gamma.py

   1 #!/usr/bin/python
   2
   3
   4 def gamma_table(start=0, stop=256, gamma=0.45):
   5     lut = []
   6     spread = stop - start
   7     for point in range(spread):
   8         p1 = float(point) / spread
   9         p1 = p1 ** gamma
  10         out = int(p1 * spread) + start
  11         if out >= stop:
  12             out = stop - 1
  13         lut.append(out)
  14
  15     if start > 0:
  16         lut[0:0] = [lut[0]] * start
  17     if stop < 256:
  18         lut.extend([lut[-1]] * (256 - stop))
  19
  20     return lut
  21
  22
  23 def srgb_to_linear_table():
  24     lut = []
  25     a = 0.055
  26     for point in range(256):
  27         p = point / 255.0
  28         if p <= 0.4545:
  29             p /= 12.92
  30         else:
  31             p = ((p + a) / (1 + a)) ** 2.4
  32         lut.append(int(p * 255))
  33     return lut
  34
  35 def linear_to_srgb_table():
  36     lut = []
  37     a = 0.055
  38     for point in range(256):
  39         p = point / 255.0
  40         if p <= 0.0031308:
  41             p *= 12.92
  42         else:
  43             p = (1 + a) * (p ** (1 / 2.4)) - a
  44         lut.append(int(p * 255))
  45     return lut
  46
  47
  48 def cformat(table, name="SOME_TABLE", wrap=75, unused=True):
  49     table = list(table)
  50     outs = []
  51     if unused:
  52         outs.append('UNUSED')
  53
  54     outs.extend(("static guint8 %s [%s] = {" % (name, len(table)),
  55                  '    %s' % table[0]))
  56     for v in table[1:]:
  57         if len(outs[-1]) >= wrap:
  58             outs[-1] += ','
  59             outs.append('    %s' % v)
  60         else:
  61             outs[-1] += ', %s' % v
  62     outs.append('};\n')
  63
  64     print '\n'.join(outs)
  65
  66
  67 print "/* Gamma corrected lookup tables for inverting video */"
  68 print "/* generated by '%s'. DO NOT EDIT */" % __file__
  69 print '#include "gstsparrow.h"'
  70 cformat(reversed(gamma_table(gamma=2.0)), "sparrow_rgb_gamma_full_range_REVERSE")
  71 cformat(reversed(gamma_table(16, 236)), "sparrow_rgb_gamma_headroom_REVERSE")
  72
  73
  74