Source code for colour.appearance.rlab

# -*- coding: utf-8 -*-
"""
RLAB Colour Appearance Model
============================

Defines *RLAB* colour appearance model objects:

-   :attr:`colour.RLAB_VIEWING_CONDITIONS`
-   :attr:`colour.RLAB_D_FACTOR`
-   :class:`colour.RLAB_Specification`
-   :func:`colour.XYZ_to_RLAB`

References
----------
-   :cite:`Fairchild1996a` : Fairchild, M. D. (1996). Refinement of the RLAB
    color space. Color Research & Application, 21(5), 338-346.
    doi:10.1002/(SICI)1520-6378(199610)21:5<338::AID-COL3>3.0.CO;2-Z
-   :cite:`Fairchild2013w` : Fairchild, M. D. (2013). The RLAB Model. In Color
    Appearance Models (3rd ed., pp. 5563-5824). Wiley. ISBN:B00DAYO8E2
"""

from __future__ import division, unicode_literals

import numpy as np
from collections import namedtuple

from colour.algebra import spow
from colour.appearance.hunt import XYZ_TO_HPE_MATRIX, XYZ_to_rgb
from colour.utilities import (CaseInsensitiveMapping, as_float_array,
                              dot_matrix, dot_vector, from_range_degrees,
                              to_domain_100, tsplit, row_as_diagonal)

__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013-2020 - 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__ = [
    'R_MATRIX', 'RLAB_VIEWING_CONDITIONS', 'RLAB_D_FACTOR',
    'RLAB_ReferenceSpecification', 'RLAB_Specification', 'XYZ_to_RLAB'
]

R_MATRIX = np.array([
    [1.9569, -1.1882, 0.2313],
    [0.3612, 0.6388, 0.0000],
    [0.0000, 0.0000, 1.0000],
])
"""
*RLAB* colour appearance model precomputed helper matrix.

R_MATRIX : array_like, (3, 3)
"""

RLAB_VIEWING_CONDITIONS = CaseInsensitiveMapping({
    'Average': 1 / 2.3,
    'Dim': 1 / 2.9,
    'Dark': 1 / 3.5
})
RLAB_VIEWING_CONDITIONS.__doc__ = """
Reference *RLAB* colour appearance model viewing conditions.

References
----------
:cite:`Fairchild1996a`, :cite:`Fairchild2013w`

RLAB_VIEWING_CONDITIONS : CaseInsensitiveMapping
    **{'Average', 'Dim', 'Dark'}**
"""

RLAB_D_FACTOR = CaseInsensitiveMapping({
    'Hard Copy Images': 1,
    'Soft Copy Images': 0,
    'Projected Transparencies, Dark Room': 0.5
})
RLAB_D_FACTOR.__doc__ = """
*RLAB* colour appearance model *Discounting-the-Illuminant* factor values.

References
----------
:cite:`Fairchild1996a`, :cite:`Fairchild2013w`

RLAB_D_FACTOR : CaseInsensitiveMapping
    **{'Hard Copy Images',
    'Soft Copy Images',
    'Projected Transparencies, Dark Room'}**

Aliases:

-   'hard_cp_img': 'Hard Copy Images'
-   'soft_cp_img': 'Soft Copy Images'
-   'projected_dark': 'Projected Transparencies, Dark Room'
"""
RLAB_D_FACTOR['hard_cp_img'] = RLAB_D_FACTOR['Hard Copy Images']
RLAB_D_FACTOR['soft_cp_img'] = RLAB_D_FACTOR['Soft Copy Images']
RLAB_D_FACTOR['projected_dark'] = (
    RLAB_D_FACTOR['Projected Transparencies, Dark Room'])


class RLAB_ReferenceSpecification(
        namedtuple('RLAB_ReferenceSpecification',
                   ('LR', 'CR', 'hR', 'sR', 'HR', 'aR', 'bR'))):
    """
    Defines the *RLAB* colour appearance model reference specification.

    This specification has field names consistent with *Fairchild (2013)*
    reference.

    Parameters
    ----------
    LR : numeric or array_like
        Correlate of *Lightness* :math:`L^R`.
    CR : numeric or array_like
        Correlate of *achromatic chroma* :math:`C^R`.
    hR : numeric or array_like
        *Hue* angle :math:`h^R` in degrees.
    sR : numeric or array_like
        Correlate of *saturation* :math:`s^R`.
    HR : numeric or array_like
        *Hue* :math:`h` composition :math:`H^R`.
    aR : numeric or array_like
        Red-green chromatic response :math:`a^R`.
    bR : numeric or array_like
        Yellow-blue chromatic response :math:`b^R`.

    References
    ----------
    :cite:`Fairchild1996a`, :cite:`Fairchild2013w`
    """


[docs]class RLAB_Specification( namedtuple('RLAB_Specification', ('J', 'C', 'h', 's', 'HC', 'a', 'b'))): """ Defines the *RLAB* colour appearance model specification. This specification has field names consistent with the remaining colour appearance models in :mod:`colour.appearance` but diverge from *Fairchild (2013)* reference. Parameters ---------- J : numeric or array_like Correlate of *Lightness* :math:`L^R`. C : numeric or array_like Correlate of *achromatic chroma* :math:`C^R`. h : numeric or array_like *Hue* angle :math:`h^R` in degrees. s : numeric or array_like Correlate of *saturation* :math:`s^R`. HC : numeric or array_like *Hue* :math:`h` composition :math:`H^C`. a : numeric or array_like Red-green chromatic response :math:`a^R`. b : numeric or array_like Yellow-blue chromatic response :math:`b^R`. Notes ----- - This specification is the one used in the current model implementation. References ---------- :cite:`Fairchild1996a`, :cite:`Fairchild2013w` """
[docs]def XYZ_to_RLAB(XYZ, XYZ_n, Y_n, sigma=RLAB_VIEWING_CONDITIONS['Average'], D=RLAB_D_FACTOR['Hard Copy Images']): """ Computes the *RLAB* model color appearance correlates. Parameters ---------- XYZ : array_like *CIE XYZ* tristimulus values of test sample / stimulus. XYZ_n : array_like *CIE XYZ* tristimulus values of reference white. Y_n : numeric or array_like Absolute adapting luminance in :math:`cd/m^2`. sigma : numeric or array_like, optional Relative luminance of the surround, see :attr:`colour.RLAB_VIEWING_CONDITIONS` for reference. D : numeric or array_like, optional *Discounting-the-Illuminant* factor normalised to domain [0, 1]. Returns ------- RLAB_Specification *RLAB* colour appearance model specification. Notes ----- +--------------------------+-----------------------+---------------+ | **Domain** | **Scale - Reference** | **Scale - 1** | +==========================+=======================+===============+ | ``XYZ`` | [0, 100] | [0, 1] | +--------------------------+-----------------------+---------------+ | ``XYZ_n`` | [0, 100] | [0, 1] | +--------------------------+-----------------------+---------------+ +--------------------------+-----------------------+---------------+ | **Range** | **Scale - Reference** | **Scale - 1** | +==========================+=======================+===============+ | ``RLAB_Specification.h`` | [0, 360] | [0, 1] | +--------------------------+-----------------------+---------------+ References ---------- :cite:`Fairchild1996a`, :cite:`Fairchild2013w` Examples -------- >>> XYZ = np.array([19.01, 20.00, 21.78]) >>> XYZ_n = np.array([109.85, 100, 35.58]) >>> Y_n = 31.83 >>> sigma = RLAB_VIEWING_CONDITIONS['Average'] >>> D = RLAB_D_FACTOR['Hard Copy Images'] >>> XYZ_to_RLAB(XYZ, XYZ_n, Y_n, sigma, D) # doctest: +ELLIPSIS RLAB_Specification(J=49.8347069..., C=54.8700585..., h=286.4860208..., \ s=1.1010410..., HC=None, a=15.5711021..., b=-52.6142956...) """ XYZ = to_domain_100(XYZ) XYZ_n = to_domain_100(XYZ_n) Y_n = as_float_array(Y_n) D = as_float_array(D) sigma = as_float_array(sigma) # Converting to cone responses. LMS_n = XYZ_to_rgb(XYZ_n) # Computing the :math:`A` matrix. LMS_l_E = (3 * LMS_n) / (LMS_n[0] + LMS_n[1] + LMS_n[2]) LMS_p_L = ((1 + spow(Y_n[..., np.newaxis], 1 / 3) + LMS_l_E) / (1 + spow(Y_n[..., np.newaxis], 1 / 3) + (1 / LMS_l_E))) LMS_a_L = (LMS_p_L + D[..., np.newaxis] * (1 - LMS_p_L)) / LMS_n aR = row_as_diagonal(LMS_a_L) M = dot_matrix(dot_matrix(R_MATRIX, aR), XYZ_TO_HPE_MATRIX) XYZ_ref = dot_vector(M, XYZ) X_ref, Y_ref, Z_ref = tsplit(XYZ_ref) # Computing the correlate of *Lightness* :math:`L^R`. LR = 100 * spow(Y_ref, sigma) # Computing opponent colour dimensions :math:`a^R` and :math:`b^R`. aR = 430 * (spow(X_ref, sigma) - spow(Y_ref, sigma)) bR = 170 * (spow(Y_ref, sigma) - spow(Z_ref, sigma)) # Computing the *hue* angle :math:`h^R`. hR = np.degrees(np.arctan2(bR, aR)) % 360 # TODO: Implement hue composition computation. # Computing the correlate of *chroma* :math:`C^R`. CR = np.hypot(aR, bR) # Computing the correlate of *saturation* :math:`s^R`. sR = CR / LR return RLAB_Specification(LR, CR, from_range_degrees(hR), sR, None, aR, bR)