Video Synchronization 825value obtainable with composite equipment, the death knell was dealt to analogue
processing in television.
28.8.1 The 4:2:2 Protocol Description—General
Just as with audio, so with video, as more and more television equipment began to process
the signals internally in digital form, so the number of conversions could be kept to a
minimum if manufacturers provided a digital interface standard allowing various pieces
of digital video hardware to pass digital video information directly without recourse
to standard analogue connections. This section is a basic outline of the 4:2:2 protocol
(otherwise known as CCIR 601), which has been accepted as the industry standard
for digitized component TV signals. The data signals are carried in the form of binary
information coded in 8- or 10-bit words. These signals comprise the video signals
themselves and timing reference signals. Also included in the protocol are ancillary data
and identifi cation signals. The video signals are derived by coding of the analogue video
signal components. These components are luminance (Y) and color difference (Cr and Cb)
signals generated from primary signals (R, G, B). The coding parameters are specifi ed in
CCIR Recommendation 601 and the main details are reproduced in Table 28.2.
28.8.1.1 Timing Relationships
The digital active line begins at 264 words from the leading edge of the analogue
line synchronization pulse; this time is specifi ed between half amplitude points. This
relationship is shown in Figure 28.10. The start of the fi rst digital fi eld is fi xed by the
Table 28.2 : Encoding Parameter Values for the 4:2:2 Digital Video Interface
Parameters 525-line, 60 fi eld/s systems 625-line, 50 fi eld/s systems
1 Coded signals: Y, Cb, Cr. These signals are obtained from gamma precorrected RGB signals.
2 Number of samples per total
line:
● Luminance signal (Y) 858 864
● Each color-difference signal
(Cb, Cr)429 4323 Sampling structure Orthogonal line, fi eld and picture repetitive Cr and Cb samples
cosited with odd (1st, 3rd, 5th, etc.) Y samples in each line.
(Continued)