# -*- coding: utf-8 -*-
"""
ITU-R BT.1886
=============

Defines *Recommendation ITU-R BT.1886* electro-optical transfer function (EOTF
/ EOCF) and its inverse:

-   :func:`colour.models.eotf_inverse_BT1886`
-   :func:`colour.models.eotf_BT1886`

References
----------
-   :cite:`InternationalTelecommunicationUnion2011h` : International
    Telecommunication Union. (2011). Recommendation ITU-R BT.1886 - Reference
    electro-optical transfer function for flat panel displays used in HDTV
    studio production BT Series Broadcasting service.
    https://www.itu.int/dms_pubrec/itu-r/rec/bt/\
R-REC-BT.1886-0-201103-I!!PDF-E.pdf
"""

from __future__ import division, unicode_literals

import numpy as np

from colour.utilities import 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__ = ['eotf_inverse_BT1886', 'eotf_BT1886']


def eotf_inverse_BT1886(L, L_B=0, L_W=1):
    """
    Defines *Recommendation ITU-R BT.1886* inverse electro-optical transfer
    function (EOTF / EOCF).

    Parameters
    ----------
    L : numeric or array_like
        Screen luminance in :math:`cd/m^2`.
    L_B : numeric, optional
        Screen luminance for black.
    L_W : numeric, optional
        Screen luminance for white.

    Returns
    -------
    numeric or ndarray
        Input video signal level (normalised, black at :math:`V = 0`, to white
        at :math:`V = 1`.

    Notes
    -----

    +------------+-----------------------+---------------+
    | **Domain** | **Scale - Reference** | **Scale - 1** |
    +============+=======================+===============+
    | ``L``      | [0, 1]                | [0, 1]        |
    +------------+-----------------------+---------------+

    +------------+-----------------------+---------------+
    | **Range**  | **Scale - Reference** | **Scale - 1** |
    +============+=======================+===============+
    | ``V``      | [0, 1]                | [0, 1]        |
    +------------+-----------------------+---------------+

    References
    ----------
    :cite:`InternationalTelecommunicationUnion2011h`

    Examples
    --------
    >>> eotf_inverse_BT1886(0.11699185725296059)  # doctest: +ELLIPSIS
    0.4090077...
    """

    L = to_domain_1(L)

    gamma = 2.40
    gamma_d = 1 / gamma

    n = L_W ** gamma_d - L_B ** gamma_d
    a = n ** gamma
    b = L_B ** gamma_d / n

    V = (L / a) ** gamma_d - b

    return from_range_1(V)


def eotf_BT1886(V, L_B=0, L_W=1):
    """
    Defines *Recommendation ITU-R BT.1886* electro-optical transfer function
    (EOTF / EOCF).

    Parameters
    ----------
    V : numeric or array_like
        Input video signal level (normalised, black at :math:`V = 0`, to white
        at :math:`V = 1`. For content mastered per
        *Recommendation ITU-R BT.709*, 10-bit digital code values :math:`D` map
        into values of :math:`V` per the following equation:
        :math:`V = (D-64)/876`
    L_B : numeric, optional
        Screen luminance for black.
    L_W : numeric, optional
        Screen luminance for white.

    Returns
    -------
    numeric or ndarray
        Screen luminance in :math:`cd/m^2`.

    Notes
    -----

    +------------+-----------------------+---------------+
    | **Domain** | **Scale - Reference** | **Scale - 1** |
    +============+=======================+===============+
    | ``V``      | [0, 1]                | [0, 1]        |
    +------------+-----------------------+---------------+

    +------------+-----------------------+---------------+
    | **Range**  | **Scale - Reference** | **Scale - 1** |
    +============+=======================+===============+
    | ``L``      | [0, 1]                | [0, 1]        |
    +------------+-----------------------+---------------+

    References
    ----------
    :cite:`InternationalTelecommunicationUnion2011h`

    Examples
    --------
    >>> eotf_BT1886(0.409007728864150)  # doctest: +ELLIPSIS
    0.1169918...
    """

    V = to_domain_1(V)

    gamma = 2.40
    gamma_d = 1 / gamma

    n = L_W ** gamma_d - L_B ** gamma_d
    a = n ** gamma
    b = L_B ** gamma_d / n
    L = a * np.maximum(V + b, 0) ** gamma

    return from_range_1(L)
