Digital Video Signal According to ITU-BT.R.601 (CCIR 601) - Digital Video and Audio Broadcasting Technology - page 82

C B = 0.56 • (B-Y);

C R = 0.71 • (R-Y) ;

The luminance bandwidth is then limited to 5.75 MHz using a low-pass
filter. The two color difference signals are limited to 2.75 MHz, i.e. the
color resolution is clearly reduced compared with the brightness resolu-
tion. This principle is familiar from children's topics where the impression
of sharpness is simply conveyed by printed black lines. In analog televi-
sion (NTSC, PAL, SECAM), too, the color resolution is reduced to about
1.3 MHz. The low-pass filtered Y, C B and C R signals are then sampled and
digitized by means of analog/digital converters. The A/D converter in the
luminance branch operates at a sampling frequency of 13.5 MHz and the
two C B and C R color difference signals are sampled at 6.75 MHz each.

Y

13.5 MHz luminance sampling frequency

C B

SAV = Start of
active video
EAV = End of
active video

6.75 MHz chrominance sampling frequency

C R

. . . . . .

Blanking

Active video

Fig. 4.2. Sampling of the components in accordance with ITU-BT.R601

This meets the requirements of the sampling theorem: There are no
more signal components above half the sampling frequency. The three A/D
converters can all have a resolution of 8 or 10 bits. With a resolution of 10
bits, this will result in a gross data rate of 270 Mbit/s which is suitable for
distribution in the studio but much too high for TV transmission via exist-
ing channels (terrestrial, satellite or cable). The samples of all three A/D
converters are multiplexed in the following order: C B Y C R Y C B Y ... In
this digital video signal (Fig. 4.1.), the luminance value thus alternates