# CIE 1931 Chromaticity

## Chromaticity coordinates

Chromaticity coordinates $x$, $y$, and $Y$ are the CIE 1931 chromaticity diagram coordinates ($x$ and $y$) from 0 to 1, and the luminance $Y$ from 0 to 100.

## Tristimulus values

Tristimulus values $X$, $Y$, and $Z$ are the relative luminances of total luminance $Y$, blue stimulation $Z$, and $X$ is a linear combination of the cone response curves, all from 0 to 100. The conversion from tristimulus values to chromaticity coordinates is $$x = \frac{X}{X + Y + Z} \; \; \; \; y = \frac{Y}{X+Y+Z} \; \; \; \; z = \frac{Z}{X+Y+Z}$$ The conversion from chromaticity coordinates to tristimulus values is $$X = \frac{Y * x}{y} \; \; \; \; Y = \frac{Y * y}{y} \; \; \; \; Z = Y * (1 – x- y)$$ After performing either conversion, the specified color is plotted on the CIE1931 chromaticity diagram.

References:
1. Color Vision and Colorimetry: Theory and Applications, Second Edition by Daniel Malacara, SPIE Press, 2011
2. Thanks to Seth Ansell for correcting previously erroneous equation listings.

## CIE 1931 Chromaticity Diagram 