Source code for colour.colorimetry.lightness

# -*- coding: utf-8 -*-
"""
Lightness :math:`L`
===================

Defines *Lightness* :math:`L` computation objects.

The following methods are available:

-   :func:`colour.colorimetry.lightness_Glasser1958`: *Lightness* :math:`L`
    computation of given *luminance* :math:`Y` using
    *Glasser, Mckinney, Reilly and Schnelle (1958)* method.
-   :func:`colour.colorimetry.lightness_Wyszecki1963`: *Lightness* :math:`W`
    computation of given *luminance* :math:`Y` using *Wyszecki (1963)* method.
-   :func:`colour.colorimetry.lightness_CIE1976`: *Lightness* :math:`L^*`
    computation of given *luminance* :math:`Y` as per *CIE 1976*
    recommendation.
-   :func:`colour.colorimetry.lightness_Fairchild2010`: *Lightness*
    :math:`L_{hdr}` computation of given *luminance* :math:`Y` using
    *Fairchild and Wyble (2010)* method.
-   :func:`colour.colorimetry.lightness_Fairchild2011`: *Lightness*
    :math:`L_{hdr}` computation of given *luminance* :math:`Y` using
    *Fairchild and Chen (2011)* method.
-   :attr:`colour.LIGHTNESS_METHODS`: Supported *Lightness* :math:`L`
    computation methods.
-   :func:`colour.lightness`: *Lightness* :math:`L` computation of given
    *luminance* :math:`Y` using given method.

References
----------
-   :cite:`CIETC1-482004m` : CIE TC 1-48. (2004). CIE 1976 uniform colour
    spaces. In CIE 015:2004 Colorimetry, 3rd Edition (p. 24).
    ISBN:978-3-901906-33-6
-   :cite:`Fairchild2010` : Fairchild, M. D., & Wyble, D. R. (2010). hdr-CIELAB
    and hdr-IPT: Simple Models for Describing the Color of High-Dynamic-Range
    and Wide-Color-Gamut Images. Proc. of Color and Imaging Conference,
    322-326. ISBN:978-1-62993-215-6
-   :cite:`Fairchild2011` : Fairchild, M. D., & Chen, P. (2011). Brightness,
    lightness, and specifying color in high-dynamic-range scenes and images. In
    S. P. Farnand & F. Gaykema (Eds.), Proc. SPIE 7867, Image Quality and
    System Performance VIII (p. 78670O). doi:10.1117/12.872075
-   :cite:`Glasser1958a` : Glasser, L. G., McKinney, A. H., Reilly, C. D., &
    Schnelle, P. D. (1958). Cube-Root Color Coordinate System. Journal of the
    Optical Society of America, 48(10), 736. doi:10.1364/JOSA.48.000736
-   :cite:`Wikipedia2007c` : Nayatani, Y., Sobagaki, H., & Yano, K. H. T.
    (1995). Lightness dependency of chroma scales of a nonlinear
    color-appearance model and its latest formulation. Color Research &
    Application, 20(3), 156-167. doi:10.1002/col.5080200305
-   :cite:`Wyszecki1963b` : Wyszecki, Günter. (1963). Proposal for a New
    Color-Difference Formula. Journal of the Optical Society of America,
    53(11), 1318. doi:10.1364/JOSA.53.001318
-   :cite:`Wyszecki2000bd` : Wyszecki, Günther, & Stiles, W. S. (2000). CIE
    1976 (L*u*v*)-Space and Color-Difference Formula. In Color Science:
    Concepts and Methods, Quantitative Data and Formulae (p. 167). Wiley.
    ISBN:978-0-471-39918-6
"""

from __future__ import division, unicode_literals

import numpy as np

from colour.algebra import spow
from colour.biochemistry import reaction_rate_MichealisMenten
from colour.utilities import (CaseInsensitiveMapping, as_float_array, as_float,
                              filter_kwargs, from_range_100,
                              get_domain_range_scale, to_domain_1,
                              to_domain_100, usage_warning)

__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__ = [
    'lightness_Glasser1958', 'lightness_Wyszecki1963',
    'intermediate_lightness_function_CIE1976', 'lightness_CIE1976',
    'lightness_Fairchild2010', 'lightness_Fairchild2011', 'LIGHTNESS_METHODS',
    'lightness'
]


[docs]def lightness_Glasser1958(Y): """ Returns the *Lightness* :math:`L` of given *luminance* :math:`Y` using *Glasser et al. (1958)* method. Parameters ---------- Y : numeric or array_like *luminance* :math:`Y`. Returns ------- numeric or array_like *Lightness* :math:`L`. Notes ----- +------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``Y`` | [0, 100] | [0, 1] | +------------+-----------------------+---------------+ +------------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``L`` | [0, 100] | [0, 1] | +------------+-----------------------+---------------+ References ---------- :cite:`Glasser1958a` Examples -------- >>> lightness_Glasser1958(12.19722535) # doctest: +ELLIPSIS 39.8351264... """ Y = to_domain_100(Y) L = 25.29 * spow(Y, 1 / 3) - 18.38 return from_range_100(L)
[docs]def lightness_Wyszecki1963(Y): """ Returns the *Lightness* :math:`W` of given *luminance* :math:`Y` using *Wyszecki (1963)* method. Parameters ---------- Y : numeric or array_like *luminance* :math:`Y`. Returns ------- numeric or array_like *Lightness* :math:`W`. Notes ----- +------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``Y`` | [0, 100] | [0, 1] | +------------+-----------------------+---------------+ +------------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``W`` | [0, 100] | [0, 1] | +------------+-----------------------+---------------+ References ---------- :cite:`Wyszecki1963b` Examples -------- >>> lightness_Wyszecki1963(12.19722535) # doctest: +ELLIPSIS 40.5475745... """ Y = to_domain_100(Y) if np.any(Y < 1) or np.any(Y > 98): usage_warning('"W*" Lightness computation is only applicable for ' '1% < "Y" < 98%, unpredictable results may occur!') W = 25 * spow(Y, 1 / 3) - 17 return from_range_100(W)
[docs]def intermediate_lightness_function_CIE1976(Y, Y_n=100): """ Returns the intermediate value :math:`f(Y/Yn)` in the *Lightness* :math:`L^*` computation for given *luminance* :math:`Y` using given reference white *luminance* :math:`Y_n` as per *CIE 1976* recommendation. Parameters ---------- Y : numeric or array_like *luminance* :math:`Y`. Y_n : numeric or array_like, optional White reference *luminance* :math:`Y_n`. Returns ------- numeric or array_like Intermediate value :math:`f(Y/Yn)`. Notes ----- +-------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +=============+=======================+===============+ | ``Y`` | [0, 100] | [0, 100] | +-------------+-----------------------+---------------+ +-------------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +=============+=======================+===============+ | ``f_Y_Y_n`` | [0, 1] | [0, 1] | +-------------+-----------------------+---------------+ References ---------- :cite:`CIETC1-482004m`, :cite:`Wyszecki2000bd` Examples -------- >>> intermediate_lightness_function_CIE1976(12.19722535) ... # doctest: +ELLIPSIS 0.4959299... >>> intermediate_lightness_function_CIE1976(12.19722535, 95) ... # doctest: +ELLIPSIS 0.5044821... """ Y = as_float_array(Y) Y_n = as_float_array(Y_n) Y_Y_n = Y / Y_n f_Y_Y_n = as_float( np.where( Y_Y_n > (24 / 116) ** 3, spow(Y_Y_n, 1 / 3), (841 / 108) * Y_Y_n + 16 / 116, )) return f_Y_Y_n
[docs]def lightness_CIE1976(Y, Y_n=100): """ Returns the *Lightness* :math:`L^*` of given *luminance* :math:`Y` using given reference white *luminance* :math:`Y_n` as per *CIE 1976* recommendation. Parameters ---------- Y : numeric or array_like *luminance* :math:`Y`. Y_n : numeric or array_like, optional White reference *luminance* :math:`Y_n`. Returns ------- numeric or array_like *Lightness* :math:`L^*`. Notes ----- +------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``Y`` | [0, 100] | [0, 1] | +------------+-----------------------+---------------+ +------------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``L_star`` | [0, 100] | [0, 1] | +------------+-----------------------+---------------+ References ---------- :cite:`CIETC1-482004m`, :cite:`Wyszecki2000bd` Examples -------- >>> lightness_CIE1976(12.19722535) # doctest: +ELLIPSIS 41.5278758... """ Y = to_domain_100(Y) Y_n = as_float_array(Y_n) L_star = 116 * intermediate_lightness_function_CIE1976(Y, Y_n) - 16 return from_range_100(L_star)
[docs]def lightness_Fairchild2010(Y, epsilon=1.836): """ Computes *Lightness* :math:`L_{hdr}` of given *luminance* :math:`Y` using *Fairchild and Wyble (2010)* method according to *Michealis-Menten* kinetics. Parameters ---------- Y : array_like *luminance* :math:`Y`. epsilon : numeric or array_like, optional :math:`\\epsilon` exponent. Returns ------- array_like *Lightness* :math:`L_{hdr}`. Warning ------- The input domain of that definition is non standard! Notes ----- +------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``Y`` | [0, 1] | [0, 1] | +------------+-----------------------+---------------+ +------------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``L_hdr`` | [0, 100] | [0, 1] | +------------+-----------------------+---------------+ References ---------- :cite:`Fairchild2010` Examples -------- >>> lightness_Fairchild2010(12.19722535 / 100) # doctest: +ELLIPSIS 31.9963902... """ Y = to_domain_1(Y) maximum_perception = 100 L_hdr = reaction_rate_MichealisMenten( spow(Y, epsilon), maximum_perception, 0.184 ** epsilon) + 0.02 return from_range_100(L_hdr)
[docs]def lightness_Fairchild2011(Y, epsilon=0.474, method='hdr-CIELAB'): """ Computes *Lightness* :math:`L_{hdr}` of given *luminance* :math:`Y` using *Fairchild and Chen (2011)* method according to *Michealis-Menten* kinetics. Parameters ---------- Y : array_like *luminance* :math:`Y`. epsilon : numeric or array_like, optional :math:`\\epsilon` exponent. method : unicode, optional **{'hdr-CIELAB', 'hdr-IPT'}**, *Lightness* :math:`L_{hdr}` computation method. Returns ------- array_like *Lightness* :math:`L_{hdr}`. Notes ----- +------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``Y`` | [0, 1] | [0, 1] | +------------+-----------------------+---------------+ +------------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``L_hdr`` | [0, 100] | [0, 1] | +------------+-----------------------+---------------+ References ---------- :cite:`Fairchild2011` Examples -------- >>> lightness_Fairchild2011(12.19722535 / 100) # doctest: +ELLIPSIS 51.8529584... >>> lightness_Fairchild2011(12.19722535 / 100, method='hdr-IPT') ... # doctest: +ELLIPSIS 51.6431084... """ Y = to_domain_1(Y) if method.lower() == 'hdr-cielab': maximum_perception = 247 else: maximum_perception = 246 L_hdr = reaction_rate_MichealisMenten( spow(Y, epsilon), maximum_perception, 2 ** epsilon) + 0.02 return from_range_100(L_hdr)
LIGHTNESS_METHODS = CaseInsensitiveMapping({ 'Glasser 1958': lightness_Glasser1958, 'Wyszecki 1963': lightness_Wyszecki1963, 'CIE 1976': lightness_CIE1976, 'Fairchild 2010': lightness_Fairchild2010, 'Fairchild 2011': lightness_Fairchild2011 }) LIGHTNESS_METHODS.__doc__ = """ Supported *Lightness* computation methods. References ---------- :cite:`CIETC1-482004m`, :cite:`Fairchild2010`, :cite:`Fairchild2011`, :cite:`Glasser1958a`, :cite:`Wyszecki1963b`, :cite:`Wyszecki2000bd` LIGHTNESS_METHODS : CaseInsensitiveMapping **{'Glasser 1958', 'Wyszecki 1963', 'CIE 1976', 'Fairchild 2010', 'Fairchild 2011'}** Aliases: - 'Lstar1976': 'CIE 1976' """ LIGHTNESS_METHODS['Lstar1976'] = LIGHTNESS_METHODS['CIE 1976']
[docs]def lightness(Y, method='CIE 1976', **kwargs): """ Returns the *Lightness* :math:`L` of given *luminance* :math:`Y` using given method. Parameters ---------- Y : numeric or array_like *luminance* :math:`Y`. method : unicode, optional **{'CIE 1976', 'Glasser 1958', 'Wyszecki 1963', 'Fairchild 2010', 'Fairchild 2011'}**, Computation method. Other Parameters ---------------- Y_n : numeric or array_like, optional {:func:`colour.colorimetry.lightness_CIE1976`}, White reference *luminance* :math:`Y_n`. epsilon : numeric or array_like, optional {:func:`colour.colorimetry.lightness_Fairchild2010`, :func:`colour.colorimetry.lightness_Fairchild2011`}, :math:`\\epsilon` exponent. Returns ------- numeric or array_like *Lightness* :math:`L`. Notes ----- +------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``Y`` | [0, 100] | [0, 1] | +------------+-----------------------+---------------+ +------------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``L`` | [0, 100] | [0, 1] | +------------+-----------------------+---------------+ References ---------- :cite:`CIETC1-482004m`, :cite:`Fairchild2010`, :cite:`Fairchild2011`, :cite:`Glasser1958a`, :cite:`Wikipedia2007c`, :cite:`Wyszecki1963b`, :cite:`Wyszecki2000bd` Examples -------- >>> lightness(12.19722535) # doctest: +ELLIPSIS 41.5278758... >>> lightness(12.19722535, Y_n=100) # doctest: +ELLIPSIS 41.5278758... >>> lightness(12.19722535, Y_n=95) # doctest: +ELLIPSIS 42.5199307... >>> lightness(12.19722535, method='Glasser 1958') # doctest: +ELLIPSIS 39.8351264... >>> lightness(12.19722535, method='Wyszecki 1963') # doctest: +ELLIPSIS 40.5475745... >>> lightness(12.19722535, epsilon=0.710, method='Fairchild 2011') ... # doctest: +ELLIPSIS 29.8295108... """ Y = as_float_array(Y) function = LIGHTNESS_METHODS[method] domain_range_reference = get_domain_range_scale() == 'reference' domain_1 = (lightness_Fairchild2010, lightness_Fairchild2011) if function in domain_1 and domain_range_reference: Y = Y / 100 return function(Y, **filter_kwargs(function, **kwargs))