# -*- coding: utf-8 -*-
"""
YCoCg Colour Encoding
======================
Defines the *YCoCg* colour encoding related transformations:
- :func:`colour.RGB_to_YCoCg`
- :func:`colour.YCoCg_to_RGB`
References
----------
- :cite:`Malvar2003` : Malvar, H., & Sullivan, G. (2003). YCoCg-R: A Color
Space with RGB Reversibility and Low Dynamic Range.
https://www.microsoft.com/en-us/research/wp-content/uploads/2016/06/\
Malvar_Sullivan_YCoCg-R_JVT-I014r3-2.pdf
"""
from __future__ import division, unicode_literals
import numpy as np
from colour.utilities import vector_dot
__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013-2020 - Colour Developers'
__license__ = 'New BSD License - https://opensource.org/licenses/BSD-3-Clause'
__maintainer__ = 'Colour Developers'
__email__ = 'colour-developers@colour-science.org'
__status__ = 'Development'
__all__ = [
'MATRIX_RGB_TO_YCOCG',
'MATRIX_YCOCG_TO_RGB',
'RGB_to_YCoCg',
'YCoCg_to_RGB',
]
MATRIX_RGB_TO_YCOCG = np.array([
[1 / 4, 1 / 2, 1 / 4],
[1 / 2, 0, -1 / 2],
[-1 / 4, 1 / 2, -1 / 4],
])
"""
*R'G'B'* colourspace to *YCoCg* colour encoding matrix.
MATRIX_RGB_TO_YCOCG : array_like, (3, 3)
"""
MATRIX_YCOCG_TO_RGB = np.array([
[1, 1, -1],
[1, 0, 1],
[1, -1, -1],
])
"""
*YCoCg* colour encoding to *R'G'B'* colourspace matrix.
MATRIX_YCOCG_TO_RGB : array_like, (3, 3)
"""
[docs]def RGB_to_YCoCg(RGB):
"""
Converts an array of *R'G'B'* values to the corresponding *YCoCg* colour
encoding values array.
Parameters
----------
RGB : array_like
Input *R'G'B'* array.
Returns
-------
ndarray
*YCoCg* colour encoding array.
References
----------
:cite:`Malvar2003`
Examples
--------
>>> RGB_to_YCoCg(np.array([1.0, 1.0, 1.0]))
array([ 1., 0., 0.])
>>> RGB_to_YCoCg(np.array([0.75, 0.5, 0.5]))
array([ 0.5625, 0.125 , -0.0625])
"""
return vector_dot(MATRIX_RGB_TO_YCOCG, RGB)
[docs]def YCoCg_to_RGB(YCoCg):
"""
Converts an array of *YCoCg* colour encoding values to the corresponding
*R'G'B'* values array.
Parameters
----------
YCoCg : array_like
*YCoCg* colour encoding array.
Returns
-------
ndarray
Output *R'G'B'* array.
References
----------
:cite:`Malvar2003`
Examples
--------
>>> YCoCg_to_RGB(np.array([1.0, 0.0, 0.0]))
array([ 1., 1., 1.])
>>> YCoCg_to_RGB(np.array([0.5625, 0.125, -0.0625]))
array([ 0.75, 0.5 , 0.5 ])
"""
return vector_dot(MATRIX_YCOCG_TO_RGB, YCoCg)