# -*- coding: utf-8 -*-
"""
ARIB STD-B67 (Hybrid Log-Gamma)
===============================
Defines *ARIB STD-B67 (Hybrid Log-Gamma)* opto-electrical transfer function
(OETF / OECF) and its inverse:
- :func:`colour.models.oetf_ARIBSTDB67`
- :func:`colour.models.oetf_inverse_ARIBSTDB67`
See Also
--------
`RGB Colourspaces Jupyter Notebook
<http://nbviewer.jupyter.org/github/colour-science/colour-notebooks/\
blob/master/notebooks/models/rgb.ipynb>`_
References
----------
- :cite:`AssociationofRadioIndustriesandBusinesses2015a` : Association of
Radio Industries and Businesses. (2015). Essential Parameter Values for the
Extended Image Dynamic Range Television (EIDRTV) System for Programme
Production. Retrieved from
https://www.arib.or.jp/english/std_tr/broadcasting/desc/std-b67.html
"""
from __future__ import division, unicode_literals
import numpy as np
from colour.models.rgb.transfer_functions import gamma_function
from colour.utilities import (Structure, 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__ = [
'ARIBSTDB67_CONSTANTS', 'oetf_ARIBSTDB67', 'oetf_inverse_ARIBSTDB67'
]
ARIBSTDB67_CONSTANTS = Structure(a=0.17883277, b=0.28466892, c=0.55991073)
"""
*ARIB STD-B67 (Hybrid Log-Gamma)* constants.
ARIBSTDB67_CONSTANTS : Structure
"""
[docs]def oetf_ARIBSTDB67(E, r=0.5, constants=ARIBSTDB67_CONSTANTS):
"""
Defines *ARIB STD-B67 (Hybrid Log-Gamma)* opto-electrical transfer
function (OETF / OECF).
Parameters
----------
E : numeric or array_like
Voltage normalised by the reference white level and proportional to
the implicit light intensity that would be detected with a reference
camera color channel R, G, B.
r : numeric, optional
Video level corresponding to reference white level.
constants : Structure, optional
*ARIB STD-B67 (Hybrid Log-Gamma)* constants.
Returns
-------
numeric or ndarray
Resulting non-linear signal :math:`E'`.
Notes
-----
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``E`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
+------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``E_p`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
- This definition uses the *mirror* negative number handling mode of
:func:`colour.models.gamma_function` definition to the sign of negative
numbers.
References
----------
:cite:`AssociationofRadioIndustriesandBusinesses2015a`
Examples
--------
>>> oetf_ARIBSTDB67(0.18) # doctest: +ELLIPSIS
0.2121320...
"""
E = to_domain_1(E)
a = constants.a
b = constants.b
c = constants.c
E_p = np.where(E <= 1, r * gamma_function(E, 0.5, 'mirror'),
a * np.log(E - b) + c)
return as_float(from_range_1(E_p))
[docs]def oetf_inverse_ARIBSTDB67(E_p, r=0.5, constants=ARIBSTDB67_CONSTANTS):
"""
Defines *ARIB STD-B67 (Hybrid Log-Gamma)* inverse opto-electrical transfer
function (OETF / OECF).
Parameters
----------
E_p : numeric or array_like
Non-linear signal :math:`E'`.
r : numeric, optional
Video level corresponding to reference white level.
constants : Structure, optional
*ARIB STD-B67 (Hybrid Log-Gamma)* constants.
Returns
-------
numeric or ndarray
Voltage :math:`E` normalised by the reference white level and
proportional to the implicit light intensity that would be detected
with a reference camera color channel R, G, B.
Notes
-----
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``E_p`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
+------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``E`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
- This definition uses the *mirror* negative number handling mode of
:func:`colour.models.gamma_function` definition to the sign of negative
numbers.
References
----------
:cite:`AssociationofRadioIndustriesandBusinesses2015a`
Examples
--------
>>> oetf_inverse_ARIBSTDB67(0.212132034355964) # doctest: +ELLIPSIS
0.1799999...
"""
E_p = to_domain_1(E_p)
a = constants.a
b = constants.b
c = constants.c
with domain_range_scale('ignore'):
E = np.where(
E_p <= oetf_ARIBSTDB67(1),
gamma_function((E_p / r), 2, 'mirror'),
np.exp((E_p - c) / a) + b,
)
return as_float(from_range_1(E))