#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
CIE Lab Colourspace
===================
Defines the *CIE Lab* colourspace transformations:
- :func:`XYZ_to_Lab`
- :func:`Lab_to_XYZ`
- :func:`Lab_to_LCHab`
- :func:`LCHab_to_Lab`
See Also
--------
`CIE Lab Colourspace IPython Notebook
<http://nbviewer.ipython.org/github/colour-science/colour-ipython/blob/master/notebooks/models/cie_lab.ipynb>`_ # noqa
References
----------
.. [1] Wikipedia. (n.d.). Lab color space. Retrieved February 24, 2014, from
http://en.wikipedia.org/wiki/Lab_color_space
"""
from __future__ import division, unicode_literals
import numpy as np
from colour.colorimetry import ILLUMINANTS
from colour.constants import CIE_E, CIE_K
from colour.models import xy_to_XYZ
from colour.utilities import tsplit, tstack
__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__ = ['XYZ_to_Lab',
'Lab_to_XYZ',
'Lab_to_LCHab',
'LCHab_to_Lab']
[docs]def XYZ_to_Lab(XYZ,
illuminant=ILLUMINANTS.get(
'CIE 1931 2 Degree Standard Observer').get('D50')):
"""
Converts from *CIE XYZ* tristimulus values to *CIE Lab* colourspace.
Parameters
----------
XYZ : array_like
*CIE XYZ* tristimulus values.
illuminant : array_like, optional
Reference *illuminant* chromaticity coordinates.
Returns
-------
ndarray
*CIE Lab* colourspace array.
Notes
-----
- Input *CIE XYZ* tristimulus values are in domain [0, 1].
- Input *illuminant* chromaticity coordinates are in domain [0, 1].
- Output *Lightness* :math:`L^*` is in domain [0, 100].
References
----------
.. [2] Lindbloom, B. (2003). XYZ to Lab. Retrieved February 24, 2014,
from http://www.brucelindbloom.com/Eqn_XYZ_to_Lab.html
Examples
--------
>>> XYZ = np.array([0.07049534, 0.10080000, 0.09558313])
>>> XYZ_to_Lab(XYZ) # doctest: +ELLIPSIS
array([ 37.9856291..., -23.6230288..., -4.4141703...])
"""
XYZ = np.asarray(XYZ)
XYZ_r = xy_to_XYZ(illuminant)
XYZ_f = XYZ / XYZ_r
XYZ_f = np.where(XYZ_f > CIE_E,
np.power(XYZ_f, 1 / 3),
(CIE_K * XYZ_f + 16) / 116)
X_f, Y_f, Z_f = tsplit(XYZ_f)
L = 116 * Y_f - 16
a = 500 * (X_f - Y_f)
b = 200 * (Y_f - Z_f)
Lab = tstack((L, a, b))
return Lab
[docs]def Lab_to_XYZ(Lab,
illuminant=ILLUMINANTS.get(
'CIE 1931 2 Degree Standard Observer').get('D50')):
"""
Converts from *CIE Lab* colourspace to *CIE XYZ* tristimulus values.
Parameters
----------
Lab : array_like
*CIE Lab* colourspace array.
illuminant : array_like, optional
Reference *illuminant* chromaticity coordinates.
Returns
-------
ndarray
*CIE XYZ* tristimulus values.
Notes
-----
- Input *Lightness* :math:`L^*` is in domain [0, 100].
- Input *illuminant* chromaticity coordinates are in domain [0, 1].
- Output *CIE XYZ* tristimulus values are in domain [0, 1].
References
----------
.. [3] Lindbloom, B. (2008). Lab to XYZ. Retrieved February 24, 2014,
from http://www.brucelindbloom.com/Eqn_Lab_to_XYZ.html
Examples
--------
>>> Lab = np.array([37.98562910, -23.62302887, -4.41417036])
>>> Lab_to_XYZ(Lab) # doctest: +ELLIPSIS
array([ 0.0704953..., 0.1008 , 0.0955831...])
"""
L, a, b = tsplit(Lab)
XYZ_r = xy_to_XYZ(illuminant)
f_y = (L + 16) / 116
f_x = a / 500 + f_y
f_z = f_y - b / 200
x_r = np.where(f_x ** 3 > CIE_E, f_x ** 3, (116 * f_x - 16) / CIE_K)
y_r = np.where(L > CIE_K * CIE_E, ((L + 16) / 116) ** 3, L / CIE_K)
z_r = np.where(f_z ** 3 > CIE_E, f_z ** 3, (116 * f_z - 16) / CIE_K)
XYZ = tstack((x_r, y_r, z_r)) * XYZ_r
return XYZ
[docs]def Lab_to_LCHab(Lab):
"""
Converts from *CIE Lab* colourspace to *CIE LCHab* colourspace.
Parameters
----------
Lab : array_like
*CIE Lab* colourspace array.
Returns
-------
ndarray
*CIE LCHab* colourspace array.
Notes
-----
- *Lightness* :math:`L^*` is in domain [0, 100].
References
----------
.. [4] Lindbloom, B. (2007). Lab to LCH(ab). Retrieved February 24, 2014,
from http://www.brucelindbloom.com/Eqn_Lab_to_LCH.html
Examples
--------
>>> Lab = np.array([37.98562910, -23.62302887, -4.41417036])
>>> Lab_to_LCHab(Lab) # doctest: +ELLIPSIS
array([ 37.9856291..., 24.0319036..., 190.5841597...])
"""
L, a, b = tsplit(Lab)
H = np.array(180 * np.arctan2(b, a) / np.pi)
H[np.array(H < 0)] += 360
LCHab = tstack((L, np.sqrt(a ** 2 + b ** 2), H))
return LCHab
[docs]def LCHab_to_Lab(LCHab):
"""
Converts from *CIE LCHab* colourspace to *CIE Lab* colourspace.
Parameters
----------
LCHab : array_like
*CIE LCHab* colourspace array.
Returns
-------
ndarray
*CIE Lab* colourspace array.
Notes
-----
- *Lightness* :math:`L^*` is in domain [0, 100].
References
----------
.. [5] Lindbloom, B. (2006). LCH(ab) to Lab. Retrieved February 24, 2014,
from http://www.brucelindbloom.com/Eqn_LCH_to_Lab.html
Examples
--------
>>> LCHab = np.array([37.98562910, 24.03190365, 190.58415972])
>>> LCHab_to_Lab(LCHab) # doctest: +ELLIPSIS
array([ 37.9856291..., -23.6230288..., -4.4141703...])
"""
L, C, H = tsplit(LCHab)
Lab = tstack((L,
C * np.cos(np.radians(H)),
C * np.sin(np.radians(H))))
return Lab
Colour 0.3