Source code for colour.models.hunter_lab

# -*- coding: utf-8 -*-
"""
Hunter L,a,b Colour Scale
=========================

Defines the *Hunter L,a,b* colour scale transformations:

-   :func:`colour.XYZ_to_K_ab_HunterLab1966`
-   :func:`colour.XYZ_to_Hunter_Lab`
-   :func:`colour.Hunter_Lab_to_XYZ`

References
----------
-   :cite:`HunterLab2008b` : HunterLab. (2008). Hunter L,a,b Color Scale.
    http://www.hunterlab.se/wp-content/uploads/2012/11/Hunter-L-a-b.pdf
-   :cite:`HunterLab2008c` : HunterLab. (2008). Illuminant Factors in
    Universal Software and EasyMatch Coatings.
    https://support.hunterlab.com/hc/en-us/article_attachments/201437785/\
an02_02.pdf
"""

from __future__ import division, unicode_literals

import numpy as np

from colour.colorimetry import HUNTERLAB_ILLUMINANTS
from colour.utilities import from_range_100, to_domain_100, tsplit, tstack

__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__ = [
    'XYZ_to_K_ab_HunterLab1966', 'XYZ_to_Hunter_Lab', 'Hunter_Lab_to_XYZ'
]


[docs]def XYZ_to_K_ab_HunterLab1966(XYZ): """ Converts from *whitepoint* *CIE XYZ* tristimulus values to *Hunter L,a,b* :math:`K_{a}` and :math:`K_{b}` chromaticity coefficients. Parameters ---------- XYZ : array_like *Whitepoint* *CIE XYZ* tristimulus values. Returns ------- ndarray *Hunter L,a,b* :math:`K_{a}` and :math:`K_{b}` chromaticity coefficients. References ---------- :cite:`HunterLab2008c` Examples -------- >>> XYZ = np.array([109.850, 100.000, 35.585]) >>> XYZ_to_K_ab_HunterLab1966(XYZ) # doctest: +ELLIPSIS array([ 185.2378721..., 38.4219142...]) """ X, _Y, Z = tsplit(XYZ) K_a = 175 * np.sqrt(X / 98.043) K_b = 70 * np.sqrt(Z / 118.115) K_ab = tstack([K_a, K_b]) return K_ab
[docs]def XYZ_to_Hunter_Lab(XYZ, XYZ_n=HUNTERLAB_ILLUMINANTS[ 'CIE 1931 2 Degree Standard Observer']['D65'].XYZ_n, K_ab=HUNTERLAB_ILLUMINANTS[ 'CIE 1931 2 Degree Standard Observer']['D65'].K_ab): """ Converts from *CIE XYZ* tristimulus values to *Hunter L,a,b* colour scale. Parameters ---------- XYZ : array_like *CIE XYZ* tristimulus values. XYZ_n : array_like, optional Reference *illuminant* tristimulus values. K_ab : array_like, optional Reference *illuminant* chromaticity coefficients, if ``K_ab`` is set to *None* it will be computed using :func:`colour.XYZ_to_K_ab_HunterLab1966`. Returns ------- ndarray *Hunter L,a,b* colour scale array. Notes ----- +------------+-----------------------+-----------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +============+=======================+=================+ | ``XYZ`` | [0, 100] | [0, 1] | +------------+-----------------------+-----------------+ | ``XYZ_n`` | [0, 100] | [0, 1] | +------------+-----------------------+-----------------+ +------------+-----------------------+-----------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +============+=======================+=================+ | ``Lab`` | ``L`` : [0, 100] | ``L`` : [0, 1] | | | | | | | ``a`` : [-100, 100] | ``a`` : [-1, 1] | | | | | | | ``b`` : [-100, 100] | ``b`` : [-1, 1] | +------------+-----------------------+-----------------+ References ---------- :cite:`HunterLab2008b` Examples -------- >>> XYZ = np.array([0.20654008, 0.12197225, 0.05136952]) * 100 >>> D65 = HUNTERLAB_ILLUMINANTS[ ... 'CIE 1931 2 Degree Standard Observer']['D65'] >>> XYZ_to_Hunter_Lab(XYZ, D65.XYZ_n, D65.K_ab) # doctest: +ELLIPSIS array([ 34.9245257..., 47.0618985..., 14.3861510...]) """ X, Y, Z = tsplit(to_domain_100(XYZ)) X_n, Y_n, Z_n = tsplit(to_domain_100(XYZ_n)) K_a, K_b = (tsplit(XYZ_to_K_ab_HunterLab1966(XYZ_n)) if K_ab is None else tsplit(K_ab)) Y_Y_n = Y / Y_n sqrt_Y_Y_n = np.sqrt(Y_Y_n) L = 100 * sqrt_Y_Y_n a = K_a * ((X / X_n - Y_Y_n) / sqrt_Y_Y_n) b = K_b * ((Y_Y_n - Z / Z_n) / sqrt_Y_Y_n) Lab = tstack([L, a, b]) return from_range_100(Lab)
[docs]def Hunter_Lab_to_XYZ(Lab, XYZ_n=HUNTERLAB_ILLUMINANTS[ 'CIE 1931 2 Degree Standard Observer']['D65'].XYZ_n, K_ab=HUNTERLAB_ILLUMINANTS[ 'CIE 1931 2 Degree Standard Observer']['D65'].K_ab): """ Converts from *Hunter L,a,b* colour scale to *CIE XYZ* tristimulus values. Parameters ---------- Lab : array_like *Hunter L,a,b* colour scale array. XYZ_n : array_like, optional Reference *illuminant* tristimulus values. K_ab : array_like, optional Reference *illuminant* chromaticity coefficients, if ``K_ab`` is set to *None* it will be computed using :func:`colour.XYZ_to_K_ab_HunterLab1966`. Returns ------- ndarray *CIE XYZ* tristimulus values. Notes ----- +------------+-----------------------+-----------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +============+=======================+=================+ | ``Lab`` | ``L`` : [0, 100] | ``L`` : [0, 1] | | | | | | | ``a`` : [-100, 100] | ``a`` : [-1, 1] | | | | | | | ``b`` : [-100, 100] | ``b`` : [-1, 1] | +------------+-----------------------+-----------------+ | ``XYZ_n`` | [0, 100] | [0, 1] | +------------+-----------------------+-----------------+ +------------+-----------------------+-----------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +============+=======================+=================+ | ``XYZ`` | [0, 100] | [0, 1] | +------------+-----------------------+-----------------+ References ---------- :cite:`HunterLab2008b` Examples -------- >>> Lab = np.array([34.92452577, 47.06189858, 14.38615107]) >>> D65 = HUNTERLAB_ILLUMINANTS[ ... 'CIE 1931 2 Degree Standard Observer']['D65'] >>> Hunter_Lab_to_XYZ(Lab, D65.XYZ_n, D65.K_ab) array([ 20.654008, 12.197225, 5.136952]) """ L, a, b = tsplit(to_domain_100(Lab)) X_n, Y_n, Z_n = tsplit(to_domain_100(XYZ_n)) K_a, K_b = (tsplit(XYZ_to_K_ab_HunterLab1966(XYZ_n)) if K_ab is None else tsplit(K_ab)) L_100 = L / 100 L_100_2 = L_100 ** 2 Y = L_100_2 * Y_n X = ((a / K_a) * L_100 + L_100_2) * X_n Z = -((b / K_b) * L_100 - L_100_2) * Z_n XYZ = tstack([X, Y, Z]) return from_range_100(XYZ)