Simplify Color Space Conversion APIs

src/ImageSharp/ColorProfiles/ChromaticAdaptionWhitePointSource.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.ColorProfiles;
+
+/// <summary>
+/// Enumerate the possible sources of the white point used in chromatic adaptation.
+/// </summary>
+public enum ChromaticAdaptionWhitePointSource
+{
+    /// <summary>
+    /// The white point of the source color space.
+    /// </summary>
+    WhitePoint,
+
+    /// <summary>
+    /// The white point of the source working space.
+    /// </summary>
+    RgbWorkingSpace
+}

src/ImageSharp/ColorSpaces/Conversion/CieConstants.cs → src/ImageSharp/ColorProfiles/CieConstants.cs

@@ -1,7 +1,7 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-namespace SixLabors.ImageSharp.ColorSpaces.Conversion;
+namespace SixLabors.ImageSharp.ColorProfiles;
 
 /// <summary>
 /// Constants use for Cie conversion calculations
@@ -12,10 +12,10 @@ internal static class CieConstants
     /// <summary>
     /// 216F / 24389F
     /// </summary>
-    public const float Epsilon = 0.008856452F;
+    public const float Epsilon = 216f / 24389f;
 
     /// <summary>
     /// 24389F / 27F
     /// </summary>
-    public const float Kappa = 903.2963F;
+    public const float Kappa = 24389f / 27f;
 }

src/ImageSharp/ColorProfiles/CieLab.cs

@@ -0,0 +1,178 @@
+// 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 CIE L*a*b* 1976 color.
+/// <see href="https://en.wikipedia.org/wiki/Lab_color_space"/>
+/// </summary>
+[StructLayout(LayoutKind.Sequential)]
+public readonly struct CieLab : IProfileConnectingSpace<CieLab, CieXyz>
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CieLab"/> struct.
+    /// </summary>
+    /// <param name="l">The lightness dimension.</param>
+    /// <param name="a">The a (green - magenta) component.</param>
+    /// <param name="b">The b (blue - yellow) component.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public CieLab(float l, float a, float b)
+    {
+        // Not clamping as documentation about this space only indicates "usual" ranges
+        this.L = l;
+        this.A = a;
+        this.B = b;
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CieLab"/> struct.
+    /// </summary>
+    /// <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;
+        this.B = vector.Z;
+    }
+
+    /// <summary>
+    /// Gets the lightness dimension.
+    /// <remarks>A value usually ranging between 0 (black), 100 (diffuse white) or higher (specular white).</remarks>
+    /// </summary>
+    public float L { get; }
+
+    /// <summary>
+    /// Gets the a color component.
+    /// <remarks>A value usually ranging from -100 to 100. Negative is green, positive magenta.</remarks>
+    /// </summary>
+    public float A { get; }
+
+    /// <summary>
+    /// Gets the b color component.
+    /// <remarks>A value usually ranging from -100 to 100. Negative is blue, positive is yellow</remarks>
+    /// </summary>
+    public float B { get; }
+
+    /// <summary>
+    /// Compares two <see cref="CieLab"/> objects for equality.
+    /// </summary>
+    /// <param name="left">The <see cref="CieLab"/> on the left side of the operand.</param>
+    /// <param name="right">The <see cref="CieLab"/> 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 ==(CieLab left, CieLab right) => left.Equals(right);
+
+    /// <summary>
+    /// Compares two <see cref="CieLab"/> objects for inequality
+    /// </summary>
+    /// <param name="left">The <see cref="CieLab"/> on the left side of the operand.</param>
+    /// <param name="right">The <see cref="CieLab"/> 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 !=(CieLab left, CieLab right) => !left.Equals(right);
+
+    /// <inheritdoc/>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static CieLab FromProfileConnectingSpace(ColorConversionOptions options, in CieXyz source)
+    {
+        // Conversion algorithm described here:
+        // http://www.brucelindbloom.com/index.html?Eqn_XYZ_to_Lab.html
+        CieXyz whitePoint = options.TargetWhitePoint;
+        float wx = whitePoint.X, wy = whitePoint.Y, wz = whitePoint.Z;
+
+        float xr = source.X / wx, yr = source.Y / wy, zr = source.Z / wz;
+
+        const float inv116 = 1 / 116F;
+
+        float fx = xr > CieConstants.Epsilon ? MathF.Pow(xr, 0.3333333F) : ((CieConstants.Kappa * xr) + 16F) * inv116;
+        float fy = yr > CieConstants.Epsilon ? MathF.Pow(yr, 0.3333333F) : ((CieConstants.Kappa * yr) + 16F) * inv116;
+        float fz = zr > CieConstants.Epsilon ? MathF.Pow(zr, 0.3333333F) : ((CieConstants.Kappa * zr) + 16F) * inv116;
+
+        float l = (116F * fy) - 16F;
+        float a = 500F * (fx - fy);
+        float b = 200F * (fy - fz);
+
+        return new CieLab(l, a, b);
+    }
+
+    /// <inheritdoc/>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static void FromProfileConnectionSpace(ColorConversionOptions options, ReadOnlySpan<CieXyz> source, Span<CieLab> destination)
+    {
+        Guard.DestinationShouldNotBeTooShort(source, destination, nameof(destination));
+
+        for (int i = 0; i < source.Length; i++)
+        {
+            CieXyz xyz = source[i];
+            destination[i] = FromProfileConnectingSpace(options, in xyz);
+        }
+    }
+
+    /// <inheritdoc/>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public CieXyz ToProfileConnectingSpace(ColorConversionOptions options)
+    {
+        // Conversion algorithm described here: http://www.brucelindbloom.com/index.html?Eqn_Lab_to_XYZ.html
+        float l = this.L, a = this.A, b = this.B;
+        float fy = (l + 16) / 116F;
+        float fx = (a / 500F) + fy;
+        float fz = fy - (b / 200F);
+
+        float fx3 = Numerics.Pow3(fx);
+        float fz3 = Numerics.Pow3(fz);
+
+        float xr = fx3 > CieConstants.Epsilon ? fx3 : ((116F * fx) - 16F) / CieConstants.Kappa;
+        float yr = l > CieConstants.Kappa * CieConstants.Epsilon ? Numerics.Pow3((l + 16F) / 116F) : l / CieConstants.Kappa;
+        float zr = fz3 > CieConstants.Epsilon ? fz3 : ((116F * fz) - 16F) / CieConstants.Kappa;
+
+        CieXyz whitePoint = options.WhitePoint;
+        Vector3 wxyz = new(whitePoint.X, whitePoint.Y, whitePoint.Z);
+        Vector3 xyzr = new(xr, yr, zr);
+
+        return new(xyzr * wxyz);
+    }
+
+    /// <inheritdoc/>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static void ToProfileConnectionSpace(ColorConversionOptions options, ReadOnlySpan<CieLab> source, Span<CieXyz> destination)
+    {
+        Guard.DestinationShouldNotBeTooShort(source, destination, nameof(destination));
+
+        for (int i = 0; i < source.Length; i++)
+        {
+            CieLab lab = source[i];
+            destination[i] = lab.ToProfileConnectingSpace(options);
+        }
+    }
+
+    /// <inheritdoc/>
+    public static ChromaticAdaptionWhitePointSource GetChromaticAdaptionWhitePointSource()
+        => ChromaticAdaptionWhitePointSource.WhitePoint;
+
+    /// <inheritdoc/>
+    public override int GetHashCode() => HashCode.Combine(this.L, this.A, this.B);
+
+    /// <inheritdoc/>
+    public override string ToString() => FormattableString.Invariant($"CieLab({this.L:#0.##}, {this.A:#0.##}, {this.B:#0.##})");
+
+    /// <inheritdoc/>
+    public override bool Equals(object? obj) => obj is CieLab other && this.Equals(other);
+
+    /// <inheritdoc/>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public bool Equals(CieLab other)
+        => this.AsVector3Unsafe() == other.AsVector3Unsafe();
+
+    private Vector3 AsVector3Unsafe() => Unsafe.As<CieLab, Vector3>(ref Unsafe.AsRef(in this));
+}