Source code for colour.colorimetry.lightness

#!/usr/bin/env python
# -*- coding: utf-8 -*-

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

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

The following methods are available:

-   :func:`lightness_Glasser1958`: *Lightness* :math:`L^*` computation of given
    *luminance* :math:`Y` using
    Glasser, Mckinney, Reilly and Schnelle (1958)⁠⁠⁠ method.
-   :func:`lightness_Wyszecki1963`: *Lightness* :math:`W` computation of
    given *luminance* :math:`Y` using Wyszecki (1963)⁠⁠⁠⁠ method.
-   :func:`lightness_1976`: *Lightness* :math:`L^*` computation of given
    *luminance* :math:`Y` as per *CIE Lab* implementation.

See Also
--------
`Lightness IPython Notebook
<http://nbviewer.ipython.org/github/colour-science/colour-ipython/blob/master/notebooks/colorimetry/lightness.ipynb>`_  # noqa

References
----------
.. [1]  Wikipedia. (n.d.). Lightness. Retrieved April 13, 2014, from
        http://en.wikipedia.org/wiki/Lightness
"""

from __future__ import division, unicode_literals

import numpy as np

from colour.constants import CIE_E, CIE_K
from colour.utilities import CaseInsensitiveMapping, warning

__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013 - 2015 - Colour Developers'
__license__ = 'New BSD License - http://opensource.org/licenses/BSD-3-Clause'
__maintainer__ = 'Colour Developers'
__email__ = 'colour-science@googlegroups.com'
__status__ = 'Production'

__all__ = ['lightness_Glasser1958',
           'lightness_Wyszecki1963',
           'lightness_1976',
           'LIGHTNESS_METHODS',
           'lightness']


[docs]def lightness_Glasser1958(Y, **kwargs): """ Returns the *Lightness* :math:`L` of given *luminance* :math:`Y` using *Glasser, Mckinney, Reilly and Schnelle (1958)* method. Parameters ---------- Y : numeric or array_like *luminance* :math:`Y`. \*\*kwargs : \*\*, optional Unused parameter provided for signature compatibility with other *Lightness* computation objects. Returns ------- numeric or array_like *Lightness* :math:`L`. Notes ----- - Input *luminance* :math:`Y` is in domain [0, 100]. - Output *Lightness* :math:`L` is in domain [0, 100]. References ---------- .. [2] Glasser, L. G., McKinney, A. H., Reilly, C. D., & Schnelle, P. D. (1958). Cube-Root Color Coordinate System. J. Opt. Soc. Am., 48(10), 736–740. doi:10.1364/JOSA.48.000736 Examples -------- >>> lightness_Glasser1958(10.08) # doctest: +ELLIPSIS 36.2505626... """ Y = np.asarray(Y) L = 25.29 * (Y ** (1 / 3)) - 18.38 return L
[docs]def lightness_Wyszecki1963(Y, **kwargs): """ Returns the *Lightness* :math:`W` of given *luminance* :math:`Y` using *Wyszecki (1963)* method. Parameters ---------- Y : numeric or array_like *luminance* :math:`Y`. \*\*kwargs : \*\*, optional Unused parameter provided for signature compatibility with other *Lightness* computation objects. Returns ------- numeric or array_like *Lightness* :math:`W`. Notes ----- - Input *luminance* :math:`Y` is in domain [0, 100]. - Output *Lightness* :math:`W` is in domain [0, 100]. References ---------- .. [3] Wyszecki, G. (1963). Proposal for a New Color-Difference Formula. J. Opt. Soc. Am., 53(11), 1318–1319. doi:10.1364/JOSA.53.001318 Examples -------- >>> lightness_Wyszecki1963(10.08) # doctest: +ELLIPSIS 37.0041149... """ Y = np.asarray(Y) if np.any(Y < 1) or np.any(Y > 98): warning(('"W*" Lightness computation is only applicable for ' '1% < "Y" < 98%, unpredictable results may occur!')) W = 25 * (Y ** (1 / 3)) - 17 return W
[docs]def lightness_1976(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 Lab* implementation. 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 ----- - Input *luminance* :math:`Y` and :math:`Y_n` are in domain [0, 100]. - Output *Lightness* :math:`L^*` is in domain [0, 100]. References ---------- .. [4] Wyszecki, G., & 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:978-0471399186 .. [5] Lindbloom, B. (2003). A Continuity Study of the CIE L* Function. Retrieved February 24, 2014, from http://brucelindbloom.com/LContinuity.html Examples -------- >>> lightness_1976(10.08) # doctest: +ELLIPSIS array(37.9856290...) """ Y = np.asarray(Y) Y_n = np.asarray(Y_n) Lstar = Y / Y_n Lstar = np.where(Lstar <= CIE_E, CIE_K * Lstar, 116 * Lstar ** (1 / 3) - 16) return Lstar
LIGHTNESS_METHODS = CaseInsensitiveMapping( {'Glasser 1958': lightness_Glasser1958, 'Wyszecki 1963': lightness_Wyszecki1963, 'CIE 1976': lightness_1976}) """ Supported *Lightness* computations methods. LIGHTNESS_METHODS : CaseInsensitiveMapping {'Glasser 1958', 'Wyszecki 1963', 'CIE 1976'} Aliases: - 'Lstar1976': 'CIE 1976' """ LIGHTNESS_METHODS['Lstar1976'] = LIGHTNESS_METHODS['CIE 1976']
[docs]def lightness(Y, method='CIE 1976', **kwargs): """ Returns the *Lightness* :math:`L^*` using given method. Parameters ---------- Y : numeric or array_like *luminance* :math:`Y`. method : unicode, optional {'CIE 1976', 'Glasser 1958', 'Wyszecki 1963'}, Computation method. \*\*kwargs : \*\* Keywords arguments. Returns ------- numeric or array_like *Lightness* :math:`L^*`. Notes ----- - Input *luminance* :math:`Y` and optional :math:`Y_n` are in domain [0, 100]. - Output *Lightness* :math:`L^*` is in domain [0, 100]. Examples -------- >>> lightness(10.08) # doctest: +ELLIPSIS array(37.9856290...) >>> lightness(10.08, Y_n=100) # doctest: +ELLIPSIS array(37.9856290...) >>> lightness(10.08, Y_n=95) # doctest: +ELLIPSIS array(38.9165987...) >>> lightness(10.08, method='Glasser 1958') # doctest: +ELLIPSIS 36.2505626... >>> lightness(10.08, method='Wyszecki 1963') # doctest: +ELLIPSIS 37.0041149... """ return LIGHTNESS_METHODS.get(method)(Y, **kwargs)