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namespace Colourful.Implementation.Conversion
{
/// <summary>
/// Converts from <see cref="LabColor" /> to <see cref="XYZColor" />.
/// </summary>
public sealed class LabToXYZConverter : IColorConversion<LabColor, XYZColor>
{
/// <summary>
/// Default singleton instance of the converter.
/// </summary>
public static readonly LabToXYZConverter Default = new LabToXYZConverter();
/// <summary>
/// Converts from <see cref="LabColor" /> to <see cref="XYZColor" />.
/// </summary>
public XYZColor Convert(in LabColor input)
{
// conversion algorithm described here: http://www.brucelindbloom.com/index.html?Eqn_Lab_to_XYZ.html
double L = input.L, a = input.a, b = input.b;
var fy = (L + 16) / 116d;
var fx = a / 500d + fy;
var fz = fy - b / 200d;
var fx3 = MathUtils.Pow3(fx);
var fz3 = MathUtils.Pow3(fz);
var xr = fx3 > CIEConstants.Epsilon ? fx3 : (116 * fx - 16) / CIEConstants.Kappa;
var yr = L > CIEConstants.Kappa * CIEConstants.Epsilon ? MathUtils.Pow3((L + 16) / 116d) : L / CIEConstants.Kappa;
var zr = fz3 > CIEConstants.Epsilon ? fz3 : (116 * fz - 16) / CIEConstants.Kappa;
double Xr = input.WhitePoint.X, Yr = input.WhitePoint.Y, Zr = input.WhitePoint.Z;
// avoids XYZ coordinates out range (restricted by 0 and XYZ reference white)
xr = xr.CropRange(0, 1);
yr = yr.CropRange(0, 1);
zr = zr.CropRange(0, 1);
var X = xr * Xr;
var Y = yr * Yr;
var Z = zr * Zr;
var result = new XYZColor(X, Y, Z);
return result;
}
#region Overrides
/// <inheritdoc cref="object" />
public override bool Equals(object obj) => obj is LabToXYZConverter;
/// <inheritdoc cref="object" />
public override int GetHashCode() => 1;
/// <inheritdoc cref="object" />
public static bool operator ==(LabToXYZConverter left, LabToXYZConverter right) => Equals(left, right);
/// <inheritdoc cref="object" />
public static bool operator !=(LabToXYZConverter left, LabToXYZConverter right) => !Equals(left, right);
#endregion
}
}
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