Source code for colour.models.hdr_ipt

#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
hdr-IPT Colourspace
===================

Defines the *hdr-IPT* colourspace transformations:

-   :func:`XYZ_to_hdr_IPT`
-   :func:`hdr_IPT_to_XYZ`

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

References
----------
.. [1]  Fairchild, M. D., & Wyble, D. R. (2010). hdr-CIELAB and hdr-IPT:
        Simple Models for Describing the Color of High-Dynamic-Range and
        Wide-Color-Gamut Images. In Proc. of Color and Imaging Conference
        (pp. 322–326). ISBN:9781629932156
"""

from __future__ import division, unicode_literals

import numpy as np

from colour.colorimetry import lightness_Fairchild2010, luminance_Fairchild2010
from colour.models.ipt import (IPT_XYZ_TO_LMS_MATRIX, IPT_LMS_TO_XYZ_MATRIX,
                               IPT_LMS_TO_IPT_MATRIX, IPT_IPT_TO_LMS_MATRIX)
from colour.utilities import dot_vector

__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__ = ['XYZ_to_hdr_IPT', 'hdr_IPT_to_XYZ', 'exponent_hdr_IPT']


[docs]def XYZ_to_hdr_IPT(XYZ, Y_s=0.2, Y_abs=100): """ Converts from *CIE XYZ* tristimulus values to *hdr-IPT* colourspace. Parameters ---------- XYZ : array_like *CIE XYZ* tristimulus values. Y_s : numeric or array_like Relative luminance :math:`Y_s` of the surround in domain [0, 1]. Y_abs : numeric or array_like Absolute luminance :math:`Y_{abs}` of the scene diffuse white in :math:`cd/m^2`. Returns ------- ndarray *hdr-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_hdr_IPT(XYZ) # doctest: +ELLIPSIS array([ 94.6592917..., 0.3804177..., -0.2673118...]) """ e = exponent_hdr_IPT(Y_s, Y_abs)[..., np.newaxis] LMS = dot_vector(IPT_XYZ_TO_LMS_MATRIX, XYZ) LMS_prime = np.sign(LMS) * np.abs(lightness_Fairchild2010(LMS, e)) IPT = dot_vector(IPT_LMS_TO_IPT_MATRIX, LMS_prime) return IPT
[docs]def hdr_IPT_to_XYZ(IPT_hdr, Y_s=0.2, Y_abs=100): """ Converts from *hdr-IPT* colourspace to *CIE XYZ* tristimulus values. Parameters ---------- IPT_hdr : array_like *hdr-IPT* colourspace array. Y_s : numeric or array_like Relative luminance :math:`Y_s` of the surround in domain [0, 1]. Y_abs : numeric or array_like Absolute luminance :math:`Y_{abs}` of the scene diffuse white in :math:`cd/m^2`. Returns ------- ndarray *CIE XYZ* tristimulus values. Examples -------- >>> IPT_hdr = np.array([94.65929175, 0.38041773, -0.26731187]) >>> hdr_IPT_to_XYZ(IPT_hdr) # doctest: +ELLIPSIS array([ 0.9690723..., 1. , 1.1217921...]) """ e = exponent_hdr_IPT(Y_s, Y_abs)[..., np.newaxis] LMS = dot_vector(IPT_IPT_TO_LMS_MATRIX, IPT_hdr) LMS_prime = np.sign(LMS) * np.abs(luminance_Fairchild2010(LMS, e)) XYZ = dot_vector(IPT_LMS_TO_XYZ_MATRIX, LMS_prime) return XYZ
[docs]def exponent_hdr_IPT(Y_s, Y_abs): """ Computes *hdr-IPT* colourspace *Lightness* :math:`\epsilon` exponent. Parameters ---------- Y_s : numeric or array_like Relative luminance :math:`Y_s` of the surround in range [0, 1]. Y_abs : numeric or array_like Absolute luminance :math:`Y_{abs}` of the scene diffuse white in :math:`cd/m^2`. Returns ------- array_like *hdr-IPT* colourspace *Lightness* :math:`\epsilon` exponent. Examples -------- >>> exponent_hdr_IPT(0.2, 100) # doctest: +ELLIPSIS 1.6891383... """ Y_s = np.asarray(Y_s) Y_abs = np.asarray(Y_abs) lf = np.log(318) / np.log(Y_abs) sf = 1.25 - 0.25 * (Y_s / 0.184) epsilon = 1.38 * sf * lf return epsilon