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+/**
+ * @file colorspace.c
+ * @author Pascal Getreuer 2005-2010 <getreuer@gmail.com>
+ *
+ * == Summary ==
+ * This file implements routines for color transformations between the spaces
+ * sRGB, Y'UV, Y'CbCr, Y'PbPr, Y'DbDr, Y'IQ, HSV, HSL, HSI, CIEXYZ, CIELAB,
+ * CIELUV, CIELCH, and CIECAT02 LMS.
+ *
+ * == Usage ==
+ * First call GetColorTransform, specifying the source and destination color
+ * spaces as "dest<-src" or "src->dest". Then call ApplyColorTransform to
+ * perform the transform:
+@code
+ double S[3] = {173, 0.8, 0.5};
+ double D[3];
+ colortransform Trans;
+
+ if(!(GetColorTransform(&Trans, "HSI -> Lab")))
+ {
+ printf("Invalid syntax or unknown color space\n");
+ return;
+ }
+
+ ApplyColorTransform(Trans, &D[0], &D[1], &D[2], S[0], S[1], S[2]);
+@endcode
+ * "num" is a typedef defined at the beginning of colorspace.h that may be set
+ * to either double or float, depending on the application.
+ *
+ * Specific transformation routines can also be called directly. The following
+ * converts an sRGB color to CIELAB and then back to sRGB:
+@code
+ double R = 0.85, G = 0.32, B = 0.5;
+ double L, a, b;
+ Rgb2Lab(&L, &a, &b, R, G, B);
+ Lab2Rgb(&R, &G, &B, L, a, b);
+@endcode
+ * Generally, the calling syntax is
+@code
+ Foo2Bar(&B0, &B1, &B2, F0, F1, F2);
+@endcode
+ * where (F0,F1,F2) are the coordinates of a color in space "Foo" and
+ * (B0,B1,B2) are the transformed coordinates in space "Bar." For any
+ * transformation routine, its inverse has the sytax
+@code
+ Bar2Foo(&F0, &F1, &F2, B0, B1, B2);
+@endcode
+ *
+ * The conversion routines are consistently named with the first letter of a
+ * color space capitalized with following letters in lower case and omitting
+ * prime symbols. For example, "Rgb2Ydbdr" converts sRGB to Y'DbDr. For
+ * any transformation routine Foo2Bar, its inverse is Bar2Foo.
+ *
+ * All transformations assume a two degree observer angle and a D65 illuminant.
+ * The white point can be changed by modifying the WHITEPOINT_X, WHITEPOINT_Y,
+ * WHITEPOINT_Z definitions at the beginning of colorspace.h.
+ *
+ * == List of transformation routines ==
+ * - Rgb2Yuv(double *Y, double *U, double *V, double R, double G, double B)
+ * - Rgb2Ycbcr(double *Y, double *Cb, double *Cr, double R, double G, double B)
+ * - Rgb2Jpegycbcr(double *Y, double *Cb, double *Cr, double R, double G, double B)
+ * - Rgb2Ypbpr(double *Y, double *Pb, double *Pr, double R, double G, double B)
+ * - Rgb2Ydbdr(double *Y, double *Db, double *Dr, double R, double G, double B)
+ * - Rgb2Yiq(double *Y, double *I, double *Q, double R, double G, double B)
+ * - Rgb2Hsv(double *H, double *S, double *V, double R, double G, double B)
+ * - Rgb2Hsl(double *H, double *S, double *L, double R, double G, double B)
+ * - Rgb2Hsi(double *H, double *S, double *I, double R, double G, double B)
+ * - Rgb2Xyz(double *X, double *Y, double *Z, double R, double G, double B)
+ * - Xyz2Lab(double *L, double *a, double *b, double X, double Y, double Z)
+ * - Xyz2Luv(double *L, double *u, double *v, double X, double Y, double Z)
+ * - Xyz2Lch(double *L, double *C, double *h, double X, double Y, double Z)
+ * - Xyz2Cat02lms(double *L, double *M, double *S, double X, double Y, double Z)
+ * - Rgb2Lab(double *L, double *a, double *b, double R, double G, double B)
+ * - Rgb2Luv(double *L, double *u, double *v, double R, double G, double B)
+ * - Rgb2Lch(double *L, double *C, double *h, double R, double G, double B)
+ * - Rgb2Cat02lms(double *L, double *M, double *S, double R, double G, double B)
+ * (Similarly for the inverse transformations.)
+ *
+ * It is possible to transform between two arbitrary color spaces by first
+ * transforming from the source space to sRGB and then transforming from
+ * sRGB to the desired destination space. For transformations between CIE
+ * color spaces, it is convenient to use XYZ as the intermediate space. This
+ * is the strategy used by GetColorTransform and ApplyColorTransform.
+ *
+ * == References ==
+ * The definitions of these spaces and the many of the transformation formulas
+ * can be found in
+ *
+ * Poynton, "Frequently Asked Questions About Gamma"
+ * http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html
+ *
+ * Poynton, "Frequently Asked Questions About Color"
+ * http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html
+ *
+ * and Wikipedia articles
+ * http://en.wikipedia.org/wiki/SRGB
+ * http://en.wikipedia.org/wiki/YUV
+ * http://en.wikipedia.org/wiki/YCbCr
+ * http://en.wikipedia.org/wiki/YPbPr
+ * http://en.wikipedia.org/wiki/YDbDr
+ * http://en.wikipedia.org/wiki/YIQ
+ * http://en.wikipedia.org/wiki/HSL_and_HSV
+ * http://en.wikipedia.org/wiki/CIE_1931_color_space
+ * http://en.wikipedia.org/wiki/Lab_color_space
+ * http://en.wikipedia.org/wiki/CIELUV_color_space
+ * http://en.wikipedia.org/wiki/LMS_color_space
+ *
+ * == License (BSD) ==
+ * Copyright (c) 2005-2010, Pascal Getreuer
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+#include <math.h>
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+
+#include "gtkmm2ext/colorspace.h"
+
+namespace Gtkmm2ext {
+
+/** @brief Min of A and B */
+#define MIN(A,B) (((A) <= (B)) ? (A) : (B))
+
+/** @brief Max of A and B */
+#define MAX(A,B) (((A) >= (B)) ? (A) : (B))
+
+/** @brief Min of A, B, and C */
+#define MIN3(A,B,C) (((A) <= (B)) ? MIN(A,C) : MIN(B,C))
+
+/** @brief Max of A, B, and C */
+#define MAX3(A,B,C) (((A) >= (B)) ? MAX(A,C) : MAX(B,C))
+
+#ifndef M_PI
+/** @brief The constant pi */
+#define M_PI 3.14159265358979323846264338327950288
+#endif
+
+/**
+ * @brief sRGB gamma correction, transforms R to R'
+ * http://en.wikipedia.org/wiki/SRGB
+ */
+#define GAMMACORRECTION(t) \
+ (((t) <= 0.0031306684425005883) ? \
+ (12.92*(t)) : (1.055*pow((t), 0.416666666666666667) - 0.055))
+
+/**
+ * @brief Inverse sRGB gamma correction, transforms R' to R
+ */
+#define INVGAMMACORRECTION(t) \
+ (((t) <= 0.0404482362771076) ? \
+ ((t)/12.92) : pow(((t) + 0.055)/1.055, 2.4))
+
+/**
+ * @brief CIE L*a*b* f function (used to convert XYZ to L*a*b*)
+ * http://en.wikipedia.org/wiki/Lab_color_space
+ */
+#define LABF(t) \
+ ((t >= 8.85645167903563082e-3) ? \
+ pow(t,0.333333333333333) : (841.0/108.0)*(t) + (4.0/29.0))
+
+/**
+ * @brief CIE L*a*b* inverse f function
+ * http://en.wikipedia.org/wiki/Lab_color_space
+ */
+#define LABINVF(t) \
+ ((t >= 0.206896551724137931) ? \
+ ((t)*(t)*(t)) : (108.0/841.0)*((t) - (4.0/29.0)))
+
+/** @brief u'v' coordinates of the white point for CIE Lu*v* */
+#define WHITEPOINT_U ((4*WHITEPOINT_X) \
+ /(WHITEPOINT_X + 15*WHITEPOINT_Y + 3*WHITEPOINT_Z))
+#define WHITEPOINT_V ((9*WHITEPOINT_Y) \
+ /(WHITEPOINT_X + 15*WHITEPOINT_Y + 3*WHITEPOINT_Z))
+
+/** @brief Enumeration of the supported color spaces */
+#define UNKNOWN_SPACE 0
+#define RGB_SPACE 1
+#define YUV_SPACE 2
+#define YCBCR_SPACE 3
+#define JPEGYCBCR_SPACE 4
+#define YPBPR_SPACE 5
+#define YDBDR_SPACE 6
+#define YIQ_SPACE 7
+#define HSV_SPACE 8
+#define HSL_SPACE 9
+#define HSI_SPACE 10
+#define XYZ_SPACE 11
+#define LAB_SPACE 12
+#define LUV_SPACE 13
+#define LCH_SPACE 14
+#define CAT02LMS_SPACE 15
+
+#define NUM_TRANSFORM_PAIRS 18
+
+
+
+/*
+ * == Linear color transformations ==
+ *
+ * The following routines implement transformations between sRGB and
+ * the linearly-related color spaces Y'UV, Y'PbPr, Y'DbDr, and Y'IQ.
+ */
+
+
+/**
+ * @brief Convert sRGB to NTSC/PAL Y'UV Luma + Chroma
+ *
+ * @param Y, U, V pointers to hold the result
+ * @param R, G, B the input sRGB values
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/YUV
+ */
+void Rgb2Yuv(double *Y, double *U, double *V, double R, double G, double B)
+{
+ *Y = (double)( 0.299*R + 0.587*G + 0.114*B);
+ *U = (double)(-0.147*R - 0.289*G + 0.436*B);
+ *V = (double)( 0.615*R - 0.515*G - 0.100*B);
+}
+
+
+/**
+ * @brief Convert NTSC/PAL Y'UV to sRGB
+ *
+ * @param R, G, B pointers to hold the result
+ * @param Y, U, V the input YUV values
+ */
+void Yuv2Rgb(double *R, double *G, double *B, double Y, double U, double V)
+{
+ *R = (double)(Y - 3.945707070708279e-05*U + 1.1398279671717170825*V);
+ *G = (double)(Y - 0.3946101641414141437*U - 0.5805003156565656797*V);
+ *B = (double)(Y + 2.0319996843434342537*U - 4.813762626262513e-04*V);
+}
+
+
+/** @brief sRGB to Y'CbCr Luma + Chroma */
+void Rgb2Ycbcr(double *Y, double *Cb, double *Cr, double R, double G, double B)
+{
+ *Y = (double)( 65.481*R + 128.553*G + 24.966*B + 16);
+ *Cb = (double)(-37.797*R - 74.203*G + 112.0 *B + 128);
+ *Cr = (double)(112.0 *R - 93.786*G - 18.214*B + 128);
+}
+
+
+/** @brief Y'CbCr to sRGB */
+void Ycbcr2Rgb(double *R, double *G, double *B, double Y, double Cr, double Cb)
+{
+ Y -= 16;
+ Cb -= 128;
+ Cr -= 128;
+ *R = (double)(0.00456621004566210107*Y + 1.1808799897946415e-09*Cr + 0.00625892896994393634*Cb);
+ *G = (double)(0.00456621004566210107*Y - 0.00153632368604490212*Cr - 0.00318811094965570701*Cb);
+ *B = (double)(0.00456621004566210107*Y + 0.00791071623355474145*Cr + 1.1977497040190077e-08*Cb);
+}
+
+
+/** @brief sRGB to JPEG-Y'CbCr Luma + Chroma */
+void Rgb2Jpegycbcr(double *Y, double *Cb, double *Cr, double R, double G, double B)
+{
+ Rgb2Ypbpr(Y, Cb, Cr, R, G, B);
+ *Cb += (double)0.5;
+ *Cr += (double)0.5;
+}
+
+/** @brief JPEG-Y'CbCr to sRGB */
+void Jpegycbcr2Rgb(double *R, double *G, double *B, double Y, double Cb, double Cr)
+{
+ Cb -= (double)0.5;
+ Cr -= (double)0.5;
+ Ypbpr2Rgb(R, G, B, Y, Cb, Cr);
+}
+
+
+/** @brief sRGB to Y'PbPr Luma (ITU-R BT.601) + Chroma */
+void Rgb2Ypbpr(double *Y, double *Pb, double *Pr, double R, double G, double B)
+{
+ *Y = (double)( 0.299 *R + 0.587 *G + 0.114 *B);
+ *Pb = (double)(-0.1687367*R - 0.331264*G + 0.5 *B);
+ *Pr = (double)( 0.5 *R - 0.418688*G - 0.081312*B);
+}
+
+
+/** @brief Y'PbPr to sRGB */
+void Ypbpr2Rgb(double *R, double *G, double *B, double Y, double Pb, double Pr)
+{
+ *R = (double)(0.99999999999914679361*Y - 1.2188941887145875e-06*Pb + 1.4019995886561440468*Pr);
+ *G = (double)(0.99999975910502514331*Y - 0.34413567816504303521*Pb - 0.71413649331646789076*Pr);
+ *B = (double)(1.00000124040004623180*Y + 1.77200006607230409200*Pb + 2.1453384174593273e-06*Pr);
+}
+
+
+/** @brief sRGB to SECAM Y'DbDr Luma + Chroma */
+void Rgb2Ydbdr(double *Y, double *Db, double *Dr, double R, double G, double B)
+{
+ *Y = (double)( 0.299*R + 0.587*G + 0.114*B);
+ *Db = (double)(-0.450*R - 0.883*G + 1.333*B);
+ *Dr = (double)(-1.333*R + 1.116*G + 0.217*B);
+}
+
+
+/** @brief SECAM Y'DbDr to sRGB */
+void Ydbdr2Rgb(double *R, double *G, double *B, double Y, double Db, double Dr)
+{
+ *R = (double)(Y + 9.2303716147657e-05*Db - 0.52591263066186533*Dr);
+ *G = (double)(Y - 0.12913289889050927*Db + 0.26789932820759876*Dr);
+ *B = (double)(Y + 0.66467905997895482*Db - 7.9202543533108e-05*Dr);
+}
+
+
+/** @brief sRGB to NTSC YIQ */
+void Rgb2Yiq(double *Y, double *I, double *Q, double R, double G, double B)
+{
+ *Y = (double)(0.299 *R + 0.587 *G + 0.114 *B);
+ *I = (double)(0.595716*R - 0.274453*G - 0.321263*B);
+ *Q = (double)(0.211456*R - 0.522591*G + 0.311135*B);
+}
+
+
+/** @brief Convert NTSC YIQ to sRGB */
+void Yiq2Rgb(double *R, double *G, double *B, double Y, double I, double Q)
+{
+ *R = (double)(Y + 0.9562957197589482261*I + 0.6210244164652610754*Q);
+ *G = (double)(Y - 0.2721220993185104464*I - 0.6473805968256950427*Q);
+ *B = (double)(Y - 1.1069890167364901945*I + 1.7046149983646481374*Q);
+}
+
+
+
+/*
+ * == Hue Saturation Value/Lightness/Intensity color transformations ==
+ *
+ * The following routines implement transformations between sRGB and
+ * color spaces HSV, HSL, and HSI.
+ */
+
+
+/**
+ * @brief Convert an sRGB color to Hue-Saturation-Value (HSV)
+ *
+ * @param H, S, V pointers to hold the result
+ * @param R, G, B the input sRGB values scaled in [0,1]
+ *
+ * This routine transforms from sRGB to the hexcone HSV color space. The
+ * sRGB values are assumed to be between 0 and 1. The output values are
+ * H = hexagonal hue angle (0 <= H < 360),
+ * S = C/V (0 <= S <= 1),
+ * V = max(R',G',B') (0 <= V <= 1),
+ * where C = max(R',G',B') - min(R',G',B'). The inverse color transformation
+ * is given by Hsv2Rgb.
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/HSL_and_HSV
+ */
+void Rgb2Hsv(double *H, double *S, double *V, double R, double G, double B)
+{
+ double Max = MAX3(R, G, B);
+ double Min = MIN3(R, G, B);
+ double C = Max - Min;
+
+
+ *V = Max;
+
+ if(C > 0)
+ {
+ if(Max == R)
+ {
+ *H = (G - B) / C;
+
+ if(G < B)
+ *H += 6;
+ }
+ else if(Max == G)
+ *H = 2 + (B - R) / C;
+ else
+ *H = 4 + (R - G) / C;
+
+ *H *= 60;
+ *S = C / Max;
+ }
+ else
+ *H = *S = 0;
+}
+
+
+/**
+ * @brief Convert a Hue-Saturation-Value (HSV) color to sRGB
+ *
+ * @param R, G, B pointers to hold the result
+ * @param H, S, V the input HSV values
+ *
+ * The input values are assumed to be scaled as
+ * 0 <= H < 360,
+ * 0 <= S <= 1,
+ * 0 <= V <= 1.
+ * The output sRGB values are scaled between 0 and 1. This is the inverse
+ * transformation of Rgb2Hsv.
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/HSL_and_HSV
+ */
+void Hsv2Rgb(double *R, double *G, double *B, double H, double S, double V)
+{
+ double C = S * V;
+ double Min = V - C;
+ double X;
+
+
+ H -= 360*floor(H/360);
+ H /= 60;
+ X = C*(1 - fabs(H - 2*floor(H/2) - 1));
+
+ switch((int)H)
+ {
+ case 0:
+ *R = Min + C;
+ *G = Min + X;
+ *B = Min;
+ break;
+ case 1:
+ *R = Min + X;
+ *G = Min + C;
+ *B = Min;
+ break;
+ case 2:
+ *R = Min;
+ *G = Min + C;
+ *B = Min + X;
+ break;
+ case 3:
+ *R = Min;
+ *G = Min + X;
+ *B = Min + C;
+ break;
+ case 4:
+ *R = Min + X;
+ *G = Min;
+ *B = Min + C;
+ break;
+ case 5:
+ *R = Min + C;
+ *G = Min;
+ *B = Min + X;
+ break;
+ default:
+ *R = *G = *B = 0;
+ }
+}
+
+
+/**
+ * @brief Convert an sRGB color to Hue-Saturation-Lightness (HSL)
+ *
+ * @param H, S, L pointers to hold the result
+ * @param R, G, B the input sRGB values scaled in [0,1]
+ *
+ * This routine transforms from sRGB to the double hexcone HSL color space
+ * The sRGB values are assumed to be between 0 and 1. The outputs are
+ * H = hexagonal hue angle (0 <= H < 360),
+ * S = { C/(2L) if L <= 1/2 (0 <= S <= 1),
+ * { C/(2 - 2L) if L > 1/2
+ * L = (max(R',G',B') + min(R',G',B'))/2 (0 <= L <= 1),
+ * where C = max(R',G',B') - min(R',G',B'). The inverse color transformation
+ * is given by Hsl2Rgb.
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/HSL_and_HSV
+ */
+void Rgb2Hsl(double *H, double *S, double *L, double R, double G, double B)
+{
+ double Max = MAX3(R, G, B);
+ double Min = MIN3(R, G, B);
+ double C = Max - Min;
+
+
+ *L = (Max + Min)/2;
+
+ if(C > 0)
+ {
+ if(Max == R)
+ {
+ *H = (G - B) / C;
+
+ if(G < B)
+ *H += 6;
+ }
+ else if(Max == G)
+ *H = 2 + (B - R) / C;
+ else
+ *H = 4 + (R - G) / C;
+
+ *H *= 60;
+ *S = (*L <= 0.5) ? (C/(2*(*L))) : (C/(2 - 2*(*L)));
+ }
+ else
+ *H = *S = 0;
+}
+
+
+/**
+ * @brief Convert a Hue-Saturation-Lightness (HSL) color to sRGB
+ *
+ * @param R, G, B pointers to hold the result
+ * @param H, S, L the input HSL values
+ *
+ * The input values are assumed to be scaled as
+ * 0 <= H < 360,
+ * 0 <= S <= 1,
+ * 0 <= L <= 1.
+ * The output sRGB values are scaled between 0 and 1. This is the inverse
+ * transformation of Rgb2Hsl.
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/HSL_and_HSV
+ */
+void Hsl2Rgb(double *R, double *G, double *B, double H, double S, double L)
+{
+ double C = (L <= 0.5) ? (2*L*S) : ((2 - 2*L)*S);
+ double Min = L - 0.5*C;
+ double X;
+
+
+ H -= 360*floor(H/360);
+ H /= 60;
+ X = C*(1 - fabs(H - 2*floor(H/2) - 1));
+
+ switch((int)H)
+ {
+ case 0:
+ *R = Min + C;
+ *G = Min + X;
+ *B = Min;
+ break;
+ case 1:
+ *R = Min + X;
+ *G = Min + C;
+ *B = Min;
+ break;
+ case 2:
+ *R = Min;
+ *G = Min + C;
+ *B = Min + X;
+ break;
+ case 3:
+ *R = Min;
+ *G = Min + X;
+ *B = Min + C;
+ break;
+ case 4:
+ *R = Min + X;
+ *G = Min;
+ *B = Min + C;
+ break;
+ case 5:
+ *R = Min + C;
+ *G = Min;
+ *B = Min + X;
+ break;
+ default:
+ *R = *G = *B = 0;
+ }
+}
+
+
+/**
+ * @brief Convert an sRGB color to Hue-Saturation-Intensity (HSI)
+ *
+ * @param H, S, I pointers to hold the result
+ * @param R, G, B the input sRGB values scaled in [0,1]
+ *
+ * This routine transforms from sRGB to the cylindrical HSI color space. The
+ * sRGB values are assumed to be between 0 and 1. The output values are
+ * H = polar hue angle (0 <= H < 360),
+ * S = 1 - min(R',G',B')/I (0 <= S <= 1),
+ * I = (R'+G'+B')/3 (0 <= I <= 1).
+ * The inverse color transformation is given by Hsi2Rgb.
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/HSL_and_HSV
+ */
+void Rgb2Hsi(double *H, double *S, double *I, double R, double G, double B)
+{
+ double alpha = 0.5*(2*R - G - B);
+ double beta = 0.866025403784439*(G - B);
+
+
+ *I = (R + G + B)/3;
+
+ if(*I > 0)
+ {
+ *S = 1 - MIN3(R,G,B) / *I;
+ *H = atan2(beta, alpha)*(180/M_PI);
+
+ if(*H < 0)
+ *H += 360;
+ }
+ else
+ *H = *S = 0;
+}
+
+
+/**
+ * @brief Convert a Hue-Saturation-Intesity (HSI) color to sRGB
+ *
+ * @param R, G, B pointers to hold the result
+ * @param H, S, I the input HSI values
+ *
+ * The input values are assumed to be scaled as
+ * 0 <= H < 360,
+ * 0 <= S <= 1,
+ * 0 <= I <= 1.
+ * The output sRGB values are scaled between 0 and 1. This is the inverse
+ * transformation of Rgb2Hsi.
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/HSL_and_HSV
+ */
+void Hsi2Rgb(double *R, double *G, double *B, double H, double S, double I)
+{
+ H -= 360*floor(H/360);
+
+ if(H < 120)
+ {
+ *B = I*(1 - S);
+ *R = I*(1 + S*cos(H*(M_PI/180))/cos((60 - H)*(M_PI/180)));
+ *G = 3*I - *R - *B;
+ }
+ else if(H < 240)
+ {
+ H -= 120;
+ *R = I*(1 - S);
+ *G = I*(1 + S*cos(H*(M_PI/180))/cos((60 - H)*(M_PI/180)));
+ *B = 3*I - *R - *G;
+ }
+ else
+ {
+ H -= 240;
+ *G = I*(1 - S);
+ *B = I*(1 + S*cos(H*(M_PI/180))/cos((60 - H)*(M_PI/180)));
+ *R = 3*I - *G - *B;
+ }
+}
+
+
+/*
+ * == CIE color transformations ==
+ *
+ * The following routines implement transformations between sRGB and
+ * the CIE color spaces XYZ, L*a*b, L*u*v*, and L*C*H*. These
+ * transforms assume a 2 degree observer angle and a D65 illuminant.
+ */
+
+
+/**
+ * @brief Transform sRGB to CIE XYZ with the D65 white point
+ *
+ * @param X, Y, Z pointers to hold the result
+ * @param R, G, B the input sRGB values
+ *
+ * Poynton, "Frequently Asked Questions About Color," page 10
+ * Wikipedia: http://en.wikipedia.org/wiki/SRGB
+ * Wikipedia: http://en.wikipedia.org/wiki/CIE_1931_color_space
+ */
+void Rgb2Xyz(double *X, double *Y, double *Z, double R, double G, double B)
+{
+ R = INVGAMMACORRECTION(R);
+ G = INVGAMMACORRECTION(G);
+ B = INVGAMMACORRECTION(B);
+ *X = (double)(0.4123955889674142161*R + 0.3575834307637148171*G + 0.1804926473817015735*B);
+ *Y = (double)(0.2125862307855955516*R + 0.7151703037034108499*G + 0.07220049864333622685*B);
+ *Z = (double)(0.01929721549174694484*R + 0.1191838645808485318*G + 0.9504971251315797660*B);
+}
+
+
+/**
+ * @brief Transform CIE XYZ to sRGB with the D65 white point
+ *
+ * @param R, G, B pointers to hold the result
+ * @param X, Y, Z the input XYZ values
+ *
+ * Official sRGB specification (IEC 61966-2-1:1999)
+ * Poynton, "Frequently Asked Questions About Color," page 10
+ * Wikipedia: http://en.wikipedia.org/wiki/SRGB
+ * Wikipedia: http://en.wikipedia.org/wiki/CIE_1931_color_space
+ */
+void Xyz2Rgb(double *R, double *G, double *B, double X, double Y, double Z)
+{
+ double R1, B1, G1, Min;
+
+
+ R1 = (double)( 3.2406*X - 1.5372*Y - 0.4986*Z);
+ G1 = (double)(-0.9689*X + 1.8758*Y + 0.0415*Z);
+ B1 = (double)( 0.0557*X - 0.2040*Y + 1.0570*Z);
+
+ Min = MIN3(R1, G1, B1);
+
+ /* Force nonnegative values so that gamma correction is well-defined. */
+ if(Min < 0)
+ {
+ R1 -= Min;
+ G1 -= Min;
+ B1 -= Min;
+ }
+
+ /* Transform from RGB to R'G'B' */
+ *R = GAMMACORRECTION(R1);
+ *G = GAMMACORRECTION(G1);
+ *B = GAMMACORRECTION(B1);
+}
+
+
+/**
+ * Convert CIE XYZ to CIE L*a*b* (CIELAB) with the D65 white point
+ *
+ * @param L, a, b pointers to hold the result
+ * @param X, Y, Z the input XYZ values
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/Lab_color_space
+ */
+void Xyz2Lab(double *L, double *a, double *b, double X, double Y, double Z)
+{
+ X /= WHITEPOINT_X;
+ Y /= WHITEPOINT_Y;
+ Z /= WHITEPOINT_Z;
+ X = LABF(X);
+ Y = LABF(Y);
+ Z = LABF(Z);
+ *L = 116*Y - 16;
+ *a = 500*(X - Y);
+ *b = 200*(Y - Z);
+}
+
+
+/**
+ * Convert CIE L*a*b* (CIELAB) to CIE XYZ with the D65 white point
+ *
+ * @param X, Y, Z pointers to hold the result
+ * @param L, a, b the input L*a*b* values
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/Lab_color_space
+ */
+void Lab2Xyz(double *X, double *Y, double *Z, double L, double a, double b)
+{
+ L = (L + 16)/116;
+ a = L + a/500;
+ b = L - b/200;
+ *X = WHITEPOINT_X*LABINVF(a);
+ *Y = WHITEPOINT_Y*LABINVF(L);
+ *Z = WHITEPOINT_Z*LABINVF(b);
+}
+
+
+/**
+ * Convert CIE XYZ to CIE L*u*v* (CIELUV) with the D65 white point
+ *
+ * @param L, u, v pointers to hold the result
+ * @param X, Y, Z the input XYZ values
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/CIELUV_color_space
+ */
+void Xyz2Luv(double *L, double *u, double *v, double X, double Y, double Z)
+{
+ double u1, v1, Denom;
+
+
+ if((Denom = X + 15*Y + 3*Z) > 0)
+ {
+ u1 = (4*X) / Denom;
+ v1 = (9*Y) / Denom;
+ }
+ else
+ u1 = v1 = 0;
+
+ Y /= WHITEPOINT_Y;
+ Y = LABF(Y);
+ *L = 116*Y - 16;
+ *u = 13*(*L)*(u1 - WHITEPOINT_U);
+ *v = 13*(*L)*(v1 - WHITEPOINT_V);
+}
+
+
+/**
+ * Convert CIE L*u*v* (CIELUV) to CIE XYZ with the D65 white point
+ *
+ * @param X, Y, Z pointers to hold the result
+ * @param L, u, v the input L*u*v* values
+ *
+ * Wikipedia: http://en.wikipedia.org/wiki/CIELUV_color_space
+ */
+void Luv2Xyz(double *X, double *Y, double *Z, double L, double u, double v)
+{
+ *Y = (L + 16)/116;
+ *Y = WHITEPOINT_Y*LABINVF(*Y);
+
+ if(L != 0)
+ {
+ u /= L;
+ v /= L;
+ }
+
+ u = u/13 + WHITEPOINT_U;
+ v = v/13 + WHITEPOINT_V;
+ *X = (*Y) * ((9*u)/(4*v));
+ *Z = (*Y) * ((3 - 0.75*u)/v - 5);
+}
+
+
+/**
+ * Convert CIE XYZ to CIE L*C*H* with the D65 white point
+ *
+ * @param L, C, H pointers to hold the result
+ * @param X, Y, Z the input XYZ values
+ *
+ * CIE L*C*H* is related to CIE L*a*b* by
+ * a* = C* cos(H* pi/180),
+ * b* = C* sin(H* pi/180).
+ */
+void Xyz2Lch(double *L, double *C, double *H, double X, double Y, double Z)
+{
+ double a, b;
+
+
+ Xyz2Lab(L, &a, &b, X, Y, Z);
+ *C = sqrt(a*a + b*b);
+ *H = atan2(b, a)*180.0/M_PI;
+
+ if(*H < 0)
+ *H += 360;
+}
+
+/**
+ * Convert CIE L*C*H* to CIE XYZ with the D65 white point
+ *
+ * @param X, Y, Z pointers to hold the result
+ * @param L, C, H the input L*C*H* values
+ */
+void Lch2Xyz(double *X, double *Y, double *Z, double L, double C, double H)
+{
+ double a = C * cos(H*(M_PI/180.0));
+ double b = C * sin(H*(M_PI/180.0));
+
+
+ Lab2Xyz(X, Y, Z, L, a, b);
+}
+
+
+/** @brief XYZ to CAT02 LMS */
+void Xyz2Cat02lms(double *L, double *M, double *S, double X, double Y, double Z)
+{
+ *L = (double)( 0.7328*X + 0.4296*Y - 0.1624*Z);
+ *M = (double)(-0.7036*X + 1.6975*Y + 0.0061*Z);
+ *S = (double)( 0.0030*X + 0.0136*Y + 0.9834*Z);
+}
+
+
+/** @brief CAT02 LMS to XYZ */
+void Cat02lms2Xyz(double *X, double *Y, double *Z, double L, double M, double S)
+{
+ *X = (double)( 1.096123820835514*L - 0.278869000218287*M + 0.182745179382773*S);
+ *Y = (double)( 0.454369041975359*L + 0.473533154307412*M + 0.072097803717229*S);
+ *Z = (double)(-0.009627608738429*L - 0.005698031216113*M + 1.015325639954543*S);
+}
+
+
+/*
+ * == Glue functions for multi-stage transforms ==
+ */
+
+void Rgb2Lab(double *L, double *a, double *b, double R, double G, double B)
+{
+ double X, Y, Z;
+ Rgb2Xyz(&X, &Y, &Z, R, G, B);
+ Xyz2Lab(L, a, b, X, Y, Z);
+}
+
+
+void Lab2Rgb(double *R, double *G, double *B, double L, double a, double b)
+{
+ double X, Y, Z;
+ Lab2Xyz(&X, &Y, &Z, L, a, b);
+ Xyz2Rgb(R, G, B, X, Y, Z);
+}
+
+
+void Rgb2Luv(double *L, double *u, double *v, double R, double G, double B)
+{
+ double X, Y, Z;
+ Rgb2Xyz(&X, &Y, &Z, R, G, B);
+ Xyz2Luv(L, u, v, X, Y, Z);
+}
+
+
+void Luv2Rgb(double *R, double *G, double *B, double L, double u, double v)
+{
+ double X, Y, Z;
+ Luv2Xyz(&X, &Y, &Z, L, u, v);
+ Xyz2Rgb(R, G, B, X, Y, Z);
+}
+
+void Rgb2Lch(double *L, double *C, double *H, double R, double G, double B)
+{
+ double X, Y, Z;
+ Rgb2Xyz(&X, &Y, &Z, R, G, B);
+ Xyz2Lch(L, C, H, X, Y, Z);
+}
+
+
+void Lch2Rgb(double *R, double *G, double *B, double L, double C, double H)
+{
+ double X, Y, Z;
+ Lch2Xyz(&X, &Y, &Z, L, C, H);
+ Xyz2Rgb(R, G, B, X, Y, Z);
+}
+
+
+void Rgb2Cat02lms(double *L, double *M, double *S, double R, double G, double B)
+{
+ double X, Y, Z;
+ Rgb2Xyz(&X, &Y, &Z, R, G, B);
+ Xyz2Cat02lms(L, M, S, X, Y, Z);
+}
+
+
+void Cat02lms2Rgb(double *R, double *G, double *B, double L, double M, double S)
+{
+ double X, Y, Z;
+ Cat02lms2Xyz(&X, &Y, &Z, L, M, S);
+ Xyz2Rgb(R, G, B, X, Y, Z);
+}
+
+} /* namespace */
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