def highlights_recovery_blend(RGB, multipliers, threshold=0.99):
"""
Performs highlights recovery using Coffin (1997) method from *dcraw*.
Parameters
----------
RGB : array_like
*RGB* colourspace array.
multipliers : array_like
Normalised camera white level or white balance multipliers.
threshold : numeric, optional
Threshold for the highlights selection.
Returns
-------
ndarray
Highlights recovered *RGB* colourspace array.
References
----------
.. [1] Coffin, D. (2015). dcraw. Retrieved from
https://www.cybercom.net/~dcoffin/dcraw/
"""
M = np.array([[1.0000000, 1.0000000, 1.0000000],
[1.7320508, -1.7320508, 0.0000000],
[-1.0000000, -1.0000000, 2.0000000]])
clipping_level = np.min(multipliers) * threshold
Lab = dot_vector(M, RGB)
Lab_c = dot_vector(M, np.minimum(RGB, clipping_level))
s = np.sum((Lab * Lab)[..., 1:3], axis=2)
s_c = np.sum((Lab_c * Lab_c)[..., 1:3], axis=2)
ratio = np.sqrt(s_c / s)
ratio[np.logical_or(np.isnan(ratio), np.isinf(ratio))] = 1
Lab[:, :, 1:3] *= np.rollaxis(ratio[np.newaxis], 0, 3)
RGB_o = dot_vector(np.linalg.inv(M), Lab)
return RGB_o
def camera_space_to_RGB(RGB, XYZ_to_camera_matrix, RGB_to_XYZ_matrix):
"""
Converts given *RGB* array from *camera space* to given *RGB* colourspace.
Parameters
----------
RGB : array_like
Camera space *RGB* colourspace array.
XYZ_to_camera_matrix : array_like
Matrix converting from *CIE XYZ* tristimulus values to *camera space*.
RGB_to_XYZ_matrix : array_like
Matrix converting from *RGB* colourspace to *CIE XYZ* tristimulus
values.
Returns
-------
ndarray
*RGB* colourspace array.
Examples
--------
>>> RGB = np.array([0.80660, 0.81638, 0.65885])
>>> XYZ_to_camera_matrix = np.array([
... [0.47160000, 0.06030000, -0.08300000],
... [-0.77980000, 1.54740000, 0.24800000],
... [-0.14960000, 0.19370000, 0.66510000]])
>>> RGB_to_XYZ_matrix = np.array([
... [0.41238656, 0.35759149, 0.18045049],
... [0.21263682, 0.71518298, 0.07218020],
... [0.01933062, 0.11919716, 0.95037259]])
>>> camera_space_to_RGB(
... RGB,
... XYZ_to_camera_matrix,
... RGB_to_XYZ_matrix) # doctest: +ELLIPSIS
array([ 0.7564180..., 0.8683192..., 0.6044589...])
"""
M_RGB_camera = dot_matrix(XYZ_to_camera_matrix, RGB_to_XYZ_matrix)
M_RGB_camera /= np.transpose(np.sum(M_RGB_camera, axis=1)[np.newaxis])
RGB_f = dot_vector(np.linalg.inv(M_RGB_camera), RGB)
return RGB_f
