3.4. COLORIMETRY

Colorimetry is the science of measuring colors. For the measurement of colors using different coordinate systems.

From the eighth axiom of Grassmann it follows that the color can be equalized with a mixture of three primary colors , and i.e.

, (3.4.1)

Where , , - equalizing color values . Since the intensities of incoherent light sources add up linearly, the spectral density of the mixture is equal to the sum of the spectral densities of its components. According to (3.4.1), the spectral density can be replaced by the equivalent spectral density of the mixture of primary colors, i.e.

, (3.4.2)

Where primary spectral density . The relation (3.4.2) has a simple meaning: spectral densities connected by an equivalence operator cause the same color sensation. Vocalorimetry uses color coordinates that are equal to

, (3.4.3)

Where equalizing the value of the reference white. Substituting expression (3.4.3) into (3.4.2), we obtain

. (3.4.4)

From the fourth axiom of Grassmann it follows that the brightness of the color equal to the sum of the brightness of its main components. Consequently,

, (3.4.5a)

, (3.4.5b)

Where - relative luminous efficiency. Relations (3.4.4) and (3.4.5) are the quantitative basis of colorimetry.