Color Difference Channels
The color channels, C
B
and C
R
, are derived by subtracting Y from the R and B signals
and are sometimes referred to generally as B-Y and R-Y, or color difference channels.
Analog video systems such as Betacam SP use P
B
and P
R
channels, and digital video
systems use C
B
and C
R
. Each color channel format performs the same function, but the
underlying specifications are slightly different.
In digital video, the color channels are typically sampled less often than the luma
channel, reducing the video data without noticeable loss of image quality. The ratio of
sampling between the Y´, C
B
, and C
R
channels is often written as 4:2:2, 4:1:1, and so on,
depending on the sample rates used. For more information about how color is
represented in various video formats, see Volume IV, Appendix A, “Video Formats.”