Glossary of Terms
We've compiled a list of technical terms that you may need some explanation on.
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Letter Selected: A
A/D (or AD)
Refers to analog to digital conversion
Aberration
A term from optics that refers to anything affecting the fidelity of the image in regards to the original scene.
AC
Alternating current.
AC/DC
Alternating current / direct current.
Activity detection
Refers to a method built into some multiplexers for detecting movement within the camera's field of view (connected to the multiplexer), which is then used to improve camera recording update rate.
ADC
Analog to digital conversion. This is usually the very first stage of an electronic device that processes signals into digital format. The signal can be video, audio, control output and similar.
AGC
Automatic gain control. A section in an electronic circuit that has feedback and regulated a certain voltage level to fall within predetermined margins.
ALC
Automatic light control. A part of the electronics of an automatic iris lens that has a function similar to backlight compensation in photography.
Aliasing
An occurrence of sampled date interference. This can occur in CCD image projection of high spatial frequencies and is also known as Moir? patterning. It can be minimized by a technique known as optical low pass filtering.
Alphanumeric video generator (also text inserter)
A device for providing additional information, normally superimposed on the picture being displayed; this can range form one or two characters to full-screen alphanumeric text. Such generators us the incoming video signal sync pulses as a reference point for the text insertion position, which means if the video signal is of poor quality, the text stability will also be of poor quality.
Amplitude
The maximum value of a varying waveform.
Analog signal
Representation of data by continuously varying quantities. An analog electrical signal has a different value if volts or amperes for electrical representation of the original excitement (sound, light) within the dynamic range of the system.
ANSI
American National Standards Institute.
Anti-aliasing
A procedure employed to eliminate or reduce (by smoothing and filtering) the aliasing effects.
Aperture
The opening of a lens that controls the amount of light reaching the surface of the pickup device. The size of the aperture is controlled by the iris adjustment. By increasing the F-stop number (F/1.4, F/1.8, F/2.8, etc.) less light is permitted to pass to the pickup device.
Apostilb
A photometric unit for measuring luminance where, instead of candelas, lumens are used to measure the luminous flux of a source.
Archive
Long-term off-line storage. In digital systems, pictures are generally archived onto some form of hard disk, magnetic tape, floppy disk or DAT cartridge.
Artifacts
Undesirable elements of defects in a video picture. These may occur naturally in the video process and must be eliminated in order to achieve a high-quality picture. The most common are cross-color and cross-luminance.
ASCII
American Standard Code for Information Interchange. A 128-character set that includes the uppercase and lowercase English alphabet, numerals, special symbols and 32 control codes. A 7-bit binary number represents each character. Therefore, one ASCII-encoded character can be stored in one byte of computer memory.
Aspect ratio
This is the ratio between the width and height of a television or cinema picture display. The present aspect ration of the television screen is 4:3, which means four units wide by three units high. Such aspect ratio was elected in the early days of television, when the majority of movies were of the same format. The new, high-definition television format proposes a 16:9 aspect ratio.
Aspherical lens
A lens that has an aspherical surface. It is harder and more expensive to manufacture, but it offers certain advantages over a normal spherical lens.
Astigmatism
The uneven foreground and background blue that is in an image.
Asynchronous
Lacking synchronization. In video, a signal is asynchronous when its timing differs from that of the system reference signal. A foreign video signal is asynchronous before a local frame synchronizer treats it.
ATM
Asynchronous transfer mode. A transporting and switching method in which information does not occur periodically with respect to some reference such as a frame pattern.
ATSC
Advanced Television System Committee (think of it as a modern NTSC.) An American committee involved in creating the high-definition television standards.
Attenuation
The decrease in magnitude of a wave, or a signal, as it travels through a medium or an electric system. It is measured in decibels (dB).
Attenuator
A circuit that provides reduction of the amplitude of an electrical signal without introducing appreciable phase or frequency distortion.
Auto iris (AI)
An automatic method of varying the size of a lens aperture in response to changes in scene illumination
AWG
American wire gauge. A wire diameter specification based on the American Standard. The smaller the AWG number, the larger the wire diameter (see the reference table in the camera power supply section).