1582 Chapter 44
44.6.2 Digital Fixed Matrix Display Scan Conversion
In a digital or fixed matrix display, where the pixels are
in a fixed size and position, the input signal may or may
not match. Scan conversion is a necessary process to fit
the analog source image across multiple pixels in the
display. Depending on the display technology, 20–30%
of image information may be lost.
For example, if we have a fixed matrix display at
1024 ×768 and want to input a signal that is 800×600,
a mathematical algorithm is employed where the signal
information in the lower-resolution signal is reduced to
a mathematical equation and fit into the higher-resolu-
tion display. The same process takes place where a
higher-resolution image is fit mathematically into a
lower-resolution display.
In all instances where scaling and scan conversion
take place there is lost information. The quality of the
scaler or scan converter varies with each display and the
most fidelity in an image takes place where the signal
and the display resolutions match each other.
44.7 Video Signals
In order to further the understanding of displays and dis-
play technologies, it is necessary to gain a basic compre-
hension of what comprises the different types of video
signals in use today. We will now examine the core com-
ponents of all signals, and their transmission standards.
44.7.1 What Comprises a Video Signal?
Chrominance noted as (C) is the hue or color with satu-
ration in the red, green, and blue channels of a signal.
Luminance noted as (Y) is the amount of light in
each red, green, and blue channel.
Without the chrominance in a signal, the picture is
black and white.
44.7.2 Composite (aka NTSC)
An analog composite video signal is used in most home
applications. It combines the chrominance and lumi-
nance, along with a sync signal into one cable. This
facilitates the broadcast of the NTSC television signal to
our homes.
44.7.3 Y/C (aka S-Video)
This is still a composite signal, but one that nearly sepa-
rates luminance and chrominance to provide a more pre-
cise color reproduction on the screen.
44.7.4 Component VideoCommonly known as RGB (RGB sync, RGB with H
and V sync, RGB sync on green).
This type of signal totally separates red, green, blue,
and sync to give clearer definition to each of the color
channels.
Component is never used for broadcast due to its
excessive bandwidth requirement in the green channel.
Note that the sync signal can be H/V (horizontal and
vertical) or sync on green.
One version of a component signal is commonly
known as YPbPr. In the broadcast community, this is
known as a color difference signal. Since a normal RGB
signal requires too much bandwidth to broadcast the
dominant green channel, YPbPr, as a component signal,
extrapolates the green signal by subtracting from the
luminance channel (Y) both the blue component (Pb) and
the red component (Pr), leaving the green component.
This allows the economical broadcast of a compo-
nent signal by reducing the bandwidth needed by elimi-
nating the dedicated green signal.44.7.5 VGA (Video Graphics Array)VGA is the analog display standard for the PC. VGA
uses an analog monitor, and PC display adapters to out-
put analog signals. All PC CRTs and most flat panel
monitors accept VGA signals, although newer flat pan-
els may also have a DVI interface for display adapters
that output digital signals.
VGA may refer to the physical 15-pin VGA socket
on a PC in order to contrast it with a digital DVI socket
for flat panels. Or, VGA may also refer only to the orig-
inal VGA resolution of 640×480 and 16 colors.44.7.6 DVI (Digital Video Interface)DVI is a multipin connection used for passing stan-
dard-definition and high-definition digital video signals,
found on HDTV tuners, a growing number of DVD
players, HDTV-ready televisions, and some computer
displays. DVI connections transfer video signals in pure
digital form, which is especially beneficial if you’re
using a fixed-pixel display (like a LCoS, plasma, LCD,
or DLP TV). Signals are encrypted with HDCP
high-bandwidth digital content protection) to prevent
content from being re-recorded and pirated.
There are different kinds of DVI connections.
DVI-D, which is the type of DVI connection found on
most home video gear, carries digital-only signals.
DVI-I, used with some computer video cards, is capable