Tristimulus

The amounts of red, green, and blue needed to form any particular color are called the tristimulus values and are denoted X, Y, and Z, respectively. A color is then specified by its trichromatic coefficients, defined as

$x = \frac{X}{X+Y+Z}$ and $y = \frac{Y}{X+Y+Z}$ and $z={\frac {Z}{X+Y+Z}}$

It is noted from these equations that

$x+y+z=1$.

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