/// <summary>
/// Converts CIEXYZ to CIELab.
/// </summary>
public static CIELab XYZtoLab(double x, double y, double z)
{
CIELab lab = CIELab.Empty;
lab.L = 116.0 * Fxyz(y / CIEXYZ.D65.Y) - 16;
lab.A = 500.0 * (Fxyz(x / CIEXYZ.D65.X) - Fxyz(y / CIEXYZ.D65.Y));
lab.B = 200.0 * (Fxyz(y / CIEXYZ.D65.Y) - Fxyz(z / CIEXYZ.D65.Z));
return(lab);
}
private static double CIE76(RGB rgb1, RGB rgb2)
{
CIELab Lab1 = ColorModelConverter.RGBtoLab(rgb1.Red, rgb1.Green, rgb1.Blue);
CIELab Lab2 = ColorModelConverter.RGBtoLab(rgb2.Red, rgb2.Green, rgb2.Blue);
return(Math.Sqrt((
Math.Pow(Lab1.L - Lab2.L, 2)
+ Math.Pow(Lab1.A - Lab2.A, 2)
+ Math.Pow(Lab1.B - Lab2.B, 2))
));
}
private static double CIE94(RGB rgb1, RGB rgb2)
{
CIELab Lab1 = ColorModelConverter.RGBtoLab(rgb1.Red, rgb1.Green, rgb1.Blue);
CIELab Lab2 = ColorModelConverter.RGBtoLab(rgb2.Red, rgb2.Green, rgb2.Blue);
double Da = Lab1.A - Lab2.A;
double Db = Lab1.B - Lab2.B;
double C1 = Math.Sqrt(Math.Pow(Lab1.A, 2) + Math.Pow(Lab1.B, 2));
double C2 = Math.Sqrt(Math.Pow(Lab2.A, 2) + Math.Pow(Lab2.B, 2));
double Sc = 1 + K1 * C1;
double Sh = 1 + K2 * C1;
double Dl = Lab1.L - Lab2.L;
double Dc = C1 - C2;
double Dh2 = Math.Pow(Da, 2) + Math.Pow(Db, 2) - Math.Pow(Dc, 2);
return(Math.Sqrt(Math.Pow(Dl, 2) + Math.Pow(Dc / Sc, 2) + Dh2 / Math.Pow(Sh, 2)));
}
private static double CIE2000(RGB rgb1, RGB rgb2)
{
CIELab Lab1 = ColorModelConverter.RGBtoLab(rgb1.Red, rgb1.Green, rgb1.Blue);
CIELab Lab2 = ColorModelConverter.RGBtoLab(rgb2.Red, rgb2.Green, rgb2.Blue);
double L1 = Lab1.L;
double L2 = Lab2.L;
double a1 = Lab1.A;
double a2 = Lab2.A;
double b1 = Lab1.B;
double b2 = Lab2.B;
double Ltd = (L1 + L2) / 2;
double C1 = Math.Sqrt(Math.Pow(a1, 2) + Math.Pow(b1, 2));
double C2 = Math.Sqrt(Math.Pow(a2, 2) + Math.Pow(b2, 2));
double Ct = (C1 + C2) / 2;
double Ct7 = Math.Pow(Ct, 7);
double G = (1 - Math.Sqrt(Ct7 / (Ct7 + pow25_7))) / 2;
double ad1 = a1 * (1 + G);
double ad2 = a2 * (1 + G);
double Cd1 = Math.Sqrt(Math.Pow(ad1, 2) + Math.Pow(b1, 2));
double Cd2 = Math.Sqrt(Math.Pow(ad2, 2) + Math.Pow(b2, 2));
double Ctd = (Cd1 + Cd2) / 2;
double atanhd1 = Math.Atan2(b1, ad1);
double hd1 = atanhd1 + (atanhd1 >= 0 ? 0 : deg360);
double atanhd2 = Math.Atan2(b2, ad2);
double hd2 = atanhd2 + (atanhd2 >= 0 ? 0 : deg360);
double sdh = hd1 + hd2;
double dh1 = hd1 - hd2;
double adh1 = Math.Abs(dh1);
double Htd = (sdh + (adh1 > deg180 ? deg360 : 0)) / 2;
double T = 1 - 0.17 * Math.Cos(Htd - deg30) + 0.24 * Math.Cos(2 * Htd) + 0.32 * Math.Cos(2 * Htd + deg6) - 0.20 * Math.Cos(4 * Htd - deg63);
double dh2 = hd2 - hd1;
double adh2 = Math.Abs(dh2);
double dhd = adh2 <= deg180 ? dh2 : (hd2 <= hd1 ? (dh2 + deg360) : (dh2 - deg360));
double dLd = L2 - L1;
double dCd = Cd2 - Cd1;
double dHd = 2 * Math.Sqrt(Cd1 * Cd2) * Math.Sin(dhd / 2);
double Ltd2 = Math.Pow(Ltd - 50, 2);
double Sl = 1 + (K2 * Ltd2) / Math.Sqrt(20 + Ltd2);
double Sc = 1 + K1 * Ctd;
double Sh = 1 + K2 * Ctd * T;
double ctd7 = Math.Pow(Ctd, 7);
double dO = 30 * Math.Exp(-Math.Pow((Htd - deg275) / 25, 2));
double Rc = 2 * Math.Sqrt(ctd7 / (ctd7 + pow25_7));
double Rt = -Rc *Math.Sin(2 *dO);
double SDE = Math.Pow(dLd / Sl, 2) + Math.Pow(dCd / Sc, 2) + Math.Pow(dHd / Sh, 2) + Rt * (dCd / Sc) * (dHd / Sh);
return(Math.Sqrt(SDE));
}