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#include <math.h>
#define TAU 6.283185307179586476925287
void hcl2lab(double* L, double* a, double* b, double h, double c, double l) {
double r;
*L=l*0.7;
r=0.426*c;
double angle = TAU/6.0-h*TAU;
*a = sin(angle)*r;
*b = cos(angle)*r;
}
double finv(double t) {
return (t>(6.0/29.0))?(t*t*t):(3*(6.0/29.0)*(6.0/29.0)*(t-4.0/29.0));
}
void lab2xyz(double* x, double* y, double* z, double l, double a, double b) {
double sl = (l+0.16)/1.16;
double ill[3] = {0.9643,1.00,0.8251}; //D50
*y = ill[1] * finv(sl);
*x = ill[0] * finv(sl + (a/5.0));
*z = ill[2] * finv(sl - (b/2.0));
}
void hcl2xyz(double *x, double *y, double *z, double h, double c, double l) {
double L, a, b;
hcl2lab(&L,&a,&b,h,c,l);
lab2xyz(x,y,z,L,a,b);
}
double correct(double cl) {
double a = 0.055;
return (cl<=0.0031308)?(12.92*cl):((1+a)*pow(cl,1/2.4)-a);
}
/* Convert from XYZ doubles to sRGB bytes */
void xyz2rgb(unsigned char* r, unsigned char* g, unsigned char* b, double x, double y, double z) {
double rl = 3.2406*x - 1.5372*y - 0.4986*z;
double gl = -0.9689*x + 1.8758*y + 0.0415*z;
double bl = 0.0557*x - 0.2040*y + 1.0570*z;
int clip = (rl < 0.001 || rl > 0.999 || gl < 0.001 || gl > 0.999 || bl < 0.001 || bl > 0.999);
if(clip) {
rl = (rl<0.001)?0.0:((rl>0.999)?1.0:rl);
gl = (gl<0.001)?0.0:((gl>0.999)?1.0:gl);
bl = (bl<0.001)?0.0:((bl>0.999)?1.0:bl);
}
*r = (unsigned char)(255.0*correct(rl));
*g = (unsigned char)(255.0*correct(gl));
*b = (unsigned char)(255.0*correct(bl));
}
/* Convert from LAB doubles to sRGB bytes */
void lab2rgb(unsigned char* R, unsigned char* G, unsigned char* 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 xyz2pix(void* rgb, double x, double y, double z) {
unsigned char* ptr = (unsigned char*)rgb;
xyz2rgb(ptr,ptr+1,ptr+2,x,y,z);
}
void lab2pix(void* rgb, double l, double a, double b) {
unsigned char* ptr = (unsigned char*)rgb;
lab2rgb(ptr,ptr+1,ptr+2,l,a,b);
}
/* Convert from a qualitative parameter h and a quantitative parameter l to a 24-bit pixel */
void hl2pix(void* rgb, double h, double l) {
unsigned char* ptr = (unsigned char*)rgb;
double L,r;
L = l*0.7; //L of L*a*b*
r = l*0.301+0.125; //chroma
double angle = TAU/6.0-h*TAU;
double a = sin(angle)*r;
double b = cos(angle)*r;
lab2rgb(ptr,ptr+1,ptr+2,L,a,b);
}
/* Convert from a qualitative parameter h and two quantitative parameter c and l to a 24-bit pixel */
void hcl2pix(void* rgb, double h, double c, double l) {
double L, a, b;
hcl2lab(&L,&a,&b,h,c,l);
lab2pix(rgb,L,a,b);
}