gamma.py

   1 #!/usr/bin/env python3
   2
   3 import imageio
   4 import numpy
   5
   6 def read_image(in_file):
   7   # read double image
   8   image = imageio.imread(in_file) / 255.
   9
  10   # gamma decode
  11   linear = image < .0031308 * 12.92
  12   image[linear] /= 12.92
  13   image[~linear] = ((image[~linear] + .055) / 1.055) ** 2.4
  14
  15   return image
  16
  17 def write_image(out_file, image):
  18   image = numpy.copy(image)
  19
  20   # gamma encode
  21   linear = image < .0031308
  22   image[linear] *= 12.92
  23   image[~linear] = 1.055 * image[~linear] ** (1. / 2.4) - .055
  24
  25   # write double image
  26   image[image < 0.] = 0.
  27   image[image > 1.] = 1.
  28   imageio.imwrite(
  29     out_file,
  30     numpy.round(image * 255.).astype(numpy.uint8)
  31   )
  32
  33 if __name__ == '__main__':
  34   import sys
  35
  36   if len(sys.argv) < 3:
  37     print(f'usage: {sys.argv[0]:s} in_file out_file')
  38     sys.exit(1)
  39   in_file = sys.argv[1]
  40   out_file = sys.argv[2]
  41
  42   write_image(out_file, read_image(in_file))