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Glossary - A

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A/D: Also known as just AD or A2D. This refers to a Analog to Digital converter. An example of an A2D is on a DVR board. The analog signal from a camera is converted to digital format for the computer to store/analyze.

Aberration: Term used in optics. This refers to anything which affects the fidelity of an image in respect to the original scene.

AC: Alternating current or AC electricity is different from the DC electricity you get from batteries, in that it moves back and forth instead of flowing directly through the wire.

Activity Detection: Also known as Motion Detection. Refers to how some multiplexers/DVR's have the built in capability to detect movement within the cameras field of view. This is used to improving recording efficiency.

ADC: Analog to Digital Conversion. It is the first stage in which an electronic device processes a signal into a digital format. The signal can be video, audio, control output or other.

AGC: Automatic Gain Control. A part of an electronic circuit which regulates a voltage level to fall within a predetermined margin. Feedback is provided to control the level.

ALC: Automatic Light Control. Similar to the function of back light compensation in photography. It is part of the electronics of an automatic iris lens.

Aliasing: Is sampled data interference. This can happen in CCD image projection of high spatial frequencies. It can be lessened by a method known as optical low-pass filtering. Aliasing is also known as Moire patterning.

Alphanumeric video generator: Also known as 'Text inserted'. This is a device which will superimpose text onto an image being displayed. This can range from a few characters to a full screen.

Amplitude: The maximum value of a varying wave form.

Analog Signal: Representation of data by continously varying quantities. An analog electrical signal has a different value of volts or amperes for electrical representation of the original excitement (sound, light, ...) within the dynamic range of the system.

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