frudawski

# ciewhitepoint

The ciewhitepoint function returns the white point in CIE 1931 x and y chromaticity of any CIE standard illuminant. The function uses the reference spectra in the ciespec function and the ciespec2wp function to derive the white points.

Note: This might lead to different results compared to other calculation tools that are based on tabled values, see example of standard illuminant ‘E’.

Any errors in the data set or in results generated with the Lighting Toolbox are not in the liability of the CIE nor me, see licence.

Usage:

[XYZ,xyz] = ciewhitepoint('illuminant','observer')

Where:

CIE standard illuminants:

Examples

CIE whitepoint of standard illuminant ‘A’:

[XYZ,xyz] = ciewhitepoint('A')

Result:

XYZ =

1.0984   1.0000   0.3559

xyz =

0.4475   0.4074   0.1450

CIE whitepoint of standard illuminant ‘A’, ‘E’ and ‘D65’:

[XYZ,xyz] = ciewhitepoint({'A','E','D65'})

Result:

XYZ =

1.0984   1.0000   0.3559
1.0001   1.0000   1.0003
0.9505   1.0000   1.0888

xyz =

0.4475   0.4074   0.1450
0.3333   0.3333   0.3334
0.3127   0.3290   0.3582

CIE whitepoint of standard illuminant ‘A’ for 10° standard observer:

[XYZ,xyz] = ciewhitepoint('A','xyz10')

Result:

XYZ =

1.1114   1.0000   0.3521

xyz =

0.4511   0.4059   0.1429

CIE whitepoint of standard illuminant ‘E’:

[XYZ,xyz] = ciewhitepoint('E')

Result:

XYZ =

1.0001   1.0000   1.0003

xyz =

0.3333   0.3333   0.3334

Note: standard illuminant E is defined as equi-energy spectrum. This is often understood as x = y = z = \frac{1}{3}. This is a simplification, as shown below (see also CIE TR 15:2018, p. 4), and might lead to different results:

format long
[XYZ,xyz] = ciewhitepoint('E')
format short

Result:

XYZ =

1.000080035889627   1.000000000000000   1.000330668134761

xyz =

0.333314380777352   0.333287705799316   0.333397913423332

Determine the tristimulus values X,Y,Z for standard illuminant ‘D65’ with an resulting e.g. illuminance of E = 15000~\textrm{lx}:

XYZ = ciewhitepoint('D65').*15000

Result:

XYZ =

1.4257e+04   1.5000e+04   1.6332e+04

Determine and plot the whitepoint of CIE standard illuminant ‘FL4’:

[~,xyz] = ciewhitepoint('FL4')
cie1931(xyz(1),xyz(2))

Result:

xyz =

0.4402   0.4033   0.1565

References:

ISO/CIE 11664-1:2019(E): Colorimetry - Part 1: CIE standard colorimetric observers. Commission International de l’Éclairage (CIE), Vienna Austria, 2019.

ISO 11664-2:2007(E)/CIE S 014-2/E:2006: Colorimetry - Part 2: CIE standard illuminants. Commission International de l’Éclairage (CIE), Vienna Austria, 2007.

CIE 15:2018: Colorimetry, 4th Edition. Commission International de l’Éclairage (CIE), Vienna Austria, 2018, ISBN: 978-3-902842-13-8 , (DOI: 10.25039/TR.015.2018).