# -*- coding: utf-8 -*-
"""
Gamma Colour Component Transfer Function
========================================
Defines gamma encoding / decoding colour component transfer function related
objects:
- :func:`colour.gamma_function`
See Also
--------
`RGB Colourspaces Jupyter Notebook
<http://nbviewer.jupyter.org/github/colour-science/colour-notebooks/\
blob/master/notebooks/models/rgb.ipynb>`_
"""
from __future__ import division, unicode_literals
import numpy as np
from colour.algebra import spow
from colour.utilities import as_float_array, as_float
__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__ = 'Production'
__all__ = ['gamma_function']
[docs]def gamma_function(a, exponent=1, negative_number_handling='Indeterminate'):
"""
Defines a typical gamma encoding / decoding function.
Parameters
----------
a : numeric or array_like
Array to encode / decode.
exponent : numeric or array_like, optional
Encoding / decoding exponent.
negative_number_handling : unicode, optional
**{'Indeterminate', 'Mirror', 'Preserve', 'Clamp'}**,
Defines the behaviour for ``a`` negative numbers and / or the
definition return value:
- *Indeterminate*: The behaviour will be indeterminate and
definition return value might contain *nans*.
- *Mirror*: The definition return value will be mirrored around
abscissa and ordinate axis, i.e. Blackmagic Design: Davinci Resolve
behaviour.
- *Preserve*: The definition will preserve any negative number in
``a``, i.e. The Foundry Nuke behaviour.
- *Clamp*: The definition will clamp any negative number in ``a`` to
0.
Returns
-------
numeric or ndarray
Encoded / decoded array.
Raises
------
ValueError
If the negative number handling method is not defined.
Examples
--------
>>> gamma_function(0.18, 2.2) # doctest: +ELLIPSIS
0.0229932...
>>> gamma_function(-0.18, 2.0) # doctest: +ELLIPSIS
0.0323999...
>>> gamma_function(-0.18, 2.2)
nan
>>> gamma_function(-0.18, 2.2, 'Mirror') # doctest: +ELLIPSIS
-0.0229932...
>>> gamma_function(-0.18, 2.2, 'Preserve') # doctest: +ELLIPSIS
-0.1...
>>> gamma_function(-0.18, 2.2, 'Clamp') # doctest: +ELLIPSIS
0.0
"""
a = as_float_array(a)
exponent = as_float_array(exponent)
negative_number_handling = negative_number_handling.lower()
if negative_number_handling == 'indeterminate':
return as_float(a ** exponent)
elif negative_number_handling == 'mirror':
return spow(a, exponent)
elif negative_number_handling == 'preserve':
return as_float(np.where(a <= 0, a, a ** exponent))
elif negative_number_handling == 'clamp':
return as_float(np.where(a <= 0, 0, a ** exponent))
else:
raise ValueError(
'Undefined negative number handling method: "{0}", must be one of '
'"{1}".'.format(
negative_number_handling,
', '.join(['Indeterminate', 'Mirror', 'Preserve', 'Clamp'])))