Glossary of Video Terms and Acronyms - Isotest

Video Terms and Acronyms
Glossary
quencies with the objective of flat response to 400 TV lines (in NTSC) for a
subjective improvement in image quality.
Aperture Delay – In ADCs, aperture delay is the time from an edge of the
input clock of the ADC until the time the part actually takes the sample.
The smaller this number, the better.
Aperture Jitter – The uncertainty in the aperture delay. This means the
aperture delay time changes a little bit over time, and that little bit of
change is the aperture jitter.
Aperture, Camera – The available maximum dimensions of the optical
image on the active surface of the photo-sensor, within which good quality
image information is being recorded. The camera aperture determines the
maximum usable scene information captured and introduced into the system,
and available for subsequent processing and display. These dimensions
are usually defined by standards. (Note: Not to be confused with lens
aperture, which defines the luminous flux transmission of the optical path.)
Aperture, Clean – The concept of a clean aperture in a digital system
defines an inner picture area (within the production aperture) within which
the picture information is subjectively uncontaminated by all edge transient
distortions (SMPTE 260M). Filtrations for bandwidth limitation, multiple digital
blanking, cascaded spatial filtering, etc., introduce transient disturbances
at the picture boundaries, both horizontally and vertically. It is not
possible to impose any bounds on the number of cascaded digital processes
that might be encountered in the practical post-production system.
Hence, the clean aperture is defined to represent an acceptable (and practical)
worst-case level of production.
Aperture, Display – The available maximum dimensions (mapped back
into the camera aperture) for the system's ability to display good quality
image information. The information available for display is usually cropped
from the total captured by the cascade of tolerances that may be incorporated
in the system, and also by intentional design features that may be
introduced in the display.
Aperture, Production – A production aperture for a studio digital device
defines an active picture area produced by signal sources such as cameras,
telecines, digital video tape recorders, and computer-generated pictures.
It is recommended that all of this video information be carefully produced,
stored, and properly processed by subsequent digital equipment. In
particular, digital blanking in all studio equipment should rigorously conform
to this specified production aperture (SMPTE 260M). The width of the
analog active horizontal line is measured at the 50% points of the analog
video signal. However, the analog blanking may differ from equipment to
equipment, and the digital blanking may not always coincide with the analog
blanking.
Aperture, Safe Action – As defined by a test pattern, a safe action aperture
indicates the safe action image area within which all significant action
must take place, and the safe title image area, within which the most
important information must be confined, to ensure visibility of the information
on the majority of home television receivers. SMPTE RP 27.3 defines
these areas for 35 mm and 16 mm film and for 2x2-inch slides.
API (Application Program Interface) – a) The software used within an
application program to activate various functions and services performed
by the operating system. b) The Windows operating system refers to API
10 www.tektronix.com/video_audio
functions as those which open and close windows, interpret mouse movement,
read the keyboard, etc. These control-type functions are called
"hooks" to the operating system.
APL (Average Picture Level) – The average signal level (with respect to
blanking) during active picture time, expressed as a percentage of the difference
between the blanking and reference white levels.
Application – An application runs in a module, communicating with the
host, and provides facilities to the user over and above those provided
directly by the host. An application may process the transport stream.
Application Window – The workspace (window) available to an application.
The size can be adjusted by the user and limited only by the size of
the monitor's display.
APS (Advanced Photo System) – A new photographic system conceived
by Kodak and developed jointly with Canon, Fuji, Minolta, and Nikon. The
APS was launched in April 1996. APS also represents the file format used
to store data on the new film's magnetic coating.
Apt-X100 – The apt-X100 is a proprietary audio compression algorithm
from APT, Ltd., which features an adaptive differential PCM (ADPCM) algorithm
in four sub-bands. The algorithm provides a fixed 4:1 compression
with low delay and bandwidths ranging from 7.5 kHz to 22.5 kHz and output
bit rates from 64 to 384 kbit/s, depending on the sampling rate.
APU (Audio Presentation Unit 13818-1) – A 13818-1 audio frame.
Architecture – Logical structure of a computer system.
Archive – a) Off-line storage of video/audio onto backup tapes, floppy
disks, optical disks, etc. b) A collection of several files bundled into one file
by a program (such as ar, tar, bar, or cpio) for shipment or archiving. This
method is very reliable and can contain large amounts of data.
Arithmetic and Logic Unit (ALU) – One of three essential components of
a microprocessor. The other two are the registers and the control block.
The ALU performs various forms of addition, subtraction, and logic operations,
such as ANDing the contents of two registers or masking the contents
of a register.
Arithmetic Coding – Perhaps the major drawback to each of the Huffman
encoding techniques is their poor performance when processing texts
where one symbol has a probability of occurrence approaching unity.
Although the entropy associated with such symbols is extremely low, each
symbol must still be encoded as a discrete value. Arithmetic coding
removes this restriction by representing messages as intervals of the real
numbers between 0 and 1. Initially, the range of values for coding a text is
the entire interval (0, 1). As encoding proceeds, this range narrows while
the number of bits required to represent it expands. Frequently occurring
characters reduce the range less than characters occurring infrequently,
and thus add fewer bits to the length of an encoded message.
ARP – Address Resolution Protocol.
ARS – See Automatic Route Selection.
Artifacts – a) Artifacts can range from noise and snow, to spots. Anything
that is visually wrong with the picture is an artifact. Artifacts however do
not include picture errors caused by improperly adjusted displays. Artifacts
are visual errors caused by the signal being sent to the display. b) A defect