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
|
/*
* Jitter offset table
*
* $Id$
*
* ***** BEGIN GPL LICENSE BLOCK *****
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* The Original Code is Copyright (C) 2001-2002 by NaN Holding BV.
* All rights reserved.
*
* The Original Code is: all of this file.
*
* Contributor(s): none yet.
*
* ***** END GPL LICENSE BLOCK *****
*/
#include "gammaCorrectionTables.h"
#include <stdlib.h>
#include <math.h>
/* WARNING; optimized, cannot be used to do gamma(invgamma()) and expect */
/* result remain identical (ton) */
/* gamma is only used here for correcting adding colors or alpha */
#define RE_DEFAULT_GAMMA 2.0
/* This 400 is sort of based on the number of intensity levels needed for */
/* the typical dynamic range of a medium, in this case CRTs. (Foley) */
/* (Actually, it says the number should be between 400 and 535.) */
#define RE_GAMMA_TABLE_SIZE 400
/* These indicate the status of the gamma lookup table --------------------- */
static float gamma_range_table[RE_GAMMA_TABLE_SIZE + 1];
static float gamfactor_table[RE_GAMMA_TABLE_SIZE];
static float inv_gamma_range_table[RE_GAMMA_TABLE_SIZE + 1];
static float inv_gamfactor_table[RE_GAMMA_TABLE_SIZE];
static float color_domain_table[RE_GAMMA_TABLE_SIZE + 1];
static float color_step;
static float inv_color_step;
static float valid_gamma;
static float valid_inv_gamma;
/* ------------------------------------------------------------------------- */
float gammaCorrect(float c)
{
int i;
float res = 0.0;
i = floor(c * inv_color_step);
/* Clip to range [0,1]: outside, just do the complete calculation. */
/* We may have some performance problems here. Stretching up the LUT */
/* may help solve that, by exchanging LUT size for the interpolation. */
/* Negative colors are explicitly handled. */
if (i < 0) res = -pow(abs(c), valid_gamma);
else if (i >= RE_GAMMA_TABLE_SIZE ) res = pow(c, valid_gamma);
else res = gamma_range_table[i] +
( (c - color_domain_table[i]) * gamfactor_table[i]);
return res;
} /* end of float gammaCorrect(float col) */
/* ------------------------------------------------------------------------- */
float invGammaCorrect(float col)
{
int i;
float res = 0.0;
i = floor(col*inv_color_step);
/* Negative colors are explicitly handled. */
if (i < 0) res = -pow(abs(col), valid_inv_gamma);
else if (i >= RE_GAMMA_TABLE_SIZE) res = pow(col, valid_inv_gamma);
else res = inv_gamma_range_table[i] +
( (col - color_domain_table[i]) * inv_gamfactor_table[i]);
return res;
} /* end of float invGammaCorrect(float col) */
/* ------------------------------------------------------------------------- */
void makeGammaTables(float gamma)
{
/* we need two tables: one forward, one backward */
int i;
valid_gamma = gamma;
valid_inv_gamma = 1.0 / gamma;
color_step = 1.0 / RE_GAMMA_TABLE_SIZE;
inv_color_step = (float) RE_GAMMA_TABLE_SIZE;
/* We could squeeze out the two range tables to gain some memory. */
for (i = 0; i < RE_GAMMA_TABLE_SIZE; i++) {
color_domain_table[i] = i * color_step;
gamma_range_table[i] = pow(color_domain_table[i],
valid_gamma);
inv_gamma_range_table[i] = pow(color_domain_table[i],
valid_inv_gamma);
}
/* The end of the table should match 1.0 carefully. In order to avoid */
/* rounding errors, we just set this explicitly. The last segment may */
/* have a different length than the other segments, but our */
/* interpolation is insensitive to that. */
color_domain_table[RE_GAMMA_TABLE_SIZE] = 1.0;
gamma_range_table[RE_GAMMA_TABLE_SIZE] = 1.0;
inv_gamma_range_table[RE_GAMMA_TABLE_SIZE] = 1.0;
/* To speed up calculations, we make these calc factor tables. They are */
/* multiplication factors used in scaling the interpolation. */
for (i = 0; i < RE_GAMMA_TABLE_SIZE; i++ ) {
gamfactor_table[i] = inv_color_step
* (gamma_range_table[i + 1] - gamma_range_table[i]) ;
inv_gamfactor_table[i] = inv_color_step
* (inv_gamma_range_table[i + 1] - inv_gamma_range_table[i]) ;
}
} /* end of void makeGammaTables(float gamma) */
/* ------------------------------------------------------------------------- */
/* eof */
|