Nits - Colorspaces (#880)

* Add missing periods

* Only perform matrix inversion once in CieXyzToLinearRgbConverter

* Eliminate unnessary ToVector3 call

* Seal GammaWorkingSpace

* Address stylecop violation

* Add periods

* Fix colorspace companding

src/ImageSharp/ColorSpaces/CieXyChromaticityCoordinates.cs

@@ -8,7 +8,7 @@ using System.Runtime.CompilerServices;
 namespace SixLabors.ImageSharp.ColorSpaces
 {
     /// <summary>
-    /// Represents the coordinates of CIEXY chromaticity space
+    /// Represents the coordinates of CIEXY chromaticity space.
     /// </summary>
     public readonly struct CieXyChromaticityCoordinates : IEquatable<CieXyChromaticityCoordinates>
     {

src/ImageSharp/ColorSpaces/Companding/GammaCompanding.cs

@@ -7,7 +7,7 @@ using System.Runtime.CompilerServices;
 namespace SixLabors.ImageSharp.ColorSpaces.Companding
 {
     /// <summary>
-    /// Implements gamma companding
+    /// Implements gamma companding.
     /// </summary>
     /// <remarks>
     /// <see href="http://www.brucelindbloom.com/index.html?Eqn_RGB_to_XYZ.html"/>

src/ImageSharp/ColorSpaces/Companding/LCompanding.cs

@@ -8,7 +8,7 @@ using SixLabors.ImageSharp.ColorSpaces.Conversion;
 namespace SixLabors.ImageSharp.ColorSpaces.Companding
 {
     /// <summary>
-    /// Implements L* companding
+    /// Implements L* companding.
     /// </summary>
     /// <remarks>
     /// For more info see:
@@ -24,7 +24,7 @@ namespace SixLabors.ImageSharp.ColorSpaces.Companding
         /// <returns>The <see cref="float"/> representing the linear channel value.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public static float Expand(float channel)
-            => channel <= 0.08 ? 100 * channel / CieConstants.Kappa : ImageMaths.Pow3((channel + 0.16F) / 1.16F);
+            => channel <= 0.08F ? (100F * channel) / CieConstants.Kappa : ImageMaths.Pow3((channel + 0.16F) / 1.16F);
 
         /// <summary>
         /// Compresses an uncompanded channel (linear) to its nonlinear equivalent.
@@ -33,6 +33,6 @@ namespace SixLabors.ImageSharp.ColorSpaces.Companding
         /// <returns>The <see cref="float"/> representing the nonlinear channel value.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public static float Compress(float channel)
-            => channel <= CieConstants.Epsilon ? channel * CieConstants.Kappa / 100F : MathF.Pow(1.16F * channel, 0.3333333F) - 0.16F;
+            => channel <= CieConstants.Epsilon ? (channel * CieConstants.Kappa) / 100F : (1.16F * MathF.Pow(channel, 0.3333333F)) - 0.16F;
     }
 }

src/ImageSharp/ColorSpaces/Companding/Rec2020Companding.cs

@@ -7,14 +7,19 @@ using System.Runtime.CompilerServices;
 namespace SixLabors.ImageSharp.ColorSpaces.Companding
 {
     /// <summary>
-    /// Implements Rec. 2020 companding function (for 12-bits).
+    /// Implements Rec. 2020 companding function.
     /// </summary>
     /// <remarks>
     /// <see href="http://en.wikipedia.org/wiki/Rec._2020"/>
-    /// For 10-bits, companding is identical to <see cref="Rec709Companding"/>
     /// </remarks>
     public static class Rec2020Companding
     {
+        private const float Alpha = 1.09929682680944F;
+        private const float AlphaMinusOne = Alpha - 1F;
+        private const float Beta = 0.018053968510807F;
+        private const float InverseBeta = Beta * 4.5F;
+        private const float Epsilon = 1 / 0.45F;
+
         /// <summary>
         /// Expands a companded channel to its linear equivalent with respect to the energy.
         /// </summary>
@@ -22,7 +27,7 @@ namespace SixLabors.ImageSharp.ColorSpaces.Companding
         /// <returns>The <see cref="float"/> representing the linear channel value.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public static float Expand(float channel)
-            => channel < 0.08145F ? channel / 4.5F : MathF.Pow((channel + 0.0993F) / 1.0993F, 2.222222F);
+            => channel < InverseBeta ? channel / 4.5F : MathF.Pow((channel + AlphaMinusOne) / Alpha, Epsilon);
 
         /// <summary>
         /// Compresses an uncompanded channel (linear) to its nonlinear equivalent.
@@ -31,6 +36,6 @@ namespace SixLabors.ImageSharp.ColorSpaces.Companding
         /// <returns>The <see cref="float"/> representing the nonlinear channel value.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public static float Compress(float channel)
-            => channel < 0.0181F ? 4500F * channel : (1.0993F * channel) - 0.0993F;
+            => channel < Beta ? 4.5F * channel : (Alpha * MathF.Pow(channel, 0.45F)) - AlphaMinusOne;
     }
 }

src/ImageSharp/ColorSpaces/Companding/Rec709Companding.cs

@@ -14,6 +14,8 @@ namespace SixLabors.ImageSharp.ColorSpaces.Companding
     /// </remarks>
     public static class Rec709Companding
     {
+        private const float Epsilon = 1 / 0.45F;
+
         /// <summary>
         /// Expands a companded channel to its linear equivalent with respect to the energy.
         /// </summary>
@@ -21,7 +23,7 @@ namespace SixLabors.ImageSharp.ColorSpaces.Companding
         /// <returns>The <see cref="float"/> representing the linear channel value.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public static float Expand(float channel)
-            => channel < 0.081F ? channel / 4.5F : MathF.Pow((channel + 0.099F) / 1.099F, 2.222222F);
+            => channel < 0.081F ? channel / 4.5F : MathF.Pow((channel + 0.099F) / 1.099F, Epsilon);
 
         /// <summary>
         /// Compresses an uncompanded channel (linear) to its nonlinear equivalent.
@@ -30,6 +32,6 @@ namespace SixLabors.ImageSharp.ColorSpaces.Companding
         /// <returns>The <see cref="float"/> representing the nonlinear channel value.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public static float Compress(float channel)
-            => channel < 0.018F ? 4500F * channel : (1.099F * channel) - 0.099F;
+            => channel < 0.018F ? 4.5F * channel : (1.099F * MathF.Pow(channel, 0.45F)) - 0.099F;
     }
 }

src/ImageSharp/ColorSpaces/Conversion/ColorSpaceConverter.CieLch.cs

@@ -26,10 +26,8 @@ namespace SixLabors.ImageSharp.ColorSpaces.Conversion
         /// <returns>The <see cref="CieLch"/></returns>
         public CieLch ToCieLch(in CieLab color)
         {
-            // Adaptation
             CieLab adapted = this.Adapt(color);
 
-            // Conversion
             return CieLabToCieLchConverter.Convert(adapted);
         }
 

src/ImageSharp/ColorSpaces/Conversion/Implementation/Converters/CieXyzAndCieXyyConverter.cs

@@ -7,7 +7,7 @@ using System.Runtime.CompilerServices;
 namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
 {
     /// <summary>
-    /// Color converter between CIE XYZ and CIE xyY
+    /// Color converter between CIE XYZ and CIE xyY.
     /// <see href="http://www.brucelindbloom.com/"/> for formulas.
     /// </summary>
     internal sealed class CieXyzAndCieXyyConverter

src/ImageSharp/ColorSpaces/Conversion/Implementation/Converters/CieXyzToLinearRgbConverter.cs

@@ -28,11 +28,15 @@ namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
         public CieXyzToLinearRgbConverter(RgbWorkingSpaceBase workingSpace)
         {
             this.TargetWorkingSpace = workingSpace;
-            this.conversionMatrix = GetRgbToCieXyzMatrix(workingSpace);
+
+            // Gets the inverted Rgb -> Xyz matrix
+            Matrix4x4.Invert(GetRgbToCieXyzMatrix(workingSpace), out Matrix4x4 inverted);
+
+            this.conversionMatrix = inverted;
         }
 
         /// <summary>
-        /// Gets the target working space
+        /// Gets the target working space.
         /// </summary>
         public RgbWorkingSpaceBase TargetWorkingSpace { get; }
 
@@ -40,12 +44,12 @@ namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
         /// Performs the conversion from the <see cref="CieXyz"/> input to an instance of <see cref="LinearRgb"/> type.
         /// </summary>
         /// <param name="input">The input color instance.</param>
-        /// <returns>The converted result</returns>
+        /// <returns>The converted result.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public LinearRgb Convert(in CieXyz input)
         {
-            Matrix4x4.Invert(this.conversionMatrix, out Matrix4x4 inverted);
-            var vector = Vector3.Transform(input.ToVector3(), inverted);
+            var vector = Vector3.Transform(input.ToVector3(), this.conversionMatrix);
+
             return new LinearRgb(vector, this.TargetWorkingSpace);
         }
     }

src/ImageSharp/ColorSpaces/Conversion/Implementation/Converters/CmykAndRgbConverter.cs

@@ -8,7 +8,7 @@ using System.Runtime.CompilerServices;
 namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
 {
     /// <summary>
-    /// Color converter between <see cref="Cmyk"/> and <see cref="Rgb"/>
+    /// Color converter between <see cref="Cmyk"/> and <see cref="Rgb"/>.
     /// </summary>
     internal sealed class CmykAndRgbConverter
     {
@@ -28,7 +28,7 @@ namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
         /// Performs the conversion from the <see cref="Rgb"/> input to an instance of <see cref="Cmyk"/> type.
         /// </summary>
         /// <param name="input">The input color instance.</param>
-        /// <returns>The converted result</returns>
+        /// <returns>The converted result.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public Cmyk Convert(in Rgb input)
         {

src/ImageSharp/ColorSpaces/Conversion/Implementation/Converters/LinearRgbToRgbConverter.cs

@@ -6,7 +6,7 @@ using System.Runtime.CompilerServices;
 namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
 {
     /// <summary>
-    /// Color converter between <see cref="LinearRgb"/> and <see cref="Rgb"/>
+    /// Color converter between <see cref="LinearRgb"/> and <see cref="Rgb"/>.
     /// </summary>
     internal sealed class LinearRgbToRgbConverter
     {
@@ -14,16 +14,15 @@ namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
         /// Performs the conversion from the <see cref="LinearRgb"/> input to an instance of <see cref="Rgb"/> type.
         /// </summary>
         /// <param name="input">The input color instance.</param>
-        /// <returns>The converted result</returns>
+        /// <returns>The converted result.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public Rgb Convert(in LinearRgb input)
         {
-            var vector = input.ToVector3();
-            vector.X = input.WorkingSpace.Compress(vector.X);
-            vector.Y = input.WorkingSpace.Compress(vector.Y);
-            vector.Z = input.WorkingSpace.Compress(vector.Z);
-
-            return new Rgb(vector, input.WorkingSpace);
+            return new Rgb(
+                r: input.WorkingSpace.Compress(input.R),
+                g: input.WorkingSpace.Compress(input.G),
+                b: input.WorkingSpace.Compress(input.B),
+                workingSpace: input.WorkingSpace);
         }
     }
 }

src/ImageSharp/ColorSpaces/Conversion/Implementation/Converters/RgbToLinearRgbConverter.cs

@@ -6,7 +6,7 @@ using System.Runtime.CompilerServices;
 namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
 {
     /// <summary>
-    /// Color converter between Rgb and LinearRgb
+    /// Color converter between Rgb and LinearRgb.
     /// </summary>
     internal class RgbToLinearRgbConverter
     {
@@ -14,16 +14,15 @@ namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
         /// Performs the conversion from the <see cref="Rgb"/> input to an instance of <see cref="LinearRgb"/> type.
         /// </summary>
         /// <param name="input">The input color instance.</param>
-        /// <returns>The converted result</returns>
+        /// <returns>The converted result.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public LinearRgb Convert(in Rgb input)
         {
-            var vector = input.ToVector3();
-            vector.X = input.WorkingSpace.Expand(vector.X);
-            vector.Y = input.WorkingSpace.Expand(vector.Y);
-            vector.Z = input.WorkingSpace.Expand(vector.Z);
-
-            return new LinearRgb(vector, input.WorkingSpace);
+            return new LinearRgb(
+                r: input.WorkingSpace.Expand(input.R),
+                g: input.WorkingSpace.Expand(input.G),
+                b: input.WorkingSpace.Expand(input.B),
+                workingSpace: input.WorkingSpace);
         }
     }
 }

src/ImageSharp/ColorSpaces/Conversion/Implementation/Converters/YCbCrAndRgbConverter.cs

@@ -19,7 +19,7 @@ namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
         /// Performs the conversion from the <see cref="YCbCr"/> input to an instance of <see cref="Rgb"/> type.
         /// </summary>
         /// <param name="input">The input color instance.</param>
-        /// <returns>The converted result</returns>
+        /// <returns>The converted result.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public Rgb Convert(in YCbCr input)
         {
@@ -38,7 +38,7 @@ namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
         /// Performs the conversion from the <see cref="Rgb"/> input to an instance of <see cref="YCbCr"/> type.
         /// </summary>
         /// <param name="input">The input color instance.</param>
-        /// <returns>The converted result</returns>
+        /// <returns>The converted result.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
         public YCbCr Convert(in Rgb input)
         {

src/ImageSharp/ColorSpaces/Conversion/Implementation/WorkingSpaces/GammaWorkingSpace.cs

@@ -10,7 +10,7 @@ namespace SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation
     /// <summary>
     /// The gamma working space.
     /// </summary>
-    public class GammaWorkingSpace : RgbWorkingSpaceBase
+    public sealed class GammaWorkingSpace : RgbWorkingSpaceBase
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="GammaWorkingSpace" /> class.

tests/ImageSharp.Tests/Colorspaces/Companding/CompandingTests.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
-using System.Linq;
 using System.Numerics;
 using SixLabors.ImageSharp.ColorSpaces.Companding;
 using Xunit;
@@ -10,9 +9,7 @@ using Xunit;
 namespace SixLabors.ImageSharp.Tests.Colorspaces.Companding
 {
     /// <summary>
-    /// Tests various companding algorithms. Numbers are hand calculated from formulas online.
-    /// TODO: Oddly the formula for converting to/from Rec 2020 and 709 from Wikipedia seems to cause the value to 
-    /// fail a round trip. They're large spaces so this is a surprise. More reading required!!
+    /// Tests various companding algorithms. Expanded numbers are hand calculated from formulas online.
     /// </summary>
     public class CompandingTests
     {
@@ -24,7 +21,7 @@ namespace SixLabors.ImageSharp.Tests.Colorspaces.Companding
             const float input = .667F;
             float e = Rec2020Companding.Expand(input);
             float c = Rec2020Companding.Compress(e);
-            CompandingIsCorrectImpl(e, c, .4484759F, .3937096F);
+            CompandingIsCorrectImpl(e, c, .4484759F, input);
         }
 
         [Fact]
@@ -33,7 +30,7 @@ namespace SixLabors.ImageSharp.Tests.Colorspaces.Companding
             const float input = .667F;
             float e = Rec709Companding.Expand(input);
             float c = Rec709Companding.Compress(e);
-            CompandingIsCorrectImpl(e, c, .4483577F, .3937451F);
+            CompandingIsCorrectImpl(e, c, .4483577F, input);
         }
 
         [Fact]
@@ -42,7 +39,7 @@ namespace SixLabors.ImageSharp.Tests.Colorspaces.Companding
             const float input = .667F;
             float e = SRgbCompanding.Expand(input);
             float c = SRgbCompanding.Compress(e);
-            CompandingIsCorrectImpl(e, c, .40242353F, .667F);
+            CompandingIsCorrectImpl(e, c, .40242353F, input);
         }
 
         [Theory]
@@ -98,7 +95,7 @@ namespace SixLabors.ImageSharp.Tests.Colorspaces.Companding
             const float input = .667F;
             float e = GammaCompanding.Expand(input, gamma);
             float c = GammaCompanding.Compress(e, gamma);
-            CompandingIsCorrectImpl(e, c, .41027668F, .667F);
+            CompandingIsCorrectImpl(e, c, .41027668F, input);
         }
 
         [Fact]
@@ -107,7 +104,7 @@ namespace SixLabors.ImageSharp.Tests.Colorspaces.Companding
             const float input = .667F;
             float e = LCompanding.Expand(input);
             float c = LCompanding.Compress(e);
-            CompandingIsCorrectImpl(e, c, .36236193F, .58908917F);
+            CompandingIsCorrectImpl(e, c, .36236193F, input);
         }
 
         private static void CompandingIsCorrectImpl(float e, float c, float expanded, float compressed)