"""
CAM16 Colour Appearance Model
=============================
Define the *CAM16* colour appearance model objects:
- :class:`colour.appearance.InductionFactors_CAM16`
- :attr:`colour.VIEWING_CONDITIONS_CAM16`
- :class:`colour.CAM_Specification_CAM16`
- :func:`colour.XYZ_to_CAM16`
- :func:`colour.CAM16_to_XYZ`
References
----------
- :cite:`Li2017` : Li, C., Li, Z., Wang, Z., Xu, Y., Luo, M. R., Cui, G.,
Melgosa, M., Brill, M. H., & Pointer, M. (2017). Comprehensive color
solutions: CAM16, CAT16, and CAM16-UCS. Color Research & Application,
42(6), 703-718. doi:10.1002/col.22131
"""
from __future__ import annotations
from collections import namedtuple
from dataclasses import astuple, dataclass, field
import numpy as np
from colour.adaptation import CAT_CAT16
from colour.algebra import spow, vecmul
from colour.appearance.ciecam02 import (
VIEWING_CONDITIONS_CIECAM02,
InductionFactors_CIECAM02,
P,
achromatic_response_forward,
achromatic_response_inverse,
brightness_correlate,
chroma_correlate,
colourfulness_correlate,
degree_of_adaptation,
eccentricity_factor,
hue_angle,
hue_quadrature,
lightness_correlate,
matrix_post_adaptation_non_linear_response_compression,
opponent_colour_dimensions_forward,
opponent_colour_dimensions_inverse,
post_adaptation_non_linear_response_compression_forward,
post_adaptation_non_linear_response_compression_inverse,
saturation_correlate,
temporary_magnitude_quantity_inverse,
viewing_conditions_dependent_parameters,
)
from colour.hints import ArrayLike, NDArrayFloat
from colour.utilities import (
CanonicalMapping,
MixinDataclassArithmetic,
as_float,
as_float_array,
from_range_100,
from_range_degrees,
has_only_nan,
ones,
to_domain_100,
to_domain_degrees,
tsplit,
)
__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__ = [
"MATRIX_16",
"MATRIX_INVERSE_16",
"InductionFactors_CAM16",
"VIEWING_CONDITIONS_CAM16",
"CAM_Specification_CAM16",
"XYZ_to_CAM16",
"CAM16_to_XYZ",
]
MATRIX_16: NDArrayFloat = CAT_CAT16
"""Adaptation matrix :math:`M_{16}`."""
MATRIX_INVERSE_16: NDArrayFloat = np.linalg.inv(MATRIX_16)
"""Inverse adaptation matrix :math:`M^{-1}_{16}`."""
[docs]
class InductionFactors_CAM16(namedtuple("InductionFactors_CAM16", ("F", "c", "N_c"))):
"""
*CAM16* colour appearance model induction factors.
Parameters
----------
F
Maximum degree of adaptation :math:`F`.
c
Exponential non-linearity :math:`c`.
N_c
Chromatic induction factor :math:`N_c`.
Notes
-----
- The *CAM16* colour appearance model induction factors are the same as
*CIECAM02* colour appearance model.
References
----------
:cite:`Li2017`
"""
VIEWING_CONDITIONS_CAM16: CanonicalMapping = CanonicalMapping(
VIEWING_CONDITIONS_CIECAM02
)
VIEWING_CONDITIONS_CAM16.__doc__ = """
Reference *CAM16* colour appearance model viewing conditions.
References
----------
:cite:`Li2017`
"""
[docs]
@dataclass
class CAM_Specification_CAM16(MixinDataclassArithmetic):
"""
Define the *CAM16* colour appearance model specification.
Parameters
----------
J
Correlate of *Lightness* :math:`J`.
C
Correlate of *chroma* :math:`C`.
h
*Hue* angle :math:`h` in degrees.
s
Correlate of *saturation* :math:`s`.
Q
Correlate of *brightness* :math:`Q`.
M
Correlate of *colourfulness* :math:`M`.
H
*Hue* :math:`h` quadrature :math:`H`.
HC
*Hue* :math:`h` composition :math:`H^C`.
References
----------
:cite:`Li2017`
"""
J: float | NDArrayFloat | None = field(default_factory=lambda: None)
C: float | NDArrayFloat | None = field(default_factory=lambda: None)
h: float | NDArrayFloat | None = field(default_factory=lambda: None)
s: float | NDArrayFloat | None = field(default_factory=lambda: None)
Q: float | NDArrayFloat | None = field(default_factory=lambda: None)
M: float | NDArrayFloat | None = field(default_factory=lambda: None)
H: float | NDArrayFloat | None = field(default_factory=lambda: None)
HC: float | NDArrayFloat | None = field(default_factory=lambda: None)
[docs]
def XYZ_to_CAM16(
XYZ: ArrayLike,
XYZ_w: ArrayLike,
L_A: ArrayLike,
Y_b: ArrayLike,
surround: (
InductionFactors_CIECAM02 | InductionFactors_CAM16
) = VIEWING_CONDITIONS_CAM16["Average"],
discount_illuminant: bool = False,
compute_H: bool = True,
) -> CAM_Specification_CAM16:
"""
Compute the *CAM16* colour appearance model correlates from given
*CIE XYZ* tristimulus values.
Parameters
----------
XYZ
*CIE XYZ* tristimulus values of test sample / stimulus.
XYZ_w
*CIE XYZ* tristimulus values of reference white.
L_A
Adapting field *luminance* :math:`L_A` in :math:`cd/m^2`, (often taken
to be 20% of the luminance of a white object in the scene).
Y_b
Luminous factor of background :math:`Y_b` such as
:math:`Y_b = 100 x L_b / L_w` where :math:`L_w` is the luminance of the
light source and :math:`L_b` is the luminance of the background. For
viewing images, :math:`Y_b` can be the average :math:`Y` value for the
pixels in the entire image, or frequently, a :math:`Y` value of 20,
approximate an :math:`L^*` of 50 is used.
surround
Surround viewing conditions induction factors.
discount_illuminant
Truth value indicating if the illuminant should be discounted.
compute_H
Whether to compute *Hue* :math:`h` quadrature :math:`H`. :math:`H` is
rarely used, and expensive to compute.
Returns
-------
:class:`colour.CAM_Specification_CAM16`
*CAM16* colour appearance model specification.
Notes
-----
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``XYZ`` | [0, 100] | [0, 1] |
+------------+-----------------------+---------------+
| ``XYZ_w`` | [0, 100] | [0, 1] |
+------------+-----------------------+---------------+
+-------------------------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+===============================+=======================+===============+
| ``CAM_Specification_CAM16.J`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.C`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.h`` | [0, 360] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.s`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.Q`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.M`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.H`` | [0, 400] | [0, 1] |
+-------------------------------+-----------------------+---------------+
References
----------
:cite:`Li2017`
Examples
--------
>>> XYZ = np.array([19.01, 20.00, 21.78])
>>> XYZ_w = np.array([95.05, 100.00, 108.88])
>>> L_A = 318.31
>>> Y_b = 20.0
>>> surround = VIEWING_CONDITIONS_CAM16["Average"]
>>> XYZ_to_CAM16(XYZ, XYZ_w, L_A, Y_b, surround) # doctest: +ELLIPSIS
CAM_Specification_CAM16(J=41.7312079..., C=0.1033557..., \
h=217.0679597..., s=2.3450150..., Q=195.3717089..., M=0.1074367..., \
H=275.5949861..., HC=None)
"""
XYZ = to_domain_100(XYZ)
XYZ_w = to_domain_100(XYZ_w)
_X_w, Y_w, _Z_w = tsplit(XYZ_w)
L_A = as_float_array(L_A)
Y_b = as_float_array(Y_b)
# Step 0
# Converting *CIE XYZ* tristimulus values to sharpened *RGB* values.
RGB_w = vecmul(MATRIX_16, XYZ_w)
# Computing degree of adaptation :math:`D`.
D = (
np.clip(degree_of_adaptation(surround.F, L_A), 0, 1)
if not discount_illuminant
else ones(L_A.shape)
)
n, F_L, N_bb, N_cb, z = viewing_conditions_dependent_parameters(Y_b, Y_w, L_A)
D_RGB = D[..., None] * Y_w[..., None] / RGB_w + 1 - D[..., None]
RGB_wc = D_RGB * RGB_w
# Applying forward post-adaptation non-linear response compression.
RGB_aw = post_adaptation_non_linear_response_compression_forward(RGB_wc, F_L)
# Computing achromatic responses for the whitepoint.
A_w = achromatic_response_forward(RGB_aw, N_bb)
# Step 1
# Converting *CIE XYZ* tristimulus values to sharpened *RGB* values.
RGB = vecmul(MATRIX_16, XYZ)
# Step 2
RGB_c = D_RGB * RGB
# Step 3
# Applying forward post-adaptation non-linear response compression.
RGB_a = post_adaptation_non_linear_response_compression_forward(RGB_c, F_L)
# Step 4
# Converting to preliminary cartesian coordinates.
a, b = tsplit(opponent_colour_dimensions_forward(RGB_a))
# Computing the *hue* angle :math:`h`.
h = hue_angle(a, b)
# Step 5
# Computing eccentricity factor *e_t*.
e_t = eccentricity_factor(h)
# Computing hue :math:`h` quadrature :math:`H`.
H = hue_quadrature(h) if compute_H else np.full(h.shape, np.nan)
# TODO: Compute hue composition.
# Step 6
# Computing achromatic responses for the stimulus.
A = achromatic_response_forward(RGB_a, N_bb)
# Step 7
# Computing the correlate of *Lightness* :math:`J`.
J = lightness_correlate(A, A_w, surround.c, z)
# Step 8
# Computing the correlate of *brightness* :math:`Q`.
Q = brightness_correlate(surround.c, J, A_w, F_L)
# Step 9
# Computing the correlate of *chroma* :math:`C`.
C = chroma_correlate(J, n, surround.N_c, N_cb, e_t, a, b, RGB_a)
# Computing the correlate of *colourfulness* :math:`M`.
M = colourfulness_correlate(C, F_L)
# Computing the correlate of *saturation* :math:`s`.
s = saturation_correlate(M, Q)
return CAM_Specification_CAM16(
as_float(from_range_100(J)),
as_float(from_range_100(C)),
as_float(from_range_degrees(h)),
as_float(from_range_100(s)),
as_float(from_range_100(Q)),
as_float(from_range_100(M)),
as_float(from_range_degrees(H, 400)),
None,
)
[docs]
def CAM16_to_XYZ(
specification: CAM_Specification_CAM16,
XYZ_w: ArrayLike,
L_A: ArrayLike,
Y_b: ArrayLike,
surround: (
InductionFactors_CIECAM02 | InductionFactors_CAM16
) = VIEWING_CONDITIONS_CAM16["Average"],
discount_illuminant: bool = False,
) -> NDArrayFloat:
"""
Convert from *CAM16* specification to *CIE XYZ* tristimulus values.
Parameters
----------
specification
*CAM16* colour appearance model specification. Correlate of
*Lightness* :math:`J`, correlate of *chroma* :math:`C` or correlate of
*colourfulness* :math:`M` and *hue* angle :math:`h` in degrees must be
specified, e.g., :math:`JCh` or :math:`JMh`.
XYZ_w
*CIE XYZ* tristimulus values of reference white.
L_A
Adapting field *luminance* :math:`L_A` in :math:`cd/m^2`, (often taken
to be 20% of the luminance of a white object in the scene).
Y_b
Luminous factor of background :math:`Y_b` such as
:math:`Y_b = 100 x L_b / L_w` where :math:`L_w` is the luminance of the
light source and :math:`L_b` is the luminance of the background. For
viewing images, :math:`Y_b` can be the average :math:`Y` value for the
pixels in the entire image, or frequently, a :math:`Y` value of 20,
approximate an :math:`L^*` of 50 is used.
surround
Surround viewing conditions.
discount_illuminant
Discount the illuminant.
Returns
-------
:class:`numpy.ndarray`
*CIE XYZ* tristimulus values.
Raises
------
ValueError
If neither :math:`C` or :math:`M` correlates have been defined in the
``specification`` argument.
Notes
-----
+-------------------------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+===============================+=======================+===============+
| ``CAM_Specification_CAM16.J`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.C`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.h`` | [0, 360] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.s`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.Q`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.M`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``CAM_Specification_CAM16.H`` | [0, 360] | [0, 1] |
+-------------------------------+-----------------------+---------------+
| ``XYZ_w`` | [0, 100] | [0, 1] |
+-------------------------------+-----------------------+---------------+
+-----------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+===========+=======================+===============+
| ``XYZ`` | [0, 100] | [0, 1] |
+-----------+-----------------------+---------------+
References
----------
:cite:`Li2017`
Examples
--------
>>> specification = CAM_Specification_CAM16(
... J=41.731207905126638, C=0.103355738709070, h=217.067959767393010
... )
>>> XYZ_w = np.array([95.05, 100.00, 108.88])
>>> L_A = 318.31
>>> Y_b = 20.0
>>> CAM16_to_XYZ(specification, XYZ_w, L_A, Y_b) # doctest: +ELLIPSIS
array([ 19.01..., 20... , 21.78...])
"""
J, C, h, _s, _Q, M, _H, _HC = astuple(specification)
J = to_domain_100(J)
C = to_domain_100(C)
h = to_domain_degrees(h)
M = to_domain_100(M)
L_A = as_float_array(L_A)
XYZ_w = to_domain_100(XYZ_w)
_X_w, Y_w, _Z_w = tsplit(XYZ_w)
# Step 0
# Converting *CIE XYZ* tristimulus values to sharpened *RGB* values.
RGB_w = vecmul(MATRIX_16, XYZ_w)
# Computing degree of adaptation :math:`D`.
D = (
np.clip(degree_of_adaptation(surround.F, L_A), 0, 1)
if not discount_illuminant
else ones(L_A.shape)
)
n, F_L, N_bb, N_cb, z = viewing_conditions_dependent_parameters(Y_b, Y_w, L_A)
D_RGB = D[..., None] * Y_w[..., None] / RGB_w + 1 - D[..., None]
RGB_wc = D_RGB * RGB_w
# Applying forward post-adaptation non-linear response compression.
RGB_aw = post_adaptation_non_linear_response_compression_forward(RGB_wc, F_L)
# Computing achromatic responses for the whitepoint.
A_w = achromatic_response_forward(RGB_aw, N_bb)
# Step 1
if has_only_nan(C) and not has_only_nan(M):
C = M / spow(F_L, 0.25)
elif has_only_nan(C):
raise ValueError(
'Either "C" or "M" correlate must be defined in '
'the "CAM_Specification_CAM16" argument!'
)
# Step 2
# Computing temporary magnitude quantity :math:`t`.
t = temporary_magnitude_quantity_inverse(C, J, n)
# Computing eccentricity factor *e_t*.
e_t = eccentricity_factor(h)
# Computing achromatic response :math:`A` for the stimulus.
A = achromatic_response_inverse(A_w, J, surround.c, z)
# Computing *P_1* to *P_3*.
P_n = P(surround.N_c, N_cb, e_t, t, A, N_bb)
_P_1, P_2, _P_3 = tsplit(P_n)
# Step 3
# Computing opponent colour dimensions :math:`a` and :math:`b`.
ab = opponent_colour_dimensions_inverse(P_n, h)
a, b = tsplit(ab) * np.where(t == 0, 0, 1)
# Step 4
# Applying post-adaptation non-linear response compression matrix.
RGB_a = matrix_post_adaptation_non_linear_response_compression(P_2, a, b)
# Step 5
# Applying inverse post-adaptation non-linear response compression.
RGB_c = post_adaptation_non_linear_response_compression_inverse(RGB_a, F_L)
# Step 6
RGB = RGB_c / D_RGB
# Step 7
XYZ = vecmul(MATRIX_INVERSE_16, RGB)
return from_range_100(XYZ)
