Source code for colour.models.rgb.transfer_functions.itur_bt_601

# -*- coding: utf-8 -*-
"""
ITU-R BT.601-7
==============

Defines the *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`

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
"""

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) 2013-2021 - 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): """ 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))