#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Absolute Luminance Calibration - Lagarde (2016)
===============================================
Defines *Lagarde (2016)* panoramic images absolute *Luminance* calibration
objects:
- :func:`absolute_luminance_calibration_Lagarde2016`
- :func:`upper_hemisphere_illuminance_Lagarde2016`
- :func:`upper_hemisphere_illuminance_weights_Lagarde2016`
References
----------
.. [1] Lagarde, S., Lachambre, S., & Jover, C. (2016). An Artist-Friendly
Workflow for Panoramic HDRI. Retrieved from
http://blog.selfshadow.com/publications/s2016-shading-course/\
unity/s2016_pbs_unity_hdri_notes.pdf
"""
from __future__ import division, unicode_literals
import numpy as np
from colour import RGB_COLOURSPACES, RGB_luminance
__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2015-2017 - Colour Developers'
__license__ = 'New BSD License - http://opensource.org/licenses/BSD-3-Clause'
__maintainer__ = 'Colour Developers'
__email__ = 'colour-science@googlegroups.com'
__status__ = 'Production'
__all__ = ['upper_hemisphere_illuminance_Lagarde2016',
'upper_hemisphere_illuminance_weights_Lagarde2016',
'absolute_luminance_calibration_Lagarde2016']
[docs]def upper_hemisphere_illuminance_Lagarde2016(
RGB,
colourspace=RGB_COLOURSPACES['sRGB']):
"""
Computes upper hemisphere illuminance :math:`E_v` of given RGB panoramic
image.
Parameters
----------
RGB : array_like
*RGB* panoramic image array.
colourspace : `colour.RGB_Colourspace`, optional
*RGB* colourspace used for internal *Luminance* computation.
Returns
-------
numeric
Upper hemisphere illuminance :math:`E_v`.
Examples
--------
>>> RGB = np.ones((16, 32, 3))
>>> upper_hemisphere_illuminance_Lagarde2016(RGB) # doctest: +ELLIPSIS
2.9344691...
"""
RGB = np.asarray(RGB)
height, width, channels = RGB.shape
L = RGB_luminance(RGB, colourspace.primaries, colourspace.whitepoint)
theta = np.linspace(0, 1, height) * np.pi
theta_cos = np.cos(theta)[..., np.newaxis]
theta_sin = np.sin(theta)[..., np.newaxis]
E_v = np.sum(np.where(theta_cos > 0, L * theta_cos * theta_sin, 0))
E_v *= 2 * np.pi ** 2 / (width * height)
return E_v
[docs]def upper_hemisphere_illuminance_weights_Lagarde2016(height, width):
"""
Computes upper hemisphere illuminance weights for use with applications
unable to perform the computation directly, i.e. *Adobe Photoshop*.
Parameters
----------
height : int
Output array height.
width : int
Output array width.
Returns
-------
ndarray
Upper hemisphere illuminance weights.
Examples
--------
>>> upper_hemisphere_illuminance_weights_Lagarde2016( # doctest: +ELLIPSIS
... 16, 1)
array([[ 0... ],
[ 4.0143297...],
[ 7.3345454...],
[ 9.3865515...],
[ 9.8155376...],
[ 8.5473281...],
[ 5.8012079...],
[ 2.0520061...],
[ 0... ],
[ 0... ],
[ 0... ],
[ 0... ],
[ 0... ],
[ 0... ],
[ 0... ],
[ 0... ]])
"""
w = np.zeros((height, width))
theta = (np.linspace(0, 1, height) * np.pi)
theta = np.tile(theta[..., np.newaxis], (1, width))
theta_cos = np.cos(theta)
theta_sin = np.sin(theta)
w[theta_cos > 0] = (theta_cos[theta_cos > 0] * theta_sin[theta_cos > 0] *
2 * np.pi ** 2)
return w
[docs]def absolute_luminance_calibration_Lagarde2016(
RGB,
measured_illuminance,
colourspace=RGB_COLOURSPACES['sRGB']):
"""
Performs absolute *Luminance* calibration of given *RGB* panoramic image
using *Lagarde (2016)* method.
Parameters
----------
RGB : array_like
*RGB* panoramic image to calibrate.
measured_illuminance : numeric
Measured illuminance :math:`E_v`.
colourspace : `colour.RGB_Colourspace`, optional
*RGB* colourspace used for internal *Luminance* computation.
Returns
-------
ndarray
Absolute *Luminance* calibrated *RGB* panoramic image.
Examples
--------
>>> RGB = np.ones((4, 8, 3))
>>> absolute_luminance_calibration_Lagarde2016( # doctest: +ELLIPSIS
... RGB, 500)
array([[[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...]],
<BLANKLINE>
[[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...]],
<BLANKLINE>
[[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...]],
<BLANKLINE>
[[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...],
[ 233.9912506..., 233.9912506..., 233.9912506...]]])
"""
RGB = np.asarray(RGB)
E_v = upper_hemisphere_illuminance_Lagarde2016(RGB, colourspace)
return RGB / E_v * measured_illuminance