src/util/format_srgb.py

   1
   2 CopyRight = '''
   3 /**************************************************************************
   4  *
   5  * Copyright 2010 VMware, Inc.
   6  * All Rights Reserved.
   7  *
   8  * Permission is hereby granted, free of charge, to any person obtaining a
   9  * copy of this software and associated documentation files (the
  10  * "Software"), to deal in the Software without restriction, including
  11  * without limitation the rights to use, copy, modify, merge, publish,
  12  * distribute, sub license, and/or sell copies of the Software, and to
  13  * permit persons to whom the Software is furnished to do so, subject to
  14  * the following conditions:
  15  *
  16  * The above copyright notice and this permission notice (including the
  17  * next paragraph) shall be included in all copies or substantial portions
  18  * of the Software.
  19  *
  20  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  21  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  22  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
  23  * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
  24  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  25  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  26  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  27  *
  28  **************************************************************************/
  29
  30 /**
  31  * @file
  32  * SRGB translation.
  33  *
  34  * @author Brian Paul <brianp@vmware.com>
  35  * @author Michal Krol <michal@vmware.com>
  36  * @author Jose Fonseca <jfonseca@vmware.com>
  37  */
  38 '''
  39
  40
  41 import math
  42 import struct
  43
  44
  45 def srgb_to_linear(x):
  46     if x <= 0.04045:
  47         return x / 12.92
  48     else:
  49         return math.pow((x + 0.055) / 1.055, 2.4)
  50
  51
  52 def linear_to_srgb(x):
  53     if x >= 0.0031308:
  54         return 1.055 * math.pow(x, 0.41666666) - 0.055
  55     else:
  56         return 12.92 * x
  57
  58
  59 def generate_srgb_tables():
  60     print 'const float'
  61     print 'util_format_srgb_8unorm_to_linear_float_table[256] = {'
  62     for j in range(0, 256, 4):
  63         print '   ',
  64         for i in range(j, j + 4):
  65             print '%.7e,' % (srgb_to_linear(i / 255.0),),
  66         print
  67     print '};'
  68     print
  69     print 'const uint8_t'
  70     print 'util_format_srgb_to_linear_8unorm_table[256] = {'
  71     for j in range(0, 256, 16):
  72         print '   ',
  73         for i in range(j, j + 16):
  74             print '%3u,' % (int(srgb_to_linear(i / 255.0) * 255.0 + 0.5),),
  75         print
  76     print '};'
  77     print
  78     print 'const uint8_t'
  79     print 'util_format_linear_to_srgb_8unorm_table[256] = {'
  80     for j in range(0, 256, 16):
  81         print '   ',
  82         for i in range(j, j + 16):
  83             print '%3u,' % (int(linear_to_srgb(i / 255.0) * 255.0 + 0.5),),
  84         print
  85     print '};'
  86     print
  87
  88 # calculate the table interpolation values used in float linear to unorm8 srgb
  89     numexp = 13
  90     mantissa_msb = 3
  91 # stepshift is just used to only use every x-th float to make things faster,
  92 # 5 is largest value which still gives exact same table as 0
  93     stepshift = 5
  94     nbuckets = numexp << mantissa_msb
  95     bucketsize = (1 << (23 - mantissa_msb)) >> stepshift
  96     mantshift = 12
  97     valtable = []
  98     sum_aa = float(bucketsize)
  99     sum_ab = 0.0
 100     sum_bb = 0.0
 101     for i in range(0, bucketsize):
 102         j = (i << stepshift) >> mantshift
 103         sum_ab += j
 104         sum_bb += j*j
 105     inv_det = 1.0 / (sum_aa * sum_bb - sum_ab * sum_ab)
 106
 107     for bucket in range(0, nbuckets):
 108         start = ((127 - numexp) << 23) + bucket*(bucketsize << stepshift)
 109         sum_a = 0.0
 110         sum_b = 0.0
 111
 112         for i in range(0, bucketsize):
 113             j = (i << stepshift) >> mantshift
 114             fint = start + (i << stepshift)
 115             ffloat = struct.unpack('f', struct.pack('I', fint))[0]
 116             val = linear_to_srgb(ffloat) * 255.0 + 0.5
 117             sum_a += val
 118             sum_b += j*val
 119
 120         solved_a = inv_det * (sum_bb*sum_a - sum_ab*sum_b)
 121         solved_b = inv_det * (sum_aa*sum_b - sum_ab*sum_a)
 122
 123         scaled_a = solved_a * 65536.0 / 512.0
 124         scaled_b = solved_b * 65536.0
 125
 126         int_a = int(scaled_a + 0.5)
 127         int_b = int(scaled_b + 0.5)
 128
 129         valtable.append((int_a << 16) + int_b)
 130
 131     print 'const unsigned'
 132     print 'util_format_linear_to_srgb_helper_table[104] = {'
 133
 134     for j in range(0, nbuckets, 4):
 135         print '   ',
 136         for i in range(j, j + 4):
 137             print '0x%08x,' % (valtable[i],),
 138         print
 139     print '};'
 140     print
 141
 142 def main():
 143     print '/* This file is autogenerated by u_format_srgb.py. Do not edit directly. */'
 144     print
 145     # This will print the copyright message on the top of this file
 146     print CopyRight.strip()
 147     print
 148     print '#include "format_srgb.h"'
 149     print
 150     generate_srgb_tables()
 151
 152
 153 if __name__ == '__main__':
 154     main()