CMYK to RGB converter performance tweaks

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromCmykAvx.cs

@@ -30,7 +30,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                     ref Unsafe.As<float, Vector256<float>>(ref MemoryMarshal.GetReference(values.Component3));
 
                 // Used for the color conversion
-                var scale = Vector256.Create(1 / this.MaximumValue);
+                var scale = Vector256.Create(1 / (this.MaximumValue * this.MaximumValue));
 
                 nint n = values.Component0.Length / Vector256<float>.Count;
                 for (nint i = 0; i < n; i++)
@@ -41,9 +41,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                     Vector256<float> k = Unsafe.Add(ref c3Base, i);
 
                     k = Avx.Multiply(k, scale);
-                    c = Avx.Multiply(Avx.Multiply(c, k), scale);
-                    m = Avx.Multiply(Avx.Multiply(m, k), scale);
-                    y = Avx.Multiply(Avx.Multiply(y, k), scale);
+                    c = Avx.Multiply(c, k);
+                    m = Avx.Multiply(m, k);
+                    y = Avx.Multiply(y, k);
                 }
             }
         }

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromCmykScalar.cs

@@ -24,17 +24,18 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                 Span<float> c2 = values.Component2;
                 Span<float> c3 = values.Component3;
 
-                float scale = 1 / maxValue;
+                float scale = 1 / (maxValue * maxValue);
                 for (int i = 0; i < c0.Length; i++)
                 {
                     float c = c0[i];
                     float m = c1[i];
                     float y = c2[i];
-                    float k = c3[i] / maxValue;
+                    float k = c3[i];
 
-                    c0[i] = c * k * scale;
-                    c1[i] = m * k * scale;
-                    c2[i] = y * k * scale;
+                    k *= scale;
+                    c0[i] = c * k;
+                    c1[i] = m * k;
+                    c2[i] = y * k;
                 }
             }
         }

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromCmykVector.cs

@@ -27,7 +27,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                 ref Vector<float> kBase =
                     ref Unsafe.As<float, Vector<float>>(ref MemoryMarshal.GetReference(values.Component3));
 
-                var scale = new Vector<float>(1 / this.MaximumValue);
+                var scale = new Vector<float>(1 / (this.MaximumValue * this.MaximumValue));
 
                 nint n = values.Component0.Length / Vector<float>.Count;
                 for (nint i = 0; i < n; i++)
@@ -35,11 +35,12 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                     ref Vector<float> c = ref Unsafe.Add(ref cBase, i);
                     ref Vector<float> m = ref Unsafe.Add(ref mBase, i);
                     ref Vector<float> y = ref Unsafe.Add(ref yBase, i);
-                    Vector<float> k = Unsafe.Add(ref kBase, i) * scale;
+                    Vector<float> k = Unsafe.Add(ref kBase, i);
 
-                    c = c * k * scale;
-                    m = m * k * scale;
-                    y = y * k * scale;
+                    k *= scale;
+                    c *= k;
+                    m *= k;
+                    y *= k;
                 }
             }