Source code for colour.appearance.zcam

"""
ZCAM Colour Appearance Model
============================

Defines the *ZCAM* colour appearance model objects:

-   :class:`colour.appearance.InductionFactors_ZCAM`
-   :attr:`colour.VIEWING_CONDITIONS_ZCAM`
-   :class:`colour.CAM_Specification_ZCAM`
-   :func:`colour.XYZ_to_ZCAM`
-   :func:`colour.ZCAM_to_XYZ`

References
----------
-   :cite:`Safdar2018` : Safdar, M., Hardeberg, J. Y., Kim, Y. J., & Luo, M. R.
    (2018). A Colour Appearance Model based on J z a z b z Colour Space. Color
    and Imaging Conference, 2018(1), 96-101.
    doi:10.2352/ISSN.2169-2629.2018.26.96
-   :cite:`Safdar2021` : Safdar, M., Hardeberg, J. Y., & Ronnier Luo, M.
    (2021). ZCAM, a colour appearance model based on a high dynamic range
    uniform colour space. Optics Express, 29(4), 6036. doi:10.1364/OE.413659
-   :cite:`Zhai2018` : Zhai, Q., & Luo, M. R. (2018). Study of chromatic
    adaptation via neutral white matches on different viewing media. Optics
    Express, 26(6), 7724. doi:10.1364/OE.26.007724
"""

from __future__ import annotations

import numpy as np
from collections import namedtuple
from dataclasses import astuple, dataclass, field

from colour.adaptation import chromatic_adaptation_Zhai2018
from colour.appearance.ciecam02 import (
    VIEWING_CONDITIONS_CIECAM02,
    degree_of_adaptation,
    hue_angle,
)
from colour.algebra import sdiv, sdiv_mode, spow
from colour.colorimetry import CCS_ILLUMINANTS
from colour.hints import (
    ArrayLike,
    Boolean,
    Dict,
    FloatingOrArrayLike,
    FloatingOrNDArray,
    NDArray,
    Optional,
)
from colour.models import Izazbz_to_XYZ, XYZ_to_Izazbz, xy_to_XYZ
from colour.utilities import (
    CanonicalMapping,
    MixinDataclassArithmetic,
    as_float,
    as_float_array,
    as_int_array,
    domain_range_scale,
    from_range_1,
    from_range_degrees,
    has_only_nan,
    ones,
    to_domain_1,
    to_domain_degrees,
    tsplit,
    tstack,
)

__author__ = "Colour Developers"
__copyright__ = "Copyright 2013 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__ = [
    "InductionFactors_ZCAM",
    "VIEWING_CONDITIONS_ZCAM",
    "CAM_Specification_ZCAM",
    "XYZ_to_ZCAM",
    "ZCAM_to_XYZ",
]


[docs]class InductionFactors_ZCAM( namedtuple("InductionFactors_ZCAM", ("F_s", "F", "c", "N_c")) ): """ *ZCAM* colour appearance model induction factors. Parameters ---------- F_s Surround impact :math:`F_s`. F Maximum degree of adaptation :math:`F`. c Exponential non-linearity :math:`c`. N_c Chromatic induction factor :math:`N_c`. Notes ----- - The *ZCAM* colour appearance model induction factors are inherited from the *CIECAM02* colour appearance model. References ---------- :cite:`Safdar2021` """
VIEWING_CONDITIONS_ZCAM: CanonicalMapping = CanonicalMapping( { "Average": InductionFactors_ZCAM( 0.69, *VIEWING_CONDITIONS_CIECAM02["Average"] ), "Dim": InductionFactors_ZCAM( 0.59, *VIEWING_CONDITIONS_CIECAM02["Dim"] ), "Dark": InductionFactors_ZCAM( 0.525, *VIEWING_CONDITIONS_CIECAM02["Dark"] ), } ) VIEWING_CONDITIONS_ZCAM.__doc__ = """ Reference *ZCAM* colour appearance model viewing conditions. References ---------- :cite:`Safdar2021` """ HUE_DATA_FOR_HUE_QUADRATURE: Dict = { "h_i": np.array([33.44, 89.29, 146.30, 238.36, 393.44]), "e_i": np.array([0.68, 0.64, 1.52, 0.77, 0.68]), "H_i": np.array([0.0, 100.0, 200.0, 300.0, 400.0]), } @dataclass class CAM_ReferenceSpecification_ZCAM(MixinDataclassArithmetic): """ Define the *ZCAM* colour appearance model reference specification. This specification has field names consistent with :cite:`Safdar2021` reference. Parameters ---------- J_z Correlate of *Lightness* :math:`J_z`. C_z Correlate of *chroma* :math:`C_z`. h_z *Hue* angle :math:`h_z` in degrees. S_z Correlate of *saturation* :math:`S_z`. Q_z Correlate of *brightness* :math:`Q_z`. M_z Correlate of *colourfulness* :math:`M_z`. H *Hue* :math:`h` quadrature :math:`H`. H_z *Hue* :math:`h` composition :math:`H_z`. V_z Correlate of *vividness* :math:`V_z`. K_z Correlate of *blackness* :math:`K_z`. W_z Correlate of *whiteness* :math:`W_z`. References ---------- :cite:`Safdar2021` """ J_z: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) C_z: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) h_z: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) S_z: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) Q_z: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) M_z: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) H: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) H_z: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) V_z: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) K_z: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) W_z: Optional[FloatingOrNDArray] = field(default_factory=lambda: None)
[docs]@dataclass class CAM_Specification_ZCAM(MixinDataclassArithmetic): """ Define the *ZCAM* colour appearance model specification. Parameters ---------- J *Lightness* :math:`J` is the "brightness of an area (:math:`Q`) judged relative to the brightness of a similarly illuminated area that appears to be white or highly transmitting (:math:`Q_w`)", i.e., :math:`J = (Q/Q_w)`. It is a visual scale with two well defined levels i.e., zero and 100 for a pure black and a reference white, respectively. Note that in HDR visual field, samples could have a higher luminance than that of the reference white, so the lightness could be over 100. Subscripts :math:`s` and :math:`w` are used to annotate the sample and the reference white, respectively. C *Chroma* :math:`C` is "colourfulness of an area (:math:`M`) judged as a proportion of the brightness of a similarly illuminated area that appears white or highly transmitting (:math:`Q_w`)", i.e., :math:`C = (M/Q_w)`. It is an open-end scale with origin as a colour in the neutral axis. It can be estimated as the magnitude of the chromatic difference between the test colour and a neutral colour having the lightness same as the test colour. h *Hue* angle :math:`h` is a scale ranged from :math:`0^{\\circ}` to :math:`360^{\\circ}` with the hues following rainbow sequence. The same distance between pairs of hues in a constant lightness and chroma shows the same perceived colour difference. s *Saturation* :math:`s` is the "colourfulness (:math:`M`) of an area judged in proportion to its brightness (:math:`Q`)", i.e., :math:`s = (M/Q)`. It can also be defined as the chroma of an area judged in proportion to its lightness, i.e., :math:`s = (C/J)`. It is an open-end scale with all neutral colours to have saturation of zero. For example, the red bricks in a building would exhibit different colours when illuminated by daylight. Those (directly) under daylight will appear to be bright and colourful, and those under shadow will appear darker and less colourful. However, the two areas have the same saturation. Q *Brightness* :math:`Q` is an "attribute of a visual perception according to which an area appears to emit, or reflect, more or less light". It is an open-end scale with origin as pure black or complete darkness. It is an absolute scale according to the illumination condition i.e., an increase of brightness of an object when the illuminance of light is increased. This is a visual phenomenon known as Stevens effect. M *Colourfulness* :math:`M` is an "attribute of a visual perception according to which the perceived colour of an area appears to be more or less chromatic". It is an open-end scale with origin as a neutral colour i.e., appearance of no hue. It is an absolute scale according to the illumination condition i.e., an increase of colourfulness of an object when the illuminance of light is increased. This is a visual phenomenon known as Hunt effect. H *Hue* :math:`h` quadrature :math:`H_C` is an "attribute of a visual perception according to which an area appears to be similar to one of the colours: red, yellow, green, and blue, or to a combination of adjacent pairs of these colours considered in a closed ring". It has a 0-400 scale, i.e., hue quadrature of 0, 100, 200, 300, and 400 range from unitary red to, yellow, green, blue, and back to red, respectively. For example, a cyan colour consists of 50% green and 50% blue, corresponding to a hue quadrature of 250. HC *Hue* :math:`h` composition :math:`H^C` used to define the hue appearance of a sample. Note that hue circles formed by the equal hue angle and equal hue composition appear to be quite different. V *Vividness* :math:`V` is an "attribute of colour used to indicate the degree of departure of the colour (of stimulus) from a neutral black colour", i.e., :math:`V = \\sqrt{J^2 + C^2}`. It is an open-end scale with origin at pure black. This reflects the visual phenomena of an object illuminated by a light to increase both the lightness and the chroma. K *Blackness* :math:`K` is a visual attribute according to which an area appears to contain more or less black content. It is a scale in the Natural Colour System (NCS) and can also be defined in resemblance to a pure black. It is an open-end scale with 100 as pure black (luminance of 0 :math:`cd/m^2`), i.e., :math:`K = (100 - \\sqrt{J^2 + C^2} = (100 - V)`. The visual effect can be illustrated by mixing a black to a colour pigment. The more black pigment is added, the higher blackness will be. A blacker colour will have less lightness and/or chroma than a less black colour. W *Whiteness* :math:`W` is a visual attribute according to which an area appears to contain more or less white content. It is a scale of the NCS and can also be defined in resemblance to a pure white. It is an open-end scale with 100 as reference white, i.e., :math:`W = (100 - \\sqrt{(100 - J)^2 + C^2} = (100 - D)`. The visual effect can be illustrated by mixing a white to a colour pigment. The more white pigment is added, the higher whiteness will be. A whiter colour will have a lower chroma and higher lightness than the less white colour. References ---------- :cite:`Safdar2021` """ J: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) C: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) h: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) s: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) Q: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) M: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) H: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) HC: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) V: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) K: Optional[FloatingOrNDArray] = field(default_factory=lambda: None) W: Optional[FloatingOrNDArray] = field(default_factory=lambda: None)
TVS_D65: NDArray = xy_to_XYZ( CCS_ILLUMINANTS["CIE 1931 2 Degree Standard Observer"]["D65"] )
[docs]def XYZ_to_ZCAM( XYZ: ArrayLike, XYZ_w: ArrayLike, L_A: FloatingOrArrayLike, Y_b: FloatingOrArrayLike, surround: InductionFactors_ZCAM = VIEWING_CONDITIONS_ZCAM["Average"], discount_illuminant: Boolean = False, ) -> CAM_Specification_ZCAM: """ Compute the *ZCAM* colour appearance model correlates from given *CIE XYZ* tristimulus values. Parameters ---------- XYZ Absolute *CIE XYZ* tristimulus values of test sample / stimulus. XYZ_w Absolute *CIE XYZ* tristimulus values of the white under reference illuminant. L_A Test adapting field *luminance* :math:`L_A` in :math:`cd/m^2` such as :math:`L_A = L_w * Y_b / 100` (where :math:`L_w` is luminance of the reference white and :math:`Y_b` is the background luminance factor). Y_b Luminous factor of background :math:`Y_b` such as :math:`Y_b = 100 * 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. Returns ------- :class:`colour.CAM_Specification_ZCAM` *ZCAM* colour appearance model specification. Warnings -------- The underlying *SMPTE ST 2084:2014* transfer function is an absolute transfer function. Notes ----- - *Safdar, Hardeberg and Luo (2021)* does not specify how the chromatic adaptation to *CIE Standard Illuminant D65* in *Step 0* should be performed. A one-step *Von Kries* chromatic adaptation transform is not symmetrical or transitive when a degree of adaptation is involved. *Safdar, Hardeberg and Luo (2018)* uses *Zhai and Luo (2018)* two-steps chromatic adaptation transform, thus it seems sensible to adopt this transform for the *ZCAM* colour appearance model until more information is available. It is worth noting that a one-step *Von Kries* chromatic adaptation transform with support for degree of adaptation produces values closer to the supplemental document compared to the *Zhai and Luo (2018)* two-steps chromatic adaptation transform but then the *ZCAM* colour appearance model does not round-trip properly. - The underlying *SMPTE ST 2084:2014* transfer function is an absolute transfer function, thus the domain and range values for the *Reference* and *1* scales are only indicative that the data is not affected by scale transformations. +------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +============+=======================+===============+ | ``XYZ`` | [UN] | [UN] | +------------+-----------------------+---------------+ | ``XYZ_tw`` | [UN] | [UN] | +------------+-----------------------+---------------+ | ``XYZ_rw`` | [UN] | [UN] | +------------+-----------------------+---------------+ +-------------------------------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +===============================+=======================+===============+ | ``CAM_Specification_ZCAM.J`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.C`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.h`` | [0, 360] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.s`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.Q`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.M`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.H`` | [0, 400] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.HC`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.V`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.K`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.H`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ References ---------- :cite:`Safdar2018`, :cite:`Safdar2021`, :cite:`Zhai2018` Examples -------- >>> XYZ = np.array([185, 206, 163]) >>> XYZ_w = np.array([256, 264, 202]) >>> L_A = 264 >>> Y_b = 100 >>> surround = VIEWING_CONDITIONS_ZCAM['Average'] >>> XYZ_to_ZCAM(XYZ, XYZ_w, L_A, Y_b, surround) ... # doctest: +ELLIPSIS CAM_Specification_ZCAM(J=92.2504437..., C=3.0216926..., h=196.3245737..., \ s=19.1319556..., Q=321.3408463..., M=10.5256217..., H=237.6114442..., \ HC=None, V=34.7006776..., K=25.8835968..., W=91.6821728...) """ XYZ = to_domain_1(XYZ) XYZ_w = to_domain_1(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) F_s, _F, _c, _N_c = surround # Step 0 (Forward) - Chromatic adaptation from reference illuminant to # "CIE Standard Illuminant D65" illuminant using "CAT02". # Computing degree of adaptation :math:`D`. D = ( degree_of_adaptation(surround.F, L_A) if not discount_illuminant else ones(L_A.shape) ) XYZ_D65 = chromatic_adaptation_Zhai2018( XYZ, XYZ_w, TVS_D65, D, D, transform="CAT02" ) # Step 1 (Forward) - Computing factors related with viewing conditions and # independent of the test stimulus. # Background factor :math:`F_b` F_b = np.sqrt(Y_b / Y_w) # Luminance level adaptation factor :math:`F_L` F_L = 0.171 * spow(L_A, 1 / 3) * (1 - np.exp(-48 / 9 * L_A)) # Step 2 (Forward) - Computing achromatic response (:math:`I_z` and # :math:`I_{z,w}`), redness-greenness (:math:`a_z` and :math:`a_{z,w}`), # and yellowness-blueness (:math:`b_z`, :math:`b_{z,w}`). with domain_range_scale("ignore"): I_z, a_z, b_z = tsplit(XYZ_to_Izazbz(XYZ_D65, method="Safdar 2021")) I_z_w, _a_z_w, b_z_w = tsplit( XYZ_to_Izazbz(XYZ_w, method="Safdar 2021") ) # Step 3 (Forward) - Computing hue angle :math:`h_z` h_z = hue_angle(a_z, b_z) # Step 4 (Forward) - Computing hue quadrature :math:`H`. H = hue_quadrature(h_z) # Computing eccentricity factor :math:`e_z`. e_z = 1.015 + np.cos(np.radians(89.038 + h_z % 360)) # Step 5 (Forward) - Computing brightness :math:`Q_z`, # lightness :math:`J_z`, colourfulness :math`M_z`, and chroma :math:`C_z` Q_z_p = (1.6 * F_s) / (F_b**0.12) Q_z_m = F_s**2.2 * F_b**0.5 * spow(F_L, 0.2) Q_z = 2700 * spow(I_z, Q_z_p) * Q_z_m Q_z_w = 2700 * spow(I_z_w, Q_z_p) * Q_z_m J_z = 100 * Q_z / Q_z_w M_z = ( 100 * (a_z**2 + b_z**2) ** 0.37 * ( (spow(e_z, 0.068) * spow(F_L, 0.2)) / (F_b**0.1 * spow(I_z_w, 0.78)) ) ) C_z = 100 * M_z / Q_z_w # Step 6 (Forward) - Computing saturation :math:`S_z`, # vividness :math:`V_z`, blackness :math:`K_z`, and whiteness :math:`W_z`. with sdiv_mode(): S_z = 100 * spow(F_L, 0.6) * np.sqrt(sdiv(M_z, Q_z)) V_z = np.sqrt((J_z - 58) ** 2 + 3.4 * C_z**2) K_z = 100 - 0.8 * np.sqrt(J_z**2 + 8 * C_z**2) W_z = 100 - np.sqrt((100 - J_z) ** 2 + C_z**2) return CAM_Specification_ZCAM( as_float(from_range_1(J_z)), as_float(from_range_1(C_z)), as_float(from_range_degrees(h_z)), as_float(from_range_1(S_z)), as_float(from_range_1(Q_z)), as_float(from_range_1(M_z)), as_float(from_range_degrees(H, 400)), None, as_float(from_range_1(V_z)), as_float(from_range_1(K_z)), as_float(from_range_1(W_z)), )
[docs]def ZCAM_to_XYZ( specification: CAM_Specification_ZCAM, XYZ_w: ArrayLike, L_A: FloatingOrArrayLike, Y_b: FloatingOrArrayLike, surround: InductionFactors_ZCAM = VIEWING_CONDITIONS_ZCAM["Average"], discount_illuminant: Boolean = False, ) -> NDArray: """ Convert from *ZCAM* specification to *CIE XYZ* tristimulus values. Parameters ---------- specification *ZCAM* 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 Absolute *CIE XYZ* tristimulus values of the white under reference illuminant. L_A Test adapting field *luminance* :math:`L_A` in :math:`cd/m^2` such as :math:`L_A = L_w * Y_b / 100` (where :math:`L_w` is luminance of the reference white and :math:`Y_b` is the background luminance factor). 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. Returns ------- :class:`numpy.ndarray` *CIE XYZ* tristimulus values. Raises ------ ValueError If neither *C* or *M* correlates have been defined in the ``CAM_Specification_ZCAM`` argument. Warnings -------- The underlying *SMPTE ST 2084:2014* transfer function is an absolute transfer function. Notes ----- - *Safdar, Hardeberg and Luo (2021)* does not specify how the chromatic adaptation to *CIE Standard Illuminant D65* in *Step 0* should be performed. A one-step *Von Kries* chromatic adaptation transform is not symetrical or transitive when a degree of adptation is involved. *Safdar, Hardeberg and Luo (2018)* uses *Zhai and Luo (2018)* two-steps chromatic adaptation transform, thus it seems sensible to adopt this transform for the *ZCAM* colour appearance model until more information is available. It is worth noting that a one-step *Von Kries* chromatic adaptation transform with support for degree of adaptation produces values closer to the supplemental document compared to the *Zhai and Luo (2018)* two-steps chromatic adaptation transform but then the *ZCAM* colour appearance model does not round-trip properly. - *Step 4* of the inverse model uses a rounded exponent of 1.3514 preventing the model to round-trip properly. Given that this implementation takes some liberties with respect to the chromatic adaptation transform to use, it was deemed appropriate to use an exponent value that enables the *ZCAM* colour appearance model to round-trip. - The underlying *SMPTE ST 2084:2014* transfer function is an absolute transfer function, thus the domain and range values for the *Reference* and *1* scales are only indicative that the data is not affected by scale transformations. +-------------------------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +===============================+=======================+===============+ | ``CAM_Specification_ZCAM.J`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.C`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.h`` | [0, 360] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.s`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.Q`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.M`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.H`` | [0, 400] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.HC`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.V`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.K`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ | ``CAM_Specification_ZCAM.H`` | [UN] | [0, 1] | +-------------------------------+-----------------------+---------------+ +-----------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +===========+=======================+===============+ | ``XYZ`` | [UN] | [UN] | +-----------+-----------------------+---------------+ References ---------- :cite:`Safdar2018`, :cite:`Safdar2021`, :cite:`Zhai2018` Examples -------- >>> specification = CAM_Specification_ZCAM(J=92.250443780723629, ... C=3.0216926733329013, ... h=196.32457375575581) >>> XYZ_w = np.array([256, 264, 202]) >>> L_A = 264 >>> Y_b = 100 >>> surround = VIEWING_CONDITIONS_ZCAM['Average'] >>> ZCAM_to_XYZ(specification, XYZ_w, L_A, Y_b, surround) ... # doctest: +ELLIPSIS array([ 185., 206., 163.]) """ J_z, C_z, h_z, _S_z, _Q_z, M_z, _H, _H_Z, _V_z, _K_z, _W_z = astuple( specification ) J_z = to_domain_1(J_z) C_z = to_domain_1(C_z) h_z = to_domain_degrees(h_z) M_z = to_domain_1(M_z) XYZ_w = to_domain_1(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) F_s, F, c, N_c = surround # Step 0 (Forward) - Chromatic adaptation from reference illuminant to # "CIE Standard Illuminant D65" illuminant using "CAT02". # Computing degree of adaptation :math:`D`. D = ( degree_of_adaptation(surround.F, L_A) if not discount_illuminant else ones(L_A.shape) ) # Step 1 (Forward) - Computing factors related with viewing conditions and # independent of the test stimulus. # Background factor :math:`F_b` F_b = np.sqrt(Y_b / Y_w) # Luminance level adaptation factor :math:`F_L` F_L = 0.171 * spow(L_A, 1 / 3) * (1 - np.exp(-48 / 9 * L_A)) # Step 2 (Forward) - Computing achromatic response (:math:`I_{z,w}`), # redness-greenness (:math:`a_{z,w}`), and yellowness-blueness # (:math:`b_{z,w}`). with domain_range_scale("ignore"): I_z_w, _A_z_w, B_z_w = tsplit( XYZ_to_Izazbz(XYZ_w, method="Safdar 2021") ) # Step 1 (Inverse) - Computing achromatic response (:math:`I_z`). Q_z_p = (1.6 * F_s) / spow(F_b, 0.12) Q_z_m = spow(F_s, 2.2) * spow(F_b, 0.5) * spow(F_L, 0.2) Q_z_w = 2700 * spow(I_z_w, Q_z_p) * Q_z_m I_z_p = spow(F_b, 0.12) / (1.6 * F_s) I_z_d = 2700 * 100 * Q_z_m I_z = spow((J_z * Q_z_w) / I_z_d, I_z_p) # Step 2 (Inverse) - Computing chroma :math:`C_z`. if has_only_nan(M_z) and not has_only_nan(C_z): M_z = (C_z * Q_z_w) / 100 elif has_only_nan(M_z): raise ValueError( 'Either "C" or "M" correlate must be defined in ' 'the "CAM_Specification_ZCAM" argument!' ) # Step 3 (Inverse) - Computing hue angle :math:`h_z` # :math:`h_z` is currently required as an input. # Computing eccentricity factor :math:`e_z`. e_z = 1.015 + np.cos(np.radians(89.038 + h_z % 360)) h_z_r = np.radians(h_z) # Step 4 (Inverse) - Computing redness-greenness (:math:`a_z`), and # yellowness-blueness (:math:`b_z`). # C_z_p_e = 1.3514 C_z_p_e = 50 / 37 C_z_p = spow( (M_z * spow(I_z_w, 0.78) * spow(F_b, 0.1)) / (100 * spow(e_z, 0.068) * spow(F_L, 0.2)), C_z_p_e, ) a_z = C_z_p * np.cos(h_z_r) b_z = C_z_p * np.sin(h_z_r) # Step 5 (Inverse) - Computing tristimulus values :math:`XYZ_{D65}`. with domain_range_scale("ignore"): XYZ_D65 = Izazbz_to_XYZ(tstack([I_z, a_z, b_z]), method="Safdar 2021") XYZ = chromatic_adaptation_Zhai2018( XYZ_D65, TVS_D65, XYZ_w, D, D, transform="CAT02" ) return from_range_1(XYZ)
def hue_quadrature(h: FloatingOrArrayLike) -> FloatingOrNDArray: """ Return the hue quadrature from given hue :math:`h` angle in degrees. Parameters ---------- h Hue :math:`h` angle in degrees. Returns ------- :class:`numpy.floating` or :class:`numpy.ndarray` Hue quadrature. Examples -------- >>> hue_quadrature(196.3185839) # doctest: +ELLIPSIS 237.6052911... """ h = as_float_array(h) h_i = HUE_DATA_FOR_HUE_QUADRATURE["h_i"] e_i = HUE_DATA_FOR_HUE_QUADRATURE["e_i"] H_i = HUE_DATA_FOR_HUE_QUADRATURE["H_i"] # :math:`h_p` = :math:`h_z` + 360 if :math:`h_z` < :math:`h_1, i.e. h_i[0] h[h <= h_i[0]] += 360 # *np.searchsorted* returns an erroneous index if a *nan* is used as input. h[np.asarray(np.isnan(h))] = 0 i = as_int_array(np.searchsorted(h_i, h, side="left") - 1) h_ii = h_i[i] e_ii = e_i[i] H_ii = H_i[i] h_ii1 = h_i[i + 1] e_ii1 = e_i[i + 1] h_h_ii = h - h_ii H = H_ii + (100 * h_h_ii / e_ii) / (h_h_ii / e_ii + (h_ii1 - h) / e_ii1) return as_float(H)