DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

1
PRE-
BROAD
EQUALIZATION PULSES
0V,576i Figure 34.3 Sync waveform of 576i for the
first field, during the vertical sync interval.
In 480i and 576i, the top and
bottom picture lines each contain
half a line of blanking, as
I mentioned in Figure 11.3, on
page 98. See 480i component
video, on page 499, and 576i
component video on page 519.
Historically, in composite NTSC,
editing took place on colorframe
(2-frame) boundaries. In
2-3 pulldown, picture content
changes between the fields of
an M-frame. A film edit may be
present at this point.
POST-
EQUALIZATION
In analog 480i, lines were historically numbered in
each field; the first field had 263 lines and the second
field had 262. Nowadays, lines are numbered through
the frame. In interlaced digital video and HDTV, the
second field has one more line than the first field.
Figure 34.3 above illustrates sync in the vertical interval
of analog 576i. The sync structure of 576i has several
gratuitous differences from 480i. There are two and
one-half lines (five pulses) each of preequalization,
broad, and postequalization pulses. In 576i – and in
HDTV – lines count through the frame; line 1 and 0 V
are defined by the first broad pulse coincident with 0 H .
The relationship between line numbers and vertical
sync components differs between 576i and 480i.
Finally, the temporal sequence of halflines differs.
MPEG-2 assimilates both systems into a common notation,
and denotes fields as top and bottom; see Interlacing
in MPEG-2, on page 98.
“Phantom” sync traces, sketched in Figure 34.4 overleaf,
arise from infrequent equalization and broad pulses
when analog sync is displayed on a waveform monitor.
Odd/even, first/second, top/bottom
In interlaced scanning, it is implicit that the first field
and the second field convey information from the same
source – that is, temporally coherent information. In
principle, an edit could cause the underlying image to
change between the first field and the second field.
Studio equipment is designed and configured to edit
between the second and first fields only. A video
sequence having edits between the first field and the
second field is said to have a field dominance problem.
CHAPTER 34 ANALOG SDTV SYNC, GENLOCK, AND INTERFACE 403