"""
Prismatic Colourspace
=====================
Define the *Prismatic* colourspace transformations:
- :func:`colour.RGB_to_Prismatic`
- :func:`colour.Prismatic_to_RGB`
References
----------
- :cite:`Shirley2015a` : Shirley, P., & Hart, D. (2015). The prismatic color
space for rgb computations (pp. 2-7).
"""
from __future__ import annotations
import numpy as np
from colour.algebra import sdiv, sdiv_mode
from colour.hints import ArrayLike, NDArrayFloat
from colour.utilities import from_range_1, to_domain_1, 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__ = [
"RGB_to_Prismatic",
"Prismatic_to_RGB",
]
[docs]
def RGB_to_Prismatic(RGB: ArrayLike) -> NDArrayFloat:
"""
Convert from *RGB* colourspace to *Prismatic* :math:`L\\rho\\gamma\\beta`
colourspace array.
Parameters
----------
RGB
*RGB* colourspace array.
Returns
-------
:class:`numpy.ndarray`
*Prismatic* :math:`L\\rho\\gamma\\beta` colourspace array.
Notes
-----
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``RGB`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
+------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``Lrgb`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
References
----------
:cite:`Shirley2015a`
Examples
--------
>>> RGB = np.array([0.25, 0.50, 0.75])
>>> RGB_to_Prismatic(RGB) # doctest: +ELLIPSIS
array([ 0.75... , 0.1666666..., 0.3333333..., 0.5... ])
Adjusting saturation of given *RGB* colourspace array:
>>> saturation = 0.5
>>> Lrgb = RGB_to_Prismatic(RGB)
>>> Lrgb[..., 1:] = 1 / 3 + saturation * (Lrgb[..., 1:] - 1 / 3)
>>> Prismatic_to_RGB(Lrgb) # doctest: +ELLIPSIS
array([ 0.45..., 0.6..., 0.75...])
"""
RGB = to_domain_1(RGB)
L = np.max(RGB, axis=-1)
s = np.sum(RGB, axis=-1)
with sdiv_mode():
one_s = sdiv(1, s[..., None])
r, g, b = tsplit(one_s * RGB)
Lrgb = tstack([L, r, g, b])
return from_range_1(Lrgb)
[docs]
def Prismatic_to_RGB(Lrgb: ArrayLike) -> NDArrayFloat:
"""
Convert from *Prismatic* :math:`L\\rho\\gamma\\beta` colourspace array to
*RGB* colourspace.
Parameters
----------
Lrgb
*Prismatic* :math:`L\\rho\\gamma\\beta` colourspace array.
Returns
-------
:class:`numpy.ndarray`
*RGB* colourspace array.
Notes
-----
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``Lrgb`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
+------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``RGB`` | [0, 1] | [0, 1] |
+------------+-----------------------+---------------+
References
----------
:cite:`Shirley2015a`
Examples
--------
>>> Lrgb = np.array([0.75000000, 0.16666667, 0.33333333, 0.50000000])
>>> Prismatic_to_RGB(Lrgb) # doctest: +ELLIPSIS
array([ 0.25... , 0.4999999..., 0.75... ])
"""
Lrgb = to_domain_1(Lrgb)
rgb = Lrgb[..., 1:]
m = np.max(rgb, axis=-1)
with sdiv_mode():
RGB = sdiv(Lrgb[..., 0][..., None], m[..., None])
RGB = RGB * rgb
return from_range_1(RGB)
