
             }
 
             indices = this.configuration.MemoryAllocator.Allocate2D<byte>(this.imageDescriptor.Width, this.imageDescriptor.Height, AllocationOptions.Clean);
             this.ReadFrameIndices(stream, indices);
 
             Span<byte> rawColorTable = default;
-            if (localColorTable != null)
+            if (hasLocalColorTable)
             {
-                rawColorTable = localColorTable.GetSpan();
+                rawColorTable = this.currentLocalColorTable!.GetSpan()[..this.currentLocalColorTableSize];
             }
             else if (this.globalColorTable != null)
             {
@@ -448,7 +462,6 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
         }
         finally
         {
-            localColorTable?.Dispose();
             indices?.Dispose();
         }
     }
@@ -509,7 +522,10 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
                 prevFrame = previousFrame;
             }
 
-            currentFrame = image!.Frames.CreateFrame();
+            // We create a clone of the 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
+            currentFrame = image!.Frames.AddFrame(previousFrame);
 
             this.SetFrameMetadata(currentFrame.Metadata);
 
@@ -631,7 +647,10 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
         // Skip the color table for this frame if local.
         if (this.imageDescriptor.LocalColorTableFlag)
         {
-            stream.Skip(this.imageDescriptor.LocalColorTableSize * 3);
+            // Read and store the local color table. We allocate the maximum possible size and slice to match.
+            int length = this.currentLocalColorTableSize = this.imageDescriptor.LocalColorTableSize * 3;
+            this.currentLocalColorTable ??= this.configuration.MemoryAllocator.Allocate<byte>(768, AllocationOptions.Clean);
+            stream.Read(this.currentLocalColorTable.GetSpan()[..length]);
         }
 
         // Skip the frame indices. Pixels length + mincode size.
@@ -682,7 +701,6 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
         {
             GifFrameMetadata gifMeta = metadata.GetGifMetadata();
             gifMeta.ColorTableMode = GifColorTableMode.Global;
-            gifMeta.ColorTableLength = this.logicalScreenDescriptor.GlobalColorTableSize;
         }
 
         if (this.imageDescriptor.LocalColorTableFlag
@@ -690,13 +708,23 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
         {
             GifFrameMetadata gifMeta = metadata.GetGifMetadata();
             gifMeta.ColorTableMode = GifColorTableMode.Local;
-            gifMeta.ColorTableLength = this.imageDescriptor.LocalColorTableSize;
+
+            Color[] colorTable = new Color[this.imageDescriptor.LocalColorTableSize];
+            ref Rgb24 localBase = ref MemoryMarshal.GetReference(MemoryMarshal.Cast<byte, Rgb24>(this.currentLocalColorTable!.GetSpan()[..this.currentLocalColorTableSize]));
+            for (int i = 0; i < colorTable.Length; i++)
+            {
+                colorTable[i] = new Color(Unsafe.Add(ref localBase, (uint)i));
+            }
+
+            gifMeta.DecodedLocalColorTable = colorTable;
         }
 
         // Graphics control extensions is optional.
         if (this.graphicsControlExtension != default)
         {
             GifFrameMetadata gifMeta = metadata.GetGifMetadata();
+            gifMeta.HasTransparency = this.graphicsControlExtension.TransparencyFlag;
+            gifMeta.TransparencyIndex = this.graphicsControlExtension.TransparencyIndex;
             gifMeta.FrameDelay = this.graphicsControlExtension.DelayTime;
             gifMeta.DisposalMethod = this.graphicsControlExtension.DisposalMethod;
         }
@@ -751,14 +779,21 @@ internal sealed class GifDecoderCore : IImageDecoderInternals
         if (this.logicalScreenDescriptor.GlobalColorTableFlag)
         {
             int globalColorTableLength = this.logicalScreenDescriptor.GlobalColorTableSize * 3;
-            this.gifMetadata.GlobalColorTableLength = globalColorTableLength;
-
             if (globalColorTableLength > 0)
             {
                 this.globalColorTable = this.memoryAllocator.Allocate<byte>(globalColorTableLength, AllocationOptions.Clean);
 
-                // Read the global color table data from the stream
+                // Read the global color table data from the stream and preserve it in the gif metadata
                 stream.Read(this.globalColorTable.GetSpan());
+
+                Color[] colorTable = new Color[this.logicalScreenDescriptor.GlobalColorTableSize];
+                ref Rgb24 globalBase = ref MemoryMarshal.GetReference(MemoryMarshal.Cast<byte, Rgb24>(this.globalColorTable.GetSpan()));
+                for (int i = 0; i < colorTable.Length; i++)
+                {
+                    colorTable[i] = new Color(Unsafe.Add(ref globalBase, (uint)i));
+                }
+
+                this.gifMetadata.DecodedGlobalColorTable = colorTable;
             }
         }
     }

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -4,11 +4,15 @@
 using System.Buffers;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.Arm;
+using System.Runtime.Intrinsics.X86;
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
 namespace SixLabors.ImageSharp.Formats.Gif;
@@ -36,7 +40,12 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
     /// <summary>
     /// The quantizer used to generate the color palette.
     /// </summary>
-    private readonly IQuantizer quantizer;
+    private IQuantizer? quantizer;
+
+    /// <summary>
+    /// Whether the quantizer was supplied via options.
+    /// </summary>
+    private readonly bool hasQuantizer;
 
     /// <summary>
     /// The color table mode: Global or local.
@@ -64,6 +73,7 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
         this.memoryAllocator = configuration.MemoryAllocator;
         this.skipMetadata = encoder.SkipMetadata;
         this.quantizer = encoder.Quantizer;
+        this.hasQuantizer = encoder.Quantizer is not null;
         this.colorTableMode = encoder.ColorTableMode;
         this.pixelSamplingStrategy = encoder.PixelSamplingStrategy;
     }
@@ -88,6 +98,21 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
 
         // Quantize the image returning a palette.
         IndexedImageFrame<TPixel>? quantized;
+
+        if (this.quantizer is null)
+        {
+            // Is this a gif with color information. If so use that, otherwise use octree.
+            if (gifMetadata.ColorTableMode == GifColorTableMode.Global && gifMetadata.DecodedGlobalColorTable.Length > 0)
+            {
+                // We avoid dithering by default to preserve the original colors.
+                this.quantizer = new PaletteQuantizer(gifMetadata.DecodedGlobalColorTable, new() { Dither = null });
+            }
+            else
+            {
+                this.quantizer = KnownQuantizers.Octree;
+            }
+        }
+
         using (IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration))
         {
             if (useGlobalTable)
@@ -109,7 +134,13 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
         WriteHeader(stream);
 
         // Write the LSD.
-        int index = GetTransparentIndex(quantized);
+        image.Frames.RootFrame.Metadata.TryGetGifMetadata(out GifFrameMetadata? frameMetadata);
+        int index = GetTransparentIndex(quantized, frameMetadata);
+        if (index == -1)
+        {
+            index = gifMetadata.BackgroundColor;
+        }
+
         this.WriteLogicalScreenDescriptor(metadata, image.Width, image.Height, index, useGlobalTable, stream);
 
         if (useGlobalTable)
@@ -141,6 +172,14 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
     {
         PaletteQuantizer<TPixel> paletteQuantizer = default;
         bool hasPaletteQuantizer = false;
+
+        // Create a buffer to store de-duplicated pixel indices for encoding.
+        // These are used when the color table is global but we must always allocate since we don't know
+        // in advance whether the frames will use a local palette.
+        Buffer2D<byte> indices = this.memoryAllocator.Allocate2D<byte>(image.Width, image.Height);
+
+        // Store the first frame as a reference for de-duplication comparison.
+        IndexedImageFrame<TPixel> previousQuantized = quantized;
         for (int i = 0; i < image.Frames.Count; i++)
         {
             // Gather the metadata for this frame.
@@ -155,15 +194,21 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
                 // since the palette is unchanging. This allows a reduction of memory usage across
                 // multi frame gifs using a global palette.
                 hasPaletteQuantizer = true;
-                paletteQuantizer = new(this.configuration, this.quantizer.Options, palette);
+                paletteQuantizer = new(this.configuration, this.quantizer!.Options, palette);
             }
 
-            this.EncodeFrame(stream, frame, i, useLocal, frameMetadata, ref quantized!, ref paletteQuantizer);
+            this.EncodeFrame(stream, frame, i, useLocal, frameMetadata, indices, ref previousQuantized, ref quantized!, ref paletteQuantizer);
 
             // Clean up for the next run.
-            quantized.Dispose();
+            if (quantized != previousQuantized)
+            {
+                quantized.Dispose();
+            }
         }
 
+        previousQuantized.Dispose();
+        indices.Dispose();
+
         if (hasPaletteQuantizer)
         {
             paletteQuantizer.Dispose();
@@ -176,47 +221,55 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
         int frameIndex,
         bool useLocal,
         GifFrameMetadata? metadata,
+        Buffer2D<byte> indices,
+        ref IndexedImageFrame<TPixel> previousQuantized,
         ref IndexedImageFrame<TPixel> quantized,
-        ref PaletteQuantizer<TPixel> paletteQuantizer)
+        ref PaletteQuantizer<TPixel> globalPaletteQuantizer)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         // The first frame has already been quantized so we do not need to do so again.
+        int transparencyIndex = -1;
         if (frameIndex > 0)
         {
             if (useLocal)
             {
                 // Reassign using the current frame and details.
-                QuantizerOptions? options = null;
+                if (metadata?.DecodedLocalColorTable.Length > 0)
-                int colorTableLength = metadata?.ColorTableLength ?? 0;
-                if (colorTableLength > 0)
                 {
-                    options = new()
+                    // We can use the color data from the decoded metadata here.
-                    {
+                    // We avoid dithering by default to preserve the original colors.
-                        Dither = this.quantizer.Options.Dither,
+                    PaletteQuantizer localQuantizer = new(metadata.DecodedLocalColorTable, new() { Dither = null });
-                        DitherScale = this.quantizer.Options.DitherScale,
+                    using IQuantizer<TPixel> frameQuantizer = localQuantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, localQuantizer.Options);
-                        MaxColors = colorTableLength
+                    quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(frame, frame.Bounds());
-                    };
+                }
+                else
+                {
+                    // We must quantize the frame to generate a local color table.
+                    IQuantizer localQuantizer = this.hasQuantizer ? this.quantizer! : KnownQuantizers.Octree;
+                    using IQuantizer<TPixel> frameQuantizer = localQuantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, localQuantizer.Options);
+                    quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(frame, frame.Bounds());
                 }
-
-                using IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration, options ?? this.quantizer.Options);
-                quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(frame, frame.Bounds());
             }
             else
             {
                 // Quantize the image using the global palette.
-                quantized = paletteQuantizer.QuantizeFrame(frame, frame.Bounds());
+                quantized = globalPaletteQuantizer.QuantizeFrame(frame, frame.Bounds());
+                transparencyIndex = GetTransparentIndex(quantized, metadata);
+
+                // De-duplicate pixels comparing to the previous frame.
+                // Only global is supported for now as the color palettes as the operation required to compare
+                // and offset the index lookups is too expensive for local palettes.
+                DeDuplicatePixels(previousQuantized, quantized, indices, transparencyIndex);
             }
 
             this.bitDepth = ColorNumerics.GetBitsNeededForColorDepth(quantized.Palette.Length);
         }
-
+        else
-        // Do we have extension information to write?
-        int index = GetTransparentIndex(quantized);
-        if (metadata != null || index > -1)
         {
-            this.WriteGraphicalControlExtension(metadata ?? new(), index, stream);
+            transparencyIndex = GetTransparentIndex(quantized, metadata);
         }
 
+        this.WriteGraphicalControlExtension(metadata, transparencyIndex, stream);
         this.WriteImageDescriptor(frame, useLocal, stream);
 
         if (useLocal)
@@ -224,18 +277,103 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
             this.WriteColorTable(quantized, stream);
         }
 
-        this.WriteImageData(quantized, stream);
+        // Assign the correct buffer to compress.
+        // If we are using a local palette or it's the first run then we want to use the quantized frame.
+        Buffer2D<byte> buffer = useLocal || frameIndex == 0 ? ((IPixelSource)quantized).PixelBuffer : indices;
+        this.WriteImageData(buffer, stream);
+
+        // Swap the buffers.
+        (quantized, previousQuantized) = (previousQuantized, quantized);
+    }
+
+    private static void DeDuplicatePixels<TPixel>(
+        IndexedImageFrame<TPixel> background,
+        IndexedImageFrame<TPixel> source,
+        Buffer2D<byte> indices,
+        int transparencyIndex)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        // TODO: This should be the background color if not transparent.
+        byte replacementIndex = unchecked((byte)transparencyIndex);
+        for (int y = 0; y < background.Height; y++)
+        {
+            ref byte backgroundRowBase = ref MemoryMarshal.GetReference(background.DangerousGetRowSpan(y));
+            ref byte sourceRowBase = ref MemoryMarshal.GetReference(source.DangerousGetRowSpan(y));
+            ref byte indicesRowBase = ref MemoryMarshal.GetReference(indices.DangerousGetRowSpan(y));
+
+            uint x = 0;
+            if (Avx2.IsSupported)
+            {
+                int remaining = background.Width;
+                Vector256<byte> transparentVector = Vector256.Create(replacementIndex);
+                while (remaining >= Vector256<byte>.Count)
+                {
+                    Vector256<byte> b = Unsafe.ReadUnaligned<Vector256<byte>>(ref Unsafe.Add(ref backgroundRowBase, x));
+                    Vector256<byte> s = Unsafe.ReadUnaligned<Vector256<byte>>(ref Unsafe.Add(ref sourceRowBase, x));
+                    Vector256<byte> m = Avx2.CompareEqual(b, s);
+                    Vector256<byte> i = Avx2.BlendVariable(s, transparentVector, m);
+
+                    Unsafe.WriteUnaligned(ref Unsafe.Add(ref indicesRowBase, x), i);
+
+                    x += (uint)Vector256<byte>.Count;
+                    remaining -= Vector256<byte>.Count;
+                }
+            }
+            else if (Sse2.IsSupported)
+            {
+                int remaining = background.Width;
+                Vector128<byte> transparentVector = Vector128.Create(replacementIndex);
+                while (remaining >= Vector128<byte>.Count)
+                {
+                    Vector128<byte> b = Unsafe.ReadUnaligned<Vector128<byte>>(ref Unsafe.Add(ref backgroundRowBase, x));
+                    Vector128<byte> s = Unsafe.ReadUnaligned<Vector128<byte>>(ref Unsafe.Add(ref sourceRowBase, x));
+                    Vector128<byte> m = Sse2.CompareEqual(b, s);
+                    Vector128<byte> i = SimdUtils.HwIntrinsics.BlendVariable(s, transparentVector, m);
+
+                    Unsafe.WriteUnaligned(ref Unsafe.Add(ref indicesRowBase, x), i);
+
+                    x += (uint)Vector128<byte>.Count;
+                    remaining -= Vector128<byte>.Count;
+                }
+            }
+            else if (AdvSimd.Arm64.IsSupported)
+            {
+                int remaining = background.Width;
+                Vector128<byte> transparentVector = Vector128.Create(replacementIndex);
+                while (remaining >= Vector128<byte>.Count)
+                {
+                    Vector128<byte> b = Unsafe.ReadUnaligned<Vector128<byte>>(ref Unsafe.Add(ref backgroundRowBase, x));
+                    Vector128<byte> s = Unsafe.ReadUnaligned<Vector128<byte>>(ref Unsafe.Add(ref sourceRowBase, x));
+                    Vector128<byte> m = AdvSimd.CompareEqual(b, s);
+                    Vector128<byte> i = SimdUtils.HwIntrinsics.BlendVariable(s, transparentVector, m);
+
+                    Unsafe.WriteUnaligned(ref Unsafe.Add(ref indicesRowBase, x), i);
+
+                    x += (uint)Vector128<byte>.Count;
+                    remaining -= Vector128<byte>.Count;
+                }
+            }
+
+            for (; x < (uint)background.Width; x++)
+            {
+                byte b = Unsafe.Add(ref backgroundRowBase, x);
+                byte s = Unsafe.Add(ref sourceRowBase, x);
+                ref byte i = ref Unsafe.Add(ref indicesRowBase, x);
+                i = (b == s) ? replacementIndex : s;
+            }
+        }
     }
 
     /// <summary>
     /// Returns the index of the most transparent color in the palette.
     /// </summary>
-    /// <param name="quantized">The quantized frame.</param>
+    /// <param name="quantized">The current quantized frame.</param>
+    /// <param name="metadata">The current gif frame metadata.</param>
     /// <typeparam name="TPixel">The pixel format.</typeparam>
     /// <returns>
     /// The <see cref="int"/>.
     /// </returns>
-    private static int GetTransparentIndex<TPixel>(IndexedImageFrame<TPixel> quantized)
+    private static int GetTransparentIndex<TPixel>(IndexedImageFrame<TPixel> quantized, GifFrameMetadata? metadata)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         // Transparent pixels are much more likely to be found at the end of a palette.
@@ -255,6 +393,11 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
             }
         }
 
+        if (metadata?.HasTransparency == true && index == -1)
+        {
+            index = metadata.TransparencyIndex;
+        }
+
         return index;
     }
 
@@ -271,14 +414,14 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
     /// <param name="metadata">The image metadata.</param>
     /// <param name="width">The image width.</param>
     /// <param name="height">The image height.</param>
-    /// <param name="transparencyIndex">The transparency index to set the default background index to.</param>
+    /// <param name="backgroundIndex">The index to set the default background index to.</param>
     /// <param name="useGlobalTable">Whether to use a global or local color table.</param>
     /// <param name="stream">The stream to write to.</param>
     private void WriteLogicalScreenDescriptor(
         ImageMetadata metadata,
         int width,
         int height,
-        int transparencyIndex,
+        int backgroundIndex,
         bool useGlobalTable,
         Stream stream)
     {
@@ -316,7 +459,7 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
             width: (ushort)width,
             height: (ushort)height,
             packed: packedValue,
-            backgroundColorIndex: unchecked((byte)transparencyIndex),
+            backgroundColorIndex: unchecked((byte)backgroundIndex),
             ratio);
 
         Span<byte> buffer = stackalloc byte[20];
@@ -412,16 +555,26 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
     /// <param name="metadata">The metadata of the image or frame.</param>
     /// <param name="transparencyIndex">The index of the color in the color palette to make transparent.</param>
     /// <param name="stream">The stream to write to.</param>
-    private void WriteGraphicalControlExtension(GifFrameMetadata metadata, int transparencyIndex, Stream stream)
+    private void WriteGraphicalControlExtension(GifFrameMetadata? metadata, int transparencyIndex, Stream stream)
     {
+        bool hasTransparency;
+        if (metadata is null)
+        {
+            hasTransparency = transparencyIndex > -1;
+        }
+        else
+        {
+            hasTransparency = metadata.HasTransparency;
+        }
+
         byte packedValue = GifGraphicControlExtension.GetPackedValue(
-            disposalMethod: metadata.DisposalMethod,
+            disposalMethod: metadata!.DisposalMethod,
-            transparencyFlag: transparencyIndex > -1);
+            transparencyFlag: hasTransparency);
 
         GifGraphicControlExtension extension = new(
             packed: packedValue,
             delayTime: (ushort)metadata.FrameDelay,
-            transparencyIndex: unchecked((byte)transparencyIndex));
+            transparencyIndex: hasTransparency ? unchecked((byte)transparencyIndex) : byte.MinValue);
 
         this.WriteExtension(extension, stream);
     }
@@ -521,13 +674,11 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
     /// <summary>
     /// Writes the image pixel data to the stream.
     /// </summary>
-    /// <typeparam name="TPixel">The pixel format.</typeparam>
+    /// <param name="indices">The <see cref="Buffer2D{Byte}"/> containing indexed pixels.</param>
-    /// <param name="image">The <see cref="IndexedImageFrame{TPixel}"/> containing indexed pixels.</param>
     /// <param name="stream">The stream to write to.</param>
-    private void WriteImageData<TPixel>(IndexedImageFrame<TPixel> image, Stream stream)
+    private void WriteImageData(Buffer2D<byte> indices, Stream stream)
-        where TPixel : unmanaged, IPixel<TPixel>
     {
         using LzwEncoder encoder = new(this.memoryAllocator, (byte)this.bitDepth);
-        encoder.Encode(((IPixelSource)image).PixelBuffer, stream);
+        encoder.Encode(indices, stream);
     }
 }

src/ImageSharp/Formats/Gif/GifFrameMetadata.cs

@@ -22,9 +22,16 @@ public class GifFrameMetadata : IDeepCloneable
     private GifFrameMetadata(GifFrameMetadata other)
     {
         this.ColorTableMode = other.ColorTableMode;
-        this.ColorTableLength = other.ColorTableLength;
         this.FrameDelay = other.FrameDelay;
         this.DisposalMethod = other.DisposalMethod;
+
+        if (other.DecodedLocalColorTable.Length > 0)
+        {
+            this.DecodedLocalColorTable = other.DecodedLocalColorTable.ToArray();
+        }
+
+        this.HasTransparency = other.HasTransparency;
+        this.TransparencyIndex = other.TransparencyIndex;
     }
 
     /// <summary>
@@ -33,11 +40,21 @@ public class GifFrameMetadata : IDeepCloneable
     public GifColorTableMode ColorTableMode { get; set; }
 
     /// <summary>
-    /// Gets or sets the length of the color table.
+    /// Gets the decoded global color table, if any.
-    /// If not 0, then this field indicates the maximum number of colors to use when quantizing the
+    /// </summary>
-    /// image frame.
+    public ReadOnlyMemory<Color> DecodedLocalColorTable { get; internal set; }
+
+    /// <summary>
+    /// Gets or sets a value indicating whether the frame has transparency
+    /// </summary>
+    public bool HasTransparency { get; set; }
+
+    /// <summary>
+    /// Gets or sets the transparency index.
+    /// When <see cref="HasTransparency"/> is set to <see langword="true"/> this value indicates the index within
+    /// the color palette at which the transparent color is located.
     /// </summary>
-    public int ColorTableLength { get; set; }
+    public byte TransparencyIndex { get; set; }
 
     /// <summary>
     /// Gets or sets the frame delay for animated images.

src/ImageSharp/Formats/Gif/GifMetadata.cs

@@ -23,7 +23,12 @@ public class GifMetadata : IDeepCloneable
     {
         this.RepeatCount = other.RepeatCount;
         this.ColorTableMode = other.ColorTableMode;
-        this.GlobalColorTableLength = other.GlobalColorTableLength;
+        this.BackgroundColor = other.BackgroundColor;
+
+        if (other.DecodedGlobalColorTable.Length > 0)
+        {
+            this.DecodedGlobalColorTable = other.DecodedGlobalColorTable.ToArray();
+        }
 
         for (int i = 0; i < other.Comments.Count; i++)
         {
@@ -45,9 +50,15 @@ public class GifMetadata : IDeepCloneable
     public GifColorTableMode ColorTableMode { get; set; }
 
     /// <summary>
-    /// Gets or sets the length of the global color table if present.
+    /// Gets the decoded global color table, if any.
+    /// </summary>
+    public ReadOnlyMemory<Color> DecodedGlobalColorTable { get; internal set; }
+
+    /// <summary>
+    /// Gets or sets the index at the <see cref="DecodedGlobalColorTable"/> for the background color.
+    /// The background color is the color used for those pixels on the screen that are not covered by an image.
     /// </summary>
-    public int GlobalColorTableLength { get; set; }
+    public byte BackgroundColor { get; set; }
 
     /// <summary>
     /// Gets or sets the collection of comments about the graphics, credits, descriptions or any

src/ImageSharp/Formats/Gif/MetadataExtensions.cs

@@ -17,14 +17,16 @@ public static partial class MetadataExtensions
     /// </summary>
     /// <param name="source">The metadata this method extends.</param>
     /// <returns>The <see cref="GifMetadata"/>.</returns>
-    public static GifMetadata GetGifMetadata(this ImageMetadata source) => source.GetFormatMetadata(GifFormat.Instance);
+    public static GifMetadata GetGifMetadata(this ImageMetadata source)
+        => source.GetFormatMetadata(GifFormat.Instance);
 
     /// <summary>
     /// Gets the gif format specific metadata for the image frame.
     /// </summary>
     /// <param name="source">The metadata this method extends.</param>
     /// <returns>The <see cref="GifFrameMetadata"/>.</returns>
-    public static GifFrameMetadata GetGifMetadata(this ImageFrameMetadata source) => source.GetFormatMetadata(GifFormat.Instance);
+    public static GifFrameMetadata GetGifMetadata(this ImageFrameMetadata source)
+        => source.GetFormatMetadata(GifFormat.Instance);
 
     /// <summary>
     /// Gets the gif format specific metadata for the image frame.
@@ -38,5 +40,6 @@ public static partial class MetadataExtensions
     /// <returns>
     /// <see langword="true"/> if the gif frame metadata exists; otherwise, <see langword="false"/>.
     /// </returns>
-    public static bool TryGetGifMetadata(this ImageFrameMetadata source, [NotNullWhen(true)] out GifFrameMetadata? metadata) => source.TryGetFormatMetadata(GifFormat.Instance, out metadata);
+    public static bool TryGetGifMetadata(this ImageFrameMetadata source, [NotNullWhen(true)] out GifFrameMetadata? metadata)
+        => source.TryGetFormatMetadata(GifFormat.Instance, out metadata);
 }

src/ImageSharp/Formats/Png/Filters/PaethFilter.cs

@@ -35,9 +35,9 @@ internal static class PaethFilter
         // row:  a d
         // The Paeth function predicts d to be whichever of a, b, or c is nearest to
         // p = a + b - c.
-        if (Sse41.IsSupported && bytesPerPixel is 4)
+        if (Sse2.IsSupported && bytesPerPixel is 4)
         {
-            DecodeSse41(scanline, previousScanline);
+            DecodeSse3(scanline, previousScanline);
         }
         else if (AdvSimd.Arm64.IsSupported && bytesPerPixel is 4)
         {
@@ -50,7 +50,7 @@ internal static class PaethFilter
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private static void DecodeSse41(Span<byte> scanline, Span<byte> previousScanline)
+    private static void DecodeSse3(Span<byte> scanline, Span<byte> previousScanline)
     {
         ref byte scanBaseRef = ref MemoryMarshal.GetReference(scanline);
         ref byte prevBaseRef = ref MemoryMarshal.GetReference(previousScanline);
@@ -90,8 +90,8 @@ internal static class PaethFilter
             Vector128<short> smallest = Sse2.Min(pc, Sse2.Min(pa, pb));
 
             // Paeth breaks ties favoring a over b over c.
-            Vector128<byte> mask = Sse41.BlendVariable(c, b, Sse2.CompareEqual(smallest, pb).AsByte());
+            Vector128<byte> mask = SimdUtils.HwIntrinsics.BlendVariable(c, b, Sse2.CompareEqual(smallest, pb).AsByte());
-            Vector128<byte> nearest = Sse41.BlendVariable(mask, a, Sse2.CompareEqual(smallest, pa).AsByte());
+            Vector128<byte> nearest = SimdUtils.HwIntrinsics.BlendVariable(mask, a, Sse2.CompareEqual(smallest, pa).AsByte());
 
             // Note `_epi8`: we need addition to wrap modulo 255.
             d = Sse2.Add(d, nearest);
@@ -143,8 +143,8 @@ internal static class PaethFilter
             Vector128<short> smallest = AdvSimd.Min(pc, AdvSimd.Min(pa, pb));
 
             // Paeth breaks ties favoring a over b over c.
-            Vector128<byte> mask = BlendVariable(c, b, AdvSimd.CompareEqual(smallest, pb).AsByte());
+            Vector128<byte> mask = SimdUtils.HwIntrinsics.BlendVariable(c, b, AdvSimd.CompareEqual(smallest, pb).AsByte());
-            Vector128<byte> nearest = BlendVariable(mask, a, AdvSimd.CompareEqual(smallest, pa).AsByte());
+            Vector128<byte> nearest = SimdUtils.HwIntrinsics.BlendVariable(mask, a, AdvSimd.CompareEqual(smallest, pa).AsByte());
 
             d = AdvSimd.Add(d, nearest);
 
@@ -157,27 +157,6 @@ internal static class PaethFilter
         }
     }
 
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private static Vector128<byte> BlendVariable(Vector128<byte> a, Vector128<byte> b, Vector128<byte> c)
-    {
-        // Equivalent of Sse41.BlendVariable:
-        // Blend packed 8-bit integers from a and b using mask, and store the results in
-        // dst.
-        //
-        //   FOR j := 0 to 15
-        //       i := j*8
-        //       IF mask[i+7]
-        //           dst[i+7:i] := b[i+7:i]
-        //       ELSE
-        //           dst[i+7:i] := a[i+7:i]
-        //       FI
-        //   ENDFOR
-        //
-        // Use a signed shift right to create a mask with the sign bit.
-        Vector128<short> mask = AdvSimd.ShiftRightArithmetic(c.AsInt16(), 7);
-        return AdvSimd.BitwiseSelect(mask, b.AsInt16(), a.AsInt16()).AsByte();
-    }
-
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private static void DecodeScalar(Span<byte> scanline, Span<byte> previousScanline, uint bytesPerPixel)
     {

src/ImageSharp/Formats/Png/PngEncoder.cs

@@ -11,15 +11,6 @@ namespace SixLabors.ImageSharp.Formats.Png;
 /// </summary>
 public class PngEncoder : QuantizingImageEncoder
 {
-    /// <summary>
-    /// Initializes a new instance of the <see cref="PngEncoder"/> class.
-    /// </summary>
-    public PngEncoder() =>
-
-        // We set the quantizer to null here to allow the underlying encoder to create a
-        // quantizer with options appropriate to the encoding bit depth.
-        this.Quantizer = null;
-
     /// <summary>
     /// Gets the number of bits per sample or per palette index (not per pixel).
     /// Not all values are allowed for all <see cref="ColorType" /> values.

src/ImageSharp/Formats/QuantizingImageEncoder.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
 namespace SixLabors.ImageSharp.Formats;
@@ -14,7 +13,7 @@ public abstract class QuantizingImageEncoder : ImageEncoder
     /// <summary>
     /// Gets the quantizer used to generate the color palette.
     /// </summary>
-    public IQuantizer Quantizer { get; init; } = KnownQuantizers.Octree;
+    public IQuantizer? Quantizer { get; init; }
 
     /// <summary>
     /// Gets the <see cref="IPixelSamplingStrategy"/> used for quantization when building color palettes.

src/ImageSharp/Formats/Tiff/TiffEncoder.cs

@@ -4,6 +4,7 @@
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Compression.Zlib;
 using SixLabors.ImageSharp.Formats.Tiff.Constants;
+using SixLabors.ImageSharp.Processing;
 
 namespace SixLabors.ImageSharp.Formats.Tiff;
 
@@ -12,6 +13,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff;
 /// </summary>
 public class TiffEncoder : QuantizingImageEncoder
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TiffEncoder"/> class.
+    /// </summary>
+    public TiffEncoder() => this.Quantizer = KnownQuantizers.Octree;
+
     /// <summary>
     /// Gets the number of bits per pixel.
     /// </summary>

src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs

@@ -11,6 +11,7 @@ using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
 namespace SixLabors.ImageSharp.Formats.Tiff;
@@ -85,7 +86,7 @@ internal sealed class TiffEncoderCore : IImageEncoderInternals
     {
         this.memoryAllocator = memoryAllocator;
         this.PhotometricInterpretation = options.PhotometricInterpretation;
-        this.quantizer = options.Quantizer;
+        this.quantizer = options.Quantizer ?? KnownQuantizers.Octree;
         this.pixelSamplingStrategy = options.PixelSamplingStrategy;
         this.BitsPerPixel = options.BitsPerPixel;
         this.HorizontalPredictor = options.HorizontalPredictor;
@@ -320,7 +321,7 @@ internal sealed class TiffEncoderCore : IImageEncoderInternals
             {
                 int sz = ExifWriter.WriteValue(entry, buffer, 0);
                 DebugGuard.IsTrue(sz == length, "Incorrect number of bytes written");
-                writer.WritePadded(buffer.Slice(0, sz));
+                writer.WritePadded(buffer[..sz]);
             }
             else
             {

src/ImageSharp/Memory/Buffer2D{T}.cs

@@ -173,13 +173,15 @@ public sealed class Buffer2D<T> : IDisposable
     /// Swaps the contents of 'destination' with 'source' if the buffers are owned (1),
     /// copies the contents of 'source' to 'destination' otherwise (2). Buffers should be of same size in case 2!
     /// </summary>
+    /// <param name="destination">The destination buffer.</param>
+    /// <param name="source">The source buffer.</param>
+    /// <exception cref="InvalidMemoryOperationException">Attempt to copy/swap incompatible buffers.</exception>
     internal static bool SwapOrCopyContent(Buffer2D<T> destination, Buffer2D<T> source)
     {
         bool swapped = false;
         if (MemoryGroup<T>.CanSwapContent(destination.FastMemoryGroup, source.FastMemoryGroup))
         {
-            (destination.FastMemoryGroup, source.FastMemoryGroup) =
+            (destination.FastMemoryGroup, source.FastMemoryGroup) = (source.FastMemoryGroup, destination.FastMemoryGroup);
-                (source.FastMemoryGroup, destination.FastMemoryGroup);
             destination.FastMemoryGroup.RecreateViewAfterSwap();
             source.FastMemoryGroup.RecreateViewAfterSwap();
             swapped = true;
@@ -201,7 +203,6 @@ public sealed class Buffer2D<T> : IDisposable
     }
 
     [MethodImpl(InliningOptions.ColdPath)]
-    private void ThrowYOutOfRangeException(int y) =>
+    private void ThrowYOutOfRangeException(int y)
-        throw new ArgumentOutOfRangeException(
+        => throw new ArgumentOutOfRangeException($"DangerousGetRowSpan({y}). Y was out of range. Height={this.Height}");
-            $"DangerousGetRowSpan({y}). Y was out of range. Height={this.Height}");
 }

src/ImageSharp/Processing/Processors/Quantization/QuantizerOptions.cs

@@ -25,8 +25,8 @@ public class QuantizerOptions
     /// </summary>
     public float DitherScale
     {
-        get { return this.ditherScale; }
+        get => this.ditherScale;
-        set { this.ditherScale = Numerics.Clamp(value, QuantizerConstants.MinDitherScale, QuantizerConstants.MaxDitherScale); }
+        set => this.ditherScale = Numerics.Clamp(value, QuantizerConstants.MinDitherScale, QuantizerConstants.MaxDitherScale);
     }
 
     /// <summary>
@@ -35,7 +35,7 @@ public class QuantizerOptions
     /// </summary>
     public int MaxColors
     {
-        get { return this.maxColors; }
+        get => this.maxColors;
-        set { this.maxColors = Numerics.Clamp(value, QuantizerConstants.MinColors, QuantizerConstants.MaxColors); }
+        set => this.maxColors = Numerics.Clamp(value, QuantizerConstants.MinColors, QuantizerConstants.MaxColors);
     }
 }

tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs

@@ -171,10 +171,21 @@ public class GifEncoderTests
         GifMetadata metaData = image.Metadata.GetGifMetadata();
         GifFrameMetadata frameMetadata = image.Frames.RootFrame.Metadata.GetGifMetadata();
         GifColorTableMode colorMode = metaData.ColorTableMode;
+
+        int maxColors;
+        if (colorMode == GifColorTableMode.Global)
+        {
+            maxColors = metaData.DecodedGlobalColorTable.Length;
+        }
+        else
+        {
+            maxColors = frameMetadata.DecodedLocalColorTable.Length;
+        }
+
         GifEncoder encoder = new()
         {
             ColorTableMode = colorMode,
-            Quantizer = new OctreeQuantizer(new QuantizerOptions { MaxColors = frameMetadata.ColorTableLength })
+            Quantizer = new OctreeQuantizer(new QuantizerOptions { MaxColors = maxColors })
         };
 
         image.Save(outStream, encoder);
@@ -187,15 +198,31 @@ public class GifEncoderTests
         Assert.Equal(metaData.ColorTableMode, cloneMetadata.ColorTableMode);
 
         // Gifiddle and Cyotek GifInfo say this image has 64 colors.
-        Assert.Equal(64, frameMetadata.ColorTableLength);
+        colorMode = cloneMetadata.ColorTableMode;
+        if (colorMode == GifColorTableMode.Global)
+        {
+            maxColors = metaData.DecodedGlobalColorTable.Length;
+        }
+        else
+        {
+            maxColors = frameMetadata.DecodedLocalColorTable.Length;
+        }
+
+        Assert.Equal(64, maxColors);
 
         for (int i = 0; i < image.Frames.Count; i++)
         {
-            GifFrameMetadata ifm = image.Frames[i].Metadata.GetGifMetadata();
+            GifFrameMetadata iMeta = image.Frames[i].Metadata.GetGifMetadata();
-            GifFrameMetadata cifm = clone.Frames[i].Metadata.GetGifMetadata();
+            GifFrameMetadata cMeta = clone.Frames[i].Metadata.GetGifMetadata();
+
+            if (iMeta.ColorTableMode == GifColorTableMode.Local)
+            {
+                Assert.Equal(iMeta.DecodedLocalColorTable.Length, cMeta.DecodedLocalColorTable.Length);
+            }
 
-            Assert.Equal(ifm.ColorTableLength, cifm.ColorTableLength);
+            Assert.Equal(iMeta.FrameDelay, cMeta.FrameDelay);
-            Assert.Equal(ifm.FrameDelay, cifm.FrameDelay);
+            Assert.Equal(iMeta.HasTransparency, cMeta.HasTransparency);
+            Assert.Equal(iMeta.TransparencyIndex, cMeta.TransparencyIndex);
         }
 
         image.Dispose();

tests/ImageSharp.Tests/Formats/Gif/GifFrameMetadataTests.cs

@@ -11,21 +11,22 @@ public class GifFrameMetadataTests
     [Fact]
     public void CloneIsDeep()
     {
-        var meta = new GifFrameMetadata
+        GifFrameMetadata meta = new()
         {
             FrameDelay = 1,
             DisposalMethod = GifDisposalMethod.RestoreToBackground,
-            ColorTableLength = 2
+            DecodedLocalColorTable = new[] { Color.Black, Color.White }
         };
 
-        var clone = (GifFrameMetadata)meta.DeepClone();
+        GifFrameMetadata clone = (GifFrameMetadata)meta.DeepClone();
 
         clone.FrameDelay = 2;
         clone.DisposalMethod = GifDisposalMethod.RestoreToPrevious;
-        clone.ColorTableLength = 1;
+        clone.DecodedLocalColorTable = new[] { Color.Black };
 
         Assert.False(meta.FrameDelay.Equals(clone.FrameDelay));
         Assert.False(meta.DisposalMethod.Equals(clone.DisposalMethod));
-        Assert.False(meta.ColorTableLength.Equals(clone.ColorTableLength));
+        Assert.False(meta.DecodedLocalColorTable.Length == clone.DecodedLocalColorTable.Length);
+        Assert.Equal(1, clone.DecodedLocalColorTable.Length);
     }
 }

tests/ImageSharp.Tests/Formats/Gif/GifMetadataTests.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-using Microsoft.CodeAnalysis;
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Gif;
 using SixLabors.ImageSharp.Metadata;
@@ -35,7 +34,7 @@ public class GifMetadataTests
         {
             RepeatCount = 1,
             ColorTableMode = GifColorTableMode.Global,
-            GlobalColorTableLength = 2,
+            DecodedGlobalColorTable = new[] { Color.Black, Color.White },
             Comments = new List<string> { "Foo" }
         };
 
@@ -43,11 +42,12 @@ public class GifMetadataTests
 
         clone.RepeatCount = 2;
         clone.ColorTableMode = GifColorTableMode.Local;
-        clone.GlobalColorTableLength = 1;
+        clone.DecodedGlobalColorTable = new[] { Color.Black };
 
         Assert.False(meta.RepeatCount.Equals(clone.RepeatCount));
         Assert.False(meta.ColorTableMode.Equals(clone.ColorTableMode));
-        Assert.False(meta.GlobalColorTableLength.Equals(clone.GlobalColorTableLength));
+        Assert.False(meta.DecodedGlobalColorTable.Length == clone.DecodedGlobalColorTable.Length);
+        Assert.Equal(1, clone.DecodedGlobalColorTable.Length);
         Assert.False(meta.Comments.Equals(clone.Comments));
         Assert.True(meta.Comments.SequenceEqual(clone.Comments));
     }
@@ -205,7 +205,12 @@ public class GifMetadataTests
         GifFrameMetadata gifFrameMetadata = imageInfo.FrameMetadataCollection[imageInfo.FrameMetadataCollection.Count - 1].GetGifMetadata();
 
         Assert.Equal(colorTableMode, gifFrameMetadata.ColorTableMode);
-        Assert.Equal(globalColorTableLength, gifFrameMetadata.ColorTableLength);
+
+        if (colorTableMode == GifColorTableMode.Global)
+        {
+            Assert.Equal(globalColorTableLength, gifMetadata.DecodedGlobalColorTable.Length);
+        }
+
         Assert.Equal(frameDelay, gifFrameMetadata.FrameDelay);
         Assert.Equal(disposalMethod, gifFrameMetadata.DisposalMethod);
     }

tests/ImageSharp.Tests/Image/ImageFrameCollectionTests.NonGeneric.cs

@@ -279,6 +279,7 @@ public abstract partial class ImageFrameCollectionTests
         {
             using Image source = provider.GetImage();
             using Image<TPixel> dest = new(source.GetConfiguration(), source.Width, source.Height);
+
             // Giphy.gif has 5 frames
             ImportFrameAs<Bgra32>(source.Frames, dest.Frames, 0);
             ImportFrameAs<Argb32>(source.Frames, dest.Frames, 1);
@@ -289,7 +290,7 @@ public abstract partial class ImageFrameCollectionTests
             // Drop the original empty root frame:
             dest.Frames.RemoveFrame(0);
 
-            dest.DebugSave(provider, appendSourceFileOrDescription: false, extension: "gif");
+            dest.DebugSave(provider, extension: "gif", appendSourceFileOrDescription: false);
             dest.CompareToOriginal(provider);
 
             for (int i = 0; i < 5; i++)
@@ -314,7 +315,11 @@ public abstract partial class ImageFrameCollectionTests
 
             Assert.Equal(aData.DisposalMethod, bData.DisposalMethod);
             Assert.Equal(aData.FrameDelay, bData.FrameDelay);
-            Assert.Equal(aData.ColorTableLength, bData.ColorTableLength);
+
+            if (aData.ColorTableMode == GifColorTableMode.Local && bData.ColorTableMode == GifColorTableMode.Local)
+            {
+                Assert.Equal(aData.DecodedLocalColorTable.Length, bData.DecodedLocalColorTable.Length);
+            }
         }
     }
 }

tests/ImageSharp.Tests/Metadata/ImageFrameMetadataTests.cs

@@ -4,6 +4,7 @@
 using SixLabors.ImageSharp.Formats.Gif;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Icc;
+using SixLabors.ImageSharp.Metadata.Profiles.Iptc;
 using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using ExifProfile = SixLabors.ImageSharp.Metadata.Profiles.Exif.ExifProfile;
 using ExifTag = SixLabors.ImageSharp.Metadata.Profiles.Exif.ExifTag;
@@ -22,17 +23,17 @@ public class ImageFrameMetadataTests
         const int colorTableLength = 128;
         const GifDisposalMethod disposalMethod = GifDisposalMethod.RestoreToBackground;
 
-        var metaData = new ImageFrameMetadata();
+        ImageFrameMetadata metaData = new();
         GifFrameMetadata gifFrameMetadata = metaData.GetGifMetadata();
         gifFrameMetadata.FrameDelay = frameDelay;
-        gifFrameMetadata.ColorTableLength = colorTableLength;
+        gifFrameMetadata.DecodedLocalColorTable = Enumerable.Repeat(Color.HotPink, colorTableLength).ToArray();
         gifFrameMetadata.DisposalMethod = disposalMethod;
 
-        var clone = new ImageFrameMetadata(metaData);
+        ImageFrameMetadata clone = new(metaData);
         GifFrameMetadata cloneGifFrameMetadata = clone.GetGifMetadata();
 
         Assert.Equal(frameDelay, cloneGifFrameMetadata.FrameDelay);
-        Assert.Equal(colorTableLength, cloneGifFrameMetadata.ColorTableLength);
+        Assert.Equal(colorTableLength, cloneGifFrameMetadata.DecodedLocalColorTable.Length);
         Assert.Equal(disposalMethod, cloneGifFrameMetadata.DisposalMethod);
     }
 
@@ -40,19 +41,19 @@ public class ImageFrameMetadataTests
     public void CloneIsDeep()
     {
         // arrange
-        var exifProfile = new ExifProfile();
+        ExifProfile exifProfile = new();
         exifProfile.SetValue(ExifTag.Software, "UnitTest");
         exifProfile.SetValue(ExifTag.Artist, "UnitTest");
-        var xmpProfile = new XmpProfile(new byte[0]);
+        XmpProfile xmpProfile = new(Array.Empty<byte>());
-        var iccProfile = new IccProfile()
+        IccProfile iccProfile = new()
         {
             Header = new IccProfileHeader()
             {
                 CmmType = "Unittest"
             }
         };
-        var iptcProfile = new ImageSharp.Metadata.Profiles.Iptc.IptcProfile();
+        IptcProfile iptcProfile = new();
-        var metaData = new ImageFrameMetadata()
+        ImageFrameMetadata metaData = new()
         {
             XmpProfile = xmpProfile,
             ExifProfile = exifProfile,