# -*- coding: utf-8 -*-
"""
sRGB Colourspace
================
Defines *sRGB* colourspace opto-electrical transfer function (OETF / OECF) and
its reverse:
- :func:`colour.models.oetf_sRGB`
- :func:`colour.models.oetf_reverse_sRGB`
See Also
--------
`RGB Colourspaces Jupyter Notebook
<http://nbviewer.jupyter.org/github/colour-science/colour-notebooks/\
blob/master/notebooks/models/rgb.ipynb>`_
References
----------
- :cite:`InternationalElectrotechnicalCommission1999a` : International
Electrotechnical Commission. (1999). IEC 61966-2-1:1999 - Multimedia
systems and equipment - Colour measurement and management - Part 2-1:
Colour management - Default RGB colour space - sRGB. Retrieved from
https://webstore.iec.ch/publication/6169
- :cite:`InternationalTelecommunicationUnion2015i` : 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. 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.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 - http://opensource.org/licenses/BSD-3-Clause'
__maintainer__ = 'Colour Developers'
__email__ = 'colour-science@googlegroups.com'
__status__ = 'Production'
__all__ = ['oetf_sRGB', 'oetf_reverse_sRGB']
[docs]def oetf_sRGB(L):
"""
Defines the *sRGB* colourspace 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`.
Notes
-----
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``L`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
+------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``V`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
References
----------
:cite:`InternationalElectrotechnicalCommission1999a`,
:cite:`InternationalTelecommunicationUnion2015i`
Examples
--------
>>> oetf_sRGB(0.18) # doctest: +ELLIPSIS
0.4613561...
"""
L = to_domain_1(L)
V = np.where(L <= 0.0031308, L * 12.92, 1.055 * spow(L, 1 / 2.4) - 0.055)
return as_float(from_range_1(V))
[docs]def oetf_reverse_sRGB(V):
"""
Defines the *sRGB* colourspace reverse opto-electronic transfer function
(OETF / OECF).
Parameters
----------
V : numeric or array_like
Electrical signal :math:`V`.
Returns
-------
numeric or ndarray
Corresponding *luminance* :math:`L` of the image.
Notes
-----
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``V`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
+------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``L`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
References
----------
:cite:`InternationalElectrotechnicalCommission1999a`,
:cite:`InternationalTelecommunicationUnion2015i`
Examples
--------
>>> oetf_reverse_sRGB(0.461356129500442) # doctest: +ELLIPSIS
0.1...
"""
V = to_domain_1(V)
with domain_range_scale('ignore'):
L = np.where(
V <= oetf_sRGB(0.0031308),
V / 12.92,
spow((V + 0.055) / 1.055, 2.4),
)
return as_float(from_range_1(L))