IEVref:845-03-48ID:
Language:enStatus: Obsolete
Term: excitation purity
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Definition: quantity defined by the ratio NC/ND of two collinear distances on the chromaticity diagram of the CIE 1931 or 1964 standard colorimetric systems, the first distance being that between the point C representing the colour stimulus considered and the point N representing the specified achromatic stimulus ; the second distance is that between the point N and the point D on the spectrum locus at the dominant wavelength of the colour stimulus considered. The definition leads to the following expressions :

p e = y y n y d y n MathType@MTEF@5@5@+=feaagCart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHXgaruavP1wzZbItLDhis9wBH5garmWu51MyVXgarqqtubsr4rNCHbGeaGqipG0dh9qqWrVepG0dbbL8F4rqqrVepeea0xe9LqFf0xc9q8qqaqFn0lXdHiVcFbIOFHK8Feea0dXdar=Jb9hs0dXdHuk9fr=xfr=xfrpeWZqaaiqaciWacmGadaGadeaabaGaaqaaaOqaaiaadchadaWgaaWcbaGaaeyzaaqabaGccqGH9aqpdaWcaaqaaiaadMhacqGHsislcaWG5bWaaSbaaSqaaiaab6gaaeqaaaGcbaGaamyEamaaBaaaleaacaqGKbaabeaakiabgkHiTiaadMhadaWgaaWcbaGaaeOBaaqabaaaaaaa@41AC@ or p e = x x n x d x n MathType@MTEF@5@5@+=feaagCart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHXgaruavP1wzZbItLDhis9wBH5garmWu51MyVXgarqqtubsr4rNCHbGeaGqipG0dh9qqWrVepG0dbbL8F4rqqrVepeea0xe9LqFf0xc9q8qqaqFn0lXdHiVcFbIOFHK8Feea0dXdar=Jb9hs0dXdHuk9fr=xfr=xfrpeWZqaaiqaciWacmGadaGadeaabaGaaqaaaOqaaiaadchadaWgaaWcbaGaaeyzaaqabaGccqGH9aqpdaWcaaqaaiaadIhacqGHsislcaWG4bWaaSbaaSqaaiaab6gaaeqaaaGcbaGaamiEamaaBaaaleaacaqGKbaabeaakiabgkHiTiaadIhadaWgaaWcbaGaaeOBaaqabaaaaaaa@41A8@

where (x, y), (xn, yn), (xd, yd) are the x, y-chromaticity coordinates of the points C, N, and D, respectively

NOTE 1 – In the case of purple stimuli, see Note 1 to 845-03-46.

NOTE 2 – The formulae in x and y are equivalent, but greater precision is given by the formula which has the greater value in the numerator.

NOTE 3 – Excitation purity pe, is related to colorimetric purity, pc, by the equation : pe = pc y/yd.


Publication date:1987
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Internal notes:2017-06-02: Cleanup - Remove Attached Image 845-03-48en.gif
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