"""
Hunter Rd,a,b Colour Scale
==========================
Define the *Hunter Rd,a,b* colour scale transformations.
- :func:`colour.XYZ_to_Hunter_Rdab`
- :func:`colour.Hunter_Rdab_to_XYZ`
References
----------
- :cite:`HunterLab2012a` : HunterLab. (2012). Hunter Rd,a,b Color Scale -
History and Application.
https://hunterlabdotcom.files.wordpress.com/2012/07/\
an-1016-hunter-rd-a-b-color-scale-update-12-07-03.pdf
"""
from __future__ import annotations
from colour.colorimetry import TVS_ILLUMINANTS_HUNTERLAB
from colour.hints import ( # noqa: TC001
ArrayLike,
Domain100,
Range100,
)
from colour.models import XYZ_to_K_ab_HunterLab1966
from colour.utilities import (
from_range_100,
get_domain_range_scale,
optional,
to_domain_100,
tsplit,
tstack,
)
__author__ = "Colour Developers"
__copyright__ = "Copyright 2013 Colour Developers"
__license__ = "BSD-3-Clause - https://opensource.org/licenses/BSD-3-Clause"
__maintainer__ = "Colour Developers"
__email__ = "colour-developers@colour-science.org"
__status__ = "Production"
__all__ = [
"XYZ_to_Hunter_Rdab",
"Hunter_Rdab_to_XYZ",
]
[docs]
def XYZ_to_Hunter_Rdab(
XYZ: Domain100,
XYZ_n: ArrayLike | None = None,
K_ab: ArrayLike | None = None,
) -> Range100:
"""
Convert from *CIE XYZ* tristimulus values to *Hunter Rd,a,b* colour
scale.
Parameters
----------
XYZ
*CIE XYZ* tristimulus values.
XYZ_n
Reference *illuminant* tristimulus values.
K_ab
Reference *illuminant* chromaticity coefficients. If ``K_ab`` is
set to *None*, it will be computed using
:func:`colour.XYZ_to_K_ab_HunterLab1966`.
Returns
-------
:class:`numpy.ndarray`
*Hunter Rd,a,b* colour scale array.
Notes
-----
+------------+------------------------+--------------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+========================+====================+
| ``XYZ`` | 100 | 1 |
+------------+------------------------+--------------------+
| ``XYZ_n`` | 100 | 1 |
+------------+------------------------+--------------------+
+------------+------------------------+--------------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+========================+====================+
| ``R_d_ab`` | 100 | 1 |
+------------+------------------------+--------------------+
References
----------
:cite:`HunterLab2012a`
Examples
--------
>>> import numpy as np
>>> XYZ = np.array([0.20654008, 0.12197225, 0.05136952]) * 100
>>> D65 = TVS_ILLUMINANTS_HUNTERLAB["CIE 1931 2 Degree Standard Observer"]["D65"]
>>> XYZ_to_Hunter_Rdab(XYZ, D65.XYZ_n, D65.K_ab)
... # doctest: +ELLIPSIS
array([12.197225..., 57.1253787..., 17.4624134...])
"""
X, Y, Z = tsplit(to_domain_100(XYZ))
d65 = TVS_ILLUMINANTS_HUNTERLAB["CIE 1931 2 Degree Standard Observer"]["D65"]
XYZ_n_default = XYZ_n is None
XYZ_n = to_domain_100(
optional(
XYZ_n,
d65.XYZ_n if get_domain_range_scale() == "reference" else d65.XYZ_n / 100,
)
)
X_n, Y_n, Z_n = tsplit(XYZ_n)
K_ab = d65.K_ab if K_ab is None and XYZ_n_default else K_ab
K_a, K_b = tsplit(XYZ_to_K_ab_HunterLab1966(XYZ_n) if K_ab is None else K_ab)
f = 0.51 * ((21 + 0.2 * Y) / (1 + 0.2 * Y))
Y_Yn = Y / Y_n
R_d = Y
a_Rd = K_a * f * (X / X_n - Y_Yn)
b_Rd = K_b * f * (Y_Yn - Z / Z_n)
R_d_ab = tstack([R_d, a_Rd, b_Rd])
return from_range_100(R_d_ab)
[docs]
def Hunter_Rdab_to_XYZ(
R_d_ab: Domain100,
XYZ_n: ArrayLike | None = None,
K_ab: ArrayLike | None = None,
) -> Range100:
"""
Convert from *Hunter Rd,a,b* colour scale to *CIE XYZ* tristimulus
values.
Parameters
----------
R_d_ab
*Hunter Rd,a,b* colour scale array.
XYZ_n
Reference *illuminant* tristimulus values.
K_ab
Reference *illuminant* chromaticity coefficients. If ``K_ab`` is
set to *None*, it will be computed using
:func:`colour.XYZ_to_K_ab_HunterLab1966`.
Returns
-------
:class:`numpy.ndarray`
*CIE XYZ* tristimulus values.
Notes
-----
+------------+------------------------+--------------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+========================+====================+
| ``R_d_ab`` | 100 | 1 |
+------------+------------------------+--------------------+
| ``XYZ_n`` | 100 | 1 |
+------------+------------------------+--------------------+
+------------+------------------------+--------------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+========================+====================+
| ``XYZ`` | 100 | 1 |
+------------+------------------------+--------------------+
References
----------
:cite:`HunterLab2012a`
Examples
--------
>>> import numpy as np
>>> R_d_ab = np.array([12.19722500, 57.12537874, 17.46241341])
>>> D65 = TVS_ILLUMINANTS_HUNTERLAB["CIE 1931 2 Degree Standard Observer"]["D65"]
>>> Hunter_Rdab_to_XYZ(R_d_ab, D65.XYZ_n, D65.K_ab)
array([20.654008, 12.197225, 5.136952])
"""
R_d, a_Rd, b_Rd = tsplit(to_domain_100(R_d_ab))
TVS_D65 = TVS_ILLUMINANTS_HUNTERLAB["CIE 1931 2 Degree Standard Observer"]["D65"]
XYZ_n_default = XYZ_n is None
XYZ_n = to_domain_100(
optional(
XYZ_n,
TVS_D65.XYZ_n
if get_domain_range_scale() == "reference"
else TVS_D65.XYZ_n / 100,
)
)
X_n, Y_n, Z_n = tsplit(XYZ_n)
K_ab = TVS_D65.K_ab if K_ab is None and XYZ_n_default else K_ab
K_a, K_b = tsplit(XYZ_to_K_ab_HunterLab1966(XYZ_n) if K_ab is None else K_ab)
f = 0.51 * ((21 + 0.2 * R_d) / (1 + 0.2 * R_d))
Rd_Yn = R_d / Y_n
X = (a_Rd / (K_a * f) + Rd_Yn) * X_n
Z = -(b_Rd / (K_b * f) - Rd_Yn) * Z_n
XYZ = tstack([X, R_d, Z])
return from_range_100(XYZ)
