#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
IPT Colourspace
===============
Defines the *IPT* colourspace transformations:
- :func:`XYZ_to_IPT`
- :func:`IPT_to_XYZ`
And computation of correlates:
- :func:`IPT_hue_angle`
References
----------
.. [1] Fairchild, M. D. (2013). IPT Colourspace. In Color Appearance Models
(3rd ed., pp. 8492–8567). Wiley. ISBN:B00DAYO8E2
"""
from __future__ import division, unicode_literals
import numpy as np
__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__ = ['IPT_XYZ_TO_LMS_MATRIX',
'IPT_LMS_TO_XYZ_MATRIX',
'IPT_LMS_TO_IPT_MATRIX',
'IPT_IPT_TO_LMS_MATRIX',
'XYZ_to_IPT',
'IPT_to_XYZ',
'IPT_hue_angle']
IPT_XYZ_TO_LMS_MATRIX = np.array([
[0.4002, 0.7075, -0.0807],
[-0.2280, 1.1500, 0.0612],
[0.0000, 0.0000, 0.9184]])
"""
*CIE XYZ* colourspace to *IPT* colourspace normalised cone responses matrix.
IPT_XYZ_TO_LMS_MATRIX : array_like, (3, 3)
"""
IPT_LMS_TO_XYZ_MATRIX = np.linalg.inv(IPT_XYZ_TO_LMS_MATRIX)
"""
*IPT* colourspace normalised cone responses to *CIE XYZ* colourspace matrix.
IPT_LMS_TO_XYZ_MATRIX : array_like, (3, 3)
"""
IPT_LMS_TO_IPT_MATRIX = np.array([
[0.4000, 0.4000, 0.2000],
[4.4550, -4.8510, 0.3960],
[0.8056, 0.3572, -1.1628]])
"""
*IPT* colourspace normalised cone responses to *IPT* colourspace matrix.
IPT_LMS_TO_IPT_MATRIX : array_like, (3, 3)
"""
IPT_IPT_TO_LMS_MATRIX = np.linalg.inv(IPT_LMS_TO_IPT_MATRIX)
"""
*IPT* colourspace to *IPT* colourspace normalised cone responses matrix.
IPT_IPT_TO_LMS_MATRIX : array_like, (3, 3)
"""
[docs]def XYZ_to_IPT(XYZ):
"""
Converts from *CIE XYZ* colourspace to *IPT* colourspace. [1]_
Parameters
----------
XYZ : array_like, (3,)
*CIE XYZ* colourspace matrix.
Returns
-------
ndarray, (3,)
*IPT* colourspace matrix.
Notes
-----
- Input *CIE XYZ* colourspace matrix needs to be adapted for
*CIE Standard Illuminant D Series* *D65*.
Examples
--------
>>> XYZ = np.array([0.96907232, 1, 1.12179215])
>>> XYZ_to_IPT(XYZ) # doctest: +ELLIPSIS
array([ 1.0030082..., 0.0190691..., -0.0136929...])
"""
LMS = np.dot(IPT_XYZ_TO_LMS_MATRIX, XYZ)
LMS_prime = np.sign(LMS) * np.abs(LMS) ** 0.43
IPT = np.dot(IPT_LMS_TO_IPT_MATRIX, LMS_prime)
return IPT
[docs]def IPT_to_XYZ(IPT):
"""
Converts from *IPT* colourspace to *CIE XYZ* colourspace. [1]_
Parameters
----------
IPT : array_like, (3,)
*IPT* colourspace matrix.
Returns
-------
ndarray, (3,)
*CIE XYZ* colourspace matrix.
Examples
--------
>>> IPT = np.array([1.00300825, 0.01906918, -0.01369292])
>>> IPT_to_XYZ(IPT) # doctest: +ELLIPSIS
array([ 0.9690723..., 1. , 1.1217921...])
"""
LMS = np.dot(IPT_IPT_TO_LMS_MATRIX, IPT)
LMS_prime = np.sign(LMS) * np.abs(LMS) ** (1 / 0.43)
XYZ = np.dot(IPT_LMS_TO_XYZ_MATRIX, LMS_prime)
return XYZ
[docs]def IPT_hue_angle(IPT):
"""
Computes the hue angle from *IPT* colourspace. [1]_
Parameters
----------
IPT : array_like, (3,)
*IPT* colourspace matrix.
Returns
-------
numeric
Hue angle.
Examples
--------
>>> IPT_hue_angle(([0.96907232, 1, 1.12179215])) # doctest: +ELLIPSIS
0.8427358...
"""
return np.arctan2(IPT[2], IPT[1])
Colour 0.3