Convert TiffEncoder, Use sampling strategy for local palette building

src/ImageSharp/Advanced/AotCompilerTools.cs

@@ -57,6 +57,9 @@ internal static class AotCompilerTools
     /// If you are getting the above error, you need to call this method, which will pre-seed the AoT compiler with the
     /// necessary methods to complete the SaveAsGif call. That's it, otherwise you should NEVER need this method!!!
     /// </remarks>
+    /// <exception cref="InvalidOperationException">
+    /// This method is used for AOT code generation only. Do not call it at runtime.
+    /// </exception>
     [Preserve]
     private static void SeedPixelFormats()
     {
@@ -487,8 +490,10 @@ internal static class AotCompilerTools
     private static void AotCompilePixelSamplingStrategys<TPixel>()
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        default(DefaultPixelSamplingStrategy).EnumeratePixelRegions<TPixel>(default);
-        default(ExtensivePixelSamplingStrategy).EnumeratePixelRegions<TPixel>(default);
+        default(DefaultPixelSamplingStrategy).EnumeratePixelRegions(default(Image<TPixel>));
+        default(DefaultPixelSamplingStrategy).EnumeratePixelRegions(default(ImageFrame<TPixel>));
+        default(ExtensivePixelSamplingStrategy).EnumeratePixelRegions(default(Image<TPixel>));
+        default(ExtensivePixelSamplingStrategy).EnumeratePixelRegions(default(ImageFrame<TPixel>));
     }
 
     /// <summary>
@@ -513,13 +518,13 @@ internal static class AotCompilerTools
         where TPixel : unmanaged, IPixel<TPixel>
         where TDither : struct, IDither
     {
-        var octree = default(OctreeQuantizer<TPixel>);
+        OctreeQuantizer<TPixel> octree = default;
         default(TDither).ApplyQuantizationDither<OctreeQuantizer<TPixel>, TPixel>(ref octree, default, default, default);
 
-        var palette = default(PaletteQuantizer<TPixel>);
+        PaletteQuantizer<TPixel> palette = default;
         default(TDither).ApplyQuantizationDither<PaletteQuantizer<TPixel>, TPixel>(ref palette, default, default, default);
 
-        var wu = default(WuQuantizer<TPixel>);
+        WuQuantizer<TPixel> wu = default;
         default(TDither).ApplyQuantizationDither<WuQuantizer<TPixel>, TPixel>(ref wu, default, default, default);
         default(TDither).ApplyPaletteDither<PaletteDitherProcessor<TPixel>.DitherProcessor, TPixel>(default, default, default);
     }

src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs

@@ -106,7 +106,7 @@ internal sealed class BmpEncoderCore : IImageEncoderInternals
         this.memoryAllocator = memoryAllocator;
         this.bitsPerPixel = encoder.BitsPerPixel;
         this.quantizer = encoder.Quantizer;
-        this.pixelSamplingStrategy = encoder.GlobalPixelSamplingStrategy;
+        this.pixelSamplingStrategy = encoder.PixelSamplingStrategy;
         this.infoHeaderType = encoder.SupportTransparency ? BmpInfoHeaderType.WinVersion4 : BmpInfoHeaderType.WinVersion3;
     }
 

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -70,7 +70,7 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
         this.skipMetadata = encoder.SkipMetadata;
         this.quantizer = encoder.Quantizer;
         this.colorTableMode = encoder.ColorTableMode;
-        this.pixelSamplingStrategy = encoder.GlobalPixelSamplingStrategy;
+        this.pixelSamplingStrategy = encoder.PixelSamplingStrategy;
     }
 
     /// <summary>
@@ -103,7 +103,8 @@ internal sealed class GifEncoderCore : IImageEncoderInternals
             }
             else
             {
-                quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(image.Frames.RootFrame, image.Bounds());
+                frameQuantizer.BuildPalette(this.pixelSamplingStrategy, image.Frames.RootFrame);
+                quantized = frameQuantizer.QuantizeFrame(image.Frames.RootFrame, image.Bounds());
             }
         }
 

src/ImageSharp/Formats/IEncoderOptions.cs

@@ -27,7 +27,7 @@ public interface IQuantizingEncoderOptions : IEncoderOptions
     IQuantizer Quantizer { get; init; }
 
     /// <summary>
-    /// Gets the <see cref="IPixelSamplingStrategy"/> used for quantization when building a global color palette.
+    /// Gets the <see cref="IPixelSamplingStrategy"/> used for quantization when building color palettes.
     /// </summary>
-    IPixelSamplingStrategy GlobalPixelSamplingStrategy { get; init; }
+    IPixelSamplingStrategy PixelSamplingStrategy { get; init; }
 }

src/ImageSharp/Formats/ImageEncoder.cs

@@ -33,5 +33,5 @@ public abstract class QuantizingImageEncoder : ImageEncoder, IQuantizingEncoderO
     public IQuantizer Quantizer { get; init; } = KnownQuantizers.Octree;
 
     /// <inheritdoc/>
-    public IPixelSamplingStrategy GlobalPixelSamplingStrategy { get; init; } = new DefaultPixelSamplingStrategy();
+    public IPixelSamplingStrategy PixelSamplingStrategy { get; init; } = new DefaultPixelSamplingStrategy();
 }

src/ImageSharp/Formats/Pbm/PbmEncoderCore.cs

@@ -65,7 +65,7 @@ internal sealed class PbmEncoderCore : IImageEncoderInternals
         Guard.NotNull(image, nameof(image));
         Guard.NotNull(stream, nameof(stream));
 
-        this.DeduceOptions(image);
+        this.SanitizeAndSetEncoderOptions(image);
 
         byte signature = this.DeduceSignature();
         this.WriteHeader(stream, signature, image.Size());
@@ -75,7 +75,7 @@ internal sealed class PbmEncoderCore : IImageEncoderInternals
         stream.Flush();
     }
 
-    private void DeduceOptions<TPixel>(Image<TPixel> image)
+    private void SanitizeAndSetEncoderOptions<TPixel>(Image<TPixel> image)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         this.configuration = image.GetConfiguration();

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -149,7 +149,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         ImageMetadata metadata = image.Metadata;
 
         PngMetadata pngMetadata = metadata.GetFormatMetadata(PngFormat.Instance);
-        this.DeduceOptions<TPixel>(this.encoder, pngMetadata, out this.use16Bit, out this.bytesPerPixel);
+        this.SanitizeAndSetEncoderOptions<TPixel>(this.encoder, pngMetadata, out this.use16Bit, out this.bytesPerPixel);
         Image<TPixel> clonedImage = null;
         bool clearTransparency = this.encoder.TransparentColorMode == PngTransparentColorMode.Clear;
         if (clearTransparency)
@@ -1228,7 +1228,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
     /// <param name="pngMetadata">The PNG metadata.</param>
     /// <param name="use16Bit">if set to <c>true</c> [use16 bit].</param>
     /// <param name="bytesPerPixel">The bytes per pixel.</param>
-    private void DeduceOptions<TPixel>(
+    private void SanitizeAndSetEncoderOptions<TPixel>(
         PngEncoder encoder,
         PngMetadata pngMetadata,
         out bool use16Bit,
@@ -1298,7 +1298,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
         // Create quantized frame returning the palette and set the bit depth.
         using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(image.GetConfiguration());
 
-        frameQuantizer.BuildPalette(encoder.GlobalPixelSamplingStrategy, image);
+        frameQuantizer.BuildPalette(encoder.PixelSamplingStrategy, image);
         return frameQuantizer.QuantizeFrame(image.Frames.RootFrame, image.Bounds());
     }
 

src/ImageSharp/Formats/Tiff/ITiffEncoderOptions.cs

@@ -1,46 +0,0 @@
-// Copyright (c) Six Labors.
-// Licensed under the Six Labors Split License.
-
-using SixLabors.ImageSharp.Compression.Zlib;
-using SixLabors.ImageSharp.Formats.Tiff.Constants;
-using SixLabors.ImageSharp.Processing.Processors.Quantization;
-
-namespace SixLabors.ImageSharp.Formats.Tiff;
-
-/// <summary>
-/// Encapsulates the options for the <see cref="TiffEncoder"/>.
-/// </summary>
-internal interface ITiffEncoderOptions
-{
-    /// <summary>
-    /// Gets the number of bits per pixel.
-    /// </summary>
-    TiffBitsPerPixel? BitsPerPixel { get; }
-
-    /// <summary>
-    /// Gets the compression type to use.
-    /// </summary>
-    TiffCompression? Compression { get; }
-
-    /// <summary>
-    /// Gets the compression level 1-9 for the deflate compression mode.
-    /// <remarks>Defaults to <see cref="DeflateCompressionLevel.DefaultCompression"/>.</remarks>
-    /// </summary>
-    DeflateCompressionLevel? CompressionLevel { get; }
-
-    /// <summary>
-    /// Gets the PhotometricInterpretation to use. Possible options are RGB, RGB with a color palette, gray or BiColor.
-    /// If no PhotometricInterpretation is specified or it is unsupported by the encoder, RGB will be used.
-    /// </summary>
-    TiffPhotometricInterpretation? PhotometricInterpretation { get; }
-
-    /// <summary>
-    /// Gets a value indicating which horizontal prediction to use. This can improve the compression ratio with deflate or lzw compression.
-    /// </summary>
-    TiffPredictor? HorizontalPredictor { get; }
-
-    /// <summary>
-    /// Gets the quantizer for creating a color palette image.
-    /// </summary>
-    IQuantizer Quantizer { get; }
-}

src/ImageSharp/Formats/Tiff/TiffEncoder.cs

@@ -4,47 +4,52 @@
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Compression.Zlib;
 using SixLabors.ImageSharp.Formats.Tiff.Constants;
-using SixLabors.ImageSharp.PixelFormats;
-using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
 namespace SixLabors.ImageSharp.Formats.Tiff;
 
 /// <summary>
 /// Encoder for writing the data image to a stream in TIFF format.
 /// </summary>
-public class TiffEncoder : IImageEncoder, ITiffEncoderOptions
+public class TiffEncoder : QuantizingImageEncoder
 {
-    /// <inheritdoc/>
-    public TiffBitsPerPixel? BitsPerPixel { get; set; }
-
-    /// <inheritdoc/>
-    public TiffCompression? Compression { get; set; }
-
-    /// <inheritdoc/>
-    public DeflateCompressionLevel? CompressionLevel { get; set; }
-
-    /// <inheritdoc/>
-    public TiffPhotometricInterpretation? PhotometricInterpretation { get; set; }
-
-    /// <inheritdoc/>
-    public TiffPredictor? HorizontalPredictor { get; set; }
-
-    /// <inheritdoc/>
-    public IQuantizer Quantizer { get; set; }
-
-    /// <inheritdoc/>
-    public void Encode<TPixel>(Image<TPixel> image, Stream stream)
-        where TPixel : unmanaged, IPixel<TPixel>
+    /// <summary>
+    /// Gets the number of bits per pixel.
+    /// </summary>
+    public TiffBitsPerPixel? BitsPerPixel { get; init; }
+
+    /// <summary>
+    /// Gets the compression type to use.
+    /// </summary>
+    public TiffCompression? Compression { get; init; }
+
+    /// <summary>
+    /// Gets the compression level 1-9 for the deflate compression mode.
+    /// <remarks>Defaults to <see cref="DeflateCompressionLevel.DefaultCompression" />.</remarks>
+    /// </summary>
+    public DeflateCompressionLevel? CompressionLevel { get; init; }
+
+    /// <summary>
+    /// Gets the PhotometricInterpretation to use. Possible options are RGB, RGB with a color palette, gray or BiColor.
+    /// If no PhotometricInterpretation is specified or it is unsupported by the encoder, RGB will be used.
+    /// </summary>
+    public TiffPhotometricInterpretation? PhotometricInterpretation { get; init; }
+
+    /// <summary>
+    /// Gets a value indicating which horizontal prediction to use. This can improve the compression ratio with deflate or lzw compression.
+    /// </summary>
+    public TiffPredictor? HorizontalPredictor { get; init; }
+
+    /// <inheritdoc/>
+    public override void Encode<TPixel>(Image<TPixel> image, Stream stream)
     {
-        var encode = new TiffEncoderCore(this, image.GetMemoryAllocator());
+        TiffEncoderCore encode = new(this, image.GetMemoryAllocator());
         encode.Encode(image, stream);
     }
 
     /// <inheritdoc/>
-    public Task EncodeAsync<TPixel>(Image<TPixel> image, Stream stream, CancellationToken cancellationToken)
-        where TPixel : unmanaged, IPixel<TPixel>
+    public override Task EncodeAsync<TPixel>(Image<TPixel> image, Stream stream, CancellationToken cancellationToken)
     {
-        var encoder = new TiffEncoderCore(this, image.GetMemoryAllocator());
+        TiffEncoderCore encoder = new(this, image.GetMemoryAllocator());
         return encoder.EncodeAsync(image, stream, cancellationToken);
     }
 }

src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs

@@ -10,7 +10,6 @@ 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;
@@ -40,10 +39,15 @@ internal sealed class TiffEncoderCore : IImageEncoderInternals
     private Configuration configuration;
 
     /// <summary>
-    /// The quantizer for creating color palette image.
+    /// The quantizer for creating color palette images.
     /// </summary>
     private readonly IQuantizer quantizer;
 
+    /// <summary>
+    /// The pixel sampling strategy for quantization.
+    /// </summary>
+    private readonly IPixelSamplingStrategy pixelSamplingStrategy;
+
     /// <summary>
     /// Sets the deflate compression level.
     /// </summary>
@@ -76,11 +80,12 @@ internal sealed class TiffEncoderCore : IImageEncoderInternals
     /// </summary>
     /// <param name="options">The options for the encoder.</param>
     /// <param name="memoryAllocator">The memory allocator.</param>
-    public TiffEncoderCore(ITiffEncoderOptions options, MemoryAllocator memoryAllocator)
+    public TiffEncoderCore(TiffEncoder options, MemoryAllocator memoryAllocator)
     {
         this.memoryAllocator = memoryAllocator;
         this.PhotometricInterpretation = options.PhotometricInterpretation;
-        this.quantizer = options.Quantizer ?? KnownQuantizers.Octree;
+        this.quantizer = options.Quantizer;
+        this.pixelSamplingStrategy = options.PixelSamplingStrategy;
         this.BitsPerPixel = options.BitsPerPixel;
         this.HorizontalPredictor = options.HorizontalPredictor;
         this.CompressionType = options.Compression;
@@ -215,6 +220,7 @@ internal sealed class TiffEncoderCore : IImageEncoderInternals
             this.PhotometricInterpretation,
             frame,
             this.quantizer,
+            this.pixelSamplingStrategy,
             this.memoryAllocator,
             this.configuration,
             entriesCollector,
@@ -331,7 +337,12 @@ internal sealed class TiffEncoderCore : IImageEncoderInternals
         return nextIfdMarker;
     }
 
-    private void SanitizeAndSetEncoderOptions(TiffBitsPerPixel? bitsPerPixel, int inputBitsPerPixel, TiffPhotometricInterpretation? photometricInterpretation, TiffCompression compression, TiffPredictor predictor)
+    private void SanitizeAndSetEncoderOptions(
+        TiffBitsPerPixel? bitsPerPixel,
+        int inputBitsPerPixel,
+        TiffPhotometricInterpretation? photometricInterpretation,
+        TiffCompression compression,
+        TiffPredictor predictor)
     {
         // BitsPerPixel should be the primary source of truth for the encoder options.
         if (bitsPerPixel.HasValue)

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

@@ -14,6 +14,7 @@ internal static class TiffColorWriterFactory
         TiffPhotometricInterpretation? photometricInterpretation,
         ImageFrame<TPixel> image,
         IQuantizer quantizer,
+        IPixelSamplingStrategy pixelSamplingStrategy,
         MemoryAllocator memoryAllocator,
         Configuration configuration,
         TiffEncoderEntriesCollector entriesCollector,
@@ -23,7 +24,7 @@ internal static class TiffColorWriterFactory
         switch (photometricInterpretation)
         {
             case TiffPhotometricInterpretation.PaletteColor:
-                return new TiffPaletteWriter<TPixel>(image, quantizer, memoryAllocator, configuration, entriesCollector, bitsPerPixel);
+                return new TiffPaletteWriter<TPixel>(image, quantizer, pixelSamplingStrategy, memoryAllocator, configuration, entriesCollector, bitsPerPixel);
             case TiffPhotometricInterpretation.BlackIsZero:
             case TiffPhotometricInterpretation.WhiteIsZero:
                 if (bitsPerPixel == 1)

src/ImageSharp/Formats/Tiff/Writers/TiffPaletteWriter{TPixel}.cs

@@ -17,19 +17,21 @@ internal sealed class TiffPaletteWriter<TPixel> : TiffBaseColorWriter<TPixel>
     private readonly int maxColors;
     private readonly int colorPaletteSize;
     private readonly int colorPaletteBytes;
-    private readonly IndexedImageFrame<TPixel> quantizedImage;
+    private readonly IndexedImageFrame<TPixel> quantizedFrame;
     private IMemoryOwner<byte> indexedPixelsBuffer;
 
     public TiffPaletteWriter(
-        ImageFrame<TPixel> image,
+        ImageFrame<TPixel> frame,
         IQuantizer quantizer,
+        IPixelSamplingStrategy pixelSamplingStrategy,
         MemoryAllocator memoryAllocator,
         Configuration configuration,
         TiffEncoderEntriesCollector entriesCollector,
         int bitsPerPixel)
-         : base(image, memoryAllocator, configuration, entriesCollector)
+         : base(frame, memoryAllocator, configuration, entriesCollector)
     {
         DebugGuard.NotNull(quantizer, nameof(quantizer));
+        DebugGuard.NotNull(quantizer, nameof(pixelSamplingStrategy));
         DebugGuard.NotNull(configuration, nameof(configuration));
         DebugGuard.NotNull(entriesCollector, nameof(entriesCollector));
         DebugGuard.MustBeBetweenOrEqualTo(bitsPerPixel, 4, 8, nameof(bitsPerPixel));
@@ -38,11 +40,15 @@ internal sealed class TiffPaletteWriter<TPixel> : TiffBaseColorWriter<TPixel>
         this.maxColors = this.BitsPerPixel == 4 ? 16 : 256;
         this.colorPaletteSize = this.maxColors * 3;
         this.colorPaletteBytes = this.colorPaletteSize * 2;
-        using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(this.Configuration, new QuantizerOptions()
-        {
-            MaxColors = this.maxColors
-        });
-        this.quantizedImage = frameQuantizer.BuildPaletteAndQuantizeFrame(image, image.Bounds());
+        using IQuantizer<TPixel> frameQuantizer = quantizer.CreatePixelSpecificQuantizer<TPixel>(
+            this.Configuration,
+            new QuantizerOptions()
+            {
+                MaxColors = this.maxColors
+            });
+
+        frameQuantizer.BuildPalette(pixelSamplingStrategy, frame);
+        this.quantizedFrame = frameQuantizer.QuantizeFrame(frame, frame.Bounds());
 
         this.AddColorMapTag();
     }
@@ -66,7 +72,7 @@ internal sealed class TiffPaletteWriter<TPixel> : TiffBaseColorWriter<TPixel>
             int lastRow = y + height;
             for (int row = y; row < lastRow; row++)
             {
-                ReadOnlySpan<byte> indexedPixelRow = this.quantizedImage.DangerousGetRowSpan(row);
+                ReadOnlySpan<byte> indexedPixelRow = this.quantizedFrame.DangerousGetRowSpan(row);
                 int idxPixels = 0;
                 for (int x = 0; x < halfWidth; x++)
                 {
@@ -93,7 +99,7 @@ internal sealed class TiffPaletteWriter<TPixel> : TiffBaseColorWriter<TPixel>
             int indexedPixelsRowIdx = 0;
             for (int row = y; row < lastRow; row++)
             {
-                ReadOnlySpan<byte> indexedPixelRow = this.quantizedImage.DangerousGetRowSpan(row);
+                ReadOnlySpan<byte> indexedPixelRow = this.quantizedFrame.DangerousGetRowSpan(row);
                 indexedPixelRow.CopyTo(indexedPixels.Slice(indexedPixelsRowIdx * width, width));
                 indexedPixelsRowIdx++;
             }
@@ -105,7 +111,7 @@ internal sealed class TiffPaletteWriter<TPixel> : TiffBaseColorWriter<TPixel>
     /// <inheritdoc />
     protected override void Dispose(bool disposing)
     {
-        this.quantizedImage?.Dispose();
+        this.quantizedFrame?.Dispose();
         this.indexedPixelsBuffer?.Dispose();
     }
 
@@ -114,7 +120,7 @@ internal sealed class TiffPaletteWriter<TPixel> : TiffBaseColorWriter<TPixel>
         using IMemoryOwner<byte> colorPaletteBuffer = this.MemoryAllocator.Allocate<byte>(this.colorPaletteBytes);
         Span<byte> colorPalette = colorPaletteBuffer.GetSpan();
 
-        ReadOnlySpan<TPixel> quantizedColors = this.quantizedImage.Palette.Span;
+        ReadOnlySpan<TPixel> quantizedColors = this.quantizedFrame.Palette.Span;
         int quantizedColorBytes = quantizedColors.Length * 3 * 2;
 
         // In the ColorMap, black is represented by 0, 0, 0 and white is represented by 65535, 65535, 65535.
@@ -126,7 +132,7 @@ internal sealed class TiffPaletteWriter<TPixel> : TiffBaseColorWriter<TPixel>
 
         // In a TIFF ColorMap, all the Red values come first, followed by the Green values,
         // then the Blue values. Convert the quantized palette to this format.
-        var palette = new ushort[this.colorPaletteSize];
+        ushort[] palette = new ushort[this.colorPaletteSize];
         int paletteIdx = 0;
         for (int i = 0; i < quantizedColors.Length; i++)
         {
@@ -147,7 +153,7 @@ internal sealed class TiffPaletteWriter<TPixel> : TiffBaseColorWriter<TPixel>
             palette[paletteIdx++] = quantizedColorRgb48[i].B;
         }
 
-        var colorMap = new ExifShortArray(ExifTagValue.ColorMap)
+        ExifShortArray colorMap = new(ExifTagValue.ColorMap)
         {
             Value = palette
         };

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

@@ -101,4 +101,54 @@ public class DefaultPixelSamplingStrategy : IPixelSamplingStrategy
             }
         }
     }
+
+    /// <inheritdoc />
+    public IEnumerable<Buffer2DRegion<TPixel>> EnumeratePixelRegions<TPixel>(ImageFrame<TPixel> frame)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        long maximumPixels = Math.Min(this.MaximumPixels, (long)frame.Width * frame.Height);
+        long maxNumberOfRows = maximumPixels / frame.Width;
+        long totalNumberOfRows = frame.Height;
+
+        if (totalNumberOfRows <= maxNumberOfRows)
+        {
+            yield return frame.PixelBuffer.GetRegion();
+        }
+        else
+        {
+            double r = maxNumberOfRows / (double)totalNumberOfRows;
+
+            // Use a rough approximation to make sure we don't leave out large contiguous regions:
+            if (maxNumberOfRows > 200)
+            {
+                r = Math.Round(r, 2);
+            }
+            else
+            {
+                r = Math.Round(r, 1);
+            }
+
+            r = Math.Max(this.MinimumScanRatio, r); // always visit the minimum defined portion of the image.
+
+            Rational ratio = new(r);
+
+            int denom = (int)ratio.Denominator;
+            int num = (int)ratio.Numerator;
+
+            for (int pos = 0; pos < totalNumberOfRows; pos++)
+            {
+                int subPos = pos % denom;
+                if (subPos < num)
+                {
+                    yield return GetRow(pos);
+                }
+            }
+
+            Buffer2DRegion<TPixel> GetRow(int pos)
+            {
+                int y = pos % frame.Height;
+                return frame.PixelBuffer.GetRegion(0, y, frame.Width, 1);
+            }
+        }
+    }
 }

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

@@ -20,4 +20,11 @@ public class ExtensivePixelSamplingStrategy : IPixelSamplingStrategy
             yield return frame.PixelBuffer.GetRegion();
         }
     }
+
+    /// <inheritdoc/>
+    public IEnumerable<Buffer2DRegion<TPixel>> EnumeratePixelRegions<TPixel>(ImageFrame<TPixel> frame)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        yield return frame.PixelBuffer.GetRegion();
+    }
 }

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

@@ -7,16 +7,25 @@ using SixLabors.ImageSharp.PixelFormats;
 namespace SixLabors.ImageSharp.Processing.Processors.Quantization;
 
 /// <summary>
-/// Provides an abstraction to enumerate pixel regions within a multi-framed <see cref="Image{TPixel}"/>.
+/// Provides an abstraction to enumerate pixel regions for sampling within <see cref="Image{TPixel}"/>.
 /// </summary>
 public interface IPixelSamplingStrategy
 {
     /// <summary>
-    /// Enumerates pixel regions within the image as <see cref="Buffer2DRegion{T}"/>.
+    /// Enumerates pixel regions for all frames within the image as <see cref="Buffer2DRegion{T}"/>.
     /// </summary>
     /// <param name="image">The image.</param>
     /// <typeparam name="TPixel">The pixel type.</typeparam>
     /// <returns>An enumeration of pixel regions.</returns>
     IEnumerable<Buffer2DRegion<TPixel>> EnumeratePixelRegions<TPixel>(Image<TPixel> image)
         where TPixel : unmanaged, IPixel<TPixel>;
+
+    /// <summary>
+    /// Enumerates pixel regions within a single image frame as <see cref="Buffer2DRegion{T}"/>.
+    /// </summary>
+    /// <param name="frame">The image frame.</param>
+    /// <typeparam name="TPixel">The pixel type.</typeparam>
+    /// <returns>An enumeration of pixel regions.</returns>
+    IEnumerable<Buffer2DRegion<TPixel>> EnumeratePixelRegions<TPixel>(ImageFrame<TPixel> frame)
+        where TPixel : unmanaged, IPixel<TPixel>;
 }

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

@@ -99,13 +99,39 @@ public static class QuantizerUtilities
         return destination;
     }
 
-    internal static void BuildPalette<TPixel>(
+    /// <summary>
+    /// Adds colors to the quantized palette from the given pixel regions.
+    /// </summary>
+    /// <typeparam name="TPixel">The pixel format.</typeparam>
+    /// <param name="quantizer">The pixel specific quantizer.</param>
+    /// <param name="pixelSamplingStrategy">The pixel sampling strategy.</param>
+    /// <param name="source">The source image to sample from.</param>
+    public static void BuildPalette<TPixel>(
+        this IQuantizer<TPixel> quantizer,
+        IPixelSamplingStrategy pixelSamplingStrategy,
+        Image<TPixel> source)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
+        {
+            quantizer.AddPaletteColors(region);
+        }
+    }
+
+    /// <summary>
+    /// Adds colors to the quantized palette from the given pixel regions.
+    /// </summary>
+    /// <typeparam name="TPixel">The pixel format.</typeparam>
+    /// <param name="quantizer">The pixel specific quantizer.</param>
+    /// <param name="pixelSamplingStrategy">The pixel sampling strategy.</param>
+    /// <param name="source">The source image frame to sample from.</param>
+    public static void BuildPalette<TPixel>(
         this IQuantizer<TPixel> quantizer,
         IPixelSamplingStrategy pixelSamplingStrategy,
-        Image<TPixel> image)
+        ImageFrame<TPixel> source)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(image))
+        foreach (Buffer2DRegion<TPixel> region in pixelSamplingStrategy.EnumeratePixelRegions(source))
         {
             quantizer.AddPaletteColors(region);
         }

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

@@ -144,7 +144,7 @@ public class GifEncoderTests
         GifEncoder encoder = new()
         {
             ColorTableMode = GifColorTableMode.Global,
-            GlobalPixelSamplingStrategy = new DefaultPixelSamplingStrategy(maxPixels, scanRatio)
+            PixelSamplingStrategy = new DefaultPixelSamplingStrategy(maxPixels, scanRatio)
         };
 
         string testOutputFile = provider.Utility.SaveTestOutputFile(

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

@@ -3,24 +3,21 @@
 
 using SixLabors.ImageSharp.Formats.Tiff;
 using SixLabors.ImageSharp.Formats.Tiff.Writers;
-using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Tests.Formats.Tiff;
 
 [Trait("Format", "Tiff")]
 public class TiffEncoderHeaderTests
 {
-    private static readonly MemoryAllocator MemoryAllocator = MemoryAllocator.Create();
-    private static readonly Configuration Configuration = Configuration.Default;
-    private static readonly ITiffEncoderOptions Options = new TiffEncoder();
+    private static readonly TiffEncoder Encoder = new();
 
     [Fact]
     public void WriteHeader_WritesValidHeader()
     {
-        using var stream = new MemoryStream();
-        var encoder = new TiffEncoderCore(Options, MemoryAllocator);
+        using MemoryStream stream = new();
+        TiffEncoderCore encoder = new(Encoder, Configuration.Default.MemoryAllocator);
 
-        using (var writer = new TiffStreamWriter(stream))
+        using (TiffStreamWriter writer = new(stream))
         {
             long firstIfdMarker = TiffEncoderCore.WriteHeader(writer);
         }
@@ -31,13 +28,11 @@ public class TiffEncoderHeaderTests
     [Fact]
     public void WriteHeader_ReturnsFirstIfdMarker()
     {
-        using var stream = new MemoryStream();
-        var encoder = new TiffEncoderCore(Options, MemoryAllocator);
+        using MemoryStream stream = new();
+        TiffEncoderCore encoder = new(Encoder, Configuration.Default.MemoryAllocator);
 
-        using (var writer = new TiffStreamWriter(stream))
-        {
-            long firstIfdMarker = TiffEncoderCore.WriteHeader(writer);
-            Assert.Equal(4, firstIfdMarker);
-        }
+        using TiffStreamWriter writer = new(stream);
+        long firstIfdMarker = TiffEncoderCore.WriteHeader(writer);
+        Assert.Equal(4, firstIfdMarker);
     }
 }