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using System;
namespace Colourful.Implementation.Conversion
{
/// <summary>
/// Converts from <see cref="XYZColor" /> to <see cref="LuvColor" />.
/// </summary>
public sealed class XYZToLuvConverter : IColorConversion<XYZColor, LuvColor>
{
/// <summary>
/// Constructs with <see cref="LuvColor.DefaultWhitePoint" />
/// </summary>
public XYZToLuvConverter()
: this(LuvColor.DefaultWhitePoint)
{
}
/// <summary>
/// Constructs with arbitrary white point
/// </summary>
public XYZToLuvConverter(XYZColor labWhitePoint)
{
LuvWhitePoint = labWhitePoint;
}
/// <summary>
/// Target reference white. When not set, <see cref="LuvColor.DefaultWhitePoint" /> is used.
/// </summary>
public XYZColor LuvWhitePoint { get; }
/// <summary>
/// Converts from <see cref="XYZColor" /> to <see cref="LuvColor" />.
/// </summary>
public LuvColor Convert(in XYZColor input)
{
// conversion algorithm described here: http://www.brucelindbloom.com/index.html?Eqn_XYZ_to_Luv.html
var yr = input.Y / LuvWhitePoint.Y;
var up = Compute_up(input);
var vp = Compute_vp(input);
var upr = Compute_up(LuvWhitePoint);
var vpr = Compute_vp(LuvWhitePoint);
var L = yr > CIEConstants.Epsilon ? 116 * Math.Pow(yr, 1 / 3d) - 16 : CIEConstants.Kappa * yr;
if (double.IsNaN(L) || L < 0)
L = 0;
var u = 13 * L * (up - upr);
var v = 13 * L * (vp - vpr);
if (double.IsNaN(u))
u = 0;
if (double.IsNaN(v))
v = 0;
return new LuvColor(L, u, v, LuvWhitePoint);
}
private static double Compute_up(XYZColor input) => 4 * input.X / (input.X + 15 * input.Y + 3 * input.Z);
private static double Compute_vp(XYZColor input) => 9 * input.Y / (input.X + 15 * input.Y + 3 * input.Z);
#region Overrides
/// <inheritdoc cref="object" />
public bool Equals(XYZToLuvConverter other)
{
if (other == null)
return false;
return ReferenceEquals(this, other) || LuvWhitePoint.Equals(other.LuvWhitePoint);
}
/// <inheritdoc cref="object" />
public override bool Equals(object obj) => obj is XYZToLuvConverter other && Equals(other);
/// <inheritdoc cref="object" />
public override int GetHashCode() => LuvWhitePoint.GetHashCode();
/// <inheritdoc cref="object" />
public static bool operator ==(XYZToLuvConverter left, XYZToLuvConverter right) => Equals(left, right);
/// <inheritdoc cref="object" />
public static bool operator !=(XYZToLuvConverter left, XYZToLuvConverter right) => !Equals(left, right);
#endregion
}
}
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