Fix test case made with wrong assumptions about matrix ordering

src/ImageSharp/ColorProfiles/ColorProfileConverterExtensionsIcc.cs

@@ -39,6 +39,7 @@ internal static class ColorProfileConverterExtensionsIcc
             TargetWhitePoint = new CieXyz(converter.Options.TargetIccProfile.Header.PcsIlluminant),
         });
 
+        // output of Matrix TRC calculator is descaled XYZ, needs to be re-scaled to be used as PCS
         Vector4 sourcePcs = sourceParams.Converter.Calculate(source.ToScaledVector4());
         Vector4 targetPcs;
 
@@ -56,6 +57,7 @@ internal static class ColorProfileConverterExtensionsIcc
         }
 
         // Convert to the target space.
+        // input to Matrix TRC calculator is descaled XYZ, need to descale PCS before use
         return TTo.FromScaledVector4(targetParams.Converter.Calculate(targetPcs));
     }
 

src/ImageSharp/ColorProfiles/Icc/Calculators/LutEntryCalculator.cs

@@ -37,7 +37,7 @@ internal class LutEntryCalculator : IVector4Calculator
     {
         if (this.doTransform)
         {
-            value = Vector4.Transform(value, Matrix4x4.Transpose(this.matrix));
+            value = Vector4.Transform(value, this.matrix);
         }
 
         value = CalculateLut(this.inputCurve, value);

tests/ImageSharp.Tests/TestDataIcc/Conversion/IccConversionDataLutEntry.cs

@@ -12,27 +12,37 @@ public class IccConversionDataLutEntry
     private static readonly IccLut Lut32 = CreateLut(32);
     private static readonly IccLut LutIdentity = CreateIdentityLut(0, 1);
 
+    // test cases were originally calculated unaware that
+    // IccConversionDataMatrix.Matrix3x3Random is actually the row-major transposed matrix
+    // of the typical column-major matrix
+    public static float[,] TestMatrix =
+    {
+        { 0.1f, 0.4f, 0.7f },
+        { 0.2f, 0.5f, 0.8f },
+        { 0.3f, 0.6f, 0.9f }
+    };
+
     private static readonly IccLut8TagDataEntry Lut8 = new(
-        new[] { Lut256, Lut256 },
+        [Lut256, Lut256],
         IccConversionDataClut.Clut2x1,
-        new[] { Lut256 });
+        [Lut256]);
 
     private static readonly IccLut16TagDataEntry Lut16 = new(
-        new[] { Lut32, Lut32 },
+        [Lut32, Lut32],
         IccConversionDataClut.Clut2x1,
-        new[] { LutIdentity });
+        [LutIdentity]);
 
     private static readonly IccLut8TagDataEntry Lut8Matrix = new(
-        IccConversionDataMatrix.Matrix3x3Random,
-        new[] { Lut256, Lut256, Lut256 },
+        TestMatrix,
+        [Lut256, Lut256, Lut256],
         IccConversionDataClut.Clut3x1,
-        new[] { Lut256 });
+        [Lut256]);
 
     private static readonly IccLut16TagDataEntry Lut16Matrix = new(
-        IccConversionDataMatrix.Matrix3x3Random,
-        new[] { Lut32, Lut32, Lut32 },
+        TestMatrix,
+        [Lut32, Lut32, Lut32],
         IccConversionDataClut.Clut3x1,
-        new[] { LutIdentity });
+        [LutIdentity]);
 
     private static IccLut CreateLut(int length)
     {
@@ -45,17 +55,17 @@ public class IccConversionDataLutEntry
         return new IccLut(values);
     }
 
-    private static IccLut CreateIdentityLut(float min, float max) => new(new[] { min, max });
+    private static IccLut CreateIdentityLut(float min, float max) => new([min, max]);
 
     public static object[][] Lut8ConversionTestData =
-    {
-        new object[] { Lut8, new Vector4(0.2f, 0.3f, 0, 0), new Vector4(0.4578933760499877f, 0, 0, 0) },
-        new object[] { Lut8Matrix, new Vector4(0.21f, 0.31f, 0.41f, 0), new Vector4(0.40099657491875312f, 0, 0, 0) },
-    };
+    [
+        [Lut8, new Vector4(0.2f, 0.3f, 0, 0), new Vector4(0.4578933760499877f, 0, 0, 0)],
+        [Lut8Matrix, new Vector4(0.21f, 0.31f, 0.41f, 0), new Vector4(0.40099657491875312f, 0, 0, 0)]
+    ];
 
     public static object[][] Lut16ConversionTestData =
-    {
-        new object[] { Lut16, new Vector4(0.2f, 0.3f, 0, 0), new Vector4(0.3543750030529918f, 0, 0, 0) },
-        new object[] { Lut16Matrix, new Vector4(0.21f, 0.31f, 0.41f, 0), new Vector4(0.29739562389689594f, 0, 0, 0) },
-    };
+    [
+        [Lut16, new Vector4(0.2f, 0.3f, 0, 0), new Vector4(0.3543750030529918f, 0, 0, 0)],
+        [Lut16Matrix, new Vector4(0.21f, 0.31f, 0.41f, 0), new Vector4(0.29739562389689594f, 0, 0, 0)]
+    ];
 }