colour.complementary_wavelength¶

colour.complementary_wavelength(xy, xy_n, cmfs=XYZ_ColourMatchingFunctions(name='CIE 1931 2 Degree Standard Observer', ...))[source]¶

Returns the complementary wavelength \(\lambda_c\) for given colour stimulus \(xy\) and the related \(xy_wl\) first and \(xy_{cw}\) second intersection coordinates with the spectral locus.

In the eventuality where the \(xy_wl\) first intersection coordinates are on the line of purples, the dominant wavelength will be computed in lieu.

The dominant wavelength is indicated by a negative sign and the \(xy_{cw}\) second intersection coordinates which are set by default to the same value than \(xy_wl\) first intersection coordinates will be set to the dominant wavelength intersection coordinates with the spectral locus.

Parameters:	xy (array_like) – Colour stimulus xy chromaticity coordinates. xy_n (array_like) – Achromatic stimulus xy chromaticity coordinates. cmfs (XYZ_ColourMatchingFunctions, optional) – Standard observer colour matching functions.
Returns:	Complementary wavelength, first intersection point xy chromaticity coordinates, second intersection point xy chromaticity coordinates.
Return type:	tuple

References

Examples

Complementary wavelength computation:

>>> from pprint import pprint
>>> xy = np.array([0.35000, 0.25000])
>>> xy_n = np.array([0.31270, 0.32900])
>>> cmfs = CMFS['CIE 1931 2 Degree Standard Observer']
>>> pprint(complementary_wavelength(xy, xy_n, cmfs))  
(array(520...),
 array([ 0.0743553...,  0.8338050...]),
 array([ 0.0743553...,  0.8338050...]))

Dominant wavelength is returned if the first intersection is located on the line of purples:

>>> xy = np.array([0.26415, 0.37770])
>>> pprint(complementary_wavelength(xy, xy_n, cmfs))  
(array(-504...),
 array([ 0.4897494...,  0.1514035...]),
 array([ 0.0036969...,  0.6389577...]))