3.4.3. BRIGHTNESS CALCULATION

The color coordinates define this color relative to the reference white color. Often, however, it is necessary to know not the relative, but the absolute intensities of the primary colors that reproduce the given color. This data can be obtained by calculating its brightness.

From expressions (3.4.5) it follows that the brightness colors equal to the sum of the brightness of its main components:

. (3.4.17)

Integrals

(3.4.18)

are called the luminance coefficients of the primary colors. These coefficients are the brightness of the primary colors that equalize the white reference color. Therefore, the brightness of the color can be written as

. (3.4.19)

Chromaticity color defined as

. (3.4.20)

Multiplying the left and right sides of expressions (3.4.19) and (3.4.20) respectively, after some transformations, we get

(3.4.21a)

and similarly

, (3.4.21b)

. (3.4.21b)

Thus, color coordinates can be expressed in terms of luminance and chromaticity coordinates.