Source code: gnu/java/awt/color/ToneReproductionCurve.java
1 /* ToneReproductionCurve.java -- Representation of an ICC 'curv' type TRC
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 * ToneReproductionCurve - TRCs are used to describe RGB
43 * and Grayscale profiles. The TRC is essentially the gamma
44 * function of the color space.
45 *
46 * For example, Apple RGB has a gamma of 1.8, most monitors are ~2.2,
47 * sRGB is 2.4 with a small linear part near 0.
48 * Linear spaces are of course 1.0.
49 * (The exact function is implemented in SrgbConverter)
50 *
51 * The ICC specification allows the TRC to be described as a single
52 * Gamma value, where the function is thus out = in**gamma.
53 * Alternatively, the gamma function may be represented by a lookup table
54 * of values, in which case linear interpolation is used.
55 *
56 * @author Sven de Marothy
57 */
58 public class ToneReproductionCurve
59 {
60 private float[] trc;
61 private float gamma;
62 private float[] reverseTrc;
63
64 /**
65 * Constructs a TRC from a gamma values
66 */
67 public ToneReproductionCurve(float gamma)
68 {
69 trc = null;
70 reverseTrc = null;
71 this.gamma = gamma;
72 }
73
74 /**
75 * Constructs a TRC from a set of float values
76 */
77 public ToneReproductionCurve(float[] trcValues)
78 {
79 trc = new float[trcValues.length];
80 System.arraycopy(trcValues, 0, trc, 0, trcValues.length);
81 setupReverseTrc();
82 }
83
84 /**
85 * Constructs a TRC from a set of short values normalized to
86 * the 0-65535 range (as in the ICC profile file).
87 * (Note the values are treated as unsigned)
88 */
89 public ToneReproductionCurve(short[] trcValues)
90 {
91 trc = new float[trcValues.length];
92 for (int i = 0; i < trcValues.length; i++)
93 trc[i] = (float) ((int) trcValues[i] & (0xFFFF)) / 65535.0f;
94 setupReverseTrc();
95 }
96
97 /**
98 * Performs a TRC lookup
99 */
100 public float lookup(float in)
101 {
102 float out;
103
104 if (trc == null)
105 {
106 if (in == 0f)
107 return 0.0f;
108 return (float) Math.exp(gamma * Math.log(in));
109 }
110 else
111 {
112 double alpha = in * (trc.length - 1);
113 int index = (int) Math.floor(alpha);
114 alpha = alpha - (double) index;
115 if (index >= trc.length - 1)
116 return trc[trc.length - 1];
117 if (index <= 0)
118 return trc[0];
119 out = (float) (trc[index] * (1.0 - alpha) + trc[index + 1] * alpha);
120 }
121 return out;
122 }
123
124 /**
125 * Performs an reverse lookup
126 */
127 public float reverseLookup(float in)
128 {
129 float out;
130
131 if (trc == null)
132 {
133 if (in == 0f)
134 return 0.0f;
135 return (float) Math.exp((1.0 / gamma) * Math.log(in));
136 }
137 else
138 {
139 double alpha = in * (reverseTrc.length - 1);
140 int index = (int) Math.floor(alpha);
141 alpha = alpha - (double) index;
142 if (index >= reverseTrc.length - 1)
143 return reverseTrc[reverseTrc.length - 1];
144 if (index <= 0)
145 return reverseTrc[0];
146 out = (float) (reverseTrc[index] * (1.0 - alpha)
147 + reverseTrc[index + 1] * alpha);
148 }
149 return out;
150 }
151
152 /**
153 * Calculates a reverse-lookup table.
154 * We use a whopping 10,000 entries.. This is should be more than any
155 * real-life TRC table (typically around 256-1024) so we won't be losing
156 * any precision.
157 *
158 * This will of course generate completely invalid results if the curve
159 * is not monotonic and invertable. But what's the alternative?
160 */
161 public void setupReverseTrc()
162 {
163 reverseTrc = new float[10000];
164 int j = 0;
165 for (int i = 0; i < 10000; i++)
166 {
167 float n = ((float) i) / 10000f;
168 while (trc[j + 1] < n && j < trc.length - 2)
169 j++;
170
171 if (j == trc.length - 2)
172 reverseTrc[i] = trc[trc.length - 1];
173 else
174 reverseTrc[i] = (j + (n - trc[j]) / (trc[j + 1] - trc[j])) / ((float) trc.length);
175 }
176 }
177 }