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namespace Colourful.Implementation.Conversion
{
/// <summary>
/// Converts from <see cref="LuvColor" /> to <see cref="XYZColor" />.
/// </summary>
public sealed class LuvToXYZConverter : IColorConversion<LuvColor, XYZColor>
{
/// <summary>
/// Default singleton instance of the converter.
/// </summary>
public static readonly LuvToXYZConverter Default = new LuvToXYZConverter();
/// <summary>
/// Converts from <see cref="LuvColor" /> to <see cref="XYZColor" />.
/// </summary>
public XYZColor Convert(in LuvColor input)
{
// conversion algorithm described here: http://www.brucelindbloom.com/index.html?Eqn_Luv_to_XYZ.html
double L = input.L, u = input.u, v = input.v;
var u0 = Compute_u0(input.WhitePoint);
var v0 = Compute_v0(input.WhitePoint);
var Y = L > CIEConstants.Kappa * CIEConstants.Epsilon
? MathUtils.Pow3((L + 16) / 116)
: L / CIEConstants.Kappa;
var a = (52 * L / (u + 13 * L * u0) - 1) / 3;
var b = -5 * Y;
var c = -1 / 3d;
var d = Y * (39 * L / (v + 13 * L * v0) - 5);
var X = (d - b) / (a - c);
var Z = X * a + b;
if (double.IsNaN(X) || X < 0)
X = 0;
if (double.IsNaN(Y) || Y < 0)
Y = 0;
if (double.IsNaN(Z) || Z < 0)
Z = 0;
var result = new XYZColor(X, Y, Z);
return result;
}
private static double Compute_u0(XYZColor input) => 4 * input.X / (input.X + 15 * input.Y + 3 * input.Z);
private static double Compute_v0(XYZColor input) => 9 * input.Y / (input.X + 15 * input.Y + 3 * input.Z);
#region Overrides
/// <inheritdoc cref="object" />
public override bool Equals(object obj) => obj is LuvToXYZConverter;
/// <inheritdoc cref="object" />
public override int GetHashCode() => 1;
/// <inheritdoc cref="object" />
public static bool operator ==(LuvToXYZConverter left, LuvToXYZConverter right) => Equals(left, right);
/// <inheritdoc cref="object" />
public static bool operator !=(LuvToXYZConverter left, LuvToXYZConverter right) => !Equals(left, right);
#endregion
}
}
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