
Luma and
color differences
24
This chapter describes color coding systems that are
used to convey image data derived from additive
(RGB) primaries. I outline nonlinear
R'G'B', explain the
formation of
luma, denoted Y', as a weighted sum of
these nonlinear signals, and introduce the
color differ-
ence
(chroma) components [BLy', RLy'], [CB, CR] ' and
[PB, PR]"
The design of a video coding system is necessarily
rooted in detailed knowledge of human color percep-
tion. However, once this knowledge is embodied in
a coding system, what remains is physics, mathematics,
and signal processing. This ...