#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Pivoted Log Encoding
====================
Defines the *Pivoted Log* encoding:
- :func:`log_encoding_PivotedLog`
- :func:`log_decoding_PivotedLog`
See Also
--------
`RGB Colourspaces IPython Notebook
<http://nbviewer.jupyter.org/github/colour-science/colour-notebooks/\
blob/master/notebooks/models/rgb.ipynb>`_
References
----------
.. [1] Sony Imageworks. (2012). make.py. Retrieved November 27, 2014, from
https://github.com/imageworks/OpenColorIO-Configs/\
blob/master/nuke-default/make.py
"""
from __future__ import division, unicode_literals
import numpy as np
__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013-2016 - Colour Developers'
__license__ = 'New BSD License - http://opensource.org/licenses/BSD-3-Clause'
__maintainer__ = 'Colour Developers'
__email__ = 'colour-science@googlegroups.com'
__status__ = 'Production'
__all__ = ['log_encoding_PivotedLog',
'log_decoding_PivotedLog']
[docs]def log_encoding_PivotedLog(x,
log_reference=445,
linear_reference=0.18,
negative_gamma=0.6,
density_per_code_value=0.002):
"""
Defines the *Josh Pines* style *Pivoted Log* log encoding curve /
opto-electronic transfer function.
Parameters
----------
x : numeric or array_like
Linear data :math:`x`.
log_reference : numeric or array_like
Log reference.
linear_reference : numeric or array_like
Linear reference.
negative_gamma : numeric or array_like
Negative gamma.
density_per_code_value : numeric or array_like
Density per code value.
Returns
-------
numeric or ndarray
Non-linear data :math:`y`.
Examples
--------
>>> log_encoding_PivotedLog(0.18) # doctest: +ELLIPSIS
0.4349951...
"""
x = np.asarray(x)
return ((log_reference + np.log10(x / linear_reference) /
(density_per_code_value / negative_gamma)) / 1023)
[docs]def log_decoding_PivotedLog(y,
log_reference=445,
linear_reference=0.18,
negative_gamma=0.6,
density_per_code_value=0.002):
"""
Defines the *Josh Pines* style *Pivoted Log* log decoding curve /
electro-optical transfer function.
Parameters
----------
y : numeric or array_like
Non-linear data :math:`y`.
log_reference : numeric or array_like
Log reference.
linear_reference : numeric or array_like
Linear reference.
negative_gamma : numeric or array_like
Negative gamma.
density_per_code_value : numeric or array_like
Density per code value.
Returns
-------
numeric or ndarray
Linear data :math:`x`.
Examples
--------
>>> log_decoding_PivotedLog(0.434995112414467) # doctest: +ELLIPSIS
0.1...
"""
y = np.asarray(y)
return (10 ** ((y * 1023 - log_reference) *
(density_per_code_value / negative_gamma)) *
linear_reference)