1 /**************************************************************************
2 *
3 * Copyright 2010 VMware, Inc.
4 * All Rights Reserved.
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a
7 * copy of this software and associated documentation files (the
8 * "Software"), to deal in the Software without restriction, including
9 * without limitation the rights to use, copy, modify, merge, publish,
10 * distribute, sub license, and/or sell copies of the Software, and to
11 * permit persons to whom the Software is furnished to do so, subject to
12 * the following conditions:
13 *
14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
15 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
16 * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
17 * THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM,
18 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
19 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
20 * USE OR OTHER DEALINGS IN THE SOFTWARE.
21 *
22 * The above copyright notice and this permission notice (including the
23 * next paragraph) shall be included in all copies or substantial portions
24 * of the Software.
25 *
26 **************************************************************************/
27
28 /**
29 * @file
30 * SRGB translation.
31 *
32 * @author Brian Paul <brianp@vmware.com>
33 * @author Michal Krol <michal@vmware.com>
34 * @author Jose Fonseca <jfonseca@vmware.com>
35 */
36
37 #ifndef U_FORMAT_SRGB_H_
38 #define U_FORMAT_SRGB_H_
39
40 #include <stdint.h>
41 #include <math.h>
42
43 extern const float
44 util_format_srgb_8unorm_to_linear_float_table[256];
45
46 extern const uint8_t
47 util_format_srgb_to_linear_8unorm_table[256];
48
49 extern const uint8_t
50 util_format_linear_to_srgb_8unorm_table[256];
51
52 extern const unsigned
53 util_format_linear_to_srgb_helper_table[104];
54
55
56 static inline float
util_format_srgb_to_linear_float(float cs)57 util_format_srgb_to_linear_float(float cs)
58 {
59 if (cs <= 0.0f)
60 return 0.0f;
61 else if (cs <= 0.04045f)
62 return cs / 12.92f;
63 else if (cs < 1.0f)
64 return powf((cs + 0.055) / 1.055f, 2.4f);
65 else
66 return 1.0f;
67 }
68
69
70 static inline float
util_format_linear_to_srgb_float(float cl)71 util_format_linear_to_srgb_float(float cl)
72 {
73 if (cl <= 0.0f)
74 return 0.0f;
75 else if (cl < 0.0031308f)
76 return 12.92f * cl;
77 else if (cl < 1.0f)
78 return 1.055f * powf(cl, 0.41666f) - 0.055f;
79 else
80 return 1.0f;
81 }
82
83
84 /**
85 * Convert a unclamped linear float to srgb value in the [0,255].
86 */
87 static inline uint8_t
util_format_linear_float_to_srgb_8unorm(float x)88 util_format_linear_float_to_srgb_8unorm(float x)
89 {
90 /*
91 * This is taken from https://gist.github.com/rygorous/2203834
92 * Use LUT and do linear interpolation.
93 */
94 union {
95 uint32_t ui;
96 float f;
97 } almostone, minval, f;
98 unsigned tab, bias, scale, t;
99
100 almostone.ui = 0x3f7fffff;
101 minval.ui = (127-13) << 23;
102
103 /*
104 * Clamp to [2^(-13), 1-eps]; these two values map to 0 and 1, respectively.
105 * The tests are carefully written so that NaNs map to 0, same as in the
106 * reference implementation.
107 */
108 if (!(x > minval.f))
109 x = minval.f;
110 if (x > almostone.f)
111 x = almostone.f;
112
113 /* Do the table lookup and unpack bias, scale */
114 f.f = x;
115 tab = util_format_linear_to_srgb_helper_table[(f.ui - minval.ui) >> 20];
116 bias = (tab >> 16) << 9;
117 scale = tab & 0xffff;
118
119 /* Grab next-highest mantissa bits and perform linear interpolation */
120 t = (f.ui >> 12) & 0xff;
121 return (uint8_t) ((bias + scale*t) >> 16);
122 }
123
124
125 /**
126 * Convert an 8-bit sRGB value from non-linear space to a
127 * linear RGB value in [0, 1].
128 * Implemented with a 256-entry lookup table.
129 */
130 static inline float
util_format_srgb_8unorm_to_linear_float(uint8_t x)131 util_format_srgb_8unorm_to_linear_float(uint8_t x)
132 {
133 return util_format_srgb_8unorm_to_linear_float_table[x];
134 }
135
136
137 /*
138 * XXX These 2 functions probably don't make a lot of sense (but lots
139 * of potential callers which most likely all don't make sense neither)
140 */
141
142 /**
143 * Convert a 8bit normalized value from linear to srgb.
144 */
145 static inline uint8_t
util_format_linear_to_srgb_8unorm(uint8_t x)146 util_format_linear_to_srgb_8unorm(uint8_t x)
147 {
148 return util_format_linear_to_srgb_8unorm_table[x];
149 }
150
151
152 /**
153 * Convert a 8bit normalized value from srgb to linear.
154 */
155 static inline uint8_t
util_format_srgb_to_linear_8unorm(uint8_t x)156 util_format_srgb_to_linear_8unorm(uint8_t x)
157 {
158 return util_format_srgb_to_linear_8unorm_table[x];
159 }
160
161
162 #endif /* U_FORMAT_SRGB_H_ */
163