"""
ITU-R BT.601-7
==============
Defines the *ITU-R BT.601-7* opto-electrical transfer function (OETF)
and its inverse:
- :func:`colour.models.oetf_BT601`
- :func:`colour.models.oetf_inverse_BT601`
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.
http://www.itu.int/dms_pubrec/itu-r/rec/bt/\
R-REC-BT.601-7-201103-I!!PDF-E.pdf
"""
from __future__ import annotations
import numpy as np
from colour.algebra import spow
from colour.hints import FloatingOrArrayLike, FloatingOrNDArray
from colour.utilities import (
as_float,
domain_range_scale,
from_range_1,
to_domain_1,
)
__author__ = "Colour Developers"
__copyright__ = "Copyright 2013 Colour Developers"
__license__ = "New BSD License - https://opensource.org/licenses/BSD-3-Clause"
__maintainer__ = "Colour Developers"
__email__ = "colour-developers@colour-science.org"
__status__ = "Production"
__all__ = [
"oetf_BT601",
"oetf_inverse_BT601",
]
[docs]def oetf_BT601(L: FloatingOrArrayLike) -> FloatingOrNDArray:
"""
Define *Recommendation ITU-R BT.601-7* opto-electronic transfer function
(OETF).
Parameters
----------
L
*Luminance* :math:`L` of the image.
Returns
-------
:class:`numpy.floating` or :class:`numpy.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: FloatingOrArrayLike) -> FloatingOrNDArray:
"""
Define *Recommendation ITU-R BT.601-7* inverse opto-electronic transfer
function (OETF).
Parameters
----------
E
Electrical signal :math:`E`.
Returns
-------
:class:`numpy.floating` or :class:`numpy.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))