"""
CIE L*a*b* Colourspace
======================
Define the *CIE L\\*a\\*b\\** colourspace transformations:
- :func:`colour.XYZ_to_Lab`
- :func:`colour.Lab_to_XYZ`
References
----------
- :cite:`CIETC1-482004m` : CIE TC 1-48. (2004). CIE 1976 uniform colour
spaces. In CIE 015:2004 Colorimetry, 3rd Edition (p. 24).
ISBN:978-3-901906-33-6
"""
from __future__ import annotations
import typing
from colour.colorimetry import (
CCS_ILLUMINANTS,
intermediate_lightness_function_CIE1976,
intermediate_luminance_function_CIE1976,
)
if typing.TYPE_CHECKING:
from colour.hints import ArrayLike, NDArrayFloat
from colour.models import xy_to_xyY, xyY_to_XYZ
from colour.utilities import (
from_range_1,
from_range_100,
to_domain_1,
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_Lab",
"Lab_to_XYZ",
]
[docs]
def XYZ_to_Lab(
XYZ: ArrayLike,
illuminant: ArrayLike = CCS_ILLUMINANTS["CIE 1931 2 Degree Standard Observer"][
"D65"
],
) -> NDArrayFloat:
"""
Convert from *CIE XYZ* tristimulus values to *CIE L\\*a\\*b\\**
colourspace.
Parameters
----------
XYZ
*CIE XYZ* tristimulus values.
illuminant
Reference *illuminant* *CIE xy* chromaticity coordinates or *CIE xyY*
colourspace array.
Returns
-------
:class:`numpy.ndarray`
*CIE L\\*a\\*b\\** colourspace array.
Notes
-----
+----------------+-----------------------+-----------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+================+=======================+=================+
| ``XYZ`` | [0, 1] | [0, 1] |
+----------------+-----------------------+-----------------+
| ``illuminant`` | [0, 1] | [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:`CIETC1-482004m`
Examples
--------
>>> import numpy as np
>>> XYZ = np.array([0.20654008, 0.12197225, 0.05136952])
>>> XYZ_to_Lab(XYZ) # doctest: +ELLIPSIS
array([ 41.5278752..., 52.6385830..., 26.9231792...])
"""
X, Y, Z = tsplit(to_domain_1(XYZ))
X_n, Y_n, Z_n = tsplit(xyY_to_XYZ(xy_to_xyY(illuminant)))
f_X_X_n = intermediate_lightness_function_CIE1976(X, X_n)
f_Y_Y_n = intermediate_lightness_function_CIE1976(Y, Y_n)
f_Z_Z_n = intermediate_lightness_function_CIE1976(Z, Z_n)
L = 116 * f_Y_Y_n - 16
a = 500 * (f_X_X_n - f_Y_Y_n)
b = 200 * (f_Y_Y_n - f_Z_Z_n)
Lab = tstack([L, a, b])
return from_range_100(Lab)
[docs]
def Lab_to_XYZ(
Lab: ArrayLike,
illuminant: ArrayLike = CCS_ILLUMINANTS["CIE 1931 2 Degree Standard Observer"][
"D65"
],
) -> NDArrayFloat:
"""
Convert from *CIE L\\*a\\*b\\** colourspace to *CIE XYZ* tristimulus
values.
Parameters
----------
Lab
*CIE L\\*a\\*b\\** colourspace array.
illuminant
Reference *illuminant* *CIE xy* chromaticity coordinates or *CIE xyY*
colourspace array.
Returns
-------
:class:`numpy.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] |
+----------------+-----------------------+-----------------+
| ``illuminant`` | [0, 1] | [0, 1] |
+----------------+-----------------------+-----------------+
+----------------+-----------------------+-----------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+================+=======================+=================+
| ``XYZ`` | [0, 1] | [0, 1] |
+----------------+-----------------------+-----------------+
References
----------
:cite:`CIETC1-482004m`
Examples
--------
>>> import numpy as np
>>> Lab = np.array([41.52787529, 52.63858304, 26.92317922])
>>> Lab_to_XYZ(Lab) # doctest: +ELLIPSIS
array([ 0.2065400..., 0.1219722..., 0.0513695...])
"""
L, a, b = tsplit(to_domain_100(Lab))
X_n, Y_n, Z_n = tsplit(xyY_to_XYZ(xy_to_xyY(illuminant)))
f_Y_Y_n = (L + 16) / 116
f_X_X_n = a / 500 + f_Y_Y_n
f_Z_Z_n = f_Y_Y_n - b / 200
X = intermediate_luminance_function_CIE1976(f_X_X_n, X_n)
Y = intermediate_luminance_function_CIE1976(f_Y_Y_n, Y_n)
Z = intermediate_luminance_function_CIE1976(f_Z_Z_n, Z_n)
XYZ = tstack([X, Y, Z])
return from_range_1(XYZ)
