Luma and color differences

This chapter describes color coding systems that are used to convey image data derived from additive (RGB) primaries. It outlines nonlinear R'G B' and explains the formation of luma, denoted by Y' , as a weighted sum of these nonlinear signals. The chapter introduces the color difference (chroma) components [ B'-Y', R'-Y' ], [C B , C R ], and [ P B , P R ]. The design of a video coding system is necessarily rooted in detailed knowledge of human color perception. However, once this knowledge is embodied in a coding system, physics, mathematics, and signal processing remains; the chapter concerns only the latter domains. A monochrome video system senses relative luminance ( Y ). Luminance is then transformed by the gamma correction circuitry of the camera, as described in Gamma in video, in the chapter. A color image is sensed in three components—red, green, and blue—according to additive reproduction. To minimize the visibility of noise or quantization, the RGB components should be coded nonlinearly.