Optimization: omit premultiplication for Bgr24 and Rgb24

src/ImageSharp/PixelFormats/PixelConversionModifiers.cs

@@ -3,14 +3,38 @@
 
 using System;
 
+using SixLabors.ImageSharp.ColorSpaces.Companding;
+
 namespace SixLabors.ImageSharp.PixelFormats
 {
+    /// <summary>
+    /// Flags responsible to select additional operations which could be effitiently applied in
+    /// <see cref="PixelOperations{TPixel}.ToVector4(SixLabors.ImageSharp.Configuration,System.ReadOnlySpan{TPixel},System.Span{System.Numerics.Vector4},SixLabors.ImageSharp.PixelFormats.PixelConversionModifiers)"/>
+    /// or
+    /// <see cref="PixelOperations{TPixel}.FromVector4(SixLabors.ImageSharp.Configuration,System.Span{System.Numerics.Vector4},System.Span{TPixel},SixLabors.ImageSharp.PixelFormats.PixelConversionModifiers)"/>
+    /// knowing the pixel type.
+    /// </summary>
     [Flags]
     internal enum PixelConversionModifiers
     {
+        /// <summary>
+        /// No special operation is selected
+        /// </summary>
         None = 0,
+
+        /// <summary>
+        /// Select <see cref="IPixel.ToScaledVector4"/> <see cref="IPixel.FromScaledVector4"/> instead the standard (non scaled) variants.
+        /// </summary>
         Scale = 1 << 0,
+
+        /// <summary>
+        /// Enable alpha premultiplication / unpremultiplication
+        /// </summary>
         Premultiply = 1 << 1,
+
+        /// <summary>
+        /// Enable SRGB companding (defined in <see cref="SRgbCompanding"/>).
+        /// </summary>
         SRgbCompand = 1 << 2,
     }
 }

src/ImageSharp/PixelFormats/PixelImplementations/Generated/Bgr24.PixelOperations.Generated.cs

@@ -44,13 +44,13 @@ namespace SixLabors.ImageSharp.PixelFormats
             /// <inheritdoc />
             internal override void FromVector4(Configuration configuration, Span<Vector4> sourceVectors, Span<Bgr24> destPixels, PixelConversionModifiers modifiers)
             {
-                Vector4Converters.RgbaCompatible.FromVector4(configuration, this, sourceVectors, destPixels, modifiers.Remove(PixelConversionModifiers.Scale));
+                Vector4Converters.RgbaCompatible.FromVector4(configuration, this, sourceVectors, destPixels, modifiers.Remove(PixelConversionModifiers.Scale | PixelConversionModifiers.Premultiply));
             }
 
             /// <inheritdoc />
             internal override void ToVector4(Configuration configuration, ReadOnlySpan<Bgr24> sourcePixels, Span<Vector4> destVectors, PixelConversionModifiers modifiers)
             {
-                Vector4Converters.RgbaCompatible.ToVector4(configuration, this, sourcePixels, destVectors, modifiers.Remove(PixelConversionModifiers.Scale));
+                Vector4Converters.RgbaCompatible.ToVector4(configuration, this, sourcePixels, destVectors, modifiers.Remove(PixelConversionModifiers.Scale | PixelConversionModifiers.Premultiply));
             }
 
             /// <inheritdoc />

src/ImageSharp/PixelFormats/PixelImplementations/Generated/Rgb24.PixelOperations.Generated.cs

@@ -44,13 +44,13 @@ namespace SixLabors.ImageSharp.PixelFormats
             /// <inheritdoc />
             internal override void FromVector4(Configuration configuration, Span<Vector4> sourceVectors, Span<Rgb24> destPixels, PixelConversionModifiers modifiers)
             {
-                Vector4Converters.RgbaCompatible.FromVector4(configuration, this, sourceVectors, destPixels, modifiers.Remove(PixelConversionModifiers.Scale));
+                Vector4Converters.RgbaCompatible.FromVector4(configuration, this, sourceVectors, destPixels, modifiers.Remove(PixelConversionModifiers.Scale | PixelConversionModifiers.Premultiply));
             }
 
             /// <inheritdoc />
             internal override void ToVector4(Configuration configuration, ReadOnlySpan<Rgb24> sourcePixels, Span<Vector4> destVectors, PixelConversionModifiers modifiers)
             {
-                Vector4Converters.RgbaCompatible.ToVector4(configuration, this, sourcePixels, destVectors, modifiers.Remove(PixelConversionModifiers.Scale));
+                Vector4Converters.RgbaCompatible.ToVector4(configuration, this, sourcePixels, destVectors, modifiers.Remove(PixelConversionModifiers.Scale | PixelConversionModifiers.Premultiply));
             }
 
             /// <inheritdoc />

src/ImageSharp/PixelFormats/PixelImplementations/Generated/_Common.ttinclude

@@ -22,6 +22,7 @@ using System.Runtime.InteropServices;
     // Types with Rgba32-combatible to/from Vector4 conversion
     static readonly string[] Rgba32CompatibleTypes = { "Argb32", "Bgra32", "Rgb24", "Bgr24" };
 
+
     void GenerateDefaultSelfConversionMethods(string pixelType)
     {
 #>
@@ -107,19 +108,24 @@ using System.Runtime.InteropServices;
 <#+
     }
 
-    void GenerateRgba32CompatibleVector4ConversionMethods(string pixelType)
+    void GenerateRgba32CompatibleVector4ConversionMethods(string pixelType, bool hasAlpha)
     {
+           string removeTheseModifiers = "PixelConversionModifiers.Scale";
+           if (!hasAlpha)
+           {
+               removeTheseModifiers += " | PixelConversionModifiers.Premultiply";
+           }
 #>
             /// <inheritdoc />
             internal override void FromVector4(Configuration configuration, Span<Vector4> sourceVectors, Span<<#=pixelType#>> destPixels, PixelConversionModifiers modifiers)
             {
-                Vector4Converters.RgbaCompatible.FromVector4(configuration, this, sourceVectors, destPixels, modifiers.Remove(PixelConversionModifiers.Scale));
+                Vector4Converters.RgbaCompatible.FromVector4(configuration, this, sourceVectors, destPixels, modifiers.Remove(<#=removeTheseModifiers#>));
             }
 
             /// <inheritdoc />
             internal override void ToVector4(Configuration configuration, ReadOnlySpan<<#=pixelType#>> sourcePixels, Span<Vector4> destVectors, PixelConversionModifiers modifiers)
             {
-                Vector4Converters.RgbaCompatible.ToVector4(configuration, this, sourcePixels, destVectors, modifiers.Remove(PixelConversionModifiers.Scale));
+                Vector4Converters.RgbaCompatible.ToVector4(configuration, this, sourcePixels, destVectors, modifiers.Remove(<#=removeTheseModifiers#>));
             }
 <#+
     }
@@ -130,7 +136,7 @@ using System.Runtime.InteropServices;
 
         if (Rgba32CompatibleTypes.Contains(pixelType))
         {
-            GenerateRgba32CompatibleVector4ConversionMethods(pixelType);
+            GenerateRgba32CompatibleVector4ConversionMethods(pixelType, pixelType.EndsWith("32"));
         }
 
         var matching32BitTypes = Optimized32BitTypes.Contains(pixelType) ?
@@ -151,4 +157,4 @@ using System.Runtime.InteropServices;
             GenerateDefaultConvertToMethod(pixelType, destPixelType);
         }
     }
-#>
+#>

tests/ImageSharp.Tests/PixelFormats/PixelOperations/PixelOperationsTests.Bgr24OperationsTests.cs

@@ -15,6 +15,7 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats.PixelOperations
             public Bgr24OperationsTests(ITestOutputHelper output)
                 : base(output)
             {
+                this.HasAlpha = false;
             }
 
             [Fact]

tests/ImageSharp.Tests/PixelFormats/PixelOperations/PixelOperationsTests.Rgb24OperationsTests.cs

@@ -14,6 +14,7 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats.PixelOperations
             public Rgb24OperationsTests(ITestOutputHelper output)
                 : base(output)
             {
+                this.HasAlpha = false;
             }
 
             [Fact]

tests/ImageSharp.Tests/PixelFormats/PixelOperations/PixelOperationsTests.cs

@@ -33,6 +33,8 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats.PixelOperations
                 null;
 #endif
 
+        protected bool HasAlpha { get; set; } = true;
+
         protected PixelOperationsTests(ITestOutputHelper output)
             : base(output)
         {
@@ -165,12 +167,18 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats.PixelOperations
         {
             void sourceAction(ref Vector4 v)
             {
-                Vector4Utils.Premultiply(ref v);
+                if (this.HasAlpha)
+                {
+                    Vector4Utils.Premultiply(ref v);
+                }
             }
 
             void expectedAction(ref Vector4 v)
             {
-                Vector4Utils.UnPremultiply(ref v);
+                if (this.HasAlpha)
+                {
+                    Vector4Utils.UnPremultiply(ref v);
+                }
             }
 
             Vector4[] source = CreateVector4TestData(count, (ref Vector4 v) => sourceAction(ref v));
@@ -189,12 +197,18 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats.PixelOperations
         {
             void sourceAction(ref Vector4 v)
             {
-                Vector4Utils.Premultiply(ref v);
+                if (this.HasAlpha)
+                {
+                    Vector4Utils.Premultiply(ref v);
+                }
             }
 
             void expectedAction(ref Vector4 v)
             {
-                Vector4Utils.UnPremultiply(ref v);
+                if (this.HasAlpha)
+                {
+                    Vector4Utils.UnPremultiply(ref v);
+                }
             }
 
             Vector4[] source = CreateVector4TestData(count, (ref Vector4 v) => sourceAction(ref v));
@@ -218,12 +232,20 @@ namespace SixLabors.ImageSharp.Tests.PixelFormats.PixelOperations
             void sourceAction(ref Vector4 v)
             {
                 SRgbCompanding.Expand(ref v);
-                Vector4Utils.Premultiply(ref v);
+
+                if (this.HasAlpha)
+                {
+                    Vector4Utils.Premultiply(ref v);
+                }
             }
 
             void expectedAction(ref Vector4 v)
             {
-                Vector4Utils.UnPremultiply(ref v);
+                if (this.HasAlpha)
+                {
+                    Vector4Utils.UnPremultiply(ref v);
+                }
+                
                 SRgbCompanding.Compress(ref v);
             }