Add luminance color profile type and cleanup

src/ImageSharp/ColorProfiles/CieLab.cs

@@ -4,7 +4,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using System.Runtime.Intrinsics;
 
 namespace SixLabors.ImageSharp.ColorProfiles;
 
@@ -36,7 +35,6 @@ public readonly struct CieLab : IProfileConnectingSpace<CieLab, CieXyz>
     /// <param name="vector">The vector representing the l, a, b components.</param>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public CieLab(Vector3 vector)
-        : this()
     {
         this.L = vector.X;
         this.A = vector.Y;

src/ImageSharp/ColorProfiles/CieLch.cs

@@ -4,7 +4,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using System.Runtime.Intrinsics;
 
 namespace SixLabors.ImageSharp.ColorProfiles;
 
@@ -43,6 +42,17 @@ public readonly struct CieLch : IColorProfile<CieLch, CieLab>
         this.H = vector.Z;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#pragma warning disable SA1313 // Parameter names should begin with lower-case letter
+    private CieLch(Vector3 vector, bool _)
+#pragma warning restore SA1313 // Parameter names should begin with lower-case letter
+    {
+        vector = Vector3.Clamp(vector, Min, Max);
+        this.L = vector.X;
+        this.C = vector.Y;
+        this.H = vector.Z;
+    }
+
     /// <summary>
     /// Gets the lightness dimension.
     /// <remarks>A value ranging between 0 (black), 100 (diffuse white) or higher (specular white).</remarks>
@@ -99,7 +109,7 @@ public readonly struct CieLch : IColorProfile<CieLch, CieLab>
         Vector3 v3 = source.AsVector3();
         v3 *= new Vector3(100, 400, 360);
         v3 -= new Vector3(0, 200, 0);
-        return new CieLch(v3);
+        return new CieLch(v3, true);
     }
 
     /// <inheritdoc/>

src/ImageSharp/ColorProfiles/CieLchuv.cs

@@ -4,7 +4,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using System.Runtime.Intrinsics;
 
 namespace SixLabors.ImageSharp.ColorProfiles;
 
@@ -36,7 +35,6 @@ public readonly struct CieLchuv : IColorProfile<CieLchuv, CieXyz>
     /// <param name="vector">The vector representing the l, c, h components.</param>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public CieLchuv(Vector3 vector)
-        : this()
     {
         vector = Vector3.Clamp(vector, Min, Max);
         this.L = vector.X;
@@ -44,6 +42,16 @@ public readonly struct CieLchuv : IColorProfile<CieLchuv, CieXyz>
         this.H = vector.Z;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#pragma warning disable SA1313 // Parameter names should begin with lower-case letter
+    private CieLchuv(Vector3 vector, bool _)
+#pragma warning restore SA1313 // Parameter names should begin with lower-case letter
+    {
+        this.L = vector.X;
+        this.C = vector.Y;
+        this.H = vector.Z;
+    }
+
     /// <summary>
     /// Gets the lightness dimension.
     /// <remarks>A value ranging between 0 (black), 100 (diffuse white) or higher (specular white).</remarks>
@@ -98,7 +106,7 @@ public readonly struct CieLchuv : IColorProfile<CieLchuv, CieXyz>
         Vector3 v3 = source.AsVector3();
         v3 *= new Vector3(100, 400, 360);
         v3 -= new Vector3(0, 200, 0);
-        return new CieLchuv(v3);
+        return new CieLchuv(v3, true);
     }
 
     /// <inheritdoc/>

src/ImageSharp/ColorProfiles/CieLuv.cs

@@ -37,7 +37,6 @@ public readonly struct CieLuv : IColorProfile<CieLuv, CieXyz>
     /// <param name="vector">The vector representing the l, u, v components.</param>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public CieLuv(Vector3 vector)
-        : this()
     {
         this.L = vector.X;
         this.U = vector.Y;

src/ImageSharp/ColorProfiles/CieXyy.cs

@@ -4,7 +4,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using System.Runtime.Intrinsics;
 
 namespace SixLabors.ImageSharp.ColorProfiles;
 
@@ -36,7 +35,6 @@ public readonly struct CieXyy : IColorProfile<CieXyy, CieXyz>
     /// <param name="vector">The vector representing the x, y, Y components.</param>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public CieXyy(Vector3 vector)
-        : this()
     {
         // Not clamping as documentation about this space only indicates "usual" ranges
         this.X = vector.X;

src/ImageSharp/ColorProfiles/CieXyz.cs

@@ -34,7 +34,6 @@ public readonly struct CieXyz : IProfileConnectingSpace<CieXyz, CieXyz>
     /// </summary>
     /// <param name="vector">The vector representing the x, y, z components.</param>
     public CieXyz(Vector3 vector)
-        : this()
     {
         this.X = vector.X;
         this.Y = vector.Y;

src/ImageSharp/ColorProfiles/Cmyk.cs

@@ -36,7 +36,18 @@ public readonly struct Cmyk : IColorProfile<Cmyk, Rgb>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public Cmyk(Vector4 vector)
     {
-        vector = Numerics.Clamp(vector, Min, Max);
+        vector = Vector4.Clamp(vector, Min, Max);
+        this.C = vector.X;
+        this.M = vector.Y;
+        this.Y = vector.Z;
+        this.K = vector.W;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#pragma warning disable SA1313 // Parameter names should begin with lower-case letter
+    private Cmyk(Vector4 vector, bool _)
+#pragma warning restore SA1313 // Parameter names should begin with lower-case letter
+    {
         this.C = vector.X;
         this.M = vector.Y;
         this.Y = vector.Z;
@@ -99,7 +110,7 @@ public readonly struct Cmyk : IColorProfile<Cmyk, Rgb>
 
     /// <inheritdoc/>
     public static Cmyk FromScaledVector4(Vector4 source)
-        => new(source);
+        => new(source, true);
 
     /// <inheritdoc/>
     public static void ToScaledVector4(ReadOnlySpan<Cmyk> source, Span<Vector4> destination)

src/ImageSharp/ColorProfiles/ColorConversionOptions.cs

@@ -45,6 +45,11 @@ public class ColorConversionOptions
     /// </summary>
     public RgbWorkingSpace TargetRgbWorkingSpace { get; init; } = KnownRgbWorkingSpaces.SRgb;
 
+    /// <summary>
+    /// Gets the Y (luma) coefficients to use in conversions from RGB.
+    /// </summary>
+    public Vector3 YCoefficients { get; init; } = KnownYCoefficients.BT709;
+
     /// <summary>
     /// Gets the source ICC profile.
     /// </summary>

src/ImageSharp/ColorProfiles/Hsl.cs

@@ -4,7 +4,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using System.Runtime.Intrinsics;
 
 namespace SixLabors.ImageSharp.ColorProfiles;
 
@@ -42,6 +41,16 @@ public readonly struct Hsl : IColorProfile<Hsl, Rgb>
         this.L = vector.Z;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#pragma warning disable SA1313 // Parameter names should begin with lower-case letter
+    private Hsl(Vector3 vector, bool _)
+#pragma warning restore SA1313 // Parameter names should begin with lower-case letter
+    {
+        this.H = vector.X;
+        this.S = vector.Y;
+        this.L = vector.Z;
+    }
+
     /// <summary>
     /// Gets the hue component.
     /// <remarks>A value ranging between 0 and 360.</remarks>
@@ -90,7 +99,7 @@ public readonly struct Hsl : IColorProfile<Hsl, Rgb>
 
     /// <inheritdoc/>
     public static Hsl FromScaledVector4(Vector4 source)
-        => new(source.AsVector3() * 360F);
+        => new(source.AsVector3() * 360F, true);
 
     /// <inheritdoc/>
     public static void ToScaledVector4(ReadOnlySpan<Hsl> source, Span<Vector4> destination)

src/ImageSharp/ColorProfiles/Hsv.cs

@@ -4,7 +4,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using System.Runtime.Intrinsics;
 
 namespace SixLabors.ImageSharp.ColorProfiles;
 
@@ -42,6 +41,16 @@ public readonly struct Hsv : IColorProfile<Hsv, Rgb>
         this.V = vector.Z;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#pragma warning disable SA1313 // Parameter names should begin with lower-case letter
+    private Hsv(Vector3 vector, bool _)
+#pragma warning restore SA1313 // Parameter names should begin with lower-case letter
+    {
+        this.H = vector.X;
+        this.S = vector.Y;
+        this.V = vector.Z;
+    }
+
     /// <summary>
     /// Gets the hue component.
     /// <remarks>A value ranging between 0 and 360.</remarks>
@@ -88,7 +97,7 @@ public readonly struct Hsv : IColorProfile<Hsv, Rgb>
 
     /// <inheritdoc/>
     public static Hsv FromScaledVector4(Vector4 source)
-        => new(source.AsVector3() * 360F);
+        => new(source.AsVector3() * 360F, true);
 
     /// <inheritdoc/>
     public static void ToScaledVector4(ReadOnlySpan<Hsv> source, Span<Vector4> destination)

src/ImageSharp/ColorProfiles/HunterLab.cs

@@ -4,7 +4,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using System.Runtime.Intrinsics;
 
 namespace SixLabors.ImageSharp.ColorProfiles;
 

src/ImageSharp/ColorProfiles/IColorProfile.cs

@@ -30,7 +30,7 @@ public interface IColorProfile<TSelf> : IColorProfile, IEquatable<TSelf>
     /// The vector components are typically expanded in least to greatest significance order.
     /// </summary>
     /// <returns>The <see cref="Vector4"/>.</returns>
-    Vector4 ToScaledVector4();
+    public Vector4 ToScaledVector4();
 
 #pragma warning disable CA1000 // Do not declare static members on generic types
     /// <summary>

src/ImageSharp/ColorProfiles/KnownYCoefficients.cs

@@ -0,0 +1,27 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Numerics;
+
+namespace SixLabors.ImageSharp.ColorProfiles;
+
+/// <summary>
+/// Provides standard Y (luma) coefficient sets for weighted RGB conversions.
+/// </summary>
+public static class KnownYCoefficients
+{
+    /// <summary>
+    /// ITU-R BT.601 (SD video standard).
+    /// </summary>
+    public static readonly Vector3 BT601 = new(0.299F, 0.587F, 0.114F);
+
+    /// <summary>
+    /// ITU-R BT.709 (HD video, sRGB standard).
+    /// </summary>
+    public static readonly Vector3 BT709 = new(0.2126F, 0.7152F, 0.0722F);
+
+    /// <summary>
+    /// ITU-R BT.2020 (UHD/4K video standard).
+    /// </summary>
+    public static readonly Vector3 BT2020 = new(0.2627F, 0.6780F, 0.0593F);
+}

src/ImageSharp/ColorProfiles/Lms.cs

@@ -4,7 +4,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using System.Runtime.Intrinsics;
 
 namespace SixLabors.ImageSharp.ColorProfiles;
 

src/ImageSharp/ColorProfiles/Rgb.cs

@@ -4,7 +4,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using System.Runtime.Intrinsics;
 using SixLabors.ImageSharp.ColorProfiles.WorkingSpaces;
 
 namespace SixLabors.ImageSharp.ColorProfiles;

src/ImageSharp/ColorProfiles/Y.cs

@@ -0,0 +1,136 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace SixLabors.ImageSharp.ColorProfiles;
+
+/// <summary>
+/// Represents a Y (luminance) color.
+/// </summary>
+[StructLayout(LayoutKind.Sequential)]
+public readonly struct Y : IColorProfile<Y, Rgb>
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="Y"/> struct.
+    /// </summary>
+    /// <param name="l">The luminance component.</param>
+    public Y(float l) => this.L = l;
+
+    /// <summary>
+    /// Gets the luminance component.
+    /// </summary>
+    /// <remarks>A value ranging between 0 and 1.</remarks>
+    public float L { get; }
+
+    /// <summary>
+    /// Compares two <see cref="Y"/> objects for equality.
+    /// </summary>
+    /// <param name="left">The <see cref="Y"/> on the left side of the operand.</param>
+    /// <param name="right">The <see cref="Y"/> on the right side of the operand.</param>
+    /// <returns>
+    /// True if the current left is equal to the <paramref name="right"/> parameter; otherwise, false.
+    /// </returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static bool operator ==(Y left, Y right) => left.Equals(right);
+
+    /// <summary>
+    /// Compares two <see cref="Y"/> objects for inequality.
+    /// </summary>
+    /// <param name="left">The <see cref="Y"/> on the left side of the operand.</param>
+    /// <param name="right">The <see cref="Y"/> on the right side of the operand.</param>
+    /// <returns>
+    /// True if the current left is unequal to the <paramref name="right"/> parameter; otherwise, false.
+    /// </returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static bool operator !=(Y left, Y right) => !left.Equals(right);
+
+    /// <inheritdoc/>
+    public static Y FromProfileConnectingSpace(ColorConversionOptions options, in Rgb source)
+    {
+        Vector3 weights = options.YCoefficients;
+        float l = (weights.X * source.R) + (weights.Y * source.G) + (weights.Z * source.B);
+        return new Y(l);
+    }
+
+    /// <inheritdoc/>
+    public static void FromProfileConnectionSpace(ColorConversionOptions options, ReadOnlySpan<Rgb> source, Span<Y> destination)
+    {
+        Guard.DestinationShouldNotBeTooShort(source, destination, nameof(destination));
+
+        // TODO: We can optimize this by using SIMD
+        for (int i = 0; i < source.Length; i++)
+        {
+            Rgb rgb = source[i];
+            destination[i] = FromProfileConnectingSpace(options, in rgb);
+        }
+    }
+
+    /// <inheritdoc/>
+    public Vector4 ToScaledVector4() => new(this.L);
+
+    /// <inheritdoc/>
+    public static Y FromScaledVector4(Vector4 source) => new(source.X);
+
+    /// <inheritdoc/>
+    public static void ToScaledVector4(ReadOnlySpan<Y> source, Span<Vector4> destination)
+    {
+        Guard.DestinationShouldNotBeTooShort(source, destination, nameof(destination));
+
+        // TODO: Optimize via SIMD
+        for (int i = 0; i < source.Length; i++)
+        {
+            destination[i] = source[i].ToScaledVector4();
+        }
+    }
+
+    /// <inheritdoc/>
+    public static void FromScaledVector4(ReadOnlySpan<Vector4> source, Span<Y> destination)
+    {
+        Guard.DestinationShouldNotBeTooShort(source, destination, nameof(destination));
+
+        // TODO: Optimize via SIMD
+        for (int i = 0; i < source.Length; i++)
+        {
+            destination[i] = FromScaledVector4(source[i]);
+        }
+    }
+
+    /// <inheritdoc/>
+    public Rgb ToProfileConnectingSpace(ColorConversionOptions options)
+        => new(this.L, this.L, this.L);
+
+    /// <inheritdoc/>
+    public static void ToProfileConnectionSpace(ColorConversionOptions options, ReadOnlySpan<Y> source, Span<Rgb> destination)
+    {
+        Guard.DestinationShouldNotBeTooShort(source, destination, nameof(destination));
+
+        // TODO: We can optimize this by using SIMD
+        for (int i = 0; i < source.Length; i++)
+        {
+            destination[i] = source[i].ToProfileConnectingSpace(options);
+        }
+    }
+
+    /// <inheritdoc/>
+    public static ChromaticAdaptionWhitePointSource GetChromaticAdaptionWhitePointSource()
+        => ChromaticAdaptionWhitePointSource.RgbWorkingSpace;
+
+    /// <inheritdoc/>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public override int GetHashCode()
+        => this.L.GetHashCode();
+
+    /// <inheritdoc/>
+    public override string ToString()
+        => FormattableString.Invariant($"Y({this.L:#0.##})");
+
+    /// <inheritdoc/>
+    public override bool Equals(object? obj)
+        => obj is Y other && this.Equals(other);
+
+    /// <inheritdoc/>
+    public bool Equals(Y other) => this.L == other.L;
+}

src/ImageSharp/ColorProfiles/YCbCr.cs

@@ -4,7 +4,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-using System.Runtime.Intrinsics;
 
 namespace SixLabors.ImageSharp.ColorProfiles;
 
@@ -44,6 +43,16 @@ public readonly struct YCbCr : IColorProfile<YCbCr, Rgb>
         this.Cr = vector.Z;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#pragma warning disable SA1313 // Parameter names should begin with lower-case letter
+    private YCbCr(Vector3 vector, bool _)
+#pragma warning restore SA1313 // Parameter names should begin with lower-case letter
+    {
+        this.Y = vector.X;
+        this.Cb = vector.Y;
+        this.Cr = vector.Z;
+    }
+
     /// <summary>
     /// Gets the Y luminance component.
     /// <remarks>A value ranging between 0 and 255.</remarks>
@@ -97,7 +106,7 @@ public readonly struct YCbCr : IColorProfile<YCbCr, Rgb>
     {
         Vector3 v3 = source.AsVector3();
         v3 *= Max;
-        return new YCbCr(v3);
+        return new YCbCr(v3, true);
     }
 
     /// <inheritdoc/>
@@ -174,8 +183,7 @@ public readonly struct YCbCr : IColorProfile<YCbCr, Rgb>
         // TODO: We can optimize this by using SIMD
         for (int i = 0; i < source.Length; i++)
         {
-            YCbCr ycbcr = source[i];
+            destination[i] = source[i].ToProfileConnectingSpace(options);
-            destination[i] = ycbcr.ToProfileConnectingSpace(options);
         }
     }
 

tests/ImageSharp.Tests/ColorProfiles/ApproximateColorProfileComparer.cs

@@ -22,7 +22,8 @@ internal readonly struct ApproximateColorProfileComparer :
     IEqualityComparer<Cmyk>,
     IEqualityComparer<Hsl>,
     IEqualityComparer<Hsv>,
-    IEqualityComparer<HunterLab>
+    IEqualityComparer<HunterLab>,
+    IEqualityComparer<Y>
 {
     private readonly float epsilon;
 
@@ -58,6 +59,8 @@ internal readonly struct ApproximateColorProfileComparer :
 
     public bool Equals(HunterLab x, HunterLab y) => this.Equals(x.L, y.L) && this.Equals(x.A, y.A) && this.Equals(x.B, y.B);
 
+    public bool Equals(Y x, Y y) => this.Equals(x.L, y.L);
+
     public int GetHashCode([DisallowNull] CieLab obj) => obj.GetHashCode();
 
     public int GetHashCode([DisallowNull] CieXyz obj) => obj.GetHashCode();
@@ -84,6 +87,8 @@ internal readonly struct ApproximateColorProfileComparer :
 
     public int GetHashCode([DisallowNull] HunterLab obj) => obj.GetHashCode();
 
+    public int GetHashCode([DisallowNull] Y obj) => obj.GetHashCode();
+
     private bool Equals(float x, float y)
     {
         float d = x - y;

tests/ImageSharp.Tests/ColorProfiles/RbgAndYConversionTests.cs

@@ -0,0 +1,113 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.ColorProfiles;
+
+namespace SixLabors.ImageSharp.Tests.ColorProfiles;
+
+/// <summary>
+/// Tests <see cref="Rgb"/>-<see cref="Y"/> conversions.
+/// </summary>
+/// <remarks>
+/// Test data generated mathematically
+/// </remarks>
+public class RbgAndYConversionTests
+{
+    private static readonly ApproximateColorProfileComparer Comparer = new(.001F);
+
+    [Theory]
+    [InlineData(0F, 0F, 0F, 0F)]
+    [InlineData(0.5F, 0.5F, 0.5F, 0.5F)]
+    [InlineData(1F, 1F, 1F, 1F)]
+    public void Convert_Y_To_Rgb(float y, float r, float g, float b)
+    {
+        // Arrange
+        Y input = new(y);
+        Rgb expected = new(r, g, b);
+        ColorProfileConverter converter = new();
+
+        Span<Y> inputSpan = new Y[5];
+        inputSpan.Fill(input);
+
+        Span<Rgb> actualSpan = new Rgb[5];
+
+        // Act
+        Rgb actual = converter.Convert<Y, Rgb>(input);
+        converter.Convert<Y, Rgb>(inputSpan, actualSpan);
+
+        // Assert
+        Assert.Equal(expected, actual, Comparer);
+
+        for (int i = 0; i < actualSpan.Length; i++)
+        {
+            Assert.Equal(expected, actualSpan[i], Comparer);
+        }
+    }
+
+    [Theory]
+    [InlineData(0F, 0F, 0F, 0F)]
+    [InlineData(0.5F, 0.5F, 0.5F, 0.5F)]
+    [InlineData(1F, 1F, 1F, 1F)]
+    public void Convert_Rgb_To_Y_BT601(float r, float g, float b, float y)
+    {
+        ColorConversionOptions options = new()
+        {
+            YCoefficients = KnownYCoefficients.BT601
+        };
+
+        Convert_Rgb_To_Y_Core(r, g, b, y, options);
+    }
+
+    [Theory]
+    [InlineData(0F, 0F, 0F, 0F)]
+    [InlineData(0.5F, 0.5F, 0.5F, 0.5F)]
+    [InlineData(1F, 1F, 1F, 1F)]
+    public void Convert_Rgb_To_Y_BT709(float r, float g, float b, float y)
+    {
+        ColorConversionOptions options = new()
+        {
+            YCoefficients = KnownYCoefficients.BT709
+        };
+
+        Convert_Rgb_To_Y_Core(r, g, b, y, options);
+    }
+
+    [Theory]
+    [InlineData(0F, 0F, 0F, 0F)]
+    [InlineData(0.5F, 0.5F, 0.5F, 0.49999997F)]
+    [InlineData(1F, 1F, 1F, 0.99999994F)]
+    public void Convert_Rgb_To_Y_BT2020(float r, float g, float b, float y)
+    {
+        ColorConversionOptions options = new()
+        {
+            YCoefficients = KnownYCoefficients.BT2020
+        };
+
+        Convert_Rgb_To_Y_Core(r, g, b, y, options);
+    }
+
+    private static void Convert_Rgb_To_Y_Core(float r, float g, float b, float y, ColorConversionOptions options)
+    {
+        // Arrange
+        Rgb input = new(r, g, b);
+        Y expected = new(y);
+        ColorProfileConverter converter = new(options);
+
+        Span<Rgb> inputSpan = new Rgb[5];
+        inputSpan.Fill(input);
+
+        Span<Y> actualSpan = new Y[5];
+
+        // Act
+        Y actual = converter.Convert<Rgb, Y>(input);
+        converter.Convert<Rgb, Y>(inputSpan, actualSpan);
+
+        // Assert
+        Assert.Equal(expected, actual, Comparer);
+
+        for (int i = 0; i < actualSpan.Length; i++)
+        {
+            Assert.Equal(expected, actualSpan[i], Comparer);
+        }
+    }
+}

tests/ImageSharp.Tests/ColorProfiles/YTests.cs

@@ -0,0 +1,42 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.ColorProfiles;
+
+namespace SixLabors.ImageSharp.Tests.ColorProfiles;
+
+/// <summary>
+/// Tests the <see cref="Y"/> struct.
+/// </summary>
+[Trait("Color", "Conversion")]
+public class YTests
+{
+    [Fact]
+    public void YConstructorAssignsFields()
+    {
+        const float y = .75F;
+        Y yValue = new(y);
+
+        Assert.Equal(y, yValue.L);
+    }
+
+    [Fact]
+    public void YEquality()
+    {
+        Y x = default;
+        Y y = new(1F);
+        Assert.True(default == default(Y));
+        Assert.False(default != default(Y));
+        Assert.Equal(default, default(Y));
+        Assert.Equal(new Y(1), new Y(1));
+
+        Assert.Equal(new Y(.5F), new Y(.5F));
+        Assert.False(x.Equals(y));
+        Assert.False(x.Equals((object)y));
+        Assert.False(x.GetHashCode().Equals(y.GetHashCode()));
+    }
+}