Browse our glossary of video security terms.

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Anti-Passback is an access control security measure that prevents a Cardholder from passing his or her access card to an individual behind them, and allowing them access into a secured zone.


The term "tailgating" refers to instances when one person swipes their access card and another person or vehicle "tailgates" them on the entry. Anti-Tailgating is an access control security measure that will not allow a Cardholder to exit a Zone that they never entered as a valid credentialed user.


Automatic Gain Control is an electronic circuit that amplifies the video signal when the strength of the signal falls below a certain value.

Angle of View

May be expressed in Diagonal, Horizontal or Vertical. Smaller focal lengths give a wider angle of view.


The opening of the 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.

Aspect Ratio

The ratio of width to height for the frame of the televised picture. 4:3 for standard systems

Auto Balance

A system for detecting errors in color balance in white and black areas of the picture and automatically adjusting the white and black levels of both the red and blue signals as needed for correction.

Auto Iris Lens

A lens with an electronically controlled iris, allowing the lens to maintain one light level throughout varying light conditions.



A mechanical adjustment in a camera that moves the imaging device relative to the lens to compensate for different back focal lengths of lenses. An important adjustment when a zoom lens is fitted.


A transformer that levels out impedance differences, so that a signal generated on to a coaxial cable can be transferred on to a twisted pair cable.


The dark parts of a video signal corresponding to approximately 0.3 volts.


A feature of modern CCD cameras, which electronically compensates for high background lighting, to give details that would normally be silhouetted.


Video connector used in CCTV installations.


Camera Format

The approximate size of a camera image pickup device. This measurement is derived from the diagonal line of a chip. Common formats are 1/6", 1/4", 1/3", 2/3", and 1".


Charge coupled device, a flat thin wafer that is light sensitive and forms the imaging device of most modern cameras. Size is measured diagonally and can be 1/3"-1/2" or 2/3". There are two types, frame transfer and interline transfer.


The European 625 line standard for the video signal.


An industry standard for mounting a lens to a camera with a 1" x 32 thread and a distance from the image plane of 17.52mm from the shoulder of the lens. A C-mount lens may be used with a CS-mount camera with a 5mm-adapter ring.

Coaxial Cable

A type of cable capable of passing a wide range of frequencies with very low signal loss.


The reduction in gain at one level of a picture signal with respect to the gain at another level of the same signal.


An industry standard for mounting a lens to a camera with a 1" x 32 thread and a distance from the image plane of 12.52mm from the shoulder of the lens. A CS-mount lens may not be used on a C-mount camera.


Depth of Field

The in-focus range of a lens or optical system. It is measured from the distance behind an object to the distance in front of the object when the viewing lens shows the object to be in focus.

Depth of Focus

The range of sensor-to-lens distance for which the image formed by the lens is clearly focused.

Digital Signal Processing

An algorithm within the camera that digitizes data (the image). Examples include automatic compensate for backlight interference, color balance variations and corrections related to aging of electrical components or lighting. Functions such as electronic pan and zoom, image annotation, compression of the video for network transmission, feature extraction and motion compensation can be easily and inexpensively added to the camera feature set.


The deviation of the received signal waveform from that of the original transmitted waveform.



Electronic Industries Alliance. Monochrome video signal standard used in North America and Japan: 525 lines 60Hz


An electronic circuit that introduces compensation for frequency discriminative effects of elements within the television system, particularly long coaxial transmission systems.


The most widely used LAN transmission network. Based on a bus network topology, it runs at a maximum speed over 100 meters of 10Mbit/s. It operates over conventional co-axial cable, thin wire co-axial cable and unshielded twisted pair cabling. This has several implementations - 10Base5 for use over conventional co-axial cable, 10BaseF for use over optic fiber, and 10BaseT for use over Unshielded Twisted Pair (UTP) cabling.


Field of View

The horizontal or vertical scene size at a given length from the camera to the subject.


Indicates the brightness of the image formed by the lens, controlled by the iris. The smaller the F-number the brighter the image.

Focal Length

The distance from the center of the lens to a plane at which point a sharp image of an object viewed at an infinite position. The focal length determines the size of the image and angle of field of view seen by the camera through the lens. This is the center of the lens to the image pickup device.


The number of frames per second that the camera produces.


A term used to indicate the speed of a lens. The smaller the F-number the greater amount of light passes through the lens.



An increase in voltage or power, usually expressed in dB.


This is one method used on Auto Iris and Direct Drive lenses to move the iris vanes, open and closed using a coil operation.


An electronic correction carried out by the camera circuitry to balance the brightness seen by the camera to that of the monitor.


A node that allows connection to another network using another protocol.


An alternating current (AC) that can be produced in a cable. This is usually caused by parts of the system being fed from different electrical sources resulting in different earth potentials at each end of the signal path. This results in interference of the video pictures in the form of a black shadow bar across the screen or as a tearing effect in the top comer of a picture.


An isolation transformer. There is no direct connection between input and output.



The number of variations per second (e.g. picture frames, alternating of the current, etc).


Hyper text transfer protocol.

HTTP Port 80

Normally this is the HTTP port address that cameras can communicate over.


Impedance (input or output)

The input or output characteristic of a system component that determines the type of transmission cable to be used. Expressed in ohms.

IP Address

The network location of an IP camera, which can be located using a Web browser on a PC. (example -


Mechanism within a lens to regulate the amount of light that passes through, and falls upon, the image sensor. It can be controlled manually or automatically.



Small, rapid variations in a waveform due to mechanical disturbances or to changes in the characteristic of components. Supply voltages, imperfect synchronizing signals, circuits, etc.




A transparent optical component consisting of one or more pieces of optical glass with surfaces curved (usually spherical), so that they converge or diverge the transmitted rays of an object, forming a real or virtual image of that object.

Lens Format

The approximate size of a lens-projected image. In most cases the lens will project an image slightly greater than the designated image size to insure the pickup device is completely covered. It is recommended that camera and lenses are the same format size. A lens larger format size can be used on a smaller format camera, however a smaller format lens should never be used with a larger format camera.

Lens Speed

Refers to the lens aperture or its ability to transmit light. This is measured in F-stops.

Line Locked

A camera that is synchronized to the frequency of its AC power supply.


A unit of incident light. It is the illumination on a surface one square foot in area on which a flux of one lumen is uniformly distributed, or the illumination at a surface all points of which are at a distance of one foot from a uniform source of one candela.


Luminous intensity (photometric brightness) of any surface in a given direction per unit of projected area of the surface as viewed from that direction, measured in footlamberts (fl).


International System (Sl) unit of illumination in which the meter is the unit of length. One lux equals one lumen per square meter.


Manual Iris Lens

A lens with a manual adjustment to set the iris opening (aperture) to a fixed position. This type lens is generally used in fixed lighting conditions.

Matrix Switcher

A combination of electromechanical or electronic switches which route a number of signal sources to one or more designations.


Black and white with all shades of gray.


Moving picture experts group, version 4. A form of compression that makes transmission and storage of images easier.


ND Filter

A filter that attenuates light evenly over the visible light spectrum. It reduces the light entering a lens, thus forcing the iris to open to its maximum.


The word "noise" originated in audio practice and refers to random spurts of electrical energy or interference. In some cases, it will produce a "salt-and-pepper" pattern over the televised picture. Heavy noise is sometimes referred to as "snow".


Network time protocol.

NTP Server

A central source that can set the time of all network devices.


National Television Standards Committee. Color Video Signal standard used in North American and Japanese: 525 Lines, 60Hz.



The signal level at the output of an amplifier or other device.



A device that can be remotely controlled to provide both vertical and horizontal movement for a camera.


The measurement of a video signal from the base of the sync pulse to the top of the white level. For a full video signal this should be one volt.


The ability to delay the line locking process so as to align cameras fed from AC voltages of different phases.


A device at the receiving end of an optical fiber link that converts light to electrical power.


A device that automatically switches on the infra-red lights when light levels fall to a pre-set level.


An electronic device that superimposes the view from one camera over that of another.



A product that can display the views from 4 cameras simultaneously on one monitor. It is also possible to select any individual camera for full-screen display on real time monitoring, dependent on model.



A method of combining two fields to make one frame where strict timing is not a requirement.


The ratio of light returned from a surface expressed as a percentage.


Scene illumination multiplied by reflectance. This is the amount of light returned to the camera and determines the quality of picture.


A description shown in the form of a diagram illustrating how the optical density of an optical fiber alters across its diameter.


Devices placed at regular intervals along a transmission line to detect weak signals and re-transmit them. These are seldom required in fiber optic systems. (Often incorrectly referred to as 'repeaters').


A video switcher to which the cables from the cameras are connected and which contains the switching electronics. This unit may be remotely located and connected to a desktop controller by a single cable for each monitor.



For a camera usually specified in lux to provide indication of light level required to gain a full video signal from the camera.


Ability to control the integration (of light) time to the sensor to less than 1/60 second.

Signal-to-Noise Ratio

Signal to noise ratio, a measurement of the noise level in a signal expressed in dB (decibels). In a video signal values from 45dB to 60dB produce an acceptable picture. Less than 40dB is likely to produce a "noisy" picture.

Spot Filter

A neutral density filter placed at the center of one of the elements (or on an iris blade) to increase the high end of the F-stop range of the lens.



The system by which a signal is transmitted to a remote location in order to control the operation of equipment. In CCTV systems this may include controlling pan, tilt and zoom functions, switch on lights, move to pre-set positions etc. The controller at the operating position is the transmitter and there is a receiver at the remote location. The signal can be transmitted along a simple twisted pair cable or along the same coaxial cable that carries the video signal.


The unit that is at the control position of a CCTV system and contains the keys, joysticks etc. for the remote control of pan/tilt/zoom cameras.


The video cable requires an impedance of 75 ohms at normal video signal bandwidth. This is often called 'low Z'. There is a switch on the back of the monitors to select either 75 ohm or 'high Z' (sometimes 'high/low'). If a signal is looped through more than one monitor all should be set to 'high' except at last, which should be to 'low' or 75 ohm.


A type of cable in which the optical fibers are tightly bound.


A type of industrial video recorder that can be set to record continuously over long periods. Typically, this can be from three hours to 480 hours, achieved by the tape mechanism moving in steps and recording one frame at a time. This means that if set to record over long periods much information can be lost. For instance, in the 72-hour mode, only 3 frames/second will be recorded instead of 25 frames/second in the real time mode. On receipt of an alarm signal these machines can be automatically switched to real time mode. With rapid advances in digital storage and retrieval techniques the mechanical video recorder is now nearing the end of its life in industrial security systems.



A composite video signal, transmitted along a coaxial cable, is an example of an unbalanced signal. (See balanced signal).


Video input of apiece of equipment, wired so as to allow the video signal to be fed to further equipment. Does not necessarily include extra sockets for the extra cables.

UPS (Uninterruptible Power Supply)

A battery, attached to a piece of hardware, for example a server, that provides back up power for conducting an orderly shutdown if the server's normal power supply fails.

UTP (Unshielded Twisted Pair)

The standard cabling used for telephone lines. The standard IEEE 802.3, 10BaseT, defines use of Ethernet over UTP for rates up to 10Mbit/s. The general LAN medium of choice for the 1990s.


Vertical Resolution

The number of horizontal lines that can be seen in the reproduced image of a television pattern.

Video Amplifier

A wideband amplifier used for passing picture signals.

Video Band

The frequency band width utilized to transmit a composite video signal.

Video Signal (Non-Composite)

The picture signal. A signal containing visual information and horizontal and vertical blanking (see also Composite Video Signal) but not sync.


WAN (Wide Area Network)

A network that covers a larger geographical area than a LAN and where telecommunications links are implemented, normally leased from the appropriate PTO(s). Examples of WANs include packet switched networks, public data networks and Value Added Networks.


Compression that is optimized for images containing low amounts of data. The relatively inferior image quality is offset against the low bandwidth demands on transmission mediums.


The brightest part of a video signal corresponding to approximately 1.0 volt (0.7 volts above the black level).


Term used freely to mean a PC, node, terminal or high-end desktop processor (for CAD/CAM and similar intensive applications) - in short, a device that has data input and output and operated by a user.




A color camera producing separate luminance (Y) and chrominance (C) signals to provide greatly improved picture quality from video recorders. Can only be used with a restricted range of equipment.



To enlarge or reduce, on a continuously variable basis, the size of a televised image primarily by varying lens focal length.

Zoom Lens

An optical system of continuously variable focal length, the focal plane remaining in a fixed position.

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