The CIE system of colorimetry

This chapter draws attention to color science for video involving values that are proportional to intensity. To approximate perceptual uniformity, video uses quantities such as R', G', B', and Y' that are not proportional to intensity. In color science, it is important to use lightness terminology such as brightness, intensity, luminance, value, and tristimulus value very carefully. It is especially important to differentiate physical quantities—such as intensity and luminance—from perceptual quantities—such as lightness and value. Color coordinates are analogous to coordinates on a map. Cartographers have different map projections for different functions. Some projections preserve areas, while others show latitudes and longitudes as straight lines. No single map projection fills all the needs of all map users. There are many “color spaces”. The science of colorimetry concerns the relationship between spectral power distribution (SPD) and color. The chapter also draws the weighting curves standardized by CIE to specify the way in which an SPD can be transformed into three tristimulus values.