Source code for colour.models.ipt

#!/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`

See Also
--------
`IPT Colourspace Jupyter Notebook
<http://nbviewer.jupyter.org/github/colour-science/colour-notebooks/\
blob/master/notebooks/models/ipt.ipynb>`_

References
----------
.. [1]  Fairchild, M. D. (2013). IPT Colourspace. In Color Appearance Models
        (3rd ed., pp. 6197–6223). Wiley. ISBN:B00DAYO8E2
"""

from __future__ import division, unicode_literals

import numpy as np

from colour.utilities import dot_vector, tsplit

__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013-2017 - 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]])  # yapf: disable
"""
*CIE XYZ* tristimulus values to 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)
"""
Normalised cone responses to *CIE XYZ* tristimulus values 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]])  # yapf: disable
"""
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 normalised cone responses matrix.

IPT_IPT_TO_LMS_MATRIX : array_like, (3, 3)
"""


[docs]def XYZ_to_IPT(XYZ): """ Converts from *CIE XYZ* tristimulus values to *IPT* colourspace. Parameters ---------- XYZ : array_like *CIE XYZ* tristimulus values. Returns ------- ndarray *IPT* colourspace array. Notes ----- - Input *CIE XYZ* tristimulus values needs to be adapted for *CIE Standard Illuminant D Series* *D65*. Examples -------- >>> XYZ = np.array([0.96907232, 1.00000000, 1.12179215]) >>> XYZ_to_IPT(XYZ) # doctest: +ELLIPSIS array([ 1.0030082..., 0.0190691..., -0.0136929...]) """ LMS = dot_vector(IPT_XYZ_TO_LMS_MATRIX, XYZ) LMS_prime = np.sign(LMS) * np.abs(LMS) ** 0.43 IPT = dot_vector(IPT_LMS_TO_IPT_MATRIX, LMS_prime) return IPT
[docs]def IPT_to_XYZ(IPT): """ Converts from *IPT* colourspace to *CIE XYZ* tristimulus values. Parameters ---------- IPT : array_like *IPT* colourspace array. Returns ------- ndarray *CIE XYZ* tristimulus values. Examples -------- >>> IPT = np.array([1.00300825, 0.01906918, -0.01369292]) >>> IPT_to_XYZ(IPT) # doctest: +ELLIPSIS array([ 0.9690723..., 1. , 1.1217921...]) """ LMS = dot_vector(IPT_IPT_TO_LMS_MATRIX, IPT) LMS_prime = np.sign(LMS) * np.abs(LMS) ** (1 / 0.43) XYZ = dot_vector(IPT_LMS_TO_XYZ_MATRIX, LMS_prime) return XYZ
[docs]def IPT_hue_angle(IPT): """ Computes the hue angle in degrees from *IPT* colourspace. Parameters ---------- IPT : array_like *IPT* colourspace array. Returns ------- numeric or ndarray Hue angle in degrees. Examples -------- >>> IPT = np.array([0.96907232, 1, 1.12179215]) >>> IPT_hue_angle(IPT) # doctest: +ELLIPSIS 48.2852074... """ _I, P, T = tsplit(IPT) hue = np.degrees(np.arctan2(T, P)) % 360 return hue