Add CFL

See chroma_from_luma.cc and chroma_from_luma.h

src/ImageSharp/Formats/Jxl/Processing/JxlAcStrategy.cs

@@ -4,7 +4,7 @@
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using static SixLabors.ImageSharp.Formats.Jxl.JxlFrameDimensions;
+using static SixLabors.ImageSharp.Formats.Jxl.Processing.JxlFrameDimensions;
 
 #pragma warning disable SA1405 // Debug.Assert should provide message text
 

src/ImageSharp/Formats/Jxl/Processing/JxlChromaFromLuma.cs

@@ -0,0 +1,46 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Jxl.Fields;
+using static SixLabors.ImageSharp.Formats.Jxl.Processing.JxlFrameDimensions;
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Processing;
+
+/// <summary>
+/// Shared constants for CFL (Chroma From Luma) functions.
+/// </summary>
+internal static class JxlChromaFromLuma
+{
+    /// <summary>
+    /// Tiles are 64x64.
+    /// </summary>
+    public const int ColorTileDimension = 64;
+
+    /// <summary>
+    /// Division of the color tile dimension by the block dimension. Therefore,
+    /// this is 8x8.
+    /// </summary>
+    public const int ColorTileDimensionInBlocks = ColorTileDimension / BlockDimensions;
+
+    public const int DefaultColorFactor = 84;
+
+    /// <summary>
+    /// Chroma From Luma fixed point precision, which is
+    /// 11 bits.
+    /// </summary>
+    public const int CflFixedPointPrecision = 11;
+
+    /// <summary>
+    /// 524287
+    /// </summary>
+    public const int CflFixedPointRatioMax = (256 << CflFixedPointPrecision) - 1;
+
+    /// <summary>
+    /// Shared variable U32 distributions for the color factor.
+    /// </summary>
+    public static readonly JxlU32Enc ColorFactorDistribution = new(
+        JxlFieldExpressions.Value(DefaultColorFactor),
+        JxlFieldExpressions.Value(256),
+        JxlFieldExpressions.BitsOffset(8, 2),
+        JxlFieldExpressions.BitsOffset(16, 258));
+}

src/ImageSharp/Formats/Jxl/Processing/JxlColorCorrelation.cs

@@ -0,0 +1,113 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Jxl.Fields;
+using SixLabors.ImageSharp.Formats.Jxl.Processing.Decoder;
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Processing;
+
+internal sealed class JxlColorCorrelation
+{
+    private float baseCorrelationX;
+    private float baseCorrelationB = DefaultYToBRatio;
+
+    private readonly float[] dcFactors = new float[4];
+    private uint colorFactor = JxlChromaFromLuma.DefaultColorFactor;
+    private float colorScale = 1.0f / JxlChromaFromLuma.DefaultColorFactor;
+
+    public int YToXDc { get; private set; }
+
+    public int YToBDc { get; private set; }
+
+    public float ColorFactor => this.colorFactor;
+
+    public float BaseCorrelationX
+    {
+        get => this.baseCorrelationX;
+        set => this.baseCorrelationX = value;
+    }
+
+    public float BaseCorrelationB
+    {
+        get => this.baseCorrelationB;
+        set => this.baseCorrelationB = value;
+    }
+
+    public bool IsJpegCompatible =>
+        this.BaseCorrelationX == 0 &&
+        this.BaseCorrelationB == 0 &&
+        this.YToBDc == 0 &&
+        this.YToXDc == 0 &&
+        this.ColorFactor == JxlChromaFromLuma.DefaultColorFactor;
+
+    public ReadOnlySpan<float> DcFactors => this.dcFactors;
+
+    public float YToXRatio(int xFactor) => this.BaseCorrelationX + (xFactor * this.colorScale);
+
+    public float YToBRatio(int bFactor) => this.BaseCorrelationB + (bFactor * this.colorScale);
+
+    public void SetColorFactor(uint factor)
+    {
+        this.colorFactor = factor;
+        this.colorScale = 1f / factor;
+        this.RecomputeDcFactors();
+    }
+
+    public void SetYToBDc(int yToBDc)
+    {
+        this.YToBDc = yToBDc;
+        this.RecomputeDcFactors();
+    }
+
+    public void SetYToXDc(int yToXDc)
+    {
+        this.YToXDc = yToXDc;
+        this.RecomputeDcFactors();
+    }
+
+    public void RecomputeDcFactors()
+    {
+        this.dcFactors[0] = this.YToXRatio(this.YToXDc);
+        this.dcFactors[2] = this.YToBRatio(this.YToBDc);
+    }
+
+    public bool DecodeDc(JxlBitReader reader)
+    {
+        bool allDefault = reader.ReadBoolean();
+
+        if (allDefault)
+        {
+            return true;
+        }
+
+        this.SetColorFactor(JxlU32Coder.Read(JxlChromaFromLuma.ColorFactorDistribution, reader));
+
+        if (!JxlF16Coder.Read(reader, ref this.baseCorrelationX))
+        {
+            return false;
+        }
+
+        if (MathF.Abs(this.baseCorrelationX) > 4f)
+        {
+            throw new InvalidOperationException("Base X correlation is out of range");
+        }
+
+        if (!JxlF16Coder.Read(reader, ref this.baseCorrelationB))
+        {
+            return false;
+        }
+
+        if (MathF.Abs(this.baseCorrelationB) > 4f)
+        {
+            throw new InvalidOperationException("Base B correlation is out of range");
+        }
+
+        this.YToXDc = (int)reader.ReadBits32(8) + sbyte.MinValue;
+        this.YToBDc = (int)reader.ReadBits32(8) + sbyte.MinValue;
+
+        this.RecomputeDcFactors();
+        return true;
+    }
+
+    public static int RatioJpeg(int factor) => factor * (1 << JxlChromaFromLuma.CflFixedPointPrecision) / JxlChromaFromLuma.DefaultColorFactor;
+}

src/ImageSharp/Formats/Jxl/Processing/JxlColorCorrelationMap.cs

@@ -0,0 +1,42 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Jxl.Memory.ImageTypes;
+using SixLabors.ImageSharp.Formats.Jxl.Processing.Decoder;
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Processing;
+
+/// <summary>
+/// JPEG XL Color correlation map.
+/// </summary>
+internal sealed class JxlColorCorrelationMap
+{
+    public JxlColorCorrelation Base { get; set; } = new();
+
+    public JxlImageSB? YToXMap { get; set; }
+
+    public JxlImageSB? YToBMap { get; set; }
+
+    public bool DecodeDc(JxlBitReader reader) => this.Base.DecodeDc(reader);
+
+    public static JxlColorCorrelationMap Create(Configuration configuration, int width, int height, bool xyb)
+    {
+        JxlColorCorrelationMap map = new();
+
+        (int xBlocks, int yBlocks) = (DivCeil(width, JxlChromaFromLuma.ColorTileDimension), DivCeil(height, JxlChromaFromLuma.ColorTileDimension));
+
+        map.YToXMap = new JxlImageSB(configuration, xBlocks, yBlocks);
+        map.YToBMap = new JxlImageSB(configuration, xBlocks, yBlocks);
+
+        ZeroFillImage(map.YToXMap);
+        ZeroFillImage(map.YToBMap);
+
+        if (!xyb)
+        {
+            map.Base.BaseCorrelationB = 0;
+        }
+
+        map.Base.RecomputeDcFactors();
+        return map;
+    }
+}