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/*********************************************************************
* kd-forest *
* Copyright (C) 2014 Tavian Barnes <tavianator@tavianator.com> *
* *
* This program is free software. It comes without any warranty, to *
* the extent permitted by applicable law. You can redistribute it *
* and/or modify it under the terms of the Do What The Fuck You Want *
* To Public License, Version 2, as published by Sam Hocevar. See *
* the COPYING file or http://www.wtfpl.net/ for more details. *
*********************************************************************/
#include "color.h"
#include <math.h>
void
color_unpack(uint8_t pixel[3], uint32_t color)
{
pixel[0] = (color >> 16) & 0xFF;
pixel[1] = (color >> 8) & 0xFF;
pixel[2] = color & 0xFF;
}
void
color_set_RGB(double coords[3], uint32_t color)
{
uint8_t pixel[3];
color_unpack(pixel, color);
for (int i = 0; i < 3; ++i) {
coords[i] = pixel[i]/255.0;
}
}
// Inverse gamma for sRGB
double
sRGB_C_inv(double t)
{
if (t <= 0.040449936) {
return t/12.92;
} else {
return pow((t + 0.055)/1.055, 2.4);
}
}
static void
color_set_XYZ(double XYZ[3], uint32_t color)
{
double RGB[3];
color_set_RGB(RGB, color);
RGB[0] = sRGB_C_inv(RGB[0]);
RGB[1] = sRGB_C_inv(RGB[1]);
RGB[2] = sRGB_C_inv(RGB[2]);
XYZ[0] = 0.4123808838268995*RGB[0] + 0.3575728355732478*RGB[1] + 0.1804522977447919*RGB[2];
XYZ[1] = 0.2126198631048975*RGB[0] + 0.7151387878413206*RGB[1] + 0.0721499433963131*RGB[2];
XYZ[2] = 0.0193434956789248*RGB[0] + 0.1192121694056356*RGB[1] + 0.9505065664127130*RGB[2];
}
// CIE L*a*b* and L*u*v* gamma
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;
}
}
// sRGB white point (CIE D50) in XYZ coordinates
static const double WHITE[] = {
[0] = 0.9504060171449392,
[1] = 0.9999085943425312,
[2] = 1.089062231497274,
};
void
color_set_Lab(double coords[3], uint32_t color)
{
double XYZ[3];
color_set_XYZ(XYZ, color);
double fXYZ[] = {
[0] = Lab_f(XYZ[0]/WHITE[0]),
[1] = Lab_f(XYZ[1]/WHITE[1]),
[2] = Lab_f(XYZ[2]/WHITE[2]),
};
coords[0] = 116.0*fXYZ[1] - 16.0;
coords[1] = 500.0*(fXYZ[0] - fXYZ[1]);
coords[2] = 200.0*(fXYZ[1] - fXYZ[2]);
}
void
color_set_Luv(double coords[3], uint32_t color)
{
double XYZ[3];
color_set_XYZ(XYZ, color);
double uv_denom = XYZ[0] + 15.0*XYZ[1] + 3.0*XYZ[2];
if (uv_denom == 0.0) {
coords[0] = 0.0;
coords[1] = 0.0;
coords[2] = 0.0;
return;
}
double white_uv_denom = WHITE[0] + 16.0*WHITE[1] + 3.0*WHITE[2];
double fY = Lab_f(XYZ[1]/WHITE[1]);
double uprime = 4.0*XYZ[0]/uv_denom;
double unprime = 4.0*WHITE[0]/white_uv_denom;
double vprime = 9.0*XYZ[1]/uv_denom;
double vnprime = 9.0*WHITE[1]/white_uv_denom;
coords[0] = 116.0*fY - 16.0;
coords[1] = 13.0*coords[0]*(uprime - unprime);
coords[2] = 13.0*coords[0]*(vprime - vnprime);
}
int
color_comparator(const void *a, const void *b)
{
uint8_t aRGB[3], bRGB[3];
color_unpack(aRGB, *(uint32_t *)a);
color_unpack(bRGB, *(uint32_t *)b);
int anum = aRGB[1] - aRGB[2], adenom = 2*aRGB[0] - aRGB[1] - aRGB[2];
int bnum = bRGB[1] - bRGB[2], bdenom = 2*bRGB[0] - bRGB[1] - bRGB[2];
// The hue angle is defined as atan2(sqrt(3)*n/d) (+ 2*pi if negative). But
// since atan2() is expensive, we compute an equivalent ordering while
// avoiding trig calls. First, handle the quadrants. We have:
//
// hue(n, d)
// | d >= 0 && n == 0 = 0
// | d >= 0 && n > 0 = atan(n/d)
// | d >= 0 && n < 0 = atan(n/d) + 2*pi
// | d < 0 = atan(n/d) + pi
//
// and since atan(n/d)'s range is [-pi/2, pi/2], each chunk can be strictly
// ordered relative to the other chunks.
if (adenom >= 0) {
if (anum >= 0) {
if (bdenom < 0 || bnum < 0) {
return -1;
}
} else {
if (bdenom < 0 || bnum >= 0) {
return 1;
}
}
} else if (bdenom >= 0) {
if (bnum >= 0) {
return 1;
} else {
return -1;
}
}
// Special-case zero numerators, because we treat 0/0 as 0, not NaN
if (anum == 0 || bnum == 0) {
int lhs = adenom >= 0 ? anum : -anum;
int rhs = bdenom >= 0 ? bnum : -bnum;
return lhs - rhs;
}
// The points are in the same/comparable quadrants. We can still avoid
// calculating atan(n/d) though, because it's an increasing function in n/d.
// We can also avoid a division, by noting that an/ad < bn/bd iff
// an*bd*sgn(ad*bd) < bn*ad*sgn(ad*bd). Due to the logic above, both
// denominators must have the same sign, so the sgn()s are redundant.
int lhs = anum*bdenom;
int rhs = bnum*adenom;
return lhs - rhs;
}
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