Source code for colour.temperature.hernandez1999

# -*- coding: utf-8 -*-
"""
Hernandez-Andres, Lee and Romero (1999) Correlated Colour Temperature
=====================================================================

Defines *Hernandez-Andres et al. (1999)* correlated colour temperature
:math:`T_{cp}` computations objects:

-   :func:`colour.temperature.xy_to_CCT_Hernandez1999`: Correlated colour
    temperature :math:`T_{cp}` computation of given *CIE xy* chromaticity
    coordinates using *Hernandez-Andres, Lee and Romero (1999)* method.
-   :func:`colour.temperature.CCT_to_xy_Hernandez1999`: *CIE xy* chromaticity
    coordinates computation of given correlated colour temperature
    :math:`T_{cp}` using *Hernandez-Andres, Lee and Romero (1999)* method.

References
----------
-   :cite:`Hernandez-Andres1999a` : Hernández-Andrés, J., Lee, R. L., &
    Romero, J. (1999). Calculating correlated color temperatures across the
    entire gamut of daylight and skylight chromaticities. Applied Optics,
    38(27), 5703. doi:10.1364/AO.38.005703
"""

from __future__ import division, unicode_literals

import numpy as np
from scipy.optimize import minimize

from colour.colorimetry import ILLUMINANTS
from colour.utilities import as_float_array, as_numeric, tsplit, usage_warning
from colour.utilities.deprecation import handle_arguments_deprecation

__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__ = ['xy_to_CCT_Hernandez1999', 'CCT_to_xy_Hernandez1999']


[docs]def xy_to_CCT_Hernandez1999(xy): """ Returns the correlated colour temperature :math:`T_{cp}` from given *CIE xy* chromaticity coordinates using *Hernandez-Andres et al. (1999)* method. Parameters ---------- xy : array_like *CIE xy* chromaticity coordinates. Returns ------- numeric Correlated colour temperature :math:`T_{cp}`. References ---------- :cite:`Hernandez-Andres1999a` Examples -------- >>> xy = np.array([0.31270, 0.32900]) >>> xy_to_CCT_Hernandez1999(xy) # doctest: +ELLIPSIS 6500.7420431... """ x, y = tsplit(xy) n = (x - 0.3366) / (y - 0.1735) CCT = (-949.86315 + 6253.80338 * np.exp(-n / 0.92159) + 28.70599 * np.exp(-n / 0.20039) + 0.00004 * np.exp(-n / 0.07125)) n = np.where(CCT > 50000, (x - 0.3356) / (y - 0.1691), n) CCT = np.where( CCT > 50000, 36284.48953 + 0.00228 * np.exp(-n / 0.07861) + 5.4535e-36 * np.exp(-n / 0.01543), CCT, ) return as_numeric(CCT)
[docs]def CCT_to_xy_Hernandez1999(CCT, optimisation_kwargs=None, **kwargs): """ Returns the *CIE xy* chromaticity coordinates from given correlated colour temperature :math:`T_{cp}` using *Hernandez-Andres et al. (1999)* method. Parameters ---------- CCT : numeric or array_like Correlated colour temperature :math:`T_{cp}`. optimisation_kwargs : dict_like, optional Parameters for :func:`scipy.optimize.minimize` definition. Other Parameters ---------------- \\**kwargs : dict, optional Keywords arguments for deprecation management. Returns ------- ndarray *CIE xy* chromaticity coordinates. Warnings -------- *Hernandez-Andres et al. (1999)* method for computing *CIE xy* chromaticity coordinates from given correlated colour temperature is not a bijective function and might produce unexpected results. It is given for consistency with other correlated colour temperature computation methods but should be avoided for practical applications. The current implementation relies on optimization using :func:`scipy.optimize.minimize` definition and thus has reduced precision and poor performance. References ---------- :cite:`Hernandez-Andres1999a` Examples -------- >>> CCT_to_xy_Hernandez1999(6500.7420431786531) # doctest: +ELLIPSIS array([ 0.3127..., 0.329...]) """ optimisation_kwargs = handle_arguments_deprecation({ 'ArgumentRenamed': [['optimisation_parameters', 'optimisation_kwargs'] ], }, **kwargs).get('optimisation_kwargs', optimisation_kwargs) usage_warning('"Hernandez-Andres et al. (1999)" method for computing ' '"CIE xy" chromaticity coordinates from given correlated ' 'colour temperature is not a bijective function and and' 'might produce unexpected results. It is given for ' 'consistency with other correlated colour temperature ' 'computation methods but should be avoided for practical ' 'applications.') CCT = as_float_array(CCT) shape = list(CCT.shape) CCT = np.atleast_1d(CCT.reshape([-1, 1])) def objective_function(xy, CCT): """ Objective function. """ objective = np.linalg.norm(xy_to_CCT_Hernandez1999(xy) - CCT) return 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=ILLUMINANTS['CIE 1931 2 Degree Standard Observer']['D65'], args=(CCT_i, ), **optimisation_settings).x for CCT_i in CCT ]) return as_numeric(CCT.reshape(shape + [2]))