GLOSSARY
A
AC-3: The 5.1-channel sound system specified in the Standards
for Digital-HDTV. Also known as “Dolby Digital,” AC-3 delivers CD
quality digital audio and provides five full-bandwidth channels for
front left, front right, center, surround left and surround right
speakers, plus an LFE (low frequency effect) subwoofer, for a total
of 5.1 channels.
Active scan lines: Those scan lines in a video frame that carry
picture information rather than being used for other data (such as
closed captioning) or for synchronization.
Analog TV: Analog TV is the NTSC Standard for traditional
television broadcasts. Analog signals vary continuously,
representing fluctuations in color and brightness.
Anamorphic: A means of recording a widescreen image using
special lenses or processing such that the image is distorted in the
medium but restored to proper proportions during playback.
Aspect ratio: The ratio of width to height of a screen or image;
expressed in whole numbers (4:3, 16:9) or divided out (1.33,
1.78)
ATSC (Advanced Television Systems Committee): The
industry / government body that issued the US digital TV standard.
B
Blue minus luminance (B – Y): Part of a component-video
signal; see color difference.
C
Chrominance (chroma, C): A video signal carrying only the
point-to-point color, both hue and saturation, of a video image and
not its brightness; see luminance.
Closed captioning: A system that transmits caption or subtitle
text and symbol data during the non-image portion of a video
signal. It requires special decoder circuitry for display, hence the
“closed.”
Color difference: A system of transmitting video information in
which the color signals contain the difference between a given
primary color (red, blue or green) and the luminance signal. The
color information on DVD’s and in component-video signals is
encoded in this way.
Color temperature: The specific shade of white produced by a
video monitor in response to a pure-white (luminance only) input
signal, measured in kelvins (K). Low color temperatures produce
a“white” that’s tinted reddish-orange compared with the bluish
“white” at high color temperatures.
Component video: A method of transmitting video signals that
continuously keeps the various color components separate from
each other. Consumer component-video connections carry
luminance and two color-difference signals.
Component video connection: The output of a video device
(such as a DTV set-top box) or the input of a DTV receiver or
monitor consisting of 3 primary color signals: red, green, and blue
that together convey all necessary picture information. With
current consumer video products, the 3 component signals have
been translated into luminance (Y) and two color difference signals
(PB, PR) each on separate wire.
Composite video: A single video signal that combines three video
sub signals (luminance, chrominance, and sync). Until the
development of S-video and component-video outputs, all video
connections in consumer products were composite video.
Contrast: In general, the range between the brightest and
darkest parts of an image; on a video monitor, a control that
adjusts the overall gain of the video signal on its way to the
display.
Convergence: Adjustments in a CRT-based projection monitor
that align the primary-color images produced by the three internal
CRT’s. In a direct-view color TV, convergence refers to the
alignment of the beams generated by the three electron guns.
CRT (cathode-ray tube): A vacuum tube in which electrons
emitted by a hot cathode are focused into beams and scanned
across a fluorescent screen to produce a picture.
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