Source code for colour.quality.cri

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
Colour Rendering Index
======================

Defines *colour rendering index* computation objects:

-   :class:`CRI_Specification`
-   :func:`colour_rendering_index`

See Also
--------
`Colour Rendering Index IPython Notebook
<http://nbviewer.ipython.org/github/colour-science/colour-ipython/blob/master/notebooks/quality/cri.ipynb>`_  # noqa

References
----------
.. [1]  Ohno, Y., & Davis, W. (2008). NIST CQS simulation 7.4. Retrieved from
        http://cie2.nist.gov/TC1-69/NIST CQS simulation 7.4.xls
"""

from __future__ import division, unicode_literals

import numpy as np
from collections import namedtuple

from colour.colorimetry import (
    D_illuminant_relative_spd,
    STANDARD_OBSERVERS_CMFS,
    blackbody_spd,
    spectral_to_XYZ)
from colour.quality.dataset.tcs import TCS_INDEXES_TO_NAMES, TCS_SPDS
from colour.models import UCS_to_uv, XYZ_to_UCS, XYZ_to_xyY
from colour.temperature import CCT_to_xy_CIE_D, uv_to_CCT_Robertson1968

__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013 - 2015 - Colour Developers'
__license__ = 'New BSD License - http://opensource.org/licenses/BSD-3-Clause'
__maintainer__ = 'Colour Developers'
__email__ = 'colour-science@googlegroups.com'
__status__ = 'Production'

__all__ = ['TCS_ColorimetryData',
           'TCS_ColourQualityScaleData',
           'colour_rendering_index']


[docs]class TCS_ColorimetryData(namedtuple('TCS_ColorimetryData', ('name', 'XYZ', 'uv', 'UVW'))): """ Defines the the class holding *test colour samples* colorimetry data. """
[docs]class TCS_ColourQualityScaleData( namedtuple('TCS_ColourQualityScaleData', ('name', 'Q_a'))): """ Defines the the class holding *test colour samples* colour rendering index data. """
class CRI_Specification( namedtuple( 'CRI_Specification', ('Q_a', 'Q_as', 'colorimetry_data'))): """ Defines the *colour rendering index* colour quality specification. Parameters ---------- Q_a : numeric *Colour rendering index* :math:`Q_a`. Q_as : dict Individual *colour rendering indexes* data for each sample. colorimetry_data : tuple Colorimetry data for the test and reference computations. """
[docs]def colour_rendering_index(spd_test, additional_data=False): """ Returns the *colour rendering index* :math:`Q_a` of given spectral power distribution. Parameters ---------- spd_test : SpectralPowerDistribution Test spectral power distribution. additional_data : bool, optional Output additional data. Returns ------- numeric or CRI_Specification Colour rendering index. Examples -------- >>> from colour import ILLUMINANTS_RELATIVE_SPDS >>> spd = ILLUMINANTS_RELATIVE_SPDS.get('F2') >>> colour_rendering_index(spd) # doctest: +ELLIPSIS 64.1507331... """ cmfs = STANDARD_OBSERVERS_CMFS.get('CIE 1931 2 Degree Standard Observer') shape = cmfs.shape spd_test = spd_test.clone().align(shape) tcs_spds = {} for index, tcs_spd in TCS_SPDS.items(): tcs_spds[index] = tcs_spd.clone().align(shape) XYZ = spectral_to_XYZ(spd_test, cmfs) uv = UCS_to_uv(XYZ_to_UCS(XYZ)) CCT, D_uv = uv_to_CCT_Robertson1968(uv) if CCT < 5000: spd_reference = blackbody_spd(CCT, shape) else: xy = CCT_to_xy_CIE_D(CCT) spd_reference = D_illuminant_relative_spd(xy) spd_reference.align(shape) test_tcs_colorimetry_data = _tcs_colorimetry_data( spd_test, spd_reference, tcs_spds, cmfs, chromatic_adaptation=True) reference_tcs_colorimetry_data = _tcs_colorimetry_data( spd_reference, spd_reference, tcs_spds, cmfs) Q_as = _colour_rendering_indexes( test_tcs_colorimetry_data, reference_tcs_colorimetry_data) Q_a = np.average([v.Q_a for k, v in Q_as.items() if k in (1, 2, 3, 4, 5, 6, 7, 8)]) if additional_data: return CRI_Specification(Q_a, Q_as, (test_tcs_colorimetry_data, reference_tcs_colorimetry_data)) else: return Q_a
def _tcs_colorimetry_data(spd_t, spd_r, spds_tcs, cmfs, chromatic_adaptation=False): """ Returns the *test colour samples* colorimetry data. Parameters ---------- spd_t : SpectralPowerDistribution Test spectral power distribution. spd_r : SpectralPowerDistribution Reference spectral power distribution. spds_tcs : dict *Test colour samples* spectral power distributions. cmfs : XYZ_ColourMatchingFunctions Standard observer colour matching functions. chromatic_adaptation : bool, optional Perform chromatic adaptation. Returns ------- list *Test colour samples* colorimetry data. """ XYZ_t = spectral_to_XYZ(spd_t, cmfs) uv_t = np.ravel(UCS_to_uv(XYZ_to_UCS(XYZ_t))) u_t, v_t = uv_t[0], uv_t[1] XYZ_r = spectral_to_XYZ(spd_r, cmfs) uv_r = np.ravel(UCS_to_uv(XYZ_to_UCS(XYZ_r))) u_r, v_r = uv_r[0], uv_r[1] tcs_data = [] for key, value in sorted(TCS_INDEXES_TO_NAMES.items()): spd_tcs = spds_tcs.get(value) XYZ_tcs = spectral_to_XYZ(spd_tcs, cmfs, spd_t) xyY_tcs = np.ravel(XYZ_to_xyY(XYZ_tcs)) uv_tcs = np.ravel(UCS_to_uv(XYZ_to_UCS(XYZ_tcs))) u_tcs, v_tcs = uv_tcs[0], uv_tcs[1] if chromatic_adaptation: c = lambda x, y: (4 - x - 10 * y) / y d = lambda x, y: (1.708 * y + 0.404 - 1.481 * x) / y c_t, d_t = c(u_t, v_t), d(u_t, v_t) c_r, d_r = (c(u_r, v_r), d(u_r, v_r)) tcs_c, tcs_d = c(u_tcs, v_tcs), d(u_tcs, v_tcs) u_tcs = ((10.872 + 0.404 * c_r / c_t * tcs_c - 4 * d_r / d_t * tcs_d) / (16.518 + 1.481 * c_r / c_t * tcs_c - d_r / d_t * tcs_d)) v_tcs = (5.52 / (16.518 + 1.481 * c_r / c_t * tcs_c - d_r / d_t * tcs_d)) W_tcs = 25 * xyY_tcs[-1] ** (1 / 3) - 17 U_tcs = 13 * W_tcs * (u_tcs - u_r) V_tcs = 13 * W_tcs * (v_tcs - v_r) tcs_data.append( TCS_ColorimetryData(spd_tcs.name, XYZ_tcs, uv_tcs, np.array([U_tcs, V_tcs, W_tcs]))) return tcs_data def _colour_rendering_indexes(test_data, reference_data): """ Returns the *test colour samples* rendering indexes :math:`Q_a`. Parameters ---------- test_data : list Test data. reference_data : list Reference data. Returns ------- dict *Test colour samples* colour rendering indexes. """ Q_as = {} for i, _ in enumerate(test_data): Q_as[i + 1] = TCS_ColourQualityScaleData( test_data[i].name, 100 - 4.6 * np.linalg.norm( reference_data[i].UVW - test_data[i].UVW)) return Q_as