Source code for colour.colorimetry.lightness

"""
Lightness :math:`L`
===================

Defines the *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.
-   :func:`colour.colorimetry.lightness_Abebe2017`: *Lightness* :math:`L`
    computation of given *luminance* :math:`Y` using
    *Abebe, Pouli, Larabi and Reinhard (2017)* 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:`Abebe2017a` : Abebe, M. A., Pouli, T., Larabi, M.-C., & Reinhard,
    E. (2017). Perceptual Lightness Modeling for High-Dynamic-Range Imaging.
    ACM Transactions on Applied Perception, 15(1), 1-19. doi:10.1145/3086577
-   :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 annotations

import numpy as np

from colour.algebra import spow
from colour.biochemistry import (
    reaction_rate_MichaelisMenten_Michaelis1913,
    reaction_rate_MichaelisMenten_Abebe2017,
)
from colour.hints import (
    Any,
    FloatingOrArrayLike,
    FloatingOrNDArray,
    Literal,
    Union,
)
from colour.utilities import (
    CanonicalMapping,
    as_float,
    as_float_array,
    filter_kwargs,
    from_range_100,
    get_domain_range_scale,
    to_domain_1,
    to_domain_100,
    usage_warning,
    validate_method,
)

__author__ = "Colour Developers"
__copyright__ = "Copyright 2013 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_Abebe2017",
    "LIGHTNESS_METHODS",
    "lightness",
]


[docs]def lightness_Glasser1958(Y: FloatingOrArrayLike) -> FloatingOrNDArray: """ Return the *Lightness* :math:`L` of given *luminance* :math:`Y` using *Glasser et al. (1958)* method. Parameters ---------- Y *Luminance* :math:`Y`. Returns ------- :class:`numpy.floating` or :class:`numpy.ndarray` *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 as_float(from_range_100(L))
[docs]def lightness_Wyszecki1963(Y: FloatingOrArrayLike) -> FloatingOrNDArray: """ Return the *Lightness* :math:`W` of given *luminance* :math:`Y` using *Wyszecki (1963)* method. Parameters ---------- Y *Luminance* :math:`Y`. Returns ------- :class:`numpy.floating` or :class:`numpy.ndarray` *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 as_float(from_range_100(W))
[docs]def intermediate_lightness_function_CIE1976( Y: FloatingOrArrayLike, Y_n: FloatingOrArrayLike = 100 ) -> FloatingOrNDArray: """ Return 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 *Luminance* :math:`Y`. Y_n White reference *luminance* :math:`Y_n`. Returns ------- :class:`numpy.floating` or :class:`numpy.ndarray` 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 = np.where( Y_Y_n > (24 / 116) ** 3, spow(Y_Y_n, 1 / 3), (841 / 108) * Y_Y_n + 16 / 116, ) return as_float(f_Y_Y_n)
[docs]def lightness_CIE1976( Y: FloatingOrArrayLike, Y_n: FloatingOrArrayLike = 100 ) -> FloatingOrNDArray: """ Return the *Lightness* :math:`L^*` of given *luminance* :math:`Y` using given reference white *luminance* :math:`Y_n` as per *CIE 1976* recommendation. Parameters ---------- Y *Luminance* :math:`Y`. Y_n White reference *luminance* :math:`Y_n`. Returns ------- :class:`numpy.floating` or :class:`numpy.ndarray` *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 as_float(from_range_100(L_star))
[docs]def lightness_Fairchild2010( Y: FloatingOrArrayLike, epsilon: FloatingOrArrayLike = 1.836 ) -> FloatingOrNDArray: """ Compute *Lightness* :math:`L_{hdr}` of given *luminance* :math:`Y` using *Fairchild and Wyble (2010)* method according to *Michaelis-Menten* kinetics. Parameters ---------- Y *Luminance* :math:`Y`. epsilon :math:`\\epsilon` exponent. Returns ------- :class:`numpy.floating` or :class:`numpy.ndarray` *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:`Fairchild2010` Examples -------- >>> lightness_Fairchild2010(12.19722535 / 100) # doctest: +ELLIPSIS 31.9963902... """ Y = to_domain_1(Y) maximum_perception = 100 L_hdr = ( reaction_rate_MichaelisMenten_Michaelis1913( spow(Y, epsilon), maximum_perception, spow(0.184, epsilon) ) + 0.02 ) return as_float(from_range_100(L_hdr))
[docs]def lightness_Fairchild2011( Y: FloatingOrArrayLike, epsilon: FloatingOrArrayLike = 0.474, method: Union[Literal["hdr-CIELAB", "hdr-IPT"], str] = "hdr-CIELAB", ) -> FloatingOrNDArray: """ Compute *Lightness* :math:`L_{hdr}` of given *luminance* :math:`Y` using *Fairchild and Chen (2011)* method according to *Michaelis-Menten* kinetics. Parameters ---------- Y *Luminance* :math:`Y`. epsilon :math:`\\epsilon` exponent. method *Lightness* :math:`L_{hdr}` computation method. Returns ------- :class:`numpy.floating` or :class:`numpy.ndarray` *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) method = validate_method(method, ["hdr-CIELAB", "hdr-IPT"]) if method == "hdr-cielab": maximum_perception = 247 else: maximum_perception = 246 L_hdr = ( reaction_rate_MichaelisMenten_Michaelis1913( spow(Y, epsilon), maximum_perception, spow(2, epsilon) ) + 0.02 ) return as_float(from_range_100(L_hdr))
[docs]def lightness_Abebe2017( Y: FloatingOrArrayLike, Y_n: FloatingOrArrayLike = 100, method: Union[ Literal["Michaelis-Menten", "Stevens"], str ] = "Michaelis-Menten", ) -> FloatingOrNDArray: """ Compute *Lightness* :math:`L` of given *luminance* :math:`Y` using *Abebe, Pouli, Larabi and Reinhard (2017)* method according to *Michaelis-Menten* kinetics or *Stevens's Power Law*. Parameters ---------- Y *Luminance* :math:`Y` in :math:`cd/m^2`. Y_n Adapting luminance :math:`Y_n` in :math:`cd/m^2`. method *Lightness* :math:`L` computation method. Returns ------- :class:`numpy.floating` or :class:`numpy.ndarray` *Lightness* :math:`L`. Notes ----- - *Abebe, Pouli, Larabi and Reinhard (2017)* method uses absolute luminance levels, thus the domain and range values for the *Reference* and *1* scales are only indicative that the data is not affected by scale transformations. +------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``Y`` | ``UN`` | ``UN`` | +------------+-----------------------+---------------+ | ``Y_n`` | ``UN`` | ``UN`` | +------------+-----------------------+---------------+ +------------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``L`` | ``UN`` | ``UN`` | +------------+-----------------------+---------------+ References ---------- :cite:`Abebe2017a` Examples -------- >>> lightness_Abebe2017(12.19722535) # doctest: +ELLIPSIS 0.4869555... >>> lightness_Abebe2017(12.19722535, method='Stevens') ... # doctest: +ELLIPSIS 0.4745447... """ Y = as_float_array(Y) Y_n = as_float_array(Y_n) method = validate_method(method, ["Michaelis-Menten", "Stevens"]) Y_Y_n = Y / Y_n if method == "stevens": L = np.where( Y_n <= 100, 1.226 * spow(Y_Y_n, 0.266) - 0.226, 1.127 * spow(Y_Y_n, 0.230) - 0.127, ) else: L = np.where( Y_n <= 100, reaction_rate_MichaelisMenten_Abebe2017( spow(Y_Y_n, 0.582), 1.448, 0.635, 0.813 ), reaction_rate_MichaelisMenten_Abebe2017( spow(Y_Y_n, 0.293), 1.680, 1.584, 0.096 ), ) return as_float(L)
LIGHTNESS_METHODS: CanonicalMapping = CanonicalMapping( { "Glasser 1958": lightness_Glasser1958, "Wyszecki 1963": lightness_Wyszecki1963, "CIE 1976": lightness_CIE1976, "Fairchild 2010": lightness_Fairchild2010, "Fairchild 2011": lightness_Fairchild2011, "Abebe 2017": lightness_Abebe2017, } ) LIGHTNESS_METHODS.__doc__ = """ Supported *Lightness* computation methods. References ---------- :cite:`CIETC1-482004m`, :cite:`Fairchild2010`, :cite:`Fairchild2011`, :cite:`Glasser1958a`, :cite:`Wyszecki1963b`, :cite:`Wyszecki2000bd` Aliases: - 'Lstar1976': 'CIE 1976' """ LIGHTNESS_METHODS["Lstar1976"] = LIGHTNESS_METHODS["CIE 1976"]
[docs]def lightness( Y: FloatingOrArrayLike, method: Union[ Literal[ "Abebe 2017", "CIE 1976", "Glasser 1958", "Fairchild 2010", "Fairchild 2011", "Wyszecki 1963", ], str, ] = "CIE 1976", **kwargs: Any, ) -> FloatingOrNDArray: """ Return the *Lightness* :math:`L` of given *luminance* :math:`Y` using given method. Parameters ---------- Y *Luminance* :math:`Y`. method Computation method. Other Parameters ---------------- Y_n {:func:`colour.colorimetry.lightness_Abebe2017`, :func:`colour.colorimetry.lightness_CIE1976`}, White reference *luminance* :math:`Y_n`. epsilon {:func:`colour.colorimetry.lightness_Fairchild2010`, :func:`colour.colorimetry.lightness_Fairchild2011`}, :math:`\\epsilon` exponent. Returns ------- :class:`numpy.floating` or :class:`numpy.ndarray` *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:`Abebe2017a`, :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... >>> lightness(12.19722535, epsilon=0.710, method='Fairchild 2011') ... # doctest: +ELLIPSIS 29.8295108... >>> lightness(12.19722535, method='Abebe 2017') ... # doctest: +ELLIPSIS 48.6955571... """ Y = as_float_array(Y) method = validate_method(method, LIGHTNESS_METHODS) function = LIGHTNESS_METHODS[method] # NOTE: "Abebe et al. (2017)" uses absolute luminance levels and has # undefined domain-range scale, yet we modify its behaviour consistency # with the other methods. domain_range_reference = get_domain_range_scale() == "reference" domain_range_1 = get_domain_range_scale() == "1" domain_range_100 = get_domain_range_scale() == "100" domain_1 = (lightness_Fairchild2010, lightness_Fairchild2011) domain_undefined = (lightness_Abebe2017,) if function in domain_1 and domain_range_reference: Y = Y / 100 if function in domain_undefined and domain_range_1: Y = Y * 100 L = function(Y, **filter_kwargs(function, **kwargs)) if function in domain_undefined and ( domain_range_reference or domain_range_100 ): L *= 100 return L