Source code for colour.models.rgb.transfer_functions.arib_std_b67

# -*- 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`

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.
    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) 2013-2020 - 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__ = [
    '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))