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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Copyright 2005, 2006 by Gerald Friedland, Kristian Jantz and Lars Knipping
* Conversion to C++ for Inkscape by Bob Jamison
* Released under GNU GPL v2+, read the file 'COPYING' for more information.
*/
#include <algorithm>
#include <cmath>
#include "cielab.h"
namespace Inkscape {
namespace Trace {
namespace {
/**
* Convert integer RGB values into a pixel value.
*/
uint32_t getRGB(int r, int g, int b)
{
r = std::clamp(r, 0, 255);
g = std::clamp(g, 0, 255);
b = std::clamp(b, 0, 255);
return (r << 16) | (g << 8) | b;
}
/**
* Convert float RGB values (0.0-1.0) into a pixel value.
*/
uint32_t getRGB(float r, float g, float b)
{
return getRGB((int)(r * 256.0f),
(int)(g * 256.0f),
(int)(b * 256.0f));
}
//#########################################
//# Root approximations for large speedup.
//# By njh!
//#########################################
class Tables
{
public:
static int constexpr SIZE = 16;
float cbrt[SIZE + 1];
float qn[SIZE + 1];
static auto &get()
{
static Tables const instance;
return instance;
}
private:
Tables();
};
template <typename T>
auto sq(T t)
{
return t * t;
}
// Cube root.
double cbrt(double x)
{
auto polish = [x] (double y) {
return (2.0 * y + x / sq(y)) / 3.0;
};
double y = Tables::get().cbrt[(int)(x * Tables::SIZE)]; // assuming x \in [0, 1]
y = polish(y);
y = polish(y);
return y;
}
// Quintic root.
double qnrt(double x)
{
auto polish = [x] (double y) {
return (4.0 * y + x / sq(sq(y))) / 5.0;
};
double y = Tables::get().qn[(int)(x * Tables::SIZE)]; // assuming x \in [0, 1]
y = polish(y);
y = polish(y);
return y;
}
double pow24(double x)
{
return sq(x * qnrt(x));
}
Tables::Tables()
{
auto entry = [&] (int i, float x) {
cbrt[i] = std::pow(x / SIZE, 0.3333f);
qn[i] = std::pow(x / SIZE, 0.2f);
};
entry(0, 0.5f);
for (int i = 1; i < SIZE + 1; i++) {
entry(i, i);
}
}
} // namespace
CieLab::CieLab(uint32_t rgb)
{
uint8_t ir = (rgb >> 16) & 0xff;
uint8_t ig = (rgb >> 8) & 0xff;
uint8_t ib = (rgb ) & 0xff;
float fr = ir / 255.0f;
float fg = ig / 255.0f;
float fb = ib / 255.0f;
// printf("fr:%f fg:%f fb:%f\n", fr, fg, fb);
auto to_linear = [] (float &x) {
if (x > 0.04045) {
x = pow24((x + 0.055) / 1.055);
} else {
x /= 12.92;
}
};
to_linear(fr);
to_linear(fg);
to_linear(fb);
// Use white = D65
float x = fr * 0.4124 + fg * 0.3576 + fb * 0.1805;
float y = fr * 0.2126 + fg * 0.7152 + fb * 0.0722;
float z = fr * 0.0193 + fg * 0.1192 + fb * 0.9505;
float vx = x / 0.95047;
float vy = y;
float vz = z / 1.08883;
// printf("vx:%f vy:%f vz:%f\n", vx, vy, vz);
auto f = [] (float &x) {
if (x > 0.008856) {
x = cbrt(x);
} else {
x = (7.787 * x) + (16.0 / 116.0);
}
};
f(vx);
f(vy);
f(vz);
C = 0;
L = 116.0 * vy - 16.0;
A = 500.0 * (vx - vy);
B = 200.0 * (vy - vz);
}
uint32_t CieLab::toRGB() const
{
float vy = (L + 16.0) / 116.0;
float vx = A / 500.0 + vy;
float vz = vy - B / 200.0;
auto finv = [] (float &x) {
float x3 = x * x * x;
if (x3 > 0.008856) {
x = x3;
} else {
x = (x - 16.0 / 116.0) / 7.787;
}
};
finv(vx);
finv(vy);
finv(vz);
vx *= 0.95047; // use white = D65
vz *= 1.08883;
float vr = vx * 3.2406 + vy * -1.5372 + vz * -0.4986;
float vg = vx * -0.9689 + vy * 1.8758 + vz * 0.0415;
float vb = vx * 0.0557 + vy * -0.2040 + vz * 1.0570;
auto from_linear = [] (float &x) {
if (x > 0.0031308) {
x = 1.055 * std::pow(x, 1.0 / 2.4) - 0.055;
} else {
x *= 12.92;
}
};
from_linear(vr);
from_linear(vg);
from_linear(vb);
return getRGB(vr, vg, vb);
}
float CieLab::diffSq(CieLab const &c1, CieLab const &c2)
{
return sq(c1.L - c2.L)
+ sq(c1.A - c2.A)
+ sq(c1.B - c2.B);
}
float CieLab::diff(CieLab const &c1, CieLab const &c2)
{
return std::sqrt(diffSq(c1, c2));
}
} // namespace Trace
} // namespace Inkscape
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