text: # -*- 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-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
  """
  
  
  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))
  
  
  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))
  