
Chroma subsampling filters
In chroma subsampling, the encoder discards selected
color difference samples after filtering. A decoder
approximates the missing samples by interpolation.
To perform 4:2:0 subsampling with minimum computa-
tion, some
systems
simply average C B over a 2x2 block,
and average C R over the same 2x2 block, as sketched in
Figure 10.4 in the margin. To interpolate the missing
chroma samples prior to conversion back to
R'G'B', ...