# -*- coding: utf-8 -*-
"""
ITU-R BT.601-7
==============
Defines *ITU-R BT.601-7* opto-electrical transfer function (OETF / OECF) and
its inverse:
- :func:`colour.models.oetf_BT601`
- :func:`colour.models.oetf_inverse_BT601`
See Also
--------
`RGB Colourspaces Jupyter Notebook
<http://nbviewer.jupyter.org/github/colour-science/colour-notebooks/\
blob/master/notebooks/models/rgb.ipynb>`_
References
----------
- :cite:`InternationalTelecommunicationUnion2011f` : International
Telecommunication Union. (2011). Recommendation ITU-R BT.601-7 - Studio
encoding parameters of digital television for standard 4:3 and wide-screen
16:9 aspect ratios. Retrieved from
http://www.itu.int/dms_pubrec/itu-r/rec/bt/\
R-REC-BT.601-7-201103-I!!PDF-E.pdf
"""
from __future__ import division, unicode_literals
import numpy as np
from colour.algebra import spow
from colour.utilities import (as_float, domain_range_scale, from_range_1,
to_domain_1)
__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013-2019 - Colour Developers'
__license__ = 'New BSD License - https://opensource.org/licenses/BSD-3-Clause'
__maintainer__ = 'Colour Developers'
__email__ = 'colour-science@googlegroups.com'
__status__ = 'Production'
__all__ = ['oetf_BT601', 'oetf_inverse_BT601']
[docs]def oetf_BT601(L):
"""
Defines *Recommendation ITU-R BT.601-7* 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:`E`.
Notes
-----
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``L`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
+------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``E`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
References
----------
:cite:`InternationalTelecommunicationUnion2011f`
Examples
--------
>>> oetf_BT601(0.18) # doctest: +ELLIPSIS
0.4090077...
"""
L = to_domain_1(L)
E = np.where(L < 0.018, L * 4.5, 1.099 * spow(L, 0.45) - 0.099)
return as_float(from_range_1(E))
[docs]def oetf_inverse_BT601(E):
"""
Defines *Recommendation ITU-R BT.601-7* inverse opto-electronic transfer
function (OETF / OECF).
Parameters
----------
E : numeric or array_like
Electrical signal :math:`E`.
Returns
-------
numeric or ndarray
Corresponding *luminance* :math:`L` of the image.
Notes
-----
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``E`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
+------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``L`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
References
----------
:cite:`InternationalTelecommunicationUnion2011f`
Examples
--------
>>> oetf_inverse_BT601(0.409007728864150) # doctest: +ELLIPSIS
0.1...
"""
E = to_domain_1(E)
with domain_range_scale('ignore'):
L = np.where(
E < oetf_BT601(0.018),
E / 4.5,
spow((E + 0.099) / 1.099, 1 / 0.45),
)
return as_float(from_range_1(L))