Source code for colour.models.rgb.transfer_functions.bt_709

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
ITU-R BT.709-6
==============

Defines *ITU-R BT.709-6* opto-electrical transfer function (OETF / OECF) and
electro-optical transfer function (EOTF / EOCF):

-   :func:`oetf_BT709`
-   :func:`eotf_BT709`

See Also
--------
`RGB Colourspaces Jupyter Notebook
<http://nbviewer.jupyter.org/github/colour-science/colour-notebooks/\
blob/master/notebooks/models/rgb.ipynb>`_

References
----------
.. [1]  International Telecommunication Union. (2015). Recommendation
        ITU-R BT.709-6 - Parameter values for the HDTV standards for
        production and international programme exchange BT Series Broadcasting
        service (Vol. 5). Retrieved from https://www.itu.int/dms_pubrec/\
itu-r/rec/bt/R-REC-BT.709-6-201506-I!!PDF-E.pdf
"""

from __future__ import division, unicode_literals

import numpy as np

from colour.utilities import as_numeric, warning

__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013-2017 - Colour Developers'
__license__ = 'New BSD License - http://opensource.org/licenses/BSD-3-Clause'
__maintainer__ = 'Colour Developers'
__email__ = 'colour-science@googlegroups.com'
__status__ = 'Production'

__all__ = ['oetf_BT709',
           'eotf_BT709']


[docs]def oetf_BT709(L): """ Defines *Recommendation ITU-R BT.709-6* opto-electronic transfer function (OETF / OECF). Parameters ---------- L : numeric or array_like *Luminance* :math:`L` of the image. Returns ------- numeric or ndarray Corresponding electrical signal :math:`V`. Examples -------- >>> oetf_BT709(0.18) # doctest: +ELLIPSIS 0.4090077... """ L = np.asarray(L) return as_numeric(np.where(L < 0.018, L * 4.5, 1.099 * (L ** 0.45) - 0.099))
[docs]def eotf_BT709(V): """ Defines *Recommendation ITU-R BT.709-6* electro-optical transfer function (EOTF / EOCF). Parameters ---------- V : numeric or array_like Electrical signal :math:`V`. Returns ------- numeric or ndarray Corresponding *luminance* :math:`L` of the image. Warning ------- *Recommendation ITU-R BT.709-6* doesn't specify an electro-optical transfer function. This definition is used for symmetry in unit tests and other computations but should not be used as an *EOTF*. Examples -------- >>> eotf_BT709(0.409007728864150) # doctest: +ELLIPSIS 0.1... """ warning(('*Recommendation ITU-R BT.709-6* doesn\'t specify an ' 'electro-optical transfer function. This definition is used ' 'for symmetry in unit tests and others computations but should ' 'not be used as an *EOTF*!')) V = np.asarray(V) return as_numeric(np.where(V < oetf_BT709(0.018), V / 4.5, ((V + 0.099) / 1.099) ** (1 / 0.45)))