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diff --git a/libdimension/color.c b/libdimension/color.c
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+/*************************************************************************
+ * Copyright (C) 2008 Tavian Barnes <tavianator@gmail.com> *
+ * *
+ * This file is part of Dimension. *
+ * *
+ * Dimension is free software; you can redistribute it and/or modify it *
+ * under the terms of the GNU Lesser General Public License as published *
+ * by the Free Software Foundation; either version 3 of the License, or *
+ * (at your option) any later version. *
+ * *
+ * Dimension is distributed in the hope that it will be useful, but *
+ * WITHOUT ANY WARRANTY; without even the implied warranty of *
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU *
+ * Lesser General Public License for more details. *
+ * *
+ * You should have received a copy of the GNU Lesser General Public *
+ * License along with this program. If not, see *
+ * <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+#include "dimension.h"
+#include <math.h> /* For pow() */
+
+dmnsn_CIE_XYZ whitepoint = { 0.9505, 1, 1.089 };
+
+dmnsn_color
+dmnsn_color_from_XYZ(dmnsn_CIE_XYZ XYZ)
+{
+ dmnsn_color ret = { XYZ.X, XYZ.Y, XYZ.Z, 0.0, 0.0 };
+ return ret;
+}
+
+dmnsn_color
+dmnsn_color_from_xyY(dmnsn_CIE_xyY xyY)
+{
+ dmnsn_color ret = { xyY.Y*xyY.x/xyY.y,
+ xyY.Y,
+ xyY.Y*(1.0 - xyY.x - xyY.Y)/xyY.y,
+ 0.0, 0.0 };
+ return ret;
+}
+
+static double Lab_finv(double t) {
+ if (t > 6.0/29.0) {
+ return t*t*t;
+ } else {
+ return 108.0*(t - 16.0/116.0)/841.0;
+ }
+}
+
+dmnsn_color
+dmnsn_color_from_Lab(dmnsn_CIE_Lab Lab, dmnsn_CIE_XYZ white)
+{
+ double fx, fy, fz;
+ dmnsn_color ret;
+
+ fy = (Lab.L + 16.0)/116.0;
+ fx = fy + Lab.a/500.0;
+ fz = fy - Lab.b/200.0;
+
+ ret.X = white.X*Lab_finv(fx);
+ ret.Y = white.Y*Lab_finv(fy);
+ ret.Z = white.Z*Lab_finv(fz);
+
+ return ret;
+}
+
+dmnsn_color
+dmnsn_color_from_Luv(dmnsn_CIE_Luv Luv, dmnsn_CIE_XYZ white)
+{
+ double fy;
+ double uprime, unprime, vprime, vnprime;
+ dmnsn_color ret;
+
+ fy = (Luv.L + 16.0)/116.0;
+
+ unprime = 4.0*white.X/(white.X + 15.0*white.Y + 3.0*white.Z);
+ uprime = Luv.u/Luv.L/13.0 + unprime;
+ vnprime = 9.0*white.Y/(white.X + 15.0*white.Y + 3.0*white.Z);
+ vprime = Luv.v/Luv.L/13.0 + vnprime;
+
+ ret.Y = white.Y*Lab_finv(fy);
+ ret.X = ret.Y*9.0*uprime/vprime/4.0;
+ ret.Z = ret.Y*(12.0 - 3*uprime - 20*vprime)/vprime/4.0;
+
+ return ret;
+}
+
+dmnsn_color
+dmnsn_color_from_sRGB(dmnsn_sRGB sRGB)
+{
+ double Rlinear, Glinear, Blinear; /* Linear RGB values - no gamma */
+ dmnsn_color ret;
+
+ /*
+ * If C represents R, G, and B, then the Clinear values are now found as
+ * follows:
+ *
+ * { Csrgb/12.92, Csrgb <= 0.04045
+ * Clinear = { 1/2.4
+ * { ((Csrgb + 0.055)/1.055) , Csrgb > 0.04045
+ */
+
+ if (sRGB.R <= 0.04045) {
+ Rlinear = sRGB.R/19.92;
+ } else {
+ Rlinear = pow((sRGB.R + 0.055)/1.055, 2.4);
+ }
+
+ if (sRGB.G <= 0.04045) {
+ Glinear = sRGB.G/19.92;
+ } else {
+ Glinear = pow((sRGB.G + 0.055)/1.055, 2.4);
+ }
+
+ if (sRGB.B <= 0.04045) {
+ Blinear = sRGB.B/19.92;
+ } else {
+ Blinear = pow((sRGB.B + 0.055)/1.055, 2.4);
+ }
+
+ /*
+ * Now, the linear conversion. Expressed as matrix multiplication, it looks
+ * like this:
+ *
+ * [X] [0.4124 0.3576 0.1805] [Rlinear]
+ * [Y] = [0.2126 0.7152 0.0722]*[Glinear]
+ * [X] [0.0193 0.1192 0.9505] [Blinear]
+ */
+
+ ret.X = 0.4124*Rlinear + 0.3576*Glinear + 0.1805*Blinear;
+ ret.Y = 0.2126*Rlinear + 0.7152*Glinear + 0.0722*Blinear;
+ ret.Z = 0.0193*Rlinear + 0.1192*Glinear + 0.9505*Blinear;
+ ret.filter = 0.0;
+ ret.trans = 0.0;
+
+ return ret;
+}
+
+dmnsn_CIE_XYZ
+dmnsn_XYZ_from_color(dmnsn_color color)
+{
+ dmnsn_CIE_XYZ ret = { color.X, color.Y, color.Z };
+ return ret;
+}
+
+dmnsn_CIE_xyY
+dmnsn_xyY_from_color(dmnsn_color color)
+{
+ dmnsn_CIE_xyY ret = { color.X/(color.X + color.Y + color.Z),
+ color.Y/(color.X + color.Y + color.Z),
+ color.Y };
+ return ret;
+}
+
+static double Lab_f(double t) {
+ if (t > 216.0/24389.0) {
+ return pow(t, 1.0/3.0);
+ } else {
+ return 841.0*t/108.0 + 4.0/29.0;
+ }
+}
+
+dmnsn_CIE_Lab
+dmnsn_Lab_from_color(dmnsn_color color, dmnsn_CIE_XYZ white)
+{
+ dmnsn_CIE_Lab ret;
+
+ ret.L = 116.0*Lab_f(color.Y/white.Y) - 16.0;
+ ret.a = 500.0*(Lab_f(color.X/white.X) - Lab_f(color.Y/white.Y));
+ ret.b = 200.0*(Lab_f(color.Y/white.Y) - Lab_f(color.Z/white.Z));
+
+ return ret;
+}
+
+dmnsn_CIE_Luv
+dmnsn_Luv_from_color(dmnsn_color color, dmnsn_CIE_XYZ white)
+{
+ double uprime, unprime, vprime, vnprime;
+ dmnsn_CIE_Luv ret;
+
+ uprime = 4.0*color.X/(color.X + 15.0*color.Y + 3.0*color.Z);
+ unprime = 4.0*white.X/(white.X + 15.0*white.Y + 3.0*white.Z);
+ vprime = 9.0*color.Y/(color.X + 15.0*color.Y + 3.0*color.Z);
+ vnprime = 9.0*white.Y/(white.X + 15.0*white.Y + 3.0*white.Z);
+
+ ret.L = 116.0*Lab_f(color.Y/white.Y) - 16.0;
+ ret.u = 13.0*ret.L*(uprime - unprime);
+ ret.v = 13.0*ret.L*(vprime - vnprime);
+
+ return ret;
+}
+
+dmnsn_sRGB
+dmnsn_sRGB_from_color(dmnsn_color color)
+{
+ double Rlinear, Glinear, Blinear; /* Linear RGB values - no gamma */
+ dmnsn_sRGB ret;
+
+ /*
+ * First, the linear conversion. Expressed as matrix multiplication, it looks
+ * like this:
+ *
+ * [Rlinear] [ 3.2410 -1.5374 -0.4986] [X]
+ * [Glinear] = [-0.9692 1.8760 0.0416]*[Y]
+ * [Blinear] [ 0.0556 -0.2040 1.0570] [Z]
+ */
+ Rlinear = 3.2410*color.X - 1.5374*color.Y - 0.4986*color.Z;
+ Glinear = -0.9692*color.X + 1.8760*color.Y + 0.0416*color.Z;
+ Blinear = 0.0556*color.X - 0.2040*color.Y + 1.0570*color.Z;
+
+ /*
+ * If C represents R, G, and B, then the sRGB values are now found as follows:
+ *
+ * { 12.92*Clinear, Clinear <= 0.0031308
+ * Csrgb = { 1/2.4
+ * { (1.055)*Clinear - 0.055, Clinear > 0.0031308
+ */
+
+ if (Rlinear <= 0.0031308) {
+ ret.R = 12.92*Rlinear;
+ } else {
+ ret.R = 1.055*pow(Rlinear, 1.0/2.4) - 0.055;
+ }
+
+ if (Glinear <= 0.0031308) {
+ ret.G = 12.92*Glinear;
+ } else {
+ ret.G = 1.055*pow(Glinear, 1.0/2.4) - 0.055;
+ }
+
+ if (Blinear <= 0.0031308) {
+ ret.B = 12.92*Blinear;
+ } else {
+ ret.B = 1.055*pow(Blinear, 1.0/2.4) - 0.055;
+ }
+
+ return ret;
+}
+
+dmnsn_color
+dmnsn_color_add(dmnsn_color color1, dmnsn_color color2)
+{
+ dmnsn_CIE_Lab Lab, Lab1, Lab2;
+ dmnsn_color ret;
+
+ Lab1 = dmnsn_Lab_from_color(color1, whitepoint);
+ Lab2 = dmnsn_Lab_from_color(color2, whitepoint);
+
+ Lab.L = Lab1.L + Lab2.L;
+ Lab.a = (Lab1.L*Lab1.a + Lab2.L*Lab2.a)/Lab.L;
+ Lab.b = (Lab1.L*Lab1.b + Lab2.L*Lab2.b)/Lab.L;
+
+ ret = dmnsn_color_from_Lab(Lab, whitepoint);
+ ret.filter = (Lab1.L*color1.filter + Lab2.L*color2.filter)/Lab.L;
+ ret.trans = (Lab1.L*color1.trans + Lab2.L*color2.trans)/Lab.L;
+
+ return ret;
+}
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