Source code for colour.colorimetry.luminance

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

"""
Luminance :math:`Y`
===================

Defines *luminance* :math:`Y` computation objects.

The following methods are available:

-   :func:`luminance_Newhall1943`: *luminance* :math:`Y` computation of given
    *Munsell* value :math:`V` using Newhall, Nickerson, and Judd (1943)
    method.
-   :func:`luminance_ASTMD153508`: *luminance* :math:`Y` computation of given
    *Munsell* value :math:`V` using ASTM D1535-08e1 (2008) method.
-   :func:`luminance_1976`: *luminance* :math:`Y` computation of given
    *Lightness* :math:`L^*` as per *CIE Lab* implementation.

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

from __future__ import division, unicode_literals

import numpy as np

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

__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__ = ['luminance_Newhall1943',
           'luminance_ASTMD153508',
           'luminance_1976',
           'LUMINANCE_METHODS',
           'luminance']


[docs]def luminance_Newhall1943(V, **kwargs): """ Returns the *luminance* :math:`R_Y` of given *Munsell* value :math:`V` using *Sidney M. Newhall, Dorothy Nickerson, and Deane B. Judd (1943)* method. Parameters ---------- V : numeric or array_like *Munsell* value :math:`V`. \*\*kwargs : \*\*, optional Unused parameter provided for signature compatibility with other *luminance* computation objects. Returns ------- numeric or array_like *luminance* :math:`R_Y`. Notes ----- - Input *Munsell* value :math:`V` is in domain [0, 10]. - Output *luminance* :math:`R_Y` is in domain [0, 100]. References ---------- .. [1] Newhall, S. M., Nickerson, D., & Judd, D. B. (1943). Final report of the OSA subcommittee on the spacing of the munsell colors. JOSA, 33(7), 385. doi:10.1364/JOSA.33.000385 Examples -------- >>> luminance_Newhall1943(3.74629715382) # doctest: +ELLIPSIS 10.4089874... """ V = np.asarray(V) R_Y = (1.2219 * V - 0.23111 * (V * V) + 0.23951 * (V ** 3) - 0.021009 * (V ** 4) + 0.0008404 * (V ** 5)) return R_Y
[docs]def luminance_ASTMD153508(V, **kwargs): """ Returns the *luminance* :math:`Y` of given *Munsell* value :math:`V` using ASTM D1535-08e1 (2008) method. Parameters ---------- V : numeric or array_like *Munsell* value :math:`V`. \*\*kwargs : \*\*, optional Unused parameter provided for signature compatibility with other *luminance* computation objects. Returns ------- numeric or array_like *luminance* :math:`Y`. Notes ----- - Input *Munsell* value :math:`V` is in domain [0, 10]. - Output *luminance* :math:`Y` is in domain [0, 100]. References ---------- .. [4] ASTM International. (n.d.). ASTM D1535-08e1 Standard Practice for Specifying Color by the Munsell System. doi:10.1520/D1535-08E01 Examples -------- >>> luminance_ASTMD153508(3.74629715382) # doctest: +ELLIPSIS 10.1488096... """ V = np.asarray(V) Y = (1.1914 * V - 0.22533 * (V ** 2) + 0.23352 * (V ** 3) - 0.020484 * (V ** 4) + 0.00081939 * (V ** 5)) return Y
[docs]def luminance_1976(Lstar, Y_n=100): """ Returns the *luminance* :math:`Y` of given *Lightness* :math:`L^*` with given reference white *luminance* :math:`Y_n`. Parameters ---------- L : numeric or array_like *Lightness* :math:`L^*` Yn : numeric or array_like White reference *luminance* :math:`Y_n`. Returns ------- numeric or array_like *luminance* :math:`Y`. Notes ----- - Input *Lightness* :math:`L^*` and reference white *luminance* :math:`Y_n` are in domain [0, 100]. - Output *luminance* :math:`Y` is in domain [0, 100]. References ---------- .. [2] 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 .. [3] Lindbloom, B. (2003). A Continuity Study of the CIE L* Function. Retrieved February 24, 2014, from http://brucelindbloom.com/LContinuity.html Examples -------- >>> luminance_1976(37.9856290977) # doctest: +ELLIPSIS array(10.0800000...) >>> luminance_1976(37.9856290977, 95) # doctest: +ELLIPSIS array(9.5760000...) """ Lstar = np.asarray(Lstar) Y_n = np.asarray(Y_n) Y = np.where(Lstar > CIE_K * CIE_E, Y_n * ((Lstar + 16) / 116) ** 3, Y_n * (Lstar / CIE_K)) return Y
LUMINANCE_METHODS = CaseInsensitiveMapping( {'Newhall 1943': luminance_Newhall1943, 'ASTM D1535-08': luminance_ASTMD153508, 'CIE 1976': luminance_1976}) """ Supported *luminance* computations methods. LUMINANCE_METHODS : CaseInsensitiveMapping **{'Newhall 1943', 'ASTM D1535-08', 'CIE 1976'}** Aliases: - 'astm2008': 'ASTM D1535-08' - 'cie1976': 'CIE 1976' """ LUMINANCE_METHODS['astm2008'] = ( LUMINANCE_METHODS['ASTM D1535-08']) LUMINANCE_METHODS['cie1976'] = ( LUMINANCE_METHODS['CIE 1976'])
[docs]def luminance(LV, method='CIE 1976', **kwargs): """ Returns the *luminance* :math:`Y` of given *Lightness* :math:`L^*` or given *Munsell* value :math:`V`. Parameters ---------- LV : numeric or array_like *Lightness* :math:`L^*` or *Munsell* value :math:`V`. method : unicode, optional **{'CIE 1976', 'Newhall 1943', 'ASTM D1535-08'}**, Computation method. \*\*kwargs : \*\* Keywords arguments. Returns ------- numeric or array_like *luminance* :math:`Y`. Notes ----- - Input *LV* is in domain [0, 100] or [0, 10] and optional *luminance* :math:`Y_n` is in domain [0, 100]. - Output *luminance* :math:`Y` is in domain [0, 100]. Examples -------- >>> luminance(37.9856290977) # doctest: +ELLIPSIS array(10.0800000...) >>> luminance(37.9856290977, Y_n=100) # doctest: +ELLIPSIS array(10.0800000...) >>> luminance(37.9856290977, Y_n=95) # doctest: +ELLIPSIS array(9.5760000...) >>> luminance(3.74629715382, method='Newhall 1943') # doctest: +ELLIPSIS 10.4089874... >>> luminance(3.74629715382, method='ASTM D1535-08') # doctest: +ELLIPSIS 10.1488096... """ return LUMINANCE_METHODS.get(method)(LV, **kwargs)