DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

The S-video connector is sketched
on page 409. Electrical and
mechanical details are presented
in S-video-525 (Y’/C3.58), on
page 515, and S-video-625
(Y’/C4.43), on page 531.
S-video interface
The S-video interface – sometimes denoted Y’/C,
Y’/C3.58, or Y’/C4.43 – is a hybrid of component and
composite systems. The S stands for separate: In
S-video, luma and modulated chroma signals are
conveyed across the interface on separate wires. There
are three different versions of the S-video interface:
S-video-525, S-video-525-J (for NTSC-J, in Japan), and
S-video-625. The S-video interface was first introduced
in S-VHS VCRs, and S-video remains a feature of virtually
all S-VHS and Hi8 VCRs. However, the S-video
interface is quite independent of S-VHS recording technology.
Quadrature modulation is intrinsic to S-video, so
chroma suffers some bandwidth reduction. However,
S-video does not use frequency interleaving: Luma and
chroma are not summed, so cross-luma and cross-color
artifacts are completely avoided. Because S-video
avoids the NTSC or PAL “footprint,” it offers substantially
better performance than composite NTSC or PAL.
S-video is widely used in desktop video and consumer
video. It is rarely used in the studio.
Decoder controls
A few decades ago, consumer receivers had unstable
circuitry: User adjustment was necessary to produce
acceptable color. Modern circuits are so stable that user
controls are no longer necessary, but consumers
continue to expect them. This is a shame, because
consumer adjustment of these controls is more likely to
degrade the picture than to improve it. Developers of
desktop video systems typically provide an excess of
controls; perhaps they believe that this relieves them of
implementing correct signal-processing arithmetic.
I described the brightness and contrast controls in
Chapter 3, on page 25. These controls operate in the
R’G’B’ domain; they are found in television receivers
and in computer monitors. Two other controls, which
I will now describe, are associated with NTSC and PAL
decoders.
346 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES