Source code for colour.temperature.krystek1985

"""
Krystek (1985) Correlated Colour Temperature
============================================

Defines the *Krystek (1985)* correlated colour temperature :math:`T_{cp}`
computations objects:

-   :func:`colour.temperature.uv_to_CCT_Krystek1985`: Correlated colour
    temperature :math:`T_{cp}` computation of given *CIE UCS* colourspace *uv*
    chromaticity coordinates using *Krystek (1985)* method.
-   :func:`colour.temperature.CCT_to_uv_Krystek1985`: *CIE UCS* colourspace
    *uv* chromaticity coordinates computation of given correlated colour
    temperature :math:`T_{cp}` using *Krystek (1985)* method.

References
----------
-   :cite:`Krystek1985b` : Krystek, M. (1985). An algorithm to calculate
    correlated colour temperature. Color Research & Application, 10(1), 38-40.
    doi:10.1002/col.5080100109
"""

from __future__ import annotations

import numpy as np
from scipy.optimize import minimize

from colour.hints import ArrayLike, NDArrayFloat
from colour.utilities import as_float, as_float_array, tstack

__author__ = "Colour Developers"
__copyright__ = "Copyright 2013 Colour Developers"
__license__ = "BSD-3-Clause - https://opensource.org/licenses/BSD-3-Clause"
__maintainer__ = "Colour Developers"
__email__ = "colour-developers@colour-science.org"
__status__ = "Production"

__all__ = [
    "uv_to_CCT_Krystek1985",
    "CCT_to_uv_Krystek1985",
]




def uv_to_CCT_Krystek1985(
    uv: ArrayLike, optimisation_kwargs: dict | None = None
) -> NDArrayFloat:
    """
    Return the correlated colour temperature :math:`T_{cp}` from given
    *CIE UCS* colourspace *uv* chromaticity coordinates using *Krystek (1985)*
    method.

    Parameters
    ----------
    uv
         *CIE UCS* colourspace *uv* chromaticity coordinates.
    optimisation_kwargs
        Parameters for :func:`scipy.optimize.minimize` definition.

    Returns
    -------
    :class:`numpy.ndarray`
        Correlated colour temperature :math:`T_{cp}`.

    Warnings
    --------
    *Krystek (1985)* does not give an analytical inverse transformation to
    compute the correlated colour temperature :math:`T_{cp}` from given
    *CIE UCS* colourspace *uv* chromaticity coordinates, the current
    implementation relies on optimisation using :func:`scipy.optimize.minimize`
    definition and thus has reduced precision and poor performance.

    Notes
    -----
    -   *Krystek (1985)* method computations are valid for correlated colour
        temperature :math:`T_{cp}` normalised to domain [1000, 15000].

    References
    ----------
    :cite:`Krystek1985b`

    Examples
    --------
    >>> uv_to_CCT_Krystek1985(np.array([0.20047203, 0.31029290]))
    ... # doctest: +ELLIPSIS
    6504.3894290...
    """

    uv = as_float_array(uv)
    shape = uv.shape
    uv = np.atleast_1d(uv.reshape([-1, 2]))

    def objective_function(
        CCT: NDArrayFloat, uv: NDArrayFloat
    ) -> NDArrayFloat:
        """Objective function."""

        objective = np.linalg.norm(CCT_to_uv_Krystek1985(CCT) - uv)

        return as_float(objective)

    optimisation_settings = {
        "method": "Nelder-Mead",
        "options": {
            "fatol": 1e-10,
        },
    }
    if optimisation_kwargs is not None:
        optimisation_settings.update(optimisation_kwargs)

    CCT = as_float_array(
        [
            minimize(
                objective_function,
                x0=6500,
                args=(uv_i,),
                **optimisation_settings,
            ).x
            for uv_i in uv
        ]
    )

    return as_float(np.reshape(CCT, shape[:-1]))





def CCT_to_uv_Krystek1985(CCT: ArrayLike) -> NDArrayFloat:
    """
    Return the *CIE UCS* colourspace *uv* chromaticity coordinates from given
    correlated colour temperature :math:`T_{cp}` using *Krystek (1985)* method.

    Parameters
    ----------
    CCT
        Correlated colour temperature :math:`T_{cp}`.

    Returns
    -------
    :class:`numpy.ndarray`
        *CIE UCS* colourspace *uv* chromaticity coordinates.

    Notes
    -----
    -   *Krystek (1985)* method computations are valid for correlated colour
        temperature :math:`T_{cp}` normalised to domain [1000, 15000].

    References
    ----------
    :cite:`Krystek1985b`

    Examples
    --------
    >>> CCT_to_uv_Krystek1985(6504.38938305)  # doctest: +ELLIPSIS
    array([ 0.2004720...,  0.3102929...])
    """

    T = as_float_array(CCT)

    T_2 = T**2

    u = (
        0.860117757 + 1.54118254 * 10**-4 * T + 1.28641212 * 10**-7 * T_2
    ) / (1 + 8.42420235 * 10**-4 * T + 7.08145163 * 10**-7 * T_2)
    v = (
        0.317398726 + 4.22806245 * 10**-5 * T + 4.20481691 * 10**-8 * T_2
    ) / (1 - 2.89741816 * 10**-5 * T + 1.61456053 * 10**-7 * T_2)

    return tstack([u, v])