## Chromaticity coordinates

See the introduction to color matching functions. Chromaticity
coordinates are simply the ratio of the intensities of the three primary lights
that appear identical to a series of monochromatic lights of equal energy
traversing the visible spectrum.

The chromaticity
coordinates, ,
and ,
are related to

the CMFs, ,
and ,
by:

,

,
and

(and similarly for ,
and and ,
and ).

A diagram in which
any one of the three chromaticity coordinates is plotted against any other is
called a chromaticity diagram. In this diagram, the chromaticity of a color
stimulus plots as a point, the chromaticity point.

Generally, chromaticity coordinates are
derived from the color matching functions. The CIE
1931 2-deg CMFs (CIE, 1932), however, were derived from the chromaticity
coordinates of Wright (1928) and Guild (1931).

### References

CIE (1932). *Commission Internationale de
l'Éclairage Proceedings, 1931*. Cambridge: Cambridge University Press.

Guild, J. (1931). The colorimetric properties of
the spectrum. *Philosophical Transactions of the Royal Society of London*,
*A230*, 149-187.

Wright, W. D. (1928). A re-determination of the
trichromatic coefficients of the spectral colours. *Transactions of the
Optical Society, 30*, 141-164.