Pixel
-The smallest single picture element with
which an image is constructed. The light-sensitive
elements in a CCD (chip) camera.
Preroll
-To start a videotape and let it roll for a few
seconds before it is put in the playback or record mode
so that the electronic system has time to stabilize.
RGB
-The separate red, green, and blue color
(chrominance), or "C," video signals.
Slant Track
-Same as helical scan.
Time Base Corrector (TBC)
-An electronic
accessory to a videotape recorder that helps make
playbacks or transfers electronically stable. A TBC
helps to maintain picture stability even in dubbing-up
operations.
Video Cassette
-A plastic container in which a
videotape moves from a supply reel to a take-up reel.
Used in all but the 1-inch VTRs.
VTR
-Videotape recorder or recording. Includes
video cassette recorders.
Y/C
-The separate processing of the luminance (Y)
and chrominance (C) signals.
VIDEOTAPE RECORDERS
RECORDING SYSTEMS
Analog and Digital Systems
Both analog and digital systems are used in naval
imaging facilities. The analog system is easier to
understand if you think of it in the same terms as a record
and a phonograph. Analog systems record the
continually fluctuating video signal that is created and
processed by a video source (camera) on videotape.
13-5
Videotaping is similar to audiotape recording. The
electronic impulses of television pictures (video signal)
and sound (audio signal) are recorded on the videotape
by magnetizing the iron oxide coating on the videotape.
During playback, the recorded video and audio signals
are converted again by the television set into television
pictures and sounds. However, the amount of electronic
information is many times greater for video than for
audio recording.
There are many different systems of treating and
recording the video signals. Videotape recording
systems can be divided roughly into three subsections:
analog and digital; composite (Y/C), and component;
and tape formats.
In a true component system, the R, G, B channels
are kept separate and treated as separate red, green, and
blue video signals throughout the entire recording
process. Each of the three signals remains separate even
when laid down on the videotape. The component
system requires three wires to transport a video signal.
This means that all equipment used in the component
system requires three wires to handle the video signal
that is incompatible with the NTSC system.
When the video is going to be televised, the signals
of the Y/C and component systems must be combined
into a single NTSC composite signal before it can be
broadcast.
During playback, the recorded information is retrieved
as an identical, continually fluctuating signal from the
videotape.
Digital-video systems work on the same principle
as compact disks (CD) used in your home stereo or
office computer. Digital-video systems convert the
analog video signals by sampling (selecting parts of) the
scanned image. It then translates the scanned image into
millions of independent, fixed, values called pixels. A
pixel is the smallest single picture element from which
images are constructed. Each pixel has its own color
(hue and saturation) and luminance values. These values
are expressed as binary numbers (series of zeros and
ones). The binary numbers are then stored on, and
retrieved from, videotape or other storage mediums,
such as large-capacity disks.
Composite (Y/C) and Component
Composite (Y/C) and component all refer to the way
the video signal is treated in the videotape recorder. A
composite video signal means that the luminance
information ("Y" signal), chrominance information
("C" signal), and the sync information are combined
into a single signal (Y+C+sync). Standard television
information is designed to operate with composite video
signals. Only one wire is required to transport a
composite video signal. This composite signal is usually
called NTSC, because the electronic specifications for
a composite video signal were adopted by the National
Television Standards Committee.
The major disadvantage of a composite signal is that
slight interference exists between the chrominace and
luminance information. This interference becomes
more noticeable through each videotape generation.

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