xref: /third_party/mesa3d/src/util/format_srgb.h (revision bf215546) 
1/**************************************************************************
2 *
3 * Copyright 2010 VMware, Inc.
4 * All Rights Reserved.
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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
43extern const float
44util_format_srgb_8unorm_to_linear_float_table[256];
45
46extern const uint8_t
47util_format_srgb_to_linear_8unorm_table[256];
48
49extern const uint8_t
50util_format_linear_to_srgb_8unorm_table[256];
51
52extern const unsigned
53util_format_linear_to_srgb_helper_table[104];
54
55
56static inline float
57util_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
70static inline float
71util_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 */
87static inline uint8_t
88util_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 */
130static inline float
131util_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 */
145static inline uint8_t
146util_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 */
155static inline uint8_t
156util_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