gtk/gdk/gdkcolordefs.h

/* gdkcolordefs.h
 *
 * Copyright 2024 Matthias Clasen
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library. If not, see <http://www.gnu.org/licenses/>.
 */

/* Note that this header is shared between the color state implementation
 * and tests, and must not include other headers.
 */

static inline float
srgb_oetf (float v)
{
  if (v > 0.0031308f)
    return 1.055f * powf (v, 1.f / 2.4f) - 0.055f;
  else
    return 12.92f * v;
}

static inline float
srgb_eotf (float v)
{
  if (v >= 0.04045f)
    return powf (((v + 0.055f) / (1.f + 0.055f)), 2.4f);
  else
    return v / 12.92f;
}

static inline float
pq_eotf (float v)
{
  float ninv = (1 << 14) / 2610.0;
  float minv = (1 << 5) / 2523.0;
  float c1 = 3424.0 / (1 << 12);
  float c2 = 2413.0 / (1 << 7);
  float c3 = 2392.0 / (1 << 7);

  float x = powf (MAX ((powf (v, minv) - c1), 0) / (c2 - (c3 * (powf (v, minv)))), ninv);

  return x * 10000 / 203.0;
}

static inline float
pq_oetf (float v)
{
  float x = v * 203.0 / 10000.0;
  float n = 2610.0 / (1 << 14);
  float m = 2523.0 / (1 << 5);
  float c1 = 3424.0 / (1 << 12);
  float c2 = 2413.0 / (1 << 7);
  float c3 = 2392.0 / (1 << 7);

  return powf (((c1 + (c2 * powf (x, n))) / (1 + (c3 * powf (x, n)))), m);
}

static inline float
bt709_eotf (float v)
{
  const float a = 1.099;
  const float d = 0.0812;

  if (v < d)
    return  v / 4.5f;
  else
    return powf ((v + (a - 1)) / a, 1 / 0.45f);
}

static inline float
bt709_oetf (float v)
{
  const float a = 1.099;
  const float b = 0.018;

  if (v < b)
    return v * 4.5f;
  else
    return a * powf (v, 0.45f) - (a - 1);
}

static inline float
hlg_eotf (float v)
{
  const float a = 0.17883277;
  const float b = 0.28466892;
  const float c = 0.55991073;

  if (v <= 0.5)
    return (v * v) / 3;
  else
    return (expf ((v - c) / a) + b) / 12.0;
}

static inline float
hlg_oetf (float v)
{
  const float a = 0.17883277;
  const float b = 0.28466892;
  const float c = 0.55991073;

  if (v <= 1/12.0)
    return sqrtf (3 * v);
  else
    return a * logf (12 * v - b) + c;
}

/* See http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html
 * for how to derive the abc_to_xyz matrices from chromaticity coordinates.
 */

static const float srgb_to_xyz[3][3] = {
  { 0.4124564,  0.3575761,  0.1804375 },
  { 0.2126729,  0.7151522,  0.0721750 },
  { 0.0193339,  0.1191920,  0.9503041 }
};

static const float xyz_to_srgb[3][3] = {
  {  3.2404542, -1.5371385, -0.4985314 },
  { -0.9692660,  1.8760108,  0.0415560 },
  {  0.0556434, -0.2040259,  1.0572252 },
};

static const float rec2020_to_xyz[3][3] = {
  { 0.6369580,  0.1446169,  0.1688810 },
  { 0.2627002,  0.6779981,  0.0593017 },
  { 0.0000000,  0.0280727,  1.0609851 }
};

static const float xyz_to_rec2020[3][3] = {
  {  1.7166512, -0.3556708, -0.2533663 },
  { -0.6666844,  1.6164812,  0.0157685 },
  {  0.0176399, -0.0427706,  0.9421031 },
};

static const float pal_to_xyz[3][3] = {
 { 0.4305538,  0.3415498,  0.1783523 },
 { 0.2220043,  0.7066548,  0.0713409 },
 { 0.0201822,  0.1295534,  0.9393222 },
};

static const float xyz_to_pal[3][3] = {
 {  3.0633611, -1.3933902, -0.4758237 },
 { -0.9692436,  1.8759675,  0.0415551 },
 {  0.0678610, -0.2287993,  1.0690896 },
};

static const float ntsc_to_xyz[3][3] = {
 { 0.3935209,  0.3652581,  0.1916769 },
 { 0.2123764,  0.7010599,  0.0865638 },
 { 0.0187391,  0.1119339,  0.9583847 },
};

static const float xyz_to_ntsc[3][3] = {
 {  3.5060033, -1.7397907, -0.5440583 },
 { -1.0690476,  1.9777789,  0.0351714 },
 {  0.0563066, -0.1969757,  1.0499523 },
};

static const float p3_to_xyz[3][3] = {
  { 0.4865709,  0.2656677,  0.1982173 },
  { 0.2289746,  0.6917385,  0.0792869 },
  { 0.0000000,  0.0451134,  1.0439444 },
};

static const float xyz_to_p3[3][3] = {
  {  2.4934969, -0.9313836, -0.4027108 },
  { -0.8294890,  1.7626641,  0.0236247 },
  {  0.0358458, -0.0761724,  0.9568845 },
};

/* premultiplied matrices for default conversions */

static const float rec2020_to_srgb[3][3] = {
  {  1.660227, -0.587548, -0.072838 },
  { -0.124553,  1.132926, -0.008350 },
  { -0.018155, -0.100603,  1.118998 },
};

static const float srgb_to_rec2020[3][3] = {
  { 0.627504, 0.329275, 0.043303 },
  { 0.069108, 0.919519, 0.011360 },
  { 0.016394, 0.088011, 0.895380 },
};