Source code for colour.models.hdr_cie_lab

# -*- coding: utf-8 -*-
"""
hdr-CIELAB Colourspace
======================

Defines the *hdr-CIELAB* colourspace transformations:

-   :attr:`colour.HDR_CIELAB_METHODS`: Supported *hdr-CIELAB* colourspace
    computation methods.
-   :func:`colour.XYZ_to_hdr_CIELab`
-   :func:`colour.hdr_CIELab_to_XYZ`

References
----------
-   :cite:`Fairchild2010` : 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. Proc. of Color and Imaging Conference,
    322-326. ISBN:978-1-62993-215-6
-   :cite:`Fairchild2011` : Fairchild, M. D., & Chen, P. (2011). Brightness,
    lightness, and specifying color in high-dynamic-range scenes and images. In
    S. P. Farnand & F. Gaykema (Eds.), Proc. SPIE 7867, Image Quality and
    System Performance VIII (p. 78670O). doi:10.1117/12.872075
"""

from __future__ import division, unicode_literals

import numpy as np

from colour.colorimetry import (
    ILLUMINANTS, lightness_Fairchild2010, lightness_Fairchild2011,
    luminance_Fairchild2010, luminance_Fairchild2011)
from colour.models import xy_to_xyY, xyY_to_XYZ
from colour.utilities import (as_float_array, domain_range_scale, from_range_1,
                              from_range_100, to_domain_1, to_domain_100,
                              tsplit, tstack)
from colour.utilities.documentation import DocstringTuple

__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013-2020 - Colour Developers'
__license__ = 'New BSD License - https://opensource.org/licenses/BSD-3-Clause'
__maintainer__ = 'Colour Developers'
__email__ = 'colour-developers@colour-science.org'
__status__ = 'Production'

__all__ = [
    'HDR_CIELAB_METHODS', 'exponent_hdr_CIELab', 'XYZ_to_hdr_CIELab',
    'hdr_CIELab_to_XYZ'
]

HDR_CIELAB_METHODS = DocstringTuple(('Fairchild 2010', 'Fairchild 2011'))
HDR_CIELAB_METHODS.__doc__ = """
Supported *hdr-CIELAB* colourspace computation methods.

References
----------
:cite:`Fairchild2010`, :cite:`Fairchild2011`

HDR_CIELAB_METHODS : tuple
    **{'Fairchild 2011', 'Fairchild 2010'}**
"""


def exponent_hdr_CIELab(Y_s, Y_abs, method='Fairchild 2011'):
    """
    Computes *hdr-CIELAB* colourspace *Lightness* :math:`\\epsilon` exponent
    using *Fairchild and Wyble (2010)* or *Fairchild and Chen (2011)* method.

    Parameters
    ----------
    Y_s : numeric or array_like
        Relative luminance :math:`Y_s` of the surround.
    Y_abs : numeric or array_like
        Absolute luminance :math:`Y_{abs}` of the scene diffuse white in
        :math:`cd/m^2`.
    method : unicode, optional
        **{'Fairchild 2011', 'Fairchild 2010'}**,
        Computation method.

    Returns
    -------
    array_like
        *hdr-CIELAB* colourspace *Lightness* :math:`\\epsilon` exponent.

    Notes
    -----

    +------------+-----------------------+---------------+
    | **Domain** | **Scale - Reference** | **Scale - 1** |
    +============+=======================+===============+
    | ``Y_s``    | [0, 1]                | [0, 1]        |
    +------------+-----------------------+---------------+

    Examples
    --------
    >>> exponent_hdr_CIELab(0.2, 100)  # doctest: +ELLIPSIS
    0.4738510...
    >>> exponent_hdr_CIELab(0.2, 100, method='Fairchild 2010')
    ... # doctest: +ELLIPSIS
    1.8360198...
    """

    Y_s = to_domain_1(Y_s)
    Y_abs = as_float_array(Y_abs)

    method_l = method.lower()
    assert method.lower() in [
        m.lower() for m in HDR_CIELAB_METHODS
    ], ('"{0}" method is invalid, must be one of {1}!'.format(
        method, HDR_CIELAB_METHODS))

    if method_l == 'fairchild 2010':
        epsilon = 1.50
    else:
        epsilon = 0.58

    sf = 1.25 - 0.25 * (Y_s / 0.184)
    lf = np.log(318) / np.log(Y_abs)
    if method_l == 'fairchild 2010':
        epsilon *= sf * lf
    else:
        epsilon /= sf * lf

    return epsilon


[docs]def XYZ_to_hdr_CIELab( XYZ, illuminant=ILLUMINANTS['CIE 1931 2 Degree Standard Observer']['D65'], Y_s=0.2, Y_abs=100, method='Fairchild 2011'): """ Converts from *CIE XYZ* tristimulus values to *hdr-CIELAB* colourspace. Parameters ---------- XYZ : array_like *CIE XYZ* tristimulus values. illuminant : array_like, optional Reference *illuminant* *CIE xy* chromaticity coordinates or *CIE xyY* colourspace array. Y_s : numeric or array_like Relative luminance :math:`Y_s` of the surround. Y_abs : numeric or array_like Absolute luminance :math:`Y_{abs}` of the scene diffuse white in :math:`cd/m^2`. method : unicode, optional **{'Fairchild 2011', 'Fairchild 2010'}**, Computation method. Returns ------- ndarray *hdr-CIELAB* colourspace array. Notes ----- +----------------+-------------------------+---------------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +================+=========================+=====================+ | ``XYZ`` | [0, 1] | [0, 1] | +----------------+-------------------------+---------------------+ | ``illuminant`` | [0, 1] | [0, 1] | +----------------+-------------------------+---------------------+ | ``Y_s`` | [0, 1] | [0, 1] | +----------------+-------------------------+---------------------+ +----------------+-------------------------+---------------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +================+=========================+=====================+ | ``Lab_hdr`` | ``L_hdr`` : [0, 100] | ``L_hdr`` : [0, 1] | | | | | | | ``a_hdr`` : [-100, 100] | ``a_hdr`` : [-1, 1] | | | | | | | ``b_hdr`` : [-100, 100] | ``b_hdr`` : [-1, 1] | +----------------+-------------------------+---------------------+ - Conversion to polar coordinates to compute the *chroma* :math:`C_{hdr}` and *hue* :math:`h_{hdr}` correlates can be safely performed with :func:`colour.Lab_to_LCHab` definition. - Conversion to cartesian coordinates from the *Lightness* :math:`L_{hdr}`, *chroma* :math:`C_{hdr}` and *hue* :math:`h_{hdr}` correlates can be safely performed with :func:`colour.LCHab_to_Lab` definition. References ---------- :cite:`Fairchild2010`, :cite:`Fairchild2011` Examples -------- >>> XYZ = np.array([0.20654008, 0.12197225, 0.05136952]) >>> XYZ_to_hdr_CIELab(XYZ) # doctest: +ELLIPSIS array([ 51.8700206..., 60.4763385..., 32.1455191...]) >>> XYZ_to_hdr_CIELab(XYZ, method='Fairchild 2010') # doctest: +ELLIPSIS array([ 31.9962111..., 128.0076303..., 48.7695230...]) """ X, Y, Z = tsplit(to_domain_1(XYZ)) X_n, Y_n, Z_n = tsplit(xyY_to_XYZ(xy_to_xyY(illuminant))) method_l = method.lower() assert method.lower() in [ m.lower() for m in HDR_CIELAB_METHODS ], ('"{0}" method is invalid, must be one of {1}!'.format( method, HDR_CIELAB_METHODS)) if method_l == 'fairchild 2010': lightness_callable = lightness_Fairchild2010 else: lightness_callable = lightness_Fairchild2011 e = exponent_hdr_CIELab(Y_s, Y_abs, method) # Domain and range scaling has already be handled. with domain_range_scale('ignore'): L_hdr = lightness_callable(Y / Y_n, e) a_hdr = 5 * (lightness_callable(X / X_n, e) - L_hdr) b_hdr = 2 * (L_hdr - lightness_callable(Z / Z_n, e)) Lab_hdr = tstack([L_hdr, a_hdr, b_hdr]) return from_range_100(Lab_hdr)
[docs]def hdr_CIELab_to_XYZ( Lab_hdr, illuminant=ILLUMINANTS['CIE 1931 2 Degree Standard Observer']['D65'], Y_s=0.2, Y_abs=100, method='Fairchild 2011'): """ Converts from *hdr-CIELAB* colourspace to *CIE XYZ* tristimulus values. Parameters ---------- Lab_hdr : array_like *hdr-CIELAB* colourspace array. illuminant : array_like, optional Reference *illuminant* *CIE xy* chromaticity coordinates or *CIE xyY* colourspace array. Y_s : numeric or array_like Relative luminance :math:`Y_s` of the surround. Y_abs : numeric or array_like Absolute luminance :math:`Y_{abs}` of the scene diffuse white in :math:`cd/m^2`. method : unicode, optional **{'Fairchild 2011', 'Fairchild 2010'}**, Computation method. Returns ------- ndarray *CIE XYZ* tristimulus values. Notes ----- +----------------+-------------------------+---------------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +================+=========================+=====================+ | ``Lab_hdr`` | ``L_hdr`` : [0, 100] | ``L_hdr`` : [0, 1] | | | | | | | ``a_hdr`` : [-100, 100] | ``a_hdr`` : [-1, 1] | | | | | | | ``b_hdr`` : [-100, 100] | ``b_hdr`` : [-1, 1] | +----------------+-------------------------+---------------------+ | ``illuminant`` | [0, 1] | [0, 1] | +----------------+-------------------------+---------------------+ | ``Y_s`` | [0, 1] | [0, 1] | +----------------+-------------------------+---------------------+ +----------------+-------------------------+---------------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +================+=========================+=====================+ | ``XYZ`` | [0, 1] | [0, 1] | +----------------+-------------------------+---------------------+ References ---------- :cite:`Fairchild2010`, :cite:`Fairchild2011` Examples -------- >>> Lab_hdr = np.array([51.87002062, 60.4763385, 32.14551912]) >>> hdr_CIELab_to_XYZ(Lab_hdr) # doctest: +ELLIPSIS array([ 0.2065400..., 0.1219722..., 0.0513695...]) >>> Lab_hdr = np.array([31.99621114, 128.00763036, 48.76952309]) >>> hdr_CIELab_to_XYZ(Lab_hdr, method='Fairchild 2010') ... # doctest: +ELLIPSIS array([ 0.2065400..., 0.1219722..., 0.0513695...]) """ L_hdr, a_hdr, b_hdr = tsplit(to_domain_100(Lab_hdr)) X_n, Y_n, Z_n = tsplit(xyY_to_XYZ(xy_to_xyY(illuminant))) method_l = method.lower() assert method.lower() in [ m.lower() for m in HDR_CIELAB_METHODS ], ('"{0}" method is invalid, must be one of {1}!'.format( method, HDR_CIELAB_METHODS)) if method_l == 'fairchild 2010': luminance_callable = luminance_Fairchild2010 else: luminance_callable = luminance_Fairchild2011 e = exponent_hdr_CIELab(Y_s, Y_abs, method) # Domain and range scaling has already be handled. with domain_range_scale('ignore'): Y = luminance_callable(L_hdr, e) * Y_n X = luminance_callable((a_hdr + 5 * L_hdr) / 5, e) * X_n Z = luminance_callable((-b_hdr + 2 * L_hdr) / 2, e) * Z_n XYZ = tstack([X, Y, Z]) return from_range_1(XYZ)