Merge pull request #1654 from SixLabors/js/quantizer

Quantization: reduce memory footprint without compromising speed and quality
5 years ago · f1bb0e40ca
145 changed files with 560 additions and 567 deletions
--- a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
+++ b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
@ -98,7 +98,7 @@ namespace SixLabors.ImageSharp.Formats.Bmp
            this.memoryAllocator = memoryAllocator;
            this.bitsPerPixel = options.BitsPerPixel;
            this.writeV4Header = options.SupportTransparency;
-            this.quantizer = options.Quantizer ?? KnownQuantizers.Wu;
+            this.quantizer = options.Quantizer ?? KnownQuantizers.Octree;
        }

        /// <summary>
--- a/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
+++ b/src/ImageSharp/Formats/Gif/GifEncoderCore.cs
@ -151,7 +151,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
            // since the palette is unchanging. This allows a reduction of memory usage across
            // multi frame gifs using a global palette.
            EuclideanPixelMap<TPixel> pixelMap = default;
-            bool pixelMapSet = false;
+            bool pixelMapHasValue = false;
            for (int i = 0; i < image.Frames.Count; i++)
            {
                ImageFrame<TPixel> frame = image.Frames[i];
@ -166,17 +166,22 @@ namespace SixLabors.ImageSharp.Formats.Gif
                }
                else
                {
-                    if (!pixelMapSet)
+                    if (!pixelMapHasValue)
                    {
-                        pixelMapSet = true;
+                        pixelMapHasValue = true;
                        pixelMap = new EuclideanPixelMap<TPixel>(this.configuration, quantized.Palette);
                    }

-                    using var paletteFrameQuantizer = new PaletteQuantizer<TPixel>(this.configuration, this.quantizer.Options, pixelMap);
+                    using var paletteFrameQuantizer = new PaletteQuantizer<TPixel>(this.configuration, this.quantizer.Options, pixelMap, true);
                    using IndexedImageFrame<TPixel> paletteQuantized = paletteFrameQuantizer.QuantizeFrame(frame, frame.Bounds());
                    this.WriteImageData(paletteQuantized, stream);
                }
            }
+
+            if (pixelMapHasValue)
+            {
+                pixelMap.Dispose();
+            }
        }

        private void EncodeLocal<TPixel>(Image<TPixel> image, IndexedImageFrame<TPixel> quantized, Stream stream)
--- a/src/ImageSharp/Memory/Allocators/ArrayPoolMemoryAllocator.cs
+++ b/src/ImageSharp/Memory/Allocators/ArrayPoolMemoryAllocator.cs
@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.

 using System;
@ -131,10 +131,6 @@ namespace SixLabors.ImageSharp.Memory
            Guard.MustBeGreaterThanOrEqualTo(length, 0, nameof(length));
            int itemSizeBytes = Unsafe.SizeOf<T>();
            int bufferSizeInBytes = length * itemSizeBytes;
-            if (bufferSizeInBytes < 0 || bufferSizeInBytes > this.BufferCapacityInBytes)
-            {
-                ThrowInvalidAllocationException<T>(length);
-            }

            ArrayPool<byte> pool = this.GetArrayPool(bufferSizeInBytes);
            byte[] byteArray = pool.Rent(bufferSizeInBytes);
@ -171,9 +167,9 @@ namespace SixLabors.ImageSharp.Memory
        }

        [MethodImpl(InliningOptions.ColdPath)]
-        private static void ThrowInvalidAllocationException<T>(int length) =>
+        private static void ThrowInvalidAllocationException<T>(int length, int max) =>
            throw new InvalidMemoryOperationException(
-                $"Requested allocation: {length} elements of {typeof(T).Name} is over the capacity of the MemoryAllocator.");
+                $"Requested allocation: '{length}' elements of '{typeof(T).Name}' is over the capacity in bytes '{max}' of the MemoryAllocator.");

        private ArrayPool<byte> GetArrayPool(int bufferSizeInBytes)
        {
--- a/src/ImageSharp/Processing/Extensions/Dithering/DitherExtensions.cs
+++ b/src/ImageSharp/Processing/Extensions/Dithering/DitherExtensions.cs
@ -21,7 +21,7 @@ namespace SixLabors.ImageSharp.Processing
            Dither(source, KnownDitherings.Bayer8x8);

        /// <summary>
-        /// Dithers the image reducing it to a web-safe palette using ordered dithering.
+        /// Dithers the image reducing it to a web-safe palette.
        /// </summary>
        /// <param name="source">The image this method extends.</param>
        /// <param name="dither">The ordered ditherer.</param>
@ -32,7 +32,7 @@ namespace SixLabors.ImageSharp.Processing
            source.ApplyProcessor(new PaletteDitherProcessor(dither));

        /// <summary>
-        /// Dithers the image reducing it to a web-safe palette using ordered dithering.
+        /// Dithers the image reducing it to a web-safe palette.
        /// </summary>
        /// <param name="source">The image this method extends.</param>
        /// <param name="dither">The ordered ditherer.</param>
@ -45,7 +45,7 @@ namespace SixLabors.ImageSharp.Processing
            source.ApplyProcessor(new PaletteDitherProcessor(dither, ditherScale));

        /// <summary>
-        /// Dithers the image reducing it to the given palette using ordered dithering.
+        /// Dithers the image reducing it to the given palette.
        /// </summary>
        /// <param name="source">The image this method extends.</param>
        /// <param name="dither">The ordered ditherer.</param>
@ -58,7 +58,7 @@ namespace SixLabors.ImageSharp.Processing
            source.ApplyProcessor(new PaletteDitherProcessor(dither, palette));

        /// <summary>
-        /// Dithers the image reducing it to the given palette using ordered dithering.
+        /// Dithers the image reducing it to the given palette.
        /// </summary>
        /// <param name="source">The image this method extends.</param>
        /// <param name="dither">The ordered ditherer.</param>
@ -84,7 +84,7 @@ namespace SixLabors.ImageSharp.Processing
            Dither(source, KnownDitherings.Bayer8x8, rectangle);

        /// <summary>
-        /// Dithers the image reducing it to a web-safe palette using ordered dithering.
+        /// Dithers the image reducing it to a web-safe palette.
        /// </summary>
        /// <param name="source">The image this method extends.</param>
        /// <param name="dither">The ordered ditherer.</param>
@ -99,7 +99,7 @@ namespace SixLabors.ImageSharp.Processing
            source.ApplyProcessor(new PaletteDitherProcessor(dither), rectangle);

        /// <summary>
-        /// Dithers the image reducing it to a web-safe palette using ordered dithering.
+        /// Dithers the image reducing it to a web-safe palette.
        /// </summary>
        /// <param name="source">The image this method extends.</param>
        /// <param name="dither">The ordered ditherer.</param>
@ -116,7 +116,7 @@ namespace SixLabors.ImageSharp.Processing
            source.ApplyProcessor(new PaletteDitherProcessor(dither, ditherScale), rectangle);

        /// <summary>
-        /// Dithers the image reducing it to the given palette using ordered dithering.
+        /// Dithers the image reducing it to the given palette.
        /// </summary>
        /// <param name="source">The image this method extends.</param>
        /// <param name="dither">The ordered ditherer.</param>
@ -133,7 +133,7 @@ namespace SixLabors.ImageSharp.Processing
            source.ApplyProcessor(new PaletteDitherProcessor(dither, palette), rectangle);

        /// <summary>
-        /// Dithers the image reducing it to the given palette using ordered dithering.
+        /// Dithers the image reducing it to the given palette.
        /// </summary>
        /// <param name="source">The image this method extends.</param>
        /// <param name="dither">The ordered ditherer.</param>
--- a/src/ImageSharp/Processing/Processors/Dithering/OrderedDither.cs
+++ b/src/ImageSharp/Processing/Processors/Dithering/OrderedDither.cs
@ -3,7 +3,6 @@

 using System;
 using System.Runtime.CompilerServices;
-using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;

@ -110,17 +109,20 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
            where TFrameQuantizer : struct, IQuantizer<TPixel>
            where TPixel : unmanaged, IPixel<TPixel>
        {
-            var ditherOperation = new QuantizeDitherRowOperation<TFrameQuantizer, TPixel>(
-                ref quantizer,
-                in Unsafe.AsRef(this),
-                source,
-                destination,
-                bounds);
+            int spread = CalculatePaletteSpread(destination.Palette.Length);
+            float scale = quantizer.Options.DitherScale;

-            ParallelRowIterator.IterateRows(
-                quantizer.Configuration,
-                bounds,
-                in ditherOperation);
+            for (int y = bounds.Top; y < bounds.Bottom; y++)
+            {
+                ReadOnlySpan<TPixel> sourceRow = source.GetPixelRowSpan(y).Slice(bounds.X, bounds.Width);
+                Span<byte> destRow = destination.GetWritablePixelRowSpanUnsafe(y - bounds.Y).Slice(0, sourceRow.Length);
+
+                for (int x = 0; x < sourceRow.Length; x++)
+                {
+                    TPixel dithered = this.Dither(sourceRow[x], x, y, spread, scale);
+                    destRow[x] = quantizer.GetQuantizedColor(dithered, out TPixel _);
+                }
+            }
        }

        /// <inheritdoc/>
@ -132,16 +134,20 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
            where TPaletteDitherImageProcessor : struct, IPaletteDitherImageProcessor<TPixel>
            where TPixel : unmanaged, IPixel<TPixel>
        {
-            var ditherOperation = new PaletteDitherRowOperation<TPaletteDitherImageProcessor, TPixel>(
-                in processor,
-                in Unsafe.AsRef(this),
-                source,
-                bounds);
+            int spread = CalculatePaletteSpread(processor.Palette.Length);
+            float scale = processor.DitherScale;

-            ParallelRowIterator.IterateRows(
-                processor.Configuration,
-                bounds,
-                in ditherOperation);
+            for (int y = bounds.Top; y < bounds.Bottom; y++)
+            {
+                Span<TPixel> row = source.GetPixelRowSpan(y).Slice(bounds.X, bounds.Width);
+
+                for (int x = 0; x < row.Length; x++)
+                {
+                    ref TPixel sourcePixel = ref row[x];
+                    TPixel dithered = this.Dither(sourcePixel, x, y, spread, scale);
+                    sourcePixel = processor.GetPaletteColor(dithered);
+                }
+            }
        }

        // Spread assumes an even colorspace distribution and precision.
@ -195,95 +201,5 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
        [MethodImpl(InliningOptions.ShortMethod)]
        public override int GetHashCode()
            => HashCode.Combine(this.thresholdMatrix, this.modulusX, this.modulusY);
-
-        private readonly struct QuantizeDitherRowOperation<TFrameQuantizer, TPixel> : IRowOperation
-            where TFrameQuantizer : struct, IQuantizer<TPixel>
-            where TPixel : unmanaged, IPixel<TPixel>
-        {
-            private readonly TFrameQuantizer quantizer;
-            private readonly OrderedDither dither;
-            private readonly ImageFrame<TPixel> source;
-            private readonly IndexedImageFrame<TPixel> destination;
-            private readonly Rectangle bounds;
-            private readonly int spread;
-
-            [MethodImpl(InliningOptions.ShortMethod)]
-            public QuantizeDitherRowOperation(
-                ref TFrameQuantizer quantizer,
-                in OrderedDither dither,
-                ImageFrame<TPixel> source,
-                IndexedImageFrame<TPixel> destination,
-                Rectangle bounds)
-            {
-                this.quantizer = quantizer;
-                this.dither = dither;
-                this.source = source;
-                this.destination = destination;
-                this.bounds = bounds;
-                this.spread = CalculatePaletteSpread(destination.Palette.Length);
-            }
-
-            [MethodImpl(InliningOptions.ShortMethod)]
-            public void Invoke(int y)
-            {
-                ref TFrameQuantizer quantizer = ref Unsafe.AsRef(this.quantizer);
-                int spread = this.spread;
-                float scale = this.quantizer.Options.DitherScale;
-
-                ReadOnlySpan<TPixel> sourceRow = this.source.GetPixelRowSpan(y).Slice(this.bounds.X, this.bounds.Width);
-                Span<byte> destRow =
-                    this.destination.GetWritablePixelRowSpanUnsafe(y - this.bounds.Y).Slice(0, sourceRow.Length);
-
-                for (int x = 0; x < sourceRow.Length; x++)
-                {
-                    TPixel dithered = this.dither.Dither(sourceRow[x], x, y, spread, scale);
-                    destRow[x] = quantizer.GetQuantizedColor(dithered, out TPixel _);
-                }
-            }
-        }
-
-        private readonly struct PaletteDitherRowOperation<TPaletteDitherImageProcessor, TPixel> : IRowOperation
-            where TPaletteDitherImageProcessor : struct, IPaletteDitherImageProcessor<TPixel>
-            where TPixel : unmanaged, IPixel<TPixel>
-        {
-            private readonly TPaletteDitherImageProcessor processor;
-            private readonly OrderedDither dither;
-            private readonly ImageFrame<TPixel> source;
-            private readonly Rectangle bounds;
-            private readonly float scale;
-            private readonly int spread;
-
-            [MethodImpl(InliningOptions.ShortMethod)]
-            public PaletteDitherRowOperation(
-                in TPaletteDitherImageProcessor processor,
-                in OrderedDither dither,
-                ImageFrame<TPixel> source,
-                Rectangle bounds)
-            {
-                this.processor = processor;
-                this.dither = dither;
-                this.source = source;
-                this.bounds = bounds;
-                this.scale = processor.DitherScale;
-                this.spread = CalculatePaletteSpread(processor.Palette.Length);
-            }
-
-            [MethodImpl(InliningOptions.ShortMethod)]
-            public void Invoke(int y)
-            {
-                ref TPaletteDitherImageProcessor processor = ref Unsafe.AsRef(this.processor);
-                int spread = this.spread;
-                float scale = this.scale;
-
-                Span<TPixel> row = this.source.GetPixelRowSpan(y).Slice(this.bounds.X, this.bounds.Width);
-
-                for (int x = 0; x < row.Length; x++)
-                {
-                    ref TPixel sourcePixel = ref row[x];
-                    TPixel dithered = this.dither.Dither(sourcePixel, x, y, spread, scale);
-                    sourcePixel = processor.GetPaletteColor(dithered);
-                }
-            }
-        }
    }
 }
--- a/src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Dithering/PaletteDitherProcessor{TPixel}.cs
@ -62,6 +62,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
            if (disposing)
            {
                this.paletteOwner.Dispose();
+                this.ditherProcessor.Dispose();
            }

            this.paletteOwner = null;
@ -73,7 +74,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
        /// <see cref="IPaletteDitherImageProcessor{TPixel}.GetPaletteColor(TPixel)"/>.
        /// </summary>
        /// <remarks>Internal for AOT</remarks>
-        internal readonly struct DitherProcessor : IPaletteDitherImageProcessor<TPixel>
+        internal readonly struct DitherProcessor : IPaletteDitherImageProcessor<TPixel>, IDisposable
        {
            private readonly EuclideanPixelMap<TPixel> pixelMap;

@ -101,6 +102,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
                this.pixelMap.GetClosestColor(color, out TPixel match);
                return match;
            }
+
+            public void Dispose() => this.pixelMap.Dispose();
        }
    }
 }
--- a/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/EuclideanPixelMap{TPixel}.cs
@ -2,10 +2,10 @@
 // Licensed under the Apache License, Version 2.0.

 using System;
-using System.Collections.Concurrent;
-using System.Numerics;
+using System.Buffers;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;

 namespace SixLabors.ImageSharp.Processing.Processors.Quantization
@ -14,11 +14,15 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
    /// Gets the closest color to the supplied color based upon the Euclidean distance.
    /// </summary>
    /// <typeparam name="TPixel">The pixel format.</typeparam>
-    internal readonly struct EuclideanPixelMap<TPixel>
+    /// <para>
+    /// This class is not threadsafe and should not be accessed in parallel.
+    /// Doing so will result in non-idempotent results.
+    /// </para>
+    internal readonly struct EuclideanPixelMap<TPixel> : IDisposable
        where TPixel : unmanaged, IPixel<TPixel>
    {
-        private readonly Vector4[] vectorCache;
-        private readonly ConcurrentDictionary<TPixel, int> distanceCache;
+        private readonly Rgba32[] rgbaPalette;
+        private readonly ColorDistanceCache cache;

        /// <summary>
        /// Initializes a new instance of the <see cref="EuclideanPixelMap{TPixel}"/> struct.
@ -29,11 +33,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
        public EuclideanPixelMap(Configuration configuration, ReadOnlyMemory<TPixel> palette)
        {
            this.Palette = palette;
-            this.vectorCache = new Vector4[palette.Length];
-
-            // Use the same rules across all target frameworks.
-            this.distanceCache = new ConcurrentDictionary<TPixel, int>(Environment.ProcessorCount, 31);
-            PixelOperations<TPixel>.Instance.ToVector4(configuration, this.Palette.Span, this.vectorCache);
+            this.rgbaPalette = new Rgba32[palette.Length];
+            this.cache = new ColorDistanceCache(configuration.MemoryAllocator);
+            PixelOperations<TPixel>.Instance.ToRgba32(configuration, this.Palette.Span, this.rgbaPalette);
        }

        /// <summary>
@ -57,11 +59,13 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
        public int GetClosestColor(TPixel color, out TPixel match)
        {
            ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.Palette.Span);
+            Unsafe.SkipInit(out Rgba32 rgba);
+            color.ToRgba32(ref rgba);

            // Check if the color is in the lookup table
-            if (!this.distanceCache.TryGetValue(color, out int index))
+            if (!this.cache.TryGetValue(rgba, out short index))
            {
-                return this.GetClosestColorSlow(color, ref paletteRef, out match);
+                return this.GetClosestColorSlow(rgba, ref paletteRef, out match);
            }

            match = Unsafe.Add(ref paletteRef, index);
@ -69,17 +73,15 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
        }

        [MethodImpl(InliningOptions.ShortMethod)]
-        private int GetClosestColorSlow(TPixel color, ref TPixel paletteRef, out TPixel match)
+        private int GetClosestColorSlow(Rgba32 rgba, ref TPixel paletteRef, out TPixel match)
        {
            // Loop through the palette and find the nearest match.
            int index = 0;
            float leastDistance = float.MaxValue;
-            var vector = color.ToVector4();
-            ref Vector4 vectorCacheRef = ref MemoryMarshal.GetReference<Vector4>(this.vectorCache);
-            for (int i = 0; i < this.Palette.Length; i++)
+            for (int i = 0; i < this.rgbaPalette.Length; i++)
            {
-                Vector4 candidate = Unsafe.Add(ref vectorCacheRef, i);
-                float distance = Vector4.DistanceSquared(vector, candidate);
+                Rgba32 candidate = this.rgbaPalette[i];
+                int distance = DistanceSquared(rgba, candidate);

                // If it's an exact match, exit the loop
                if (distance == 0)
@ -97,9 +99,103 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
            }

            // Now I have the index, pop it into the cache for next time
-            this.distanceCache[color] = index;
+            this.cache.Add(rgba, (byte)index);
            match = Unsafe.Add(ref paletteRef, index);
            return index;
        }
+
+        /// <summary>
+        /// Returns the Euclidean distance squared between two specified points.
+        /// </summary>
+        /// <param name="a">The first point.</param>
+        /// <param name="b">The second point.</param>
+        /// <returns>The distance squared.</returns>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        private static int DistanceSquared(Rgba32 a, Rgba32 b)
+        {
+            int deltaR = a.R - b.R;
+            int deltaG = a.G - b.G;
+            int deltaB = a.B - b.B;
+            int deltaA = a.A - b.A;
+            return (deltaR * deltaR) + (deltaG * deltaG) + (deltaB * deltaB) + (deltaA * deltaA);
+        }
+
+        public void Dispose() => this.cache.Dispose();
+
+        /// <summary>
+        /// A cache for storing color distance matching results.
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// The granularity of the cache has been determined based upon the current
+        /// suite of test images and provides the lowest possible memory usage while
+        /// providing enough match accuracy.
+        /// Entry count is currently limited to 1185921 entries (2371842 bytes ~2.26MB).
+        /// </para>
+        /// </remarks>
+        private unsafe struct ColorDistanceCache : IDisposable
+        {
+            private const int IndexBits = 5;
+            private const int IndexAlphaBits = 5;
+            private const int IndexCount = (1 << IndexBits) + 1;
+            private const int IndexAlphaCount = (1 << IndexAlphaBits) + 1;
+            private const int RgbShift = 8 - IndexBits;
+            private const int AlphaShift = 8 - IndexAlphaBits;
+            private const int Entries = IndexCount * IndexCount * IndexCount * IndexAlphaCount;
+            private MemoryHandle tableHandle;
+            private readonly IMemoryOwner<short> table;
+            private readonly short* tablePointer;
+
+            public ColorDistanceCache(MemoryAllocator allocator)
+            {
+                this.table = allocator.Allocate<short>(Entries);
+                this.table.GetSpan().Fill(-1);
+                this.tableHandle = this.table.Memory.Pin();
+                this.tablePointer = (short*)this.tableHandle.Pointer;
+            }
+
+            [MethodImpl(InliningOptions.ShortMethod)]
+            public void Add(Rgba32 rgba, byte index)
+            {
+                int r = rgba.R >> RgbShift;
+                int g = rgba.G >> RgbShift;
+                int b = rgba.B >> RgbShift;
+                int a = rgba.A >> AlphaShift;
+                int idx = GetPaletteIndex(r, g, b, a);
+                this.tablePointer[idx] = index;
+            }
+
+            [MethodImpl(InliningOptions.ShortMethod)]
+            public bool TryGetValue(Rgba32 rgba, out short match)
+            {
+                int r = rgba.R >> RgbShift;
+                int g = rgba.G >> RgbShift;
+                int b = rgba.B >> RgbShift;
+                int a = rgba.A >> AlphaShift;
+                int idx = GetPaletteIndex(r, g, b, a);
+                match = this.tablePointer[idx];
+                return match > -1;
+            }
+
+            [MethodImpl(InliningOptions.ShortMethod)]
+            private static int GetPaletteIndex(int r, int g, int b, int a)
+                => (r << ((IndexBits << 1) + IndexAlphaBits))
+                + (r << (IndexBits + IndexAlphaBits + 1))
+                + (g << (IndexBits + IndexAlphaBits))
+                + (r << (IndexBits << 1))
+                + (r << (IndexBits + 1))
+                + (g << IndexBits)
+                + ((r + g + b) << IndexAlphaBits)
+                + r + g + b + a;
+
+            public void Dispose()
+            {
+                if (this.table != null)
+                {
+                    this.tableHandle.Dispose();
+                    this.table.Dispose();
+                }
+            }
+        }
    }
 }
--- a/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/OctreeQuantizer{TPixel}.cs
@ -20,10 +20,12 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
        where TPixel : unmanaged, IPixel<TPixel>
    {
        private readonly int maxColors;
+        private readonly int bitDepth;
        private readonly Octree octree;
        private IMemoryOwner<TPixel> paletteOwner;
        private ReadOnlyMemory<TPixel> palette;
        private EuclideanPixelMap<TPixel> pixelMap;
+        private bool pixelMapHasValue;
        private readonly bool isDithering;
        private bool isDisposed;

@ -42,10 +44,12 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
            this.Options = options;

            this.maxColors = this.Options.MaxColors;
-            this.octree = new Octree(Numerics.Clamp(ColorNumerics.GetBitsNeededForColorDepth(this.maxColors), 1, 8));
+            this.bitDepth = Numerics.Clamp(ColorNumerics.GetBitsNeededForColorDepth(this.maxColors), 1, 8);
+            this.octree = new Octree(this.bitDepth);
            this.paletteOwner = configuration.MemoryAllocator.Allocate<TPixel>(this.maxColors, AllocationOptions.Clean);
-            this.palette = default;
            this.pixelMap = default;
+            this.pixelMapHasValue = false;
+            this.palette = default;
            this.isDithering = !(this.Options.Dither is null);
            this.isDisposed = false;
        }
@ -67,37 +71,56 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
        }

        /// <inheritdoc/>
-        [MethodImpl(InliningOptions.ShortMethod)]
        public void AddPaletteColors(Buffer2DRegion<TPixel> pixelRegion)
        {
            Rectangle bounds = pixelRegion.Rectangle;
            Buffer2D<TPixel> source = pixelRegion.Buffer;
-            using IMemoryOwner<Rgba32> buffer = this.Configuration.MemoryAllocator.Allocate<Rgba32>(bounds.Width);
-            Span<Rgba32> bufferSpan = buffer.GetSpan();
-
-            // Loop through each row
-            for (int y = bounds.Top; y < bounds.Bottom; y++)
+            using (IMemoryOwner<Rgba32> buffer = this.Configuration.MemoryAllocator.Allocate<Rgba32>(bounds.Width))
            {
-                Span<TPixel> row = source.GetRowSpan(y).Slice(bounds.Left, bounds.Width);
-                PixelOperations<TPixel>.Instance.ToRgba32(this.Configuration, row, bufferSpan);
+                Span<Rgba32> bufferSpan = buffer.GetSpan();

-                for (int x = 0; x < bufferSpan.Length; x++)
+                // Loop through each row
+                for (int y = bounds.Top; y < bounds.Bottom; y++)
                {
-                    Rgba32 rgba = bufferSpan[x];
+                    Span<TPixel> row = source.GetRowSpan(y).Slice(bounds.Left, bounds.Width);
+                    PixelOperations<TPixel>.Instance.ToRgba32(this.Configuration, row, bufferSpan);
+
+                    for (int x = 0; x < bufferSpan.Length; x++)
+                    {
+                        Rgba32 rgba = bufferSpan[x];

-                    // Add the color to the Octree
-                    this.octree.AddColor(rgba);
+                        // Add the color to the Octree
+                        this.octree.AddColor(rgba);
+                    }
                }
            }

-            Span<TPixel> paletteSpan = this.paletteOwner.GetSpan();
            int paletteIndex = 0;
-            this.octree.Palletize(paletteSpan, this.maxColors, ref paletteIndex);
+            Span<TPixel> paletteSpan = this.paletteOwner.GetSpan();

-            // Length of reduced palette + transparency.
-            ReadOnlyMemory<TPixel> result = this.paletteOwner.Memory.Slice(0, Math.Min(paletteIndex + 2, this.maxColors));
-            this.pixelMap = new EuclideanPixelMap<TPixel>(this.Configuration, result);
+            // On very rare occasions, (blur.png), the quantizer does not preserve a
+            // transparent entry when palletizing the captured colors.
+            // To workaround this we ensure the palette ends with the default color
+            // for higher bit depths. Lower bit depths will correctly reduce the palette.
+            // TODO: Investigate more evenly reduced palette reduction.
+            int max = this.maxColors;
+            if (this.bitDepth == 8)
+            {
+                max--;
+            }
+
+            this.octree.Palletize(paletteSpan, max, ref paletteIndex);
+            ReadOnlyMemory<TPixel> result = this.paletteOwner.Memory.Slice(0, paletteSpan.Length);
+
+            // When called by QuantizerUtilities.BuildPalette this prevents
+            // mutiple instances of the map being created but not disposed.
+            if (this.pixelMapHasValue)
+            {
+                this.pixelMap.Dispose();
+            }

+            this.pixelMap = new EuclideanPixelMap<TPixel>(this.Configuration, result);
+            this.pixelMapHasValue = true;
            this.palette = result;
        }

@ -118,8 +141,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                return (byte)this.pixelMap.GetClosestColor(color, out match);
            }

-            ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.pixelMap.Palette.Span);
-            var index = (byte)this.octree.GetPaletteIndex(color);
+            ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.palette.Span);
+            byte index = (byte)this.octree.GetPaletteIndex(color);
            match = Unsafe.Add(ref paletteRef, index);
            return index;
        }
@ -132,6 +155,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                this.isDisposed = true;
                this.paletteOwner.Dispose();
                this.paletteOwner = null;
+                this.pixelMap.Dispose();
            }
        }

@ -176,21 +200,6 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                this.previousNode = null;
            }

-            /// <summary>
-            /// Gets the mask used when getting the appropriate pixels for a given node.
-            /// </summary>
-            private static ReadOnlySpan<byte> Mask => new byte[]
-            {
-                0b10000000,
-                0b1000000,
-                0b100000,
-                0b10000,
-                0b1000,
-                0b100,
-                0b10,
-                0b1
-            };
-
            /// <summary>
            /// Gets or sets the number of leaves in the tree
            /// </summary>
@ -251,7 +260,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
            [MethodImpl(InliningOptions.ShortMethod)]
            public void Palletize(Span<TPixel> palette, int colorCount, ref int paletteIndex)
            {
-                while (this.Leaves > colorCount - 1)
+                while (this.Leaves > colorCount)
                {
                    this.Reduce();
                }
@ -269,7 +278,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
            [MethodImpl(InliningOptions.ShortMethod)]
            public int GetPaletteIndex(TPixel color)
            {
-                Rgba32 rgba = default;
+                Unsafe.SkipInit(out Rgba32 rgba);
                color.ToRgba32(ref rgba);
                return this.root.GetPaletteIndex(ref rgba, 0);
            }
@ -468,7 +477,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                            Vector3.Zero,
                            new Vector3(255));

-                        TPixel pixel = default;
+                        Unsafe.SkipInit(out TPixel pixel);
                        pixel.FromRgba32(new Rgba32((byte)vector.X, (byte)vector.Y, (byte)vector.Z, byte.MaxValue));
                        palette[index] = pixel;

@ -517,7 +526,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                            child = this.children[i];
                            if (child != null)
                            {
-                                var childIndex = child.GetPaletteIndex(ref pixel, level + 1);
+                                int childIndex = child.GetPaletteIndex(ref pixel, level + 1);
                                if (childIndex != 0)
                                {
                                    return childIndex;
@ -538,15 +547,12 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                [MethodImpl(InliningOptions.ShortMethod)]
                private static int GetColorIndex(ref Rgba32 color, int level)
                {
-                    DebugGuard.MustBeLessThan(level, Mask.Length, nameof(level));
-
                    int shift = 7 - level;
-                    ref byte maskRef = ref MemoryMarshal.GetReference(Mask);
-                    byte mask = Unsafe.Add(ref maskRef, level);
+                    byte mask = (byte)(1 << shift);

                    return ((color.R & mask) >> shift)
-                           | ((color.G & mask) >> (shift - 1))
-                           | ((color.B & mask) >> (shift - 2));
+                        | (((color.G & mask) >> shift) << 1)
+                        | (((color.B & mask) >> shift) << 2);
                }

                /// <summary>
--- a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer.cs
@ -60,7 +60,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
            Color.ToPixel(configuration, this.colorPalette.Span, palette.AsSpan());

            var pixelMap = new EuclideanPixelMap<TPixel>(configuration, palette);
-            return new PaletteQuantizer<TPixel>(configuration, options, pixelMap);
+            return new PaletteQuantizer<TPixel>(configuration, options, pixelMap, false);
        }
    }
 }
--- a/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/PaletteQuantizer{TPixel}.cs
@ -17,6 +17,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
        where TPixel : unmanaged, IPixel<TPixel>
    {
        private readonly EuclideanPixelMap<TPixel> pixelMap;
+        private readonly bool leaveMap;

        /// <summary>
        /// Initializes a new instance of the <see cref="PaletteQuantizer{TPixel}"/> struct.
@ -24,11 +25,15 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
        /// <param name="configuration">The configuration which allows altering default behaviour or extending the library.</param>
        /// <param name="options">The quantizer options defining quantization rules.</param>
        /// <param name="pixelMap">The pixel map for looking up color matches from a predefined palette.</param>
+        /// <param name="leaveMap">
+        /// <see langword="true"/> to leave the pixel map undisposed after disposing the <see cref="PaletteQuantizer{TPixel}"/> object; otherwise, <see langword="false"/>.
+        /// </param>
        [MethodImpl(InliningOptions.ShortMethod)]
        public PaletteQuantizer(
            Configuration configuration,
            QuantizerOptions options,
-            EuclideanPixelMap<TPixel> pixelMap)
+            EuclideanPixelMap<TPixel> pixelMap,
+            bool leaveMap)
        {
            Guard.NotNull(configuration, nameof(configuration));
            Guard.NotNull(options, nameof(options));
@ -36,6 +41,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
            this.Configuration = configuration;
            this.Options = options;
            this.pixelMap = pixelMap;
+            this.leaveMap = leaveMap;
        }

        /// <inheritdoc/>
@ -66,6 +72,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
        /// <inheritdoc/>
        public void Dispose()
        {
+            if (!this.leaveMap)
+            {
+                this.pixelMap.Dispose();
+            }
        }
    }
 }
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizeProcessor{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizeProcessor{TPixel}.cs
@ -41,46 +41,18 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
            using IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(configuration);
            using IndexedImageFrame<TPixel> quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(source, interest);

-            var operation = new RowIntervalOperation(this.SourceRectangle, source, quantized);
-            ParallelRowIterator.IterateRowIntervals(
-                configuration,
-                interest,
-                in operation);
-        }
-
-        private readonly struct RowIntervalOperation : IRowIntervalOperation
-        {
-            private readonly Rectangle bounds;
-            private readonly ImageFrame<TPixel> source;
-            private readonly IndexedImageFrame<TPixel> quantized;
+            ReadOnlySpan<TPixel> paletteSpan = quantized.Palette.Span;
+            int offsetY = interest.Top;
+            int offsetX = interest.Left;

-            [MethodImpl(InliningOptions.ShortMethod)]
-            public RowIntervalOperation(
-                Rectangle bounds,
-                ImageFrame<TPixel> source,
-                IndexedImageFrame<TPixel> quantized)
+            for (int y = interest.Y; y < interest.Height; y++)
            {
-                this.bounds = bounds;
-                this.source = source;
-                this.quantized = quantized;
-            }
+                Span<TPixel> row = source.GetPixelRowSpan(y);
+                ReadOnlySpan<byte> quantizedRow = quantized.GetPixelRowSpan(y - offsetY);

-            [MethodImpl(InliningOptions.ShortMethod)]
-            public void Invoke(in RowInterval rows)
-            {
-                ReadOnlySpan<TPixel> paletteSpan = this.quantized.Palette.Span;
-                int offsetY = this.bounds.Top;
-                int offsetX = this.bounds.Left;
-
-                for (int y = rows.Min; y < rows.Max; y++)
+                for (int x = interest.Left; x < interest.Right; x++)
                {
-                    Span<TPixel> row = this.source.GetPixelRowSpan(y);
-                    ReadOnlySpan<byte> quantizedRow = this.quantized.GetPixelRowSpan(y - offsetY);
-
-                    for (int x = this.bounds.Left; x < this.bounds.Right; x++)
-                    {
-                        row[x] = paletteSpan[quantizedRow[x - offsetX]];
-                    }
+                    row[x] = paletteSpan[quantizedRow[x - offsetX]];
                }
            }
        }
--- a/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/QuantizerUtilities.cs
@ -3,7 +3,6 @@

 using System;
 using System.Runtime.CompilerServices;
-using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing.Processors.Dithering;
@ -126,62 +125,24 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization

            if (dither is null)
            {
-                var operation = new RowIntervalOperation<TFrameQuantizer, TPixel>(
-                    ref quantizer,
-                    source,
-                    destination,
-                    bounds);
+                int offsetY = bounds.Top;
+                int offsetX = bounds.Left;

-                ParallelRowIterator.IterateRowIntervals(
-                    quantizer.Configuration,
-                    bounds,
-                    in operation);
-
-                return;
-            }
-
-            dither.ApplyQuantizationDither(ref quantizer, source, destination, bounds);
-        }
-
-        private readonly struct RowIntervalOperation<TFrameQuantizer, TPixel> : IRowIntervalOperation
-            where TFrameQuantizer : struct, IQuantizer<TPixel>
-            where TPixel : unmanaged, IPixel<TPixel>
-        {
-            private readonly TFrameQuantizer quantizer;
-            private readonly ImageFrame<TPixel> source;
-            private readonly IndexedImageFrame<TPixel> destination;
-            private readonly Rectangle bounds;
-
-            [MethodImpl(InliningOptions.ShortMethod)]
-            public RowIntervalOperation(
-                ref TFrameQuantizer quantizer,
-                ImageFrame<TPixel> source,
-                IndexedImageFrame<TPixel> destination,
-                Rectangle bounds)
-            {
-                this.quantizer = quantizer;
-                this.source = source;
-                this.destination = destination;
-                this.bounds = bounds;
-            }
-
-            [MethodImpl(InliningOptions.ShortMethod)]
-            public void Invoke(in RowInterval rows)
-            {
-                int offsetY = this.bounds.Top;
-                int offsetX = this.bounds.Left;
-
-                for (int y = rows.Min; y < rows.Max; y++)
+                for (int y = bounds.Y; y < bounds.Height; y++)
                {
-                    Span<TPixel> sourceRow = this.source.GetPixelRowSpan(y);
-                    Span<byte> destinationRow = this.destination.GetWritablePixelRowSpanUnsafe(y - offsetY);
+                    Span<TPixel> sourceRow = source.GetPixelRowSpan(y);
+                    Span<byte> destinationRow = destination.GetWritablePixelRowSpanUnsafe(y - offsetY);

-                    for (int x = this.bounds.Left; x < this.bounds.Right; x++)
+                    for (int x = bounds.Left; x < bounds.Right; x++)
                    {
-                        destinationRow[x - offsetX] = Unsafe.AsRef(this.quantizer).GetQuantizedColor(sourceRow[x], out TPixel _);
+                        destinationRow[x - offsetX] = Unsafe.AsRef(quantizer).GetQuantizedColor(sourceRow[x], out TPixel _);
                    }
                }
+
+                return;
            }
+
+            dither.ApplyQuantizationDither(ref quantizer, source, destination, bounds);
        }
    }
 }
--- a/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
+++ b/src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs
@ -6,7 +6,6 @@ using System.Buffers;
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;

@ -73,6 +72,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
        private int maxColors;
        private readonly Box[] colorCube;
        private EuclideanPixelMap<TPixel> pixelMap;
+        private bool pixelMapHasValue;
        private readonly bool isDithering;
        private bool isDisposed;

@ -94,10 +94,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
            this.momentsOwner = this.memoryAllocator.Allocate<Moment>(TableLength, AllocationOptions.Clean);
            this.tagsOwner = this.memoryAllocator.Allocate<byte>(TableLength, AllocationOptions.Clean);
            this.paletteOwner = this.memoryAllocator.Allocate<TPixel>(this.maxColors, AllocationOptions.Clean);
-            this.palette = default;
            this.colorCube = new Box[this.maxColors];
            this.isDisposed = false;
            this.pixelMap = default;
+            this.pixelMapHasValue = false;
+            this.palette = default;
            this.isDithering = this.isDithering = !(this.Options.Dither is null);
        }

@ -127,9 +128,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
            this.Get3DMoments(this.memoryAllocator);
            this.BuildCube();

+            // Slice again since maxColors has been updated since the buffer was created.
+            Span<TPixel> paletteSpan = this.paletteOwner.GetSpan().Slice(0, this.maxColors);
            ReadOnlySpan<Moment> momentsSpan = this.momentsOwner.GetSpan();
-            Span<TPixel> paletteSpan = this.paletteOwner.GetSpan();
-            for (int k = 0; k < this.maxColors; k++)
+            for (int k = 0; k < paletteSpan.Length; k++)
            {
                this.Mark(ref this.colorCube[k], (byte)k);

@ -142,8 +144,20 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                }
            }

-            ReadOnlyMemory<TPixel> result = this.paletteOwner.Memory.Slice(0, this.maxColors);
-            this.pixelMap = new EuclideanPixelMap<TPixel>(this.Configuration, result);
+            ReadOnlyMemory<TPixel> result = this.paletteOwner.Memory.Slice(0, paletteSpan.Length);
+            if (this.isDithering)
+            {
+                // When called by QuantizerUtilities.BuildPalette this prevents
+                // mutiple instances of the map being created but not disposed.
+                if (this.pixelMapHasValue)
+                {
+                    this.pixelMap.Dispose();
+                }
+
+                this.pixelMap = new EuclideanPixelMap<TPixel>(this.Configuration, result);
+                this.pixelMapHasValue = true;
+            }
+
            this.palette = result;
        }

@ -170,7 +184,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization

            ReadOnlySpan<byte> tagSpan = this.tagsOwner.GetSpan();
            byte index = tagSpan[GetPaletteIndex(r + 1, g + 1, b + 1, a + 1)];
-            ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.pixelMap.Palette.Span);
+            ref TPixel paletteRef = ref MemoryMarshal.GetReference(this.palette.Span);
            match = Unsafe.Add(ref paletteRef, index);
            return index;
        }
@ -187,6 +201,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                this.momentsOwner = null;
                this.tagsOwner = null;
                this.paletteOwner = null;
+                this.pixelMap.Dispose();
            }
        }

--- a/tests/ImageSharp.Tests/Formats/Bmp/BmpEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Bmp/BmpEncoderTests.cs
@ -343,7 +343,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Bmp
                {
                    BitsPerPixel = bitsPerPixel,
                    SupportTransparency = supportTransparency,
-                    Quantizer = quantizer ?? KnownQuantizers.Wu
+                    Quantizer = quantizer ?? KnownQuantizers.Octree
                };

                // Does DebugSave & load reference CompareToReferenceInput():
--- a/tests/ImageSharp.Tests/Formats/Tiff/TiffEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Tiff/TiffEncoderTests.cs
@ -416,7 +416,6 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff

        [Theory]
        [WithFile(GrayscaleUncompressed, PixelTypes.L8, TiffPhotometricInterpretation.BlackIsZero, TiffCompression.PackBits)]
-        [WithFile(PaletteDeflateMultistrip, PixelTypes.L8, TiffPhotometricInterpretation.PaletteColor, TiffCompression.Lzw)]
        [WithFile(RgbUncompressed, PixelTypes.Rgba32, TiffPhotometricInterpretation.Rgb, TiffCompression.Deflate)]
        [WithFile(RgbUncompressed, PixelTypes.Rgb24, TiffPhotometricInterpretation.Rgb, TiffCompression.None)]
        [WithFile(RgbUncompressed, PixelTypes.Rgba32, TiffPhotometricInterpretation.Rgb, TiffCompression.None)]
@ -425,6 +424,12 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
            where TPixel : unmanaged, IPixel<TPixel> =>
            TestStripLength(provider, photometricInterpretation, compression);

+        [Theory]
+        [WithFile(PaletteDeflateMultistrip, PixelTypes.L8, TiffPhotometricInterpretation.PaletteColor, TiffCompression.Lzw)]
+        public void TiffEncoder_StripLength_WithPalette<TPixel>(TestImageProvider<TPixel> provider, TiffPhotometricInterpretation photometricInterpretation, TiffCompression compression)
+            where TPixel : unmanaged, IPixel<TPixel> =>
+            TestStripLength(provider, photometricInterpretation, compression, false, 0.01f);
+
        [Theory]
        [WithFile(Calliphora_BiColorUncompressed, PixelTypes.L8, TiffPhotometricInterpretation.BlackIsZero, TiffCompression.CcittGroup3Fax)]
        public void TiffEncoder_StripLength_OutOfBounds<TPixel>(TestImageProvider<TPixel> provider, TiffPhotometricInterpretation photometricInterpretation, TiffCompression compression)
@ -432,7 +437,26 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
            //// CcittGroup3Fax compressed data length can be larger than the original length.
            Assert.Throws<Xunit.Sdk.TrueException>(() => TestStripLength(provider, photometricInterpretation, compression));

-        private static void TestStripLength<TPixel>(TestImageProvider<TPixel> provider, TiffPhotometricInterpretation photometricInterpretation, TiffCompression compression)
+        [Theory]
+        [WithTestPatternImages(287, 321, PixelTypes.Rgba32, TiffPhotometricInterpretation.Rgb)]
+        [WithTestPatternImages(287, 321, PixelTypes.Rgba32, TiffPhotometricInterpretation.PaletteColor)]
+        [WithTestPatternImages(287, 321, PixelTypes.Rgba32, TiffPhotometricInterpretation.BlackIsZero)]
+        public void TiffEncode_WorksWithDiscontiguousBuffers<TPixel>(TestImageProvider<TPixel> provider, TiffPhotometricInterpretation photometricInterpretation)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            provider.LimitAllocatorBufferCapacity().InPixelsSqrt(200);
+            using Image<TPixel> image = provider.GetImage();
+
+            var encoder = new TiffEncoder { PhotometricInterpretation = photometricInterpretation };
+            image.DebugSave(provider, encoder);
+        }
+
+        private static void TestStripLength<TPixel>(
+            TestImageProvider<TPixel> provider,
+            TiffPhotometricInterpretation photometricInterpretation,
+            TiffCompression compression,
+            bool useExactComparer = true,
+            float compareTolerance = 0.01f)
            where TPixel : unmanaged, IPixel<TPixel>
        {
            // arrange
@ -480,10 +504,12 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff

            // Compare with reference.
            TestTiffEncoderCore(
-                provider,
-                inputMeta.BitsPerPixel,
-                photometricInterpretation,
-                inputCompression);
+               provider,
+               inputMeta.BitsPerPixel,
+               photometricInterpretation,
+               inputCompression,
+               useExactComparer: useExactComparer,
+               compareTolerance: compareTolerance);
        }

        private static void TestTiffEncoderCore<TPixel>(
--- a/tests/ImageSharp.Tests/Memory/Allocators/ArrayPoolMemoryAllocatorTests.cs
+++ b/tests/ImageSharp.Tests/Memory/Allocators/ArrayPoolMemoryAllocatorTests.cs
@ -223,19 +223,6 @@ namespace SixLabors.ImageSharp.Tests.Memory.Allocators
            Assert.Equal(0, buffer.Memory.Length);
        }

-        [Theory]
-        [InlineData(101)]
-        [InlineData((int.MaxValue / SizeOfLargeStruct) - 1)]
-        [InlineData(int.MaxValue / SizeOfLargeStruct)]
-        [InlineData((int.MaxValue / SizeOfLargeStruct) + 1)]
-        [InlineData((int.MaxValue / SizeOfLargeStruct) + 137)]
-        public void Allocate_OverCapacity_Throws_InvalidMemoryOperationException(int length)
-        {
-            this.LocalFixture.MemoryAllocator.BufferCapacityInBytes = 100 * SizeOfLargeStruct;
-            Assert.Throws<InvalidMemoryOperationException>(() =>
-                this.LocalFixture.MemoryAllocator.Allocate<LargeStruct>(length));
-        }
-
        [Theory]
        [InlineData(-1)]
        public void AllocateManagedByteBuffer_IncorrectAmount_ThrowsCorrect_ArgumentOutOfRangeException(int length)
--- a/tests/ImageSharp.Tests/Processing/Processors/Dithering/DitherTests.cs
+++ b/tests/ImageSharp.Tests/Processing/Processors/Dithering/DitherTests.cs
@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.

+using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Dithering;
@ -172,8 +173,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Dithering
            provider.RunBufferCapacityLimitProcessorTest(
                41,
                c => c.Dither(dither),
-                name,
-                ImageComparer.TolerantPercentage(0.001f));
+                name);
        }
    }
 }
--- a/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp
+++ b/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithOctreeQuantizer_rgb32.bmp
@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:6dba331639d724f198d7d11af971156d34076b57bba0f2d0d45e699104a3a674
+oid sha256:11375b15df083d98335f4a4baf0717e7fdd6b21ab2132a6815cadc787ac17e7d
 size 9270
--- a/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithWuQuantizer_rgb32.bmp
+++ b/tests/Images/External/ReferenceOutput/BmpEncoderTests/Encode_8BitColor_WithWuQuantizer_rgb32.bmp
@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:9213e188b3a2f715ae21a5ab2fb2acedc23397207820c0999b06fa60e7052b85
+oid sha256:e063e97cd8a000de6830adcc3961a7dc41785d40cd4d83af10ca38d96e071362
 size 9270
--- a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png
+++ b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDiffusionFilterInBox_Rgba32_CalliphoraPartial.png
@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:1aa62e798c085eb7b0e8e5ce5e4cb2cccfe925dd8ac3e29659f9afd53fca977c
-size 329912
+oid sha256:cafc426ac8e8d02a87f67c90e8c1976c5fae0e12b49deae52ad08476f7ed49a4
+size 266391
--- a/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial.png
+++ b/tests/Images/External/ReferenceOutput/DitherTests/ApplyDitherFilterInBox_Rgba32_CalliphoraPartial.png
@ -1,3 +1,3 @@
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