PixelConversionModifierExtensions.ApplyCompanding() + tests

src/ImageSharp/PixelFormats/PixelConversionModifiersExtensions.cs

@@ -5,6 +5,9 @@ using System.Runtime.CompilerServices;
 
 namespace SixLabors.ImageSharp.PixelFormats
 {
+    /// <summary>
+    /// Extension and utility methods for <see cref="PixelConversionModifiers"/>.
+    /// </summary>
     internal static class PixelConversionModifiersExtensions
     {
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -16,5 +19,20 @@ namespace SixLabors.ImageSharp.PixelFormats
             this PixelConversionModifiers modifiers,
             PixelConversionModifiers removeThis) =>
             modifiers & ~removeThis;
+
+        /// <summary>
+        /// Applies the union of <see cref="PixelConversionModifiers.Scale"/> and <see cref="PixelConversionModifiers.SRgbCompand"/>,
+        /// if <paramref name="compand"/> is true, returns unmodified <paramref name="originalModifiers"/> otherwise.
+        /// </summary>
+        /// <remarks>
+        /// <see cref="PixelConversionModifiers.Scale"/> and <see cref="PixelConversionModifiers.SRgbCompand"/>
+        /// should be always used together!
+        /// </remarks>
+        public static PixelConversionModifiers ApplyCompanding(
+            this PixelConversionModifiers originalModifiers,
+            bool compand) =>
+            compand
+                ? originalModifiers | PixelConversionModifiers.Scale | PixelConversionModifiers.SRgbCompand
+                : originalModifiers;
     }
 }

src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeProcessor.cs

@@ -236,11 +236,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
 
             int sourceHeight = source.Height;
 
-            PixelConversionModifiers conversionModifiers = PixelConversionModifiers.Premultiply;
-            if (this.Compand)
-            {
-                conversionModifiers |= PixelConversionModifiers.Scale | PixelConversionModifiers.SRgbCompand;
-            }
+            PixelConversionModifiers conversionModifiers =
+                PixelConversionModifiers.Premultiply.ApplyCompanding(this.Compand);
 
             // Interpolate the image using the calculated weights.
             // A 2-pass 1D algorithm appears to be faster than splitting a 1-pass 2D algorithm

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

@@ -0,0 +1,65 @@
+// // Copyright (c) Six Labors and contributors.
+// // Licensed under the Apache License, Version 2.0.
+// // Copyright (c) Six Labors and contributors.
+// // Licensed under the Apache License, Version 2.0.
+// // Copyright (c) Six Labors and contributors.
+// // Licensed under the Apache License, Version 2.0.
+
+using SixLabors.ImageSharp.PixelFormats;
+
+using Xunit;
+
+namespace SixLabors.ImageSharp.Tests.PixelFormats.PixelOperations
+{
+    public class PixelConversionModifiersExtensionsTests
+    {
+        [Theory]
+        [InlineData(PixelConversionModifiers.None, PixelConversionModifiers.None, true)]
+        [InlineData(PixelConversionModifiers.None, PixelConversionModifiers.Premultiply, false)]
+        [InlineData(PixelConversionModifiers.SRgbCompand, PixelConversionModifiers.Premultiply, false)]
+        [InlineData(
+            PixelConversionModifiers.Premultiply | PixelConversionModifiers.Scale,
+            PixelConversionModifiers.Premultiply,
+            true)]
+        [InlineData(
+            PixelConversionModifiers.Premultiply | PixelConversionModifiers.Scale,
+            PixelConversionModifiers.Premultiply | PixelConversionModifiers.Scale,
+            true)]
+        [InlineData(
+            PixelConversionModifiers.Premultiply | PixelConversionModifiers.Scale,
+            PixelConversionModifiers.Scale,
+            true)]
+        internal void IsDefined(
+            PixelConversionModifiers baselineModifiers,
+            PixelConversionModifiers checkModifiers,
+            bool expected)
+        {
+            Assert.Equal(expected, baselineModifiers.IsDefined(checkModifiers));
+        }
+
+        [Theory]
+        [InlineData(PixelConversionModifiers.Premultiply | PixelConversionModifiers.Scale | PixelConversionModifiers.SRgbCompand, 
+            PixelConversionModifiers.Scale, PixelConversionModifiers.Premultiply | PixelConversionModifiers.SRgbCompand)]
+        [InlineData(PixelConversionModifiers.None, PixelConversionModifiers.Premultiply, PixelConversionModifiers.None)]
+        internal void Remove(
+            PixelConversionModifiers baselineModifiers,
+            PixelConversionModifiers toRemove,
+            PixelConversionModifiers expected)
+        {
+            PixelConversionModifiers result = baselineModifiers.Remove(toRemove);
+            Assert.Equal(expected, result);
+        }
+
+        [Theory]
+        [InlineData(PixelConversionModifiers.Premultiply, false, PixelConversionModifiers.Premultiply)]
+        [InlineData(PixelConversionModifiers.Premultiply, true, PixelConversionModifiers.Premultiply | PixelConversionModifiers.SRgbCompand | PixelConversionModifiers.Scale)]
+        internal void ApplyCompanding(
+            PixelConversionModifiers baselineModifiers,
+            bool compand,
+            PixelConversionModifiers expected)
+        {
+            PixelConversionModifiers result = baselineModifiers.ApplyCompanding(compand);
+            Assert.Equal(expected, result);
+        }
+    }
+}