colour.excitation_purity

colour.excitation_purity(xy, xy_n, cmfs=None)[source]

Returns the excitation purity \(P_e\) for given colour stimulus \(xy\).

Parameters
  • xy (array_like) – Colour stimulus CIE xy chromaticity coordinates.

  • xy_n (array_like) – Achromatic stimulus CIE xy chromaticity coordinates.

  • cmfs (XYZ_ColourMatchingFunctions, optional) – Standard observer colour matching functions, default to the CIE 1931 2 Degree Standard Observer.

Returns

Excitation purity \(P_e\).

Return type

numeric or array_like

References

[CIET14804b], [Erdb]

Examples

>>> from colour.colorimetry import MSDS_CMFS
>>> cmfs = MSDS_CMFS['CIE 1931 2 Degree Standard Observer']
>>> xy = np.array([0.54369557, 0.32107944])
>>> xy_n = np.array([0.31270000, 0.32900000])
>>> excitation_purity(xy, xy_n, cmfs)  
0.6228856...