Add CieLch

src/ImageSharp/ColorProfiles/CieLab.cs

@@ -155,9 +155,7 @@ public readonly struct CieLab : IProfileConnectingSpace<CieLab, CieXyz>
 
         CieXyz whitePoint = options.WhitePoint;
         Vector3 wxyz = new(whitePoint.X, whitePoint.Y, whitePoint.Z);
-
-        // Avoids XYZ coordinates out range (restricted by 0 and XYZ reference white)
-        Vector3 xyzr = Vector3.Clamp(new Vector3(xr, yr, zr), Vector3.Zero, Vector3.One);
+        Vector3 xyzr = new(xr, yr, zr);
 
         return new(xyzr * wxyz);
     }

src/ImageSharp/ColorProfiles/CieLch.cs

@@ -0,0 +1,166 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Numerics;
+using System.Runtime.CompilerServices;
+
+namespace SixLabors.ImageSharp.ColorProfiles;
+
+/// <summary>
+/// Represents the CIE L*C*h°, cylindrical form of the CIE L*a*b* 1976 color.
+/// <see href="https://en.wikipedia.org/wiki/Lab_color_space#Cylindrical_representation:_CIELCh_or_CIEHLC"/>
+/// </summary>
+public readonly struct CieLch : IColorProfile<CieLch, CieLab>
+{
+    /// <summary>
+    /// D50 standard illuminant.
+    /// Used when reference white is not specified explicitly.
+    /// </summary>
+    public static readonly CieXyz DefaultWhitePoint = Illuminants.D50;
+
+    private static readonly Vector3 Min = new(0, -200, 0);
+    private static readonly Vector3 Max = new(100, 200, 360);
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CieLch"/> struct.
+    /// </summary>
+    /// <param name="l">The lightness dimension.</param>
+    /// <param name="c">The chroma, relative saturation.</param>
+    /// <param name="h">The hue in degrees.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public CieLch(float l, float c, float h)
+        : this(new Vector3(l, c, h))
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CieLch"/> struct.
+    /// </summary>
+    /// <param name="vector">The vector representing the l, c, h components.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public CieLch(Vector3 vector)
+    {
+        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>
+    /// </summary>
+    public readonly float L { get; }
+
+    /// <summary>
+    /// Gets the a chroma component.
+    /// <remarks>A value ranging from 0 to 200.</remarks>
+    /// </summary>
+    public readonly float C { get; }
+
+    /// <summary>
+    /// Gets the h° hue component in degrees.
+    /// <remarks>A value ranging from 0 to 360.</remarks>
+    /// </summary>
+    public readonly float H { get; }
+
+    /// <summary>
+    /// Compares two <see cref="CieLch"/> objects for equality.
+    /// </summary>
+    /// <param name="left">The <see cref="CieLch"/> on the left side of the operand.</param>
+    /// <param name="right">The <see cref="CieLch"/> 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 ==(CieLch left, CieLch right) => left.Equals(right);
+
+    /// <summary>
+    /// Compares two <see cref="CieLch"/> objects for inequality
+    /// </summary>
+    /// <param name="left">The <see cref="CieLch"/> on the left side of the operand.</param>
+    /// <param name="right">The <see cref="CieLch"/> 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 !=(CieLch left, CieLch right) => !left.Equals(right);
+
+    /// <inheritdoc/>
+    public override int GetHashCode()
+        => HashCode.Combine(this.L, this.C, this.H);
+
+    /// <inheritdoc/>
+    public override string ToString() => FormattableString.Invariant($"CieLch({this.L:#0.##}, {this.C:#0.##}, {this.H:#0.##})");
+
+    /// <inheritdoc/>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public override bool Equals(object? obj) => obj is CieLch other && this.Equals(other);
+
+    /// <inheritdoc/>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public bool Equals(CieLch other)
+        => this.L.Equals(other.L)
+        && this.C.Equals(other.C)
+        && this.H.Equals(other.H);
+
+    /// <inheritdoc/>
+    public static CieLch FromProfileConnectingSpace(ColorConversionOptions options, in CieLab source)
+    {
+        // Conversion algorithm described here:
+        // https://en.wikipedia.org/wiki/Lab_color_space#Cylindrical_representation:_CIELCh_or_CIEHLC
+        float l = source.L, a = source.A, b = source.B;
+        float c = MathF.Sqrt((a * a) + (b * b));
+        float hRadians = MathF.Atan2(b, a);
+        float hDegrees = GeometryUtilities.RadianToDegree(hRadians);
+
+        // Wrap the angle round at 360.
+        hDegrees %= 360;
+
+        // Make sure it's not negative.
+        while (hDegrees < 0)
+        {
+            hDegrees += 360;
+        }
+
+        return new CieLch(l, c, hDegrees);
+    }
+
+    /// <inheritdoc/>
+    public static void FromProfileConnectionSpace(ColorConversionOptions options, ReadOnlySpan<CieLab> source, Span<CieLch> destination)
+    {
+        Guard.DestinationShouldNotBeTooShort(source, destination, nameof(destination));
+
+        for (int i = 0; i < source.Length; i++)
+        {
+            CieLab lab = source[i];
+            destination[i] = FromProfileConnectingSpace(options, in lab);
+        }
+    }
+
+    /// <inheritdoc/>
+    public CieLab ToProfileConnectingSpace(ColorConversionOptions options)
+    {
+        // Conversion algorithm described here:
+        // https://en.wikipedia.org/wiki/Lab_color_space#Cylindrical_representation:_CIELCh_or_CIEHLC
+        float l = this.L, c = this.C, hDegrees = this.H;
+        float hRadians = GeometryUtilities.DegreeToRadian(hDegrees);
+
+        float a = c * MathF.Cos(hRadians);
+        float b = c * MathF.Sin(hRadians);
+
+        return new CieLab(l, a, b);
+    }
+
+    /// <inheritdoc/>
+    public static void ToProfileConnectionSpace(ColorConversionOptions options, ReadOnlySpan<CieLch> source, Span<CieLab> destination)
+    {
+        Guard.DestinationShouldNotBeTooShort(source, destination, nameof(destination));
+
+        for (int i = 0; i < source.Length; i++)
+        {
+            CieLch lch = source[i];
+            destination[i] = lch.ToProfileConnectingSpace(options);
+        }
+    }
+}

src/ImageSharp/ColorProfiles/ColorProfileConverterExtensionsCieXyzCieLab.cs

@@ -0,0 +1,52 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers;
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.ColorProfiles;
+
+internal static class ColorProfileConverterExtensionsCieXyzCieLab
+{
+    public static TTo Convert<TFrom, TTo>(this ColorProfileConverter converter, TFrom source)
+        where TFrom : struct, IColorProfile<TFrom, CieXyz>
+        where TTo : struct, IColorProfile<TTo, CieLab>
+    {
+        ColorConversionOptions options = converter.Options;
+
+        // Convert to input PCS
+        CieXyz pcsFrom = source.ToProfileConnectingSpace(options);
+
+        // Adapt to target white point
+        VonKriesChromaticAdaptation.Transform(options, in pcsFrom);
+
+        // Convert between PCS
+        CieLab pcsTo = CieLab.FromProfileConnectingSpace(options, in pcsFrom);
+
+        // Convert to output from PCS
+        return TTo.FromProfileConnectingSpace(options, pcsTo);
+    }
+
+    public static void Convert<TFrom, TTo>(this ColorProfileConverter converter, ReadOnlySpan<TFrom> source, Span<TTo> destination)
+        where TFrom : struct, IColorProfile<TFrom, CieXyz>
+        where TTo : struct, IColorProfile<TTo, CieLab>
+    {
+        ColorConversionOptions options = converter.Options;
+
+        // Convert to input PCS.
+        using IMemoryOwner<CieXyz> pcsFromOwner = options.MemoryAllocator.Allocate<CieXyz>(source.Length);
+        Span<CieXyz> pcsFrom = pcsFromOwner.GetSpan();
+        TFrom.ToProfileConnectionSpace(options, source, pcsFrom);
+
+        // Adapt to target white point
+        VonKriesChromaticAdaptation.Transform(options, pcsFrom, pcsFrom);
+
+        // Convert between PCS.
+        using IMemoryOwner<CieLab> pcsToOwner = options.MemoryAllocator.Allocate<CieLab>(source.Length);
+        Span<CieLab> pcsTo = pcsToOwner.GetSpan();
+        CieLab.FromProfileConnectionSpace(options, pcsFrom, pcsTo);
+
+        // Convert to output from PCS
+        TTo.FromProfileConnectionSpace(options, pcsTo, destination);
+    }
+}

tests/ImageSharp.Tests/ColorProfiles/ApproximateColorProfileComparer.cs

@@ -12,7 +12,8 @@ namespace SixLabors.ImageSharp.Tests.ColorProfiles;
 internal readonly struct ApproximateColorProfileComparer :
     IEqualityComparer<CieLab>,
     IEqualityComparer<CieXyz>,
-    IEqualityComparer<Lms>
+    IEqualityComparer<Lms>,
+    IEqualityComparer<CieLch>
 {
     private readonly float epsilon;
 
@@ -28,12 +29,16 @@ internal readonly struct ApproximateColorProfileComparer :
 
     public bool Equals(Lms x, Lms y) => this.Equals(x.L, y.L) && this.Equals(x.M, y.M) && this.Equals(x.S, y.S);
 
+    public bool Equals(CieLch x, CieLch y) => this.Equals(x.L, y.L) && this.Equals(x.C, y.C) && this.Equals(x.H, y.H);
+
     public int GetHashCode([DisallowNull] CieLab obj) => obj.GetHashCode();
 
     public int GetHashCode([DisallowNull] CieXyz obj) => obj.GetHashCode();
 
     public int GetHashCode([DisallowNull] Lms obj) => obj.GetHashCode();
 
+    public int GetHashCode([DisallowNull] CieLch obj) => obj.GetHashCode();
+
     private bool Equals(float x, float y)
     {
         float d = x - y;

tests/ImageSharp.Tests/ColorProfiles/CieLabAndCieLchConversionTests.cs

@@ -0,0 +1,88 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.ColorProfiles;
+
+namespace SixLabors.ImageSharp.Tests.ColorProfiles;
+
+/// <summary>
+/// Tests <see cref="CieLab"/>-<see cref="CieLch"/> conversions.
+/// </summary>
+/// <remarks>
+/// Test data generated using:
+/// <see href="http://www.brucelindbloom.com/index.html?ColorCalculator.html"/>
+/// </remarks>
+public class CieLabAndCieLchConversionTests
+{
+    private static readonly ApproximateColorProfileComparer Comparer = new(.0001f);
+
+    [Theory]
+    [InlineData(0, 0, 0, 0, 0, 0)]
+    [InlineData(54.2917, 106.8391, 40.8526, 54.2917, 80.8125, 69.8851)]
+    [InlineData(100, 0, 0, 100, 0, 0)]
+    [InlineData(100, 50, 180, 100, -50, 0)]
+    [InlineData(10, 36.0555, 56.3099, 10, 20, 30)]
+    [InlineData(10, 36.0555, 123.6901, 10, -20, 30)]
+    [InlineData(10, 36.0555, 303.6901, 10, 20, -30)]
+    [InlineData(10, 36.0555, 236.3099, 10, -20, -30)]
+    public void Convert_Lch_to_Lab(float l, float c, float h, float l2, float a, float b)
+    {
+        // Arrange
+        CieLch input = new(l, c, h);
+        CieLab expected = new(l2, a, b);
+        ColorConversionOptions options = new() { WhitePoint = Illuminants.D50, TargetWhitePoint = Illuminants.D50 };
+        ColorProfileConverter converter = new(options);
+
+        Span<CieLch> inputSpan = new CieLch[5];
+        inputSpan.Fill(input);
+
+        Span<CieLab> actualSpan = new CieLab[5];
+
+        // Act
+        CieLab actual = converter.Convert<CieLch, CieLab>(input);
+        converter.Convert<CieLch, CieLab>(inputSpan, actualSpan);
+
+        // Assert
+        Assert.Equal(expected, actual, Comparer);
+
+        for (int i = 0; i < actualSpan.Length; i++)
+        {
+            Assert.Equal(expected, actualSpan[i], Comparer);
+        }
+    }
+
+    [Theory]
+    [InlineData(0, 0, 0, 0, 0, 0)]
+    [InlineData(54.2917, 80.8125, 69.8851, 54.2917, 106.8391, 40.8526)]
+    [InlineData(100, 0, 0, 100, 0, 0)]
+    [InlineData(100, -50, 0, 100, 50, 180)]
+    [InlineData(10, 20, 30, 10, 36.0555, 56.3099)]
+    [InlineData(10, -20, 30, 10, 36.0555, 123.6901)]
+    [InlineData(10, 20, -30, 10, 36.0555, 303.6901)]
+    [InlineData(10, -20, -30, 10, 36.0555, 236.3099)]
+    public void Convert_Lab_to_Lch(float l, float a, float b, float l2, float c, float h)
+    {
+        // Arrange
+        CieLab input = new(l, a, b);
+        CieLch expected = new(l2, c, h);
+        ColorConversionOptions options = new() { WhitePoint = Illuminants.D50, TargetWhitePoint = Illuminants.D50 };
+        ColorProfileConverter converter = new(options);
+
+        Span<CieLab> inputSpan = new CieLab[5];
+        inputSpan.Fill(input);
+
+        Span<CieLch> actualSpan = new CieLch[5];
+
+        // Act
+        CieLch actual = converter.Convert<CieLab, CieLch>(input);
+        converter.Convert<CieLab, CieLch>(inputSpan, actualSpan);
+
+        // Assert
+        Assert.Equal(expected, actual, Comparer);
+
+        for (int i = 0; i < actualSpan.Length; i++)
+        {
+            Assert.Equal(expected, actualSpan[i], Comparer);
+        }
+    }
+}