Source code: gnu/java/awt/color/LinearRGBConverter.java
1 /* LinearRGBConverter.java -- conversion to a linear RGB color space
2 Copyright (C) 2004 Free Software Foundation
3
4 This file is part of GNU Classpath.
5
6 GNU Classpath is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
9 any later version.
10
11 GNU Classpath is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 General Public License for more details.
15
16 You should have received a copy of the GNU General Public License
17 along with GNU Classpath; see the file COPYING. If not, write to the
18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
19 02110-1301 USA.
20
21 Linking this library statically or dynamically with other modules is
22 making a combined work based on this library. Thus, the terms and
23 conditions of the GNU General Public License cover the whole
24 combination.
25
26 As a special exception, the copyright holders of this library give you
27 permission to link this library with independent modules to produce an
28 executable, regardless of the license terms of these independent
29 modules, and to copy and distribute the resulting executable under
30 terms of your choice, provided that you also meet, for each linked
31 independent module, the terms and conditions of the license of that
32 module. An independent module is a module which is not derived from
33 or based on this library. If you modify this library, you may extend
34 this exception to your version of the library, but you are not
35 obligated to do so. If you do not wish to do so, delete this
36 exception statement from your version. */
37
38 package gnu.java.awt.color;
39
40
41 /**
42 * LinearRGBConverter - conversion routines for a linear sRGB colorspace
43 * sRGB is a standard for RGB colorspaces, adopted by the w3c.
44 *
45 * The specification is available at:
46 * http://www.w3.org/Graphics/Color/sRGB.html
47 *
48 * @author Sven de Marothy
49 */
50 public class LinearRGBConverter implements ColorSpaceConverter
51 {
52 /**
53 * linear RGB --> sRGB
54 * Use the inverse gamma curve
55 */
56 public float[] toRGB(float[] in)
57 {
58 float[] out = new float[3];
59 for (int i = 0; i < 3; i++)
60 {
61 float n = in[i];
62 if (n < 0)
63 n = 0f;
64 if (n > 1)
65 n = 1f;
66 if (n <= 0.00304f)
67 out[i] = in[0] * 12.92f;
68 else
69 out[i] = 1.055f * ((float) Math.exp((1 / 2.4) * Math.log(n)))
70 - 0.055f;
71 }
72 return out;
73 }
74
75 /**
76 * sRGB --> linear RGB
77 * Use the gamma curve (gamma=2.4 in sRGB)
78 */
79 public float[] fromRGB(float[] in)
80 {
81 float[] out = new float[3];
82
83 // Convert non-linear RGB coordinates to linear ones,
84 // numbers from the w3 spec.
85 for (int i = 0; i < 3; i++)
86 {
87 float n = in[i];
88 if (n < 0)
89 n = 0f;
90 if (n > 1)
91 n = 1f;
92 if (n <= 0.03928f)
93 out[i] = (float) (n / 12.92);
94 else
95 out[i] = (float) (Math.exp(2.4 * Math.log((n + 0.055) / 1.055)));
96 }
97 return out;
98 }
99
100 /**
101 * Linear RGB --> CIE XYZ (D50 relative)
102 * This is a simple matrix transform, the matrix (relative D65)
103 * is given in the sRGB spec. This has been combined with a
104 * linear Bradford transform for the D65-->D50 mapping, resulting
105 * in a single matrix which does the whole thing.
106 *
107 */
108 public float[] fromCIEXYZ(float[] in)
109 {
110 /*
111 * Note: The numbers which were used to calculate this only had four
112 * digits of accuracy. So don't be fooled by the number of digits here.
113 * If someone has more accurate source, feel free to update this.
114 */
115 float[] out = new float[3];
116 out[0] = (float) (3.13383065124221 * in[0] - 1.61711949411313 * in[1]
117 - 0.49071914111101 * in[2]);
118 out[1] = (float) (-0.97847026691142 * in[0] + 1.91597856031996 * in[1]
119 + 0.03340430640699 * in[2]);
120 out[2] = (float) (0.07203679486279 * in[0] - 0.22903073553113 * in[1]
121 + 1.40557835776234 * in[2]);
122 if (out[0] < 0)
123 out[0] = 0f;
124 if (out[1] < 0)
125 out[1] = 0f;
126 if (out[2] < 0)
127 out[2] = 0f;
128 if (out[0] > 1.0f)
129 out[0] = 1.0f;
130 if (out[1] > 1.0f)
131 out[1] = 1.0f;
132 if (out[2] > 1.0f)
133 out[2] = 1.0f;
134 return out;
135 }
136
137 /**
138 * Linear RGB --> CIE XYZ (D50 relative)
139 * Uses the inverse of the above matrix.
140 */
141 public float[] toCIEXYZ(float[] in)
142 {
143 float[] out = new float[3];
144 out[0] = (float) (0.43606375022190 * in[0] + 0.38514960146481 * in[1]
145 + 0.14308641888799 * in[2]);
146 out[1] = (float) (0.22245089403542 * in[0] + 0.71692584775182 * in[1]
147 + 0.06062451125578 * in[2]);
148 out[2] = (float) (0.01389851860679 * in[0] + 0.09707969011198 * in[1]
149 + 0.71399604572506 * in[2]);
150 return out;
151 }
152 }