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using System;
namespace Colourful.Implementation.Conversion
{
/// <summary>
/// Converts from <see cref="HunterLabColor" /> to <see cref="XYZColor" />.
/// </summary>
public sealed class XYZToHunterLabConverter : XYZAndHunterLabConverterBase, IColorConversion<XYZColor, HunterLabColor>
{
/// <summary>
/// Construct with <see cref="HunterLabColor.DefaultWhitePoint" />
/// </summary>
public XYZToHunterLabConverter()
: this(HunterLabColor.DefaultWhitePoint)
{
}
/// <summary>
/// Construct with arbitrary white point
/// </summary>
public XYZToHunterLabConverter(XYZColor labWhitePoint)
{
HunterLabWhitePoint = labWhitePoint;
}
/// <summary>
/// Target reference white. When not set, <see cref="LabColor.DefaultWhitePoint" /> is used.
/// </summary>
public XYZColor HunterLabWhitePoint { get; }
/// <summary>
/// Converts from <see cref="HunterLabColor" /> to <see cref="XYZColor" />.
/// </summary>
public HunterLabColor Convert(in XYZColor input)
{
// conversion algorithm described here: http://en.wikipedia.org/wiki/Lab_color_space#Hunter_Lab
double X = input.X, Y = input.Y, Z = input.Z;
double Xn = HunterLabWhitePoint.X, Yn = HunterLabWhitePoint.Y, Zn = HunterLabWhitePoint.Z;
var Ka = ComputeKa(HunterLabWhitePoint);
var Kb = ComputeKb(HunterLabWhitePoint);
var L = 100 * Math.Sqrt(Y / Yn);
var a = Ka * ((X / Xn - Y / Yn) / Math.Sqrt(Y / Yn));
var b = Kb * ((Y / Yn - Z / Zn) / Math.Sqrt(Y / Yn));
if (double.IsNaN(a))
a = 0;
if (double.IsNaN(b))
b = 0;
var output = new HunterLabColor(L, a, b, HunterLabWhitePoint);
return output;
}
}
}
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