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Diffstat (limited to 'src/trace/cielab.cpp')
| -rw-r--r-- | src/trace/cielab.cpp | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/src/trace/cielab.cpp b/src/trace/cielab.cpp new file mode 100644 index 0000000..222fb91 --- /dev/null +++ b/src/trace/cielab.cpp @@ -0,0 +1,216 @@ +// 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 |