coaxial cables (see Figure 8). By keeping these signals separate, many video
artifacts (defects) can be avoided such
as color dot crawl, color moiré patterns (e.g., on a striped or herringbone
suit), and other cross color defects.
The chroma signal, however, is still
a bandwidth limited, quadrature modulated combination of both the I and
Q color signals so it is only suitable for
standard def (SD) signals. S-Video
connections will also be accompanied
by a set of analog audio jacks.
FIGURE 8. The S-Video
connector carries separate
Y and C signals.
Component video connections
carry the original RGB (red, green, and
blue) signals as three separate
monochrome video signals (see
Figure 9). This allows full bandwidth
(high resolution) video to be transferred from one device to another.
While some devices actually accept
true RGB component signals, most
equipment these days use YPbPr
signals. These three signals are derived
from the gamma corrected R’G’B’
signals via the mathematical relationship shown in Table 2.
By sending the RGB signals
through a matrix to derive the YPbPr
signals, we again put all of the
luminance information on one signal
(Y) and use the remaining two to carry
the color information. The Pb signal
essentially represents the B-Y (blue
minus luminance); Pr represents R-Y
(red minus luminance).
This system offers many advantages over a simple RGB interface. For
example, the single Y component can
be fed into a black-and-white monitor
to give a monochrome display. Some
equipment may label these jacks
YCrCb; this is technically incorrect as
Cr and Cb refer to digital representations of the PrPb signals. Component
connections may be accompanied
by either analog audio jacks or
possibly some form
of digital audio
(DVI) standard was developed as a way for carrying
digital pixel data between
devices. As such, it is a much
better way to drive fixed-pixel
displays such as LCD, DLP,
and Plasma units.
The DVI interface has
several variations: single or
dual link, analog and/or
digital (see Figures 10a and
10b). Because of the various
configurations, not all DVI
plugs and jacks are compatible. For example, a DVI-A
plug will not fit into a DVI-D
socket because the holes for
the analog pins will not be
present. TVs that have a DVI
input will usually use a single
link DVI-D connector.
DVI supports a form of
copy protection known
as High-bandwidth Digital
Content Protection (HDCP).
This is designed to prevent
people from making pristine
digital dubs of copy
protected material such as
motion picture DVDs.
Unfortunately, this can
problems (covered next).
The High-Definition Multimedia
Interface (HDMI) shown in Figure 11
is a further improvement on (and
somewhat compatible with)
the digital DVI standard. It
adds multichannel digital
audio and also supports the
HDCP form of Digital Rights
Management (DRM), as well
as other control features.
Once again however, the use
of HDCP sometimes makes
this less of an ideal interface
between home theater
components. This is because
FIGURE 9. Component cables use
separate connections for the red,
green, and blue signals. Most sets
use a modified set of signals known
as YPbPr which are easily derived
and converted back to the RGB
signals (see text).
3YPbPr (ITU-R BT.601)
Y = 0.299 x R’ + 0.587 x G’ + 0.114 x B’
Pb = - 0.168736 x R’ - 0.331264 x G’ + 0.5 x B’
Pr = 0.5 x R’ - 0.418688 x G’ - 0.081312 x B’
Variations of the
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