Digital Video and HD, 2nd Edition

10

Constant luminance

Video systems convey colour image data using one component that approximates lightness, and two other components that represent colour, absent lightness. In Colour science for video, on page 287, I will detail how luminance can be formed as a weighted sum of linear RGB values each of which is proportional to optical power. A colour scientist uses the term constant luminance to refer to this sum being constant. Transmitting a single component from which relative luminance can be reconstructed is the principle of constant luminance. Preferably a nonlinear transfer function acts on that component to impose perceptually uniform coding.

Standard video systems do not strictly adhere to that principle; instead, they implement an ...