Add Y'Cb'Cr stage, make Epf1Stage class sealed

src/ImageSharp/Formats/Jxl/Processing/RenderPipeline/Epf1Stage.cs

@@ -13,7 +13,7 @@ namespace SixLabors.ImageSharp.Formats.Jxl.Processing.RenderPipeline;
 /// <summary>
 /// Edge Preserving Filter (type 1) stage.
 /// </summary>
-internal class Epf1Stage : RenderPipelineStageBase
+internal sealed class Epf1Stage : RenderPipelineStageBase
 {
     private readonly JxlLoopFilter loopFilter;
     private readonly JxlImageF sigma;

src/ImageSharp/Formats/Jxl/Processing/RenderPipeline/WriteToOutputStage.cs

@@ -1,8 +1,10 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Numerics;
 using SixLabors.ImageSharp.Formats.Jxl.IO.Metadata;
 using SixLabors.ImageSharp.Formats.Jxl.Processing.Image;
+using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Jxl.Processing.RenderPipeline;
 

src/ImageSharp/Formats/Jxl/Processing/RenderPipeline/YCbCrStage.cs

@@ -0,0 +1,67 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Processing.RenderPipeline;
+
+/// <summary>
+/// SIMD-based conversion from Y'Cb'Cr to RGB pixel buffers.
+/// </summary>
+internal sealed class YCbCrStage : RenderPipelineStageBase
+{
+    public YCbCrStage(Configuration configuration)
+        : base(configuration)
+    {
+    }
+
+    /// <inheritdoc />
+    public override string Name => "YCbCr";
+
+    /// <inheritdoc />
+    public override void ProcessRow(Buffer2D<Memory<float>> inputRows, Buffer2D<Memory<float>> outputRows, int xExtraLeft, int xExtraRight, int width, int xPos, int yPos)
+    {
+        // Vectors for conversion, defined by the ITU
+        Vector<float> c128 = Vector.Create(128.0f / 255);
+        Vector<float> crcr = Vector.Create(1.402f);
+        Vector<float> cgcb = Vector.Create(-0.114f * 1.772f / 0.587f);
+        Vector<float> cgcr = Vector.Create(-0.299f * 1.402f / 0.587f);
+        Vector<float> cbcb = Vector.Create(1.772f);
+
+        Span<float> row0 = this.GetInputRow(inputRows, 0, 0);
+        Span<float> row1 = this.GetInputRow(inputRows, 1, 0);
+        Span<float> row2 = this.GetInputRow(inputRows, 2, 0);
+
+        // Using refs for better performance
+        ref float row0Ref = ref MemoryMarshal.GetReference(row0);
+        ref float row1Ref = ref MemoryMarshal.GetReference(row1);
+        ref float row2Ref = ref MemoryMarshal.GetReference(row2);
+
+        for (int x = 0; x < width; x += Vector<float>.Count)
+        {
+            // Y'Cb'Cr input vectors
+            Vector<float> yVec = Vector.LoadUnsafe(ref Unsafe.Add(ref row1Ref, x)) + c128;
+            Vector<float> cbVec = Vector.LoadUnsafe(ref Unsafe.Add(ref row0Ref, x));
+            Vector<float> crVec = Vector.LoadUnsafe(ref Unsafe.Add(ref row2Ref, x));
+
+            // RGB output vectors
+            Vector<float> rVec = (crcr * crVec) + yVec;
+            Vector<float> gVec = (cgcr * crVec) + ((cgcb * cbVec) + yVec);
+            Vector<float> bVec = (cbcb * cbVec) + yVec;
+
+            // Copying to the output...
+            rVec.StoreUnsafe(ref Unsafe.Add(ref row0Ref, x));
+            gVec.StoreUnsafe(ref Unsafe.Add(ref row1Ref, x));
+            bVec.StoreUnsafe(ref Unsafe.Add(ref row2Ref, x));
+        }
+    }
+
+    /// <inheritdoc />
+    public override RenderPipelineChannelMode GetChannelMode(int channel) =>
+        channel < 3
+            ? RenderPipelineChannelMode.InPlace
+            : RenderPipelineChannelMode.Ignored;
+}