colour.polynomial_expansion¶

colour.polynomial_expansion(a, method='Cheung 2004', **kwargs)[source]¶

Performs polynomial expansion of given \(a\) array.

Parameters

a (array_like, (3, n)) – \(a\) array to expand.
method (unicode, optional) – {‘Cheung 2004’, ‘Finlayson 2015’, ‘Vandermonde’}, Computation method.

Other Parameters

degree (int) – {colour.characterisation.polynomial_expansion_Finlayson2015(), colour.characterisation.polynomial_expansion_Vandermonde()}, Expanded polynomial degree, must be one of [1, 2, 3, 4] for colour.characterisation.polynomial_expansion_Finlayson2015() definition.
terms (int) – {colour.characterisation.augmented_matrix_Cheung2004()}, Number of terms of the expanded polynomial, must be one of [3, 5, 7, 8, 10, 11, 14, 16, 17, 19, 20, 22].
root_polynomial_expansion (bool) – {colour.characterisation.polynomial_expansion_Finlayson2015()}, Whether to use the root-polynomials set for the expansion.

Returns

Expanded \(a\) array.

Return type

ndarray, (3, n)

References

[CWCR04], [FMH15], [WR04], [Wik03f]

Examples

>>> RGB = np.array([0.17224810, 0.09170660, 0.06416938])
>>> polynomial_expansion(RGB)  
array([ 0.1722481...,  0.0917066...,  0.0641693...])
>>> polynomial_expansion(RGB, 'Cheung 2004', terms=5)  
array([ 0.1722481...,  0.0917066...,  0.0641693...,  0.0010136...,  1...])