#
# sRGB transform (Python)
#
# Copyright (c) 2020 Project Nayuki. (MIT License)
# https://www.nayuki.io/page/srgb-transform-library
#
# Permission is hereby granted, free of charge, to any person obtaining a copy of
# this software and associated documentation files (the "Software"), to deal in
# the Software without restriction, including without limitation the rights to
# use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
# the Software, and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
# - The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# - The Software is provided "as is", without warranty of any kind, express or
# implied, including but not limited to the warranties of merchantability,
# fitness for a particular purpose and noninfringement. In no event shall the
# authors or copyright holders be liable for any claim, damages or other
# liability, whether in an action of contract, tort or otherwise, arising from,
# out of or in connection with the Software or the use or other dealings in the
# Software.
#
def srgb_to_linear(x):
if x <= 0.0:
return 0.0
elif x >= 1:
return 1.0
elif x < 0.04045:
return x / 12.92
else:
return ((x + 0.055) / 1.055) ** 2.4
def srgb_8bit_to_linear(x):
if (x >> 8) != 0:
raise ValueError("Value out of 8-bit range")
return _SRGB_8BIT_TO_LINEAR[x]
def linear_to_srgb(x):
if x <= 0.0:
return 0.0
elif x >= 1:
return 1.0
elif x < 0.0031308:
return x * 12.92
else:
return x ** (1 / 2.4) * 1.055 - 0.055
def linear_to_srgb_8bit(x):
if x <= 0.0:
return 0
table = _SRGB_8BIT_TO_LINEAR
if x >= 1.0:
return len(table) - 1
y = 0
i = len(table) >> 1
while i != 0:
if table[y | i] <= x:
y |= i
i >>= 1
return y if (x - table[y] <= table[y + 1] - x) else (y + 1)
_SRGB_8BIT_TO_LINEAR = [srgb_to_linear(i / 255) for i in range(256)]