Specifications

[
StarServe Installers Guide
]
page 37
Types of Baseband
Video
Composite Video
Composite Video is the most familiar format. It uses a single
cable with RCA or Phono connections, usually colour coded.
Composite refers to the fact that all components that make
the video signal are combined into a single ‘composite’
signal. This means that the ‘Luminance’ (Black & White
detail), ‘Hue’ (Red, Green & Blue colour balance), ‘Saturation’
(the richness of the colour) and sync pulses are all combined.
The way in which these components are combined is
determined by the colour-encoding format (e.g., NTSC,
SECAM and PAL). PAL is the encoding video format used in
Australia and New Zealand.
Composite video components can interact with one another,
distorting the signal. In particular, this can occur when
passing through cable, equipment or being recorded and
played back.
S-Video
To avoid the picture degradation that can occur with
composite video, manufacturers provide a different type of
video output and input format called S-Video. In S-Video
format, the chrominance (all colour information) is kept
separate from the luminance (Black & White information) and
sync information. This reduces the possibility of interaction.
S-Video signals are transferred via twin coaxial or shielded
cables, which are usually fitted with a 4-pin mini DIN plug.
Most equipment fitted with S-Video connectors also provides
standard composite video connectors.
S-Video can be recorded on videotape (S-VHS), where the
two chrominance and luminance remain separated.In
principal, the longer these two components remain separated
within a system, the less degradation of the signal. It is
generally better to use an S-Video connection as opposed to
the lower quality composite video.
Component Video
Component Video provides the best picture quality of all
analogue formats. In component video, the components of
the video signal are separated to a greater extent than
S-Video, with less chance of them interfering.
Instead of just separating the luminance/sync (Y) and the
chrominance (C) information, the chrominance information is
further separated into its own two components, the B-Y (blue
minus luminance, also called Cb or Pb) and R-Y (red minus
luminance, also called Cr or Pr).
Although not available on all video equipment, this type of
connection is becoming more popular as it produces the best
picture quality. The connections found are three RCA/Phono
sockets, generally marked Y/R-Y/B-Y or Y/Cr/Cb and often-
coloured yellow, red and blue respectively.
RGB Video
RGB is similar to component video and consists of the three
basic colour components, red, green and blue. Sometimes
the sync information is combined with the green video, and
sometimes separated. It is used primarily in European
equipment, where video connections between equipment are
made using multi-way SCART connectors (20 pin oblong
connectors). Like Component video, RGB offers the potential
of high image quality.
RGB and Component Video are not interchangeable and one
type cannot be fed directly into the other. Equipment fitted
with a SCART connector does not necessarily mean it is
capable of handling RGB video. SCART connectors are used
to convey all three types of video, Composite, S-Video and
RGB. Always refer to the manufacturers manual to determine
the video formats supported.
PAL (Phase Alteration Line) Format
The basic principle of colour video is red, green and blue
signals are encoded with a colour sub carrier, then added
together to form the composite video signal.
Video signal strength is measured in percentages of the peak
signal voltage. As the voltage approaches 100%, the picture
gets brighter. As the voltage approaches 0%, the picture
approaches black.
To determine colour hue and saturation, video monitors and
other decoding equipment compare the colour sub carrier’s
phase and amplitude with a reference signal.
The amplitude of the sine wave describes how deeply an
object is saturated with colour. When the amplitude is
increased, the displayed colour becomes deeper.
The phase of the sine wave describes the hue of the object
and the dc offset voltage of the sine wave determines how
bright an object is. As the offset voltage is decreased, the
displayed object becomes darker. This is most noticeable
when there is impedance mismatch, i.e. when a single video
source is connected to two inputs.