Source code for colour.models.rgb.transfer_functions.gamma

# -*- coding: utf-8 -*-
"""
Gamma Colour Component Transfer Function
========================================

Defines the gamma encoding / decoding colour component transfer function
related objects:

- :func:`colour.gamma_function`
"""

import numpy as np

from colour.algebra import spow
from colour.utilities import as_float_array, as_float, validate_method

__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013-2021 - 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 = validate_method( negative_number_handling, ['Indeterminate', 'Mirror', 'Preserve', 'Clamp'], '"{0}" negative number handling is invalid, it must be one of {1}!') 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))