#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Chromatic Adaptation Transforms
===============================
Defines various chromatic adaptation transforms (CAT) and objects to
calculate the chromatic adaptation matrix between two given *CIE XYZ*
colourspace matrices:
- :attr:`XYZ_SCALING_CAT`: *XYZ Scaling* CAT [1]_
- :attr:`BRADFORD_CAT`: *Bradford* CAT [1]_
- :attr:`VON_KRIES_CAT`: *Von Kries* CAT [1]_
- :attr:`FAIRCHILD_CAT`: *Fairchild* CAT [2]_
- :attr:`CAT02_CAT`: *CAT02* CAT [3]_
See Also
--------
`Chromatic Adaptation Transforms IPython Notebook
<http://nbviewer.ipython.org/github/colour-science/colour-ipython/blob/master/notebooks/adaptation/cat.ipynb>`_ # noqa
References
----------
.. [1] http://brucelindbloom.com/Eqn_ChromAdapt.html
.. [2] http://rit-mcsl.org/fairchild//files/FairchildYSh.zip
.. [3] http://en.wikipedia.org/wiki/CIECAM02#CAT02
"""
from __future__ import division, unicode_literals
import numpy as np
from colour.utilities import CaseInsensitiveMapping
__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013 - 2014 - 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_SCALING_CAT',
'BRADFORD_CAT',
'VON_KRIES_CAT',
'FAIRCHILD_CAT',
'CAT02_CAT',
'CAT02_INVERSE_CAT',
'CHROMATIC_ADAPTATION_METHODS',
'chromatic_adaptation_matrix']
XYZ_SCALING_CAT = np.array(np.identity(3)).reshape((3, 3))
"""
*XYZ Scaling* chromatic adaptation transform. [1]_
XYZ_SCALING_CAT : array_like, (3, 3)
"""
BRADFORD_CAT = np.array(
[[0.8951000, 0.2664000, -0.1614000],
[-0.7502000, 1.7135000, 0.0367000],
[0.0389000, -0.0685000, 1.0296000]])
"""
*Bradford* chromatic adaptation transform. [1]_
BRADFORD_CAT : array_like, (3, 3)
"""
VON_KRIES_CAT = np.array(
[[0.4002400, 0.7076000, -0.0808100],
[-0.2263000, 1.1653200, 0.0457000],
[0.0000000, 0.0000000, 0.9182200]])
"""
*Von Kries* chromatic adaptation transform. [1]_
VON_KRIES_CAT : array_like, (3, 3)
"""
FAIRCHILD_CAT = np.array(
[[.8562, .3372, -.1934],
[-.8360, 1.8327, .0033],
[.0357, -.0469, 1.0112]])
"""
*Fairchild* chromatic adaptation transform. [2]_
FAIRCHILD_CAT : array_like, (3, 3)
"""
CAT02_CAT = np.array(
[[0.7328, 0.4296, -0.1624],
[-0.7036, 1.6975, 0.0061],
[0.0030, 0.0136, 0.9834]])
"""
*CAT02* chromatic adaptation transform. [3]_
CAT02_CAT : array_like, (3, 3)
"""
CAT02_INVERSE_CAT = np.linalg.inv(CAT02_CAT)
"""
Inverse *CAT02* chromatic adaptation transform. [3]_
CAT02_INVERSE_CAT : array_like, (3, 3)
"""
CHROMATIC_ADAPTATION_METHODS = CaseInsensitiveMapping(
{'XYZ Scaling': XYZ_SCALING_CAT,
'Bradford': BRADFORD_CAT,
'Von Kries': VON_KRIES_CAT,
'Fairchild': FAIRCHILD_CAT,
'CAT02': CAT02_CAT})
"""
Supported chromatic adaptation transform methods.
CHROMATIC_ADAPTATION_METHODS : dict
('XYZ Scaling', 'Bradford', 'Von Kries', 'Fairchild, 'CAT02')
"""
[docs]def chromatic_adaptation_matrix(XYZ1, XYZ2, method='CAT02'):
"""
Returns the *chromatic adaptation* matrix from given source and target
*CIE XYZ* colourspace *array_like* variables.
Parameters
----------
XYZ1 : array_like, (3,)
*CIE XYZ* source *array_like* variable.
XYZ2 : array_like, (3,)
*CIE XYZ* target *array_like* variable.
method : unicode, optional
('XYZ Scaling', 'Bradford', 'Von Kries', 'Fairchild, 'CAT02'),
Chromatic adaptation method.
Returns
-------
ndarray, (3, 3)
Chromatic adaptation matrix.
Raises
------
KeyError
If chromatic adaptation method is not defined.
References
----------
.. [4] http://brucelindbloom.com/Eqn_ChromAdapt.html
(Last accessed 24 February 2014)
Examples
--------
>>> XYZ1 = np.array([1.09923822, 1.000, 0.35445412])
>>> XYZ2 = np.array([0.96907232, 1.000, 1.121792157])
>>> chromatic_adaptation_matrix(XYZ1, XYZ2) # doctest: +ELLIPSIS
array([[ 0.8714561..., -0.1320467..., 0.4039483...],
[-0.0963880..., 1.0490978..., 0.160403... ],
[ 0.0080207..., 0.0282636..., 3.0602319...]])
Using *Bradford* method:
>>> XYZ1 = np.array([1.09923822, 1.000, 0.35445412])
>>> XYZ2 = np.array([0.96907232, 1.000, 1.121792157])
>>> method = 'Bradford'
>>> chromatic_adaptation_matrix(XYZ1, XYZ2, method) # doctest: +ELLIPSIS
array([[ 0.8518131..., -0.1134786..., 0.4124804...],
[-0.1277659..., 1.0928930..., 0.1341559...],
[ 0.0845323..., -0.1434969..., 3.3075309...]])
"""
method_matrix = CHROMATIC_ADAPTATION_METHODS.get(method)
if method_matrix is None:
raise KeyError(
'"{0}" chromatic adaptation method is not defined! Supported '
'methods: "{1}".'.format(method,
CHROMATIC_ADAPTATION_METHODS.keys()))
XYZ1, XYZ2 = np.ravel(XYZ1), np.ravel(XYZ2)
if (XYZ1 == XYZ2).all():
# Skip the chromatic adaptation computation if the two input matrices
# are the same, because no adaptation is needed.
return np.identity(3)
rgb_source = np.ravel(np.dot(method_matrix, XYZ1))
rgb_target = np.ravel(np.dot(method_matrix, XYZ2))
crd = np.diagflat(np.array(
[[rgb_target[0] / rgb_source[0],
rgb_target[1] / rgb_source[1],
rgb_target[2] / rgb_source[2]]])).reshape((3, 3))
cat = np.dot(np.dot(np.linalg.inv(method_matrix), crd), method_matrix)
return cat
Colour 0.3