# CIE Chromaticity Diagram

This is an international standard for primary colors established in 1931. It allows all other colors to be defined as weighted sum of the three "primary" colors. There are no real three colors that can be combined to give all possible colors. Therefore the standard "primary" colors established by CIE don't correspond to real colors.

So the 3 "primary" colors are the virtual colors A, B, and C. Then for a given real color, its components with respect to the primaries are as follows:

x = A/(A+B+C)
y = B/(A+B+C)
z = C/(A+B+C)
Since x + y + z = 1, if x and y are known then z can be determined.

 The CIE diagram is a plot of X vs. Y for all visible colors.

 C corresponds to white light. For a color C1, the dominant wavelength is C2. The purity equals line length (C1-C) / line length (C-C2). The color gamut is the range of colors from C1 to C2. For three colors, the color gamut is the triangle that encompasses the entire area, so any 3 real colors can't generate all colors.

The pigments in the human eye have peak sensitivities at about 650 nm (red), 530 nm (green), and 425 nm (blue).

Main Color page