private ColorLAB ToLAB(ColorRGB colorRGB)
{
var r = colorRGB.R / 255.0;
var g = colorRGB.G / 255.0;
var b = colorRGB.B / 255.0;
var r2 = colorRGB.R >> 6;
var g2 = colorRGB.G >> 6;
var b2 = colorRGB.B >> 6;
var irgb = (byte)((r2 << 4) | (g2 << 2) | b2);
r = (r > 0.04045) ? Math.Pow((r + 0.055) / 1.055, 2.4) : r / 12.92;
g = (g > 0.04045) ? Math.Pow((g + 0.055) / 1.055, 2.4) : g / 12.92;
b = (b > 0.04045) ? Math.Pow((b + 0.055) / 1.055, 2.4) : b / 12.92;
var x = (r * 0.4124 + g * 0.3576 + b * 0.1805) / 0.95047;
var y = (r * 0.2126 + g * 0.7152 + b * 0.0722) / 1.00000;
var z = (r * 0.0193 + g * 0.1192 + b * 0.9505) / 1.08883;
x = (x > 0.008856) ? Math.Pow(x, 1.0 / 3.0) : (7.787 * x) + 16.0 / 116.0;
y = (y > 0.008856) ? Math.Pow(y, 1.0 / 3.0) : (7.787 * y) + 16.0 / 116.0;
z = (z > 0.008856) ? Math.Pow(z, 1.0 / 3.0) : (7.787 * z) + 16.0 / 116.0;
var lab = new ColorLAB(
(float)((116.0 * y) - 16.0),
(float)(500.0 * (x - y)),
(float)(200.0 * (y - z)),
irgb
);
return(lab);
}
public float CIEDE2000(ColorLAB other)
{
Contract.Requires(other != null);
const double kL = 1.0, kC = 1.0, kH = 1.0;
const double pow25To7 = 6103515625.0; // pow(25, 7)
var deg360InRad = Deg2rad(360f);
var deg180InRad = Deg2rad(180f);
/* Equation 2 */
double C1 = Math.Sqrt((A * A) + (B * B));
double C2 = Math.Sqrt((other.A * other.A) + (other.B * other.B));
/* Equation 3 */
double barC = (C1 + C2) / 2.0;
/* Equation 4 */
double G = 0.5 * (1.0 - Math.Sqrt(Math.Pow(barC, 7.0) / (Math.Pow(barC, 7.0) + pow25To7)));
/* Equation 5 */
double a1Prime = (1.0 + G) * A;
double a2Prime = (1.0 + G) * other.A;
/* Equation 6 */
double CPrime1 = Math.Sqrt((a1Prime * a1Prime) + (B * B));
double CPrime2 = Math.Sqrt((a2Prime * a2Prime) + (other.B * other.B));
/* Equation 7 */
double hPrime1;
if (Math.Abs(B) < 0.000001 && Math.Abs(a1Prime) < 0.000001)
{
hPrime1 = 0.0;
}
else
{
hPrime1 = Math.Atan2(B, a1Prime);
/*
* This must be converted to a hue angle in degrees between 0
* and 360 by addition of 20 to negative hue angles.
*/
if (hPrime1 < 0)
{
hPrime1 += deg360InRad;
}
}
double hPrime2;
if (Math.Abs(other.B) < 0.000001 && Math.Abs(a2Prime) < 0.000001)
{
hPrime2 = 0.0;
}
else
{
hPrime2 = Math.Atan2(other.B, a2Prime);
/*
* This must be converted to a hue angle in degrees between 0
* and 360 by addition of 2 to negative hue angles.
*/
if (hPrime2 < 0)
{
hPrime2 += deg360InRad;
}
}
/* Equation 8 */
double deltaLPrime = other.L - L;
/* Equation 9 */
double deltaCPrime = CPrime2 - CPrime1;
/* Equation 10 */
double deltahPrime;
double CPrimeProduct = CPrime1 * CPrime2;
if (Math.Abs(CPrimeProduct) < 0.000001)
{
deltahPrime = 0.0;
}
else
{
/* Avoid the Math.Abs() call */
deltahPrime = hPrime2 - hPrime1;
if (deltahPrime < -deg180InRad)
{
deltahPrime += deg360InRad;
}
else
{
if (deltahPrime > deg180InRad)
{
deltahPrime -= deg360InRad;
}
}
}
/* Equation 11 */
double deltaHPrime = 2.0 * Math.Sqrt(CPrimeProduct) * Math.Sin(deltahPrime / 2.0);
/* Equation 12 */
double barLPrime = (L + other.L) / 2.0;
/* Equation 13 */
double barCPrime = (CPrime1 + CPrime2) / 2.0;
/* Equation 14 */
double barhPrime, hPrimeSum = hPrime1 + hPrime2;
if (Math.Abs(CPrime1 * CPrime2) < 0.000001)
{
barhPrime = hPrimeSum;
}
else
{
if (Math.Abs(hPrime1 - hPrime2) <= deg180InRad)
{
barhPrime = hPrimeSum / 2.0;
}
else
{
if (hPrimeSum < deg360InRad)
{
barhPrime = (hPrimeSum + deg360InRad) / 2.0;
}
else
{
barhPrime = (hPrimeSum - deg360InRad) / 2.0;
}
}
}
/* Equation 15 */
double T = 1.0 - (0.17 * Math.Cos(barhPrime - Deg2rad(30f))) +
(0.24 * Math.Cos(2.0 * barhPrime)) +
(0.32 * Math.Cos((3.0 * barhPrime) + Deg2rad(6f))) -
(0.20 * Math.Cos((4.0 * barhPrime) - Deg2rad(63f)));
/* Equation 16 */
double deltaTheta = Deg2rad(30f) * Math.Exp(-Math.Pow((barhPrime - Deg2rad(275f)) / Deg2rad(25f), 2.0));
/* Equation 17 */
double R_C = 2.0 * Math.Sqrt(Math.Pow(barCPrime, 7.0) / (Math.Pow(barCPrime, 7.0) + pow25To7));
/* Equation 18 */
double S_L = 1 + ((0.015 * Math.Pow(barLPrime - 50.0, 2.0)) / Math.Sqrt(20 + Math.Pow(barLPrime - 50.0, 2.0)));
/* Equation 19 */
double S_C = 1 + (0.045 * barCPrime);
/* Equation 20 */
double S_H = 1 + (0.015 * barCPrime * T);
/* Equation 21 */
double R_T = (-Math.Sin(2.0 * deltaTheta)) * R_C;
/* Equation 22 */
double deltaE = Math.Sqrt(
Math.Pow(deltaLPrime / (kL * S_L), 2.0) +
Math.Pow(deltaCPrime / (kC * S_C), 2.0) +
Math.Pow(deltaHPrime / (kH * S_H), 2.0) +
(R_T * (deltaCPrime / (kC * S_C)) * (deltaHPrime / (kH * S_H))));
return((float)deltaE);
}
