Glossary of Video Terms and Acronyms - Isotest

Video Terms and Acronyms
Glossary
Acuity – See Visual Acuity.
Adaptation – Visual process whereby approximate compensation is made
for changes in the luminances and colors of stimuli, especially in the case
of changes in illuminants.
Adaptation Field – Ancillary program data (especially PCR) which are
uncoded and are transmitted at least every 100 ms after the TS header of
a data stream (PID) belonging to a program.
Adapter – A device used to achieve compatibility between two items of
audio/video equipment.
Adaption Field – Ancillary program data, especially program clock reference
(PCR), which are uncoded and are transmitted at least every 100 ms
after the TS header of a data stream (packet information, PID) belonging to
a program.
Adaptive – Changing according to conditions.
Adaptive Bit Allocation – The allocation of more bits to image areas of
high activity which does not lend itself to all types of video compression
techniques, especially when interframe sampling is used.
Adaptive Differential Pulse Code Modulation – a) A compression technique
that encodes the predictive residual instead of the original waveform
signal so that the compression efficiency is improved by a predictive gain.
Rather than transmitting PCM samples directly, the difference between the
estimate of the next sample and the actual sample is transmitted. This difference
is usually small and can thus be encoded in fewer bits than the
sample itself. b) Differential pulse code modulation that also uses adaptive
quantizing; an audio coding algorithm which provides a modest degree of
compression together with good quality. c) A technique for compressing
the transmission requirements of digital signals. ADPCM has been used by
ABC between New York and Washington to allow NTSC transmission on a
45 Mbps (DS3) telephone company data transmission circuit. d) A pulse
code modulation system typically operating at a high sampling rate whereby
coding is based on a prior knowledge of the signal to be processed (i.e.,
greater than, equal to, or less than the previous sample). The system is
adaptive in that digital bits of code signify different sizes of signal change
depending on the magnitude of the signal.
Adaptive Emphasis – An ATV technique for improving detail of dark parts
of the picture by increasing their level. If a complementary de-emphasis is
performed at the receiver, noise can be reduced. Dolby B noise reduction
(the form of Dolby noise reduction most common in consumer cassette
recorders) is a classic example of complementary adaptive emphasis.
Adaptor – A device that allows an ordinary NTSC television to receive pictures
from a non-receiver-compatible ATV system.
ADC – See A-to-D Converter.
Added Calibrator – A feature of some waveform monitors which allows
an internal 1-volt calibrator signal to be used as a reference for amplitude
measurements.
Adder – Device that forms, as output, the sum of two or more numbers
presented as inputs.
Additive – Any material in the coating of magnetic tape other than the
oxide and the binder resins; for example, plasticizers (materials used to
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soften an otherwise hard or brittle binder), lubricants (materials used to
lower the coefficient of friction of an otherwise high-friction binder), fungicides
(materials used to prevent fungus growth), dispersants (to uniformly
distribute the oxide particles), or dyes.
Additive Color System – Color specification system in which primary colors
are added together to create a desired color. An example is the
red/green/blue (RGB) system. Additive systems are generally associated
with light emitting devices (CRTs).
Additive Mix – A mix wherein the instantaneous video output signal is
equal to the weighted sum of the input video signals. Unless otherwise
specified, “mix” is taken to mean “additive mix.”
Address – Number that indicates the position of a word in the memory.
Address Bus – Set of wires (typically 32) used to transmit addresses,
usually from the microprocessor to a memory or I/O device.
Address Decoding – Process of selecting a specific address or field of
addresses to enable unique devices.
Address Dial – See SCSI Address Dial.
Addressing Modes – Various methods of specifying an address as part of
an instruction. See Direct Addressing, Indirect Addressing, Immediate
Addressing and Indexed Addressing.
Adhesion – The degree to which the coating adheres to the base film.
Anchorage may be checked by measuring the force required to separate
the coating from the base film by means of a specially designed plow blade
or, more simply, by determining whether the coating can be peeled from
the base film by means of ordinary pressure-sensitive adhesive tape.
Adjacent Channel – A television transmission channel immediately adjacent
to an existing channel. For example, channel 3 is adjacent to channels
2 and 4. There are three exceptions to what might otherwise be considered
adjacent channels: there is a small gap between channels 4 and 5, there is
a large gap between channels 6 and 7, and there is an enormous gap
between channels 13 and 14. Adjacent channels figure into ATV in two
ways. a) First, it is currently illegal to broadcast on adjacent channels in a
single location. Some ATV proponents feel that augmentation channels
might someday be allowed to be placed in adjacent channels. If half-size
(3 MHz) or smaller augmentation channels are used, all current broadcasters
could then be allowed an augmentation channel. Some proponents feel
the use of a low-power digital augmentation channel will allow adjacent
channels to be used without interference. b) Second, some ATV proposals
require that the augmentation channel be adjacent to the transmission
channel or require a larger than normal transmission channel, thus occupying
a channel and one of its adjacent channels.
Administrator – See System Administrator and Network Administrator.
ADPCM – See Adaptive Differential Pulse Code Modulation.
ADSL – See Asymmetrical Digital Subscriber Line.
ADSR (Attack, Decay, Sustain and Release) – These are the four
parameters found on a basic synthesizer envelope generator. An envelope
generator is sometimes called a transient generator and is traditionally
used to control the loudness envelope of sounds, though some modern
designs allow for far greater flexibility. The Attack, Decay, and Release