Implement Butteraugli core functions

src/ImageSharp/Formats/Jxl/Processing/Butteraugli/ButteraugliComparator.cs

@@ -0,0 +1,46 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Jxl.Memory.ImageTypes;
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Processing.Butteraugli;
+
+internal sealed class ButteraugliComparator
+{
+    private int xSize;
+    private int ySize;
+    private ButteraugliParameters parameters;
+    private readonly ButteraugliPsychoImage pi0;
+    private readonly JxlImage3F temp;
+    private bool tempInUse;
+    private readonly ButteraugliBlurTemp blurTemp;
+
+    /// <summary>
+    /// Computes the butteraugli map between the original image given in the constructor and the distorted image given here.
+    /// </summary>
+    public bool Diffmap(JxlImage3F rgb1, JxlImageF result)
+    {
+        throw new NotImplementedException();
+    }
+
+    /// <summary>
+    /// Same as Diffmap but OpsinDynamicsImage() was already applied.
+    /// </summary>
+    public bool DiffmapOpsinDynamicsImage(JxlImage3F xyb1, JxlImageF result)
+    {
+        throw new NotImplementedException();
+    }
+
+    /// <summary>
+    /// Same as above but the frequency decomposition was already applied.
+    /// </summary>
+    public bool DiffmapPsychoImage(ButteraugliPsychoImage pi1, JxlImageF diffmap)
+    {
+        throw new NotImplementedException();
+    }
+
+    public bool Mask(JxlImageF mask)
+    {
+        throw new NotImplementedException();
+    }
+}

src/ImageSharp/Formats/Jxl/Processing/Butteraugli/ButteraugliParameters.cs

@@ -9,18 +9,18 @@ namespace SixLabors.ImageSharp.Formats.Jxl.Processing.Butteraugli;
 internal struct ButteraugliParameters()
 {
     /// <summary>
-    /// Multiplier for penalizing new HF artifacts more than
+    /// Gets or sets the multiplier for penalizing new HF artifacts more than
     /// blurring away features. Value of 1.0 represents neutral.
     /// </summary>
-    public float HfAsymmetry = 1f;
+    public float HfAsymmetry { get; set; } = 1f;
 
     /// <summary>
-    /// Multiplier for the psychovisual difference in the X channel.
+    /// Gets or sets the multiplier for the psychovisual difference in the X channel.
     /// </summary>
-    public float XMultiplier = 1f;
+    public float XMultiplier { get; set; } = 1f;
 
     /// <summary>
-    /// Number of nits that correspond to 1.0f input values.
+    /// Gets or sets the number of nits that correspond to 1.0f input values.
     /// </summary>
-    public float IntensityTarget = 80f;
+    public float IntensityTarget { get; set; } = 80f;
 }

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

@@ -4,7 +4,6 @@
 using System.Buffers;
 using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.Formats.Jxl.Fields;
-using SixLabors.ImageSharp.Formats.Jxl.IO;
 using SixLabors.ImageSharp.Formats.Jxl.Memory;
 using SixLabors.ImageSharp.Formats.Jxl.Memory.ImageTypes;
 

src/ImageSharp/Formats/Jxl/Processing/JxlWeightsSeparable5.cs

@@ -3,9 +3,11 @@
 
 namespace SixLabors.ImageSharp.Formats.Jxl.Processing;
 
-internal sealed class JxlWeightsSeparable5
+internal struct JxlWeightsSeparable5
 {
-    public InlineArray12<float> Horizontal { get; set; }
+    // Don't make these a property so we can ref into them.
 
-    public InlineArray12<float> Vertical { get; set; }
+    public InlineArray12<float> Horizontal;
+
+    public InlineArray12<float> Vertical;
 }