summaryrefslogtreecommitdiffstats
path: root/libdimension/color.c
blob: 7fb73edc54ccb8d4785b319bb6008cc3a691e4d5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
/*************************************************************************
 * Copyright (C) 2009 Tavian Barnes <tavianator@gmail.com>               *
 *                                                                       *
 * This file is part of The Dimension Library.                           *
 *                                                                       *
 * The Dimension 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 3 of the *
 * License, or (at your option) any later version.                       *
 *                                                                       *
 * The Dimension 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 program.  If not, see                         *
 * <http://www.gnu.org/licenses/>.                                       *
 *************************************************************************/

#include "dimension.h"
#include <math.h> /* For pow(), sqrt() */

/* sRGB white point (CIE D50) */
const dmnsn_CIE_XYZ dmnsn_whitepoint = { .X = 0.9504060171449392,
                                         .Y = 0.9999085943425312,
                                         .Z = 1.089062231497274 };

/* Standard colors */
const dmnsn_color dmnsn_black = { .X = 0.0, .Y = 0.0, .Z = 0.0 };
const dmnsn_color dmnsn_white = { .X = 0.9504060171449392,
                                  .Y = 0.9999085943425312,
                                  .Z = 1.089062231497274 };

/* Convert a CIE XYZ color to a dmnsn_color (actually a no-op) */
dmnsn_color
dmnsn_color_from_XYZ(dmnsn_CIE_XYZ XYZ)
{
  dmnsn_color ret = { .X = XYZ.X, .Y = XYZ.Y, .Z = XYZ.Z,
                      .filter = 0.0, .trans = 0.0 };
  return ret;
}

/* Convert a CIE xyY color to a dmnsn_color */
dmnsn_color
dmnsn_color_from_xyY(dmnsn_CIE_xyY xyY)
{
  dmnsn_color ret = { .X = xyY.Y*xyY.x/xyY.y,
                      .Y = xyY.Y,
                      .Z = xyY.Y*(1.0 - xyY.x - xyY.y)/xyY.y,
                      .filter = 0.0,
                      .trans = 0.0 };
  return ret;
}

/* Inverse function of CIE L*a*b*'s `f' function, for the reverse conversion */
static double dmnsn_Lab_finv(double t) {
  if (t > 6.0/29.0) {
    return t*t*t;
  } else {
    return 108.0*(t - 16.0/116.0)/841.0;
  }
}

/* Convert a CIE L*a*b* color to a dmnsn_color, relative to the given
   whitepoint. */
dmnsn_color
dmnsn_color_from_Lab(dmnsn_CIE_Lab Lab, dmnsn_CIE_XYZ white)
{
  double fx, fy, fz;
  dmnsn_color ret;

  fy = (Lab.L + 16.0)/116.0;
  fx = fy + Lab.a/500.0;
  fz = fy - Lab.b/200.0;

  ret.X = white.X*dmnsn_Lab_finv(fx);
  ret.Y = white.Y*dmnsn_Lab_finv(fy);
  ret.Z = white.Z*dmnsn_Lab_finv(fz);
  ret.filter = 0.0;
  ret.trans  = 0.0;

  return ret;
}

/* Convert a CIE L*u*v* color to a dmnsn_color, relative to the given
   whitepoint. */
dmnsn_color
dmnsn_color_from_Luv(dmnsn_CIE_Luv Luv, dmnsn_CIE_XYZ white)
{
  double fy;
  double uprime, unprime, vprime, vnprime;
  dmnsn_color ret;

  fy = (Luv.L + 16.0)/116.0;

  unprime = 4.0*white.X/(white.X + 15.0*white.Y + 3.0*white.Z);
  uprime  = Luv.u/Luv.L/13.0 + unprime;
  vnprime = 9.0*white.Y/(white.X + 15.0*white.Y + 3.0*white.Z);
  vprime  = Luv.v/Luv.L/13.0 + vnprime;

  ret.Y = white.Y*dmnsn_Lab_finv(fy);
  ret.X = ret.Y*9.0*uprime/vprime/4.0;
  ret.Z = ret.Y*(12.0 - 3*uprime - 20*vprime)/vprime/4.0;
  ret.filter = 0.0;
  ret.trans  = 0.0;

  return ret;
}

/* Inverse function of sRGB's `C' function, for the reverse conversion */
static double dmnsn_sRGB_Cinv(double CsRGB) {
  /*
   * If C represents R, G, and B, then the Clinear values are now found as
   * follows:
   *
   *           { Csrgb/12.92,                  Csrgb <= 0.04045
   * Clinear = {                        1/2.4
   *           { ((Csrgb + 0.055)/1.055)     , Csrgb >  0.04045
   */
  if (CsRGB <= 0.040449936) {
    return CsRGB/12.92;
  } else {
    return pow((CsRGB + 0.055)/1.055, 2.4);
  }
}

/* Convert an sRGB value to a dmnsn_color */
dmnsn_color
dmnsn_color_from_sRGB(dmnsn_sRGB sRGB)
{
  double Rlinear, Glinear, Blinear; /* Linear RGB values - no gamma */
  dmnsn_color ret;

  Rlinear = dmnsn_sRGB_Cinv(sRGB.R);
  Glinear = dmnsn_sRGB_Cinv(sRGB.G);
  Blinear = dmnsn_sRGB_Cinv(sRGB.B);

  /*
   * Now, the linear conversion.  Expressed as matrix multiplication, it looks
   * like this:
   *
   *   [X]   [0.4124 0.3576 0.1805] [Rlinear]
   *   [Y] = [0.2126 0.7152 0.0722]*[Glinear]
   *   [X]   [0.0193 0.1192 0.9505] [Blinear]
   */
  ret.X = 0.4123808838268995*Rlinear + 0.3575728355732478*Glinear
    + 0.1804522977447919*Blinear;
  ret.Y = 0.2126198631048975*Rlinear + 0.7151387878413206*Glinear
    + 0.0721499433963131*Blinear;
  ret.Z = 0.0193434956789248*Rlinear + 0.1192121694056356*Glinear
    + 0.9505065664127130*Blinear;
  ret.filter = 0.0;
  ret.trans  = 0.0;

  return ret;
}

/* Convert a dmnsn_color to a CIE XYZ color (actually a no-op) */
dmnsn_CIE_XYZ
dmnsn_XYZ_from_color(dmnsn_color color)
{
  dmnsn_CIE_XYZ ret = { .X = color.X, .Y = color.Y, .Z = color.Z };
  return ret;
}

/* Convert a dmnsn_color to a CIE xyY color */
dmnsn_CIE_xyY
dmnsn_xyY_from_color(dmnsn_color color)
{
  dmnsn_CIE_xyY ret = { .x = color.X/(color.X + color.Y + color.Z),
                        .y = color.Y/(color.X + color.Y + color.Z),
                        .Y = color.Y };
  return ret;
}

/* CIE L*a*b*'s `f' function */
static double dmnsn_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;
  }
}

/* Convert a dmnsn_color to a CIE L*a*b* color, relative to the given
   whitepoint */
dmnsn_CIE_Lab
dmnsn_Lab_from_color(dmnsn_color color, dmnsn_CIE_XYZ white)
{
  dmnsn_CIE_Lab ret;

  ret.L = 116.0*dmnsn_Lab_f(color.Y/white.Y) - 16.0;
  ret.a = 500.0*(dmnsn_Lab_f(color.X/white.X) - dmnsn_Lab_f(color.Y/white.Y));
  ret.b = 200.0*(dmnsn_Lab_f(color.Y/white.Y) - dmnsn_Lab_f(color.Z/white.Z));

  return ret;
}

/* Convert a dmnsn_color to a CIE L*u*v* color, relative to the given
   whitepoint */
dmnsn_CIE_Luv
dmnsn_Luv_from_color(dmnsn_color color, dmnsn_CIE_XYZ white)
{
  double uprime, unprime, vprime, vnprime;
  dmnsn_CIE_Luv ret;

  uprime  = 4.0*color.X/(color.X + 15.0*color.Y + 3.0*color.Z);
  unprime = 4.0*white.X/(white.X + 15.0*white.Y + 3.0*white.Z);
  vprime  = 9.0*color.Y/(color.X + 15.0*color.Y + 3.0*color.Z);
  vnprime = 9.0*white.Y/(white.X + 15.0*white.Y + 3.0*white.Z);

  ret.L = 116.0*dmnsn_Lab_f(color.Y/white.Y) - 16.0;
  ret.u = 13.0*ret.L*(uprime - unprime);
  ret.v = 13.0*ret.L*(vprime - vnprime);

  return ret;
}

/* sRGB's `C' function */
static double dmnsn_sRGB_C(double Clinear) {
  /*
   * If C represents R, G, and B, then the sRGB values are now found as follows:
   *
   *         { 12.92*Clinear,                Clinear <= 0.0031308
   * Csrgb = {                1/2.4
   *         { (1.055)*Clinear      - 0.055, Clinear >  0.0031308
   */
  if (Clinear <= 0.0031308) {
    return 12.92*Clinear;
  } else {
    return 1.055*pow(Clinear, 1.0/2.4) - 0.055;
  }
}

/* Convert a dmnsn_color to an sRGB color */
dmnsn_sRGB
dmnsn_sRGB_from_color(dmnsn_color color)
{
  double Rlinear, Glinear, Blinear; /* Linear RGB values - no gamma */
  dmnsn_sRGB ret;

  /*
   * First, the linear conversion.  Expressed as matrix multiplication, it looks
   * like this:
   *
   *   [Rlinear]   [ 3.2410 -1.5374 -0.4986] [X]
   *   [Glinear] = [-0.9692  1.8760  0.0416]*[Y]
   *   [Blinear]   [ 0.0556 -0.2040  1.0570] [Z]
   */
  Rlinear =  3.2410*color.X - 1.5374*color.Y - 0.4986*color.Z;
  Glinear = -0.9692*color.X + 1.8760*color.Y + 0.0416*color.Z;
  Blinear =  0.0556*color.X - 0.2040*color.Y + 1.0570*color.Z;

  ret.R = dmnsn_sRGB_C(Rlinear);
  ret.G = dmnsn_sRGB_C(Glinear);
  ret.B = dmnsn_sRGB_C(Blinear);

  return ret;
}

/* Add two colors in a perceptually correct manner, using CIE L*a*b*. */
dmnsn_color
dmnsn_color_add(dmnsn_color color1, dmnsn_color color2)
{
  dmnsn_CIE_Lab Lab, Lab1, Lab2;
  dmnsn_color ret;

  Lab1 = dmnsn_Lab_from_color(color1, dmnsn_whitepoint);
  Lab2 = dmnsn_Lab_from_color(color2, dmnsn_whitepoint);

  Lab.L = Lab1.L + Lab2.L;
  Lab.a = Lab1.a + Lab2.a;
  Lab.b = Lab1.b + Lab2.b;

  ret = dmnsn_color_from_Lab(Lab, dmnsn_whitepoint);
  /* Weighted average of transparencies by intensity */
  ret.filter = (Lab1.L*color1.filter + Lab2.L*color2.filter)/Lab.L;
  ret.trans  = (Lab1.L*color1.trans  + Lab2.L*color2.trans)/Lab.L;

  return ret;
}

/* Find the perceptual difference between two colors, using CIE L*a*b*. */
double
dmnsn_color_difference(dmnsn_color color1, dmnsn_color color2)
{
  dmnsn_CIE_Lab Lab1, Lab2;

  Lab1 = dmnsn_Lab_from_color(color1, dmnsn_whitepoint);
  Lab2 = dmnsn_Lab_from_color(color2, dmnsn_whitepoint);

  return sqrt((Lab1.L - Lab2.L)*(Lab1.L - Lab2.L)
              + (Lab1.a - Lab2.a)*(Lab1.a - Lab2.a)
              + (Lab1.b - Lab2.b)*(Lab1.b - Lab2.b));
}