DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

100%
90%
50%
10%
0%
0 1 2 3 4 5 Y’
0 1 2 C
Figure 27.1 Transition
samples. The solid line, dots
( ), and light shading show the
luma transition; the dashed line,
open circles ( ), and heavy
shading show 4:2:2 chroma
Video signal processing 27
This chapter presents several diverse topics concerning
the representation and processing of video signals.
Transition samples
In Scanning parameters, on page 54, I mentioned that it
is necessary to avoid an instantaneous transition from
blanking to picture at the start of a line. It is also necessary
to avoid an instantaneous transition from picture to
blanking at the end of a line. In studio video, the first
and the last few active video samples on a line are
blanking transition samples. I recommend that the first
luma (Y’) sample of a line be black, and that this sample
be followed by three transition samples clipped to 10%,
50%, and 90% of the full signal amplitude. In 4:2:2,
I recommend that the first three color difference (C)
samples on a line be transition samples, clipped to
10%, 50%, and 90%. Figure 27.1 sketches the transition
samples. The transition values should be applied by
clipping, rather than by multiplication, to avoid
disturbing the transition samples of a signal that already
has a proper blanking transition.
Edge treatment
If an image row of 720 samples is to be processed
through a 25-tap FIR filter (such as that of Figure 16.26,
on page 167) to produce 720 output samples, the
calculations for 12 output samples at each end of the
line will refer to input samples outside the image. One
approach to this problem is to produce just those
output samples – 696 in this example – that can be
computed from the available input samples. However,
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