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Activity Detection
Simply looks for changes in the luminance in various selected parts of the scene, and if changes are above a set threshold, then the activity detector interprets that to be activity. Changes in light and camera vibration will also be falsely interpreted as activity. This method is used in the 'motion detection' offered by most multiplexers, and is adequate to detect activity in a scene where false detection is not important. Typically, activity detection is used to detect activity in crowded areas where activity is not the result of intruders and where human traffic is normal and expected.

Automatic Gain Control is a electronic circuit used to increase the video signal in low light conditions. This usually introduces 'noise' in the picture giving a grainy appearance.

Alarm Activated VCR
After pressing Record, a normal VCR takes about 20 seconds before it starts recording useable pictures. With an alarm activated recorder it can be set so that the tape is ready to start recording in about one second. The signal to begin recording can be from an alarm or any other input.

The 'opening' of a lens and a measure of its light gathering capability. Relative aperture is the ratio between the focal length and effective aperture. Measured in F numbers, generally speaking the lower the F the number the more light gathering power the lens has.

Aspect Ratio
The ratio of the horizontal to the vertical image size.

Signal loss in the transmission system.

Automatic Iris
A lens that adjusts automatically to allow the right amount of light to fall on the imaging device. Usually contains a small motor and amplifier, which receives a control signal from the camera to maintain a constant one-volt peak-to-peak video signal.

ADSL (Asymmetrical Digital Subscriber Line)
A new access technology that delivers high-speed communications (1.5 - 6 Mbps) over a standard two wire copper local loop.

Alarm Search
Search criteria, e.g. time, date etc. used to detect alarms from CCTV input signals.

Alternate routing
The capability of a connection orientated system to automatically set up alternate connections if the original circuit fails.

A signal in which any level is represented by a directly proportional voltage not digital.

Angle of View
This is what alters (not the focal length) when you use a lens designed for one format on another format. It decreases with format size.

ANSI (American National Standards Institute)
A standards body of the U.S.A.

API (Application Programming Interface)
Provides a way for an application to request and use the resources of a network.

Automated process to back-up information from the hard disk.

Auto Iris (AI)
An electronic circuit fitted to the iris of a lens to help compensate for large changes in light levels.

Automatic Level Control (ALC)
On auto iris lenses, also known as peak/average control. Adjusting this control allows the auto iris circuitry to either take bright spots more into consideration (average) bringing out detail in shadows,

Auto White Balance
A feature on a colour camera whereby the light is constantly monitored and adjusts the colour to maintain the white areas.


Back Focus
The mechanical aligning of the imaging device with the focal point of the lens. Most important on zoom lenses is to ensure the image stays in focus throughout the zoom range.

Back Light Compensation (BLC)
A feature of modern CCD cameras, which electronically compensates for high background lighting to give detail, which would normally silhouetted.

Video connector (the most commonly used in CCTV)

British Summertime/Greenwich Meantime/Daylight Savings Time.

Balanced Signal
A video signal is converted to a balanced signal to enable it to be transmitted along a 'twisted pair' cable. Used in situations where long cabling distances are required.

BITS and Bytes
In the binary system which consists of 1's and 0's, Bits and Bytes are used as a form of measurement. Each individual numerical value is a Bit and a byte consists of 8 bits. When used as a form of measurement a Bit is referred to as "B", and a byte is referred to as "b".


The standard screw mounting for 1/2" and 1" camera lenses. The distance from the flange surface to the focal point is 17.5 mm. A C-mount lens can be used on a camera with a CS-mount by adding an adapter ring to reduce this distance to 12.5 mm.

CCD (Charge Coupled Device)
A light sensitive imaging device. Size is measured diagonally and can be 1/4", 1/3" or 1/2. There are two basic types: frame transfer and interline transfer.

CCIR (Comitee Consultatif International des Radio communications)
The European TV standard 625 lines 50 fields.

Composite Video
The complete video signal comprising the synchronising and video information. The synchronising pulse should be 0.3 volts and the video signal about 0.7 volts.

A new generation of lenses designed for 1/2" and 1/3" cameras incorporating CS-mounts. The distance from the flange surface to the focal point is 12.5 mm. CS-mount lenses cannot be used on cameras with a C-mount configuration.

CIF (Common Interchange Format) (see also SIF)
CIF resolution measures 352x288 pixels, regardless of whether the video input is NTSC or PAL.

The use of a algorithm to digitally compress a digital picture.


Digital Audio Tape.

Digital record mode
Digital record mode on a camera can reduce the amount of video storage required on some digital recording units. The effect is most noticeable on systems employing conditional update compression techniques.

Digital Signal
An analogue signal that has been converted to a digital form so that it can be processed by a microprocessor.

Direct Drive (DD)
An auto iris requiring a DC reference from camera rather than the traditional video reference.

The result of receiving information in a coded form then transferring it into a useable medium.

Depth of Field
The area of acceptable focus for an image. The wider you set the aperture of a lens the lower the depth of field becomes.

Digital Video Management System.

DVR (digital Video Recorder)
A device that captures video, converts to digital and applies compression before storing on to a Hard Disk.


EIA (Electronic Industry Association)
US TV standard 525 lines in 60 fields.

LAN protocol to connect desktop computers and other computing equipment over shared wiring providing a total speed of 10 Mbps.

External alarm triggers recorded by a VCR running in time-lapse mode.

Denotes a 3 hour, high quality video cassette - high quality in that there is reduced oxidization on the heads offering increased picture quality and longevity of tape usage.

Denotes a 4 hour, high quality video cassette (as above).

Electronic Iris (EI)
Automatically varies a CCD camera's shutter to mimic auto iris control, allowing fixed or manual iris lens to be used in a wider range of areas.

Transferred information in a coded form to a medium.

Ext. Sync (external sync)
The ability of CCTV equipment (normally cameras), to accept one or more of the standard sync formats so as to align itself to the rest of the system.

EPOS (electronic point of sales)
More commonly referred to as a Till, within CCTV data is captured from EPOS systems and stored along with video images to detect and deter retail fraud.


Focal Length
The distance between the secondary principal point in the lens and the plane of the imaging device. The longer the focal length, the narrower is the angle of view.

Frame Store
An electronic method of capturing and storing a single frame of video. All slow scan transmitters include a frame store that holds the picture at the moment of alarm, while the control is being dialled up. When the link is confirmed, the picture is transmitted.

One half of a frame, consisting of either the odd or the even numbered lines. 50 fields are transmitted every second.

One complete TV picture made up of approximately 625 lines. 25 frames are transmitted every second.

Fast Ethernet
Ethernet standard for bumping up the speed of the shared LAN wiring from 10 Mbps to Mbps.


The non-linearity of magnitude of output signal, which usually results in poor discrimination of grey areas of a scene in low light levels. Cameras can have a built-in gamma correction circuit to compensate for this.

One method of converting the small electric currents produced by the auto iris circuits into physical movement of the iris diaphragm. Used in both auto iris and direct drive lenses.

A term used in the IP community to refer to a special purpose routing device.

One method of synchronising multiple cameras so that switching between them does not cause the picture on the monitor to 'roll'.

Gigabyte (Gb)
One million bytes or characters of information.

Gigabit Ethernet
Ethernet standard for bumping up the speed of the shared LAN wiring from 10 Mbps to 1 Gbps.


Hard Disk Drive (HDD)
The non-removable disk in a computer or DVR.

Holiday Code
A VCR timer feature that allows you to assign the Sunday timer settings to up to 20 week days per year. Normally used for Bank holidays.

HSSI (High Speed Serial Interface)
Physical interface primarily used on routers and supporting transmission up to 52 Mbps

A hub is a piece of hardware similar to a switch other than redistributes the TCP to all the channels it has available.


Method used with alarms or activity detection which allows extra frames of video from alarmed cameras to be added to a time multiplexed sequence whilst a state of alarm exists.

Iris (Iris Diaphragm)
Adjustable diaphragm that regulates the amount of light passing through the a lens.

A worldwide network of networks using the IP family of standards to enable communication among users. Users access the network through Internet Service Providers (ISPs).

Corporate network using the technologies of the Internet in private implementations. Commonly adopted technologies include browsers, web pages, and e-mail on a secure IP network.

IP (Internet Protocol)
A connectionless networking protocol. IP is the protocol of the Internet and other connectionless networks, including many corporate LANs and wide area data networks.

ISP (Internet Service Provider)
Provides subscribers connectivity to the Internet.

ITU (International Telecommunication Union)
A U.N.-sanctioned international organization of member states that creates standards for international telecommunications systems.


JPEG (Joint Photographic Expert Groups)
A compression technique, which has been widely used in the Security Industry.

A compression technique that will revolutionise the security industry JPEG2000 produces images that have less visible artefacts at equivalent file sizes.


LAN (Local Area Network)
High-speed network connecting personal computers, printers and other data equipment within an office or campus.

Line Locked
The sync pulses are locked to the AC mains frequency.

Linux is a free open-source operating system based on Unix.

SI unit of illumination equal to one lumen


MPEG (Motion Pictures Expert Group) Including MPEG2 and MPEG4 MJPEG
Standards for compressing and digitalizing stills, audio and or video streams.

A process which combines multiple network sources onto a single stream of information for transport over a transmission facility. Multiplexing devices are often referred to as muxes.

Multiplex (Time Multiplex)
Using one carrier to send more than one signal. In video multiplexers, achieving this by sending a different camera's output in each successive field or frame of a video signal, in a form that can later be retrieved as single camera pictures.

Feature allowing you to pre-programme frequently used system configurations for selection by single keystroke or optionally by alarm inputs.

MAC (Media Access Control)
Determines which end station can transmit over the shared transmission medium of a LAN at any time. Different types of LANs (such as Ethernet, token ring, and FDDI) have different MAC mechanisms.

MAN (Metropolitan Area Network)
High speed network connecting data equipment within a local region that does not extend over 50 kilometres.

Megabyte (Mb)
One million bytes or characters of information.

A communications exchange requiring the transport of various media such as voice, text, image, and video.


NICs (Network Interface Cards)
Adapters used to interface desktop devices (such as personal computers, workstations, and printers) to a LAN.

Degradation to a video signal that appears as 'snow' or graininess in the picture.

NTSC (National Television Standard Committee. See EIA)
Colour TV system used in the USA

Network management
The capability to monitor and control a network. Network management functions provide alarm, performance, configuration, accounting, and security information.


PAL (Phase Alternative Line. SEE CCIR)
UK Colour TV System.

Pan and Tilt Head
A device that can be remotely controlled to provide the vertical and horizontal movement of a camera.

Peak White Inversion
Peak White Inversion renders selected areas of a scene above a certain predefined threshold level as black. This stops the camera or lens reacting to peak white areas which would normally cause it to incorrectly control the iris mechanism thus preventing underexposure of the scene

PIR (Passive Infra Red)
A range of frequencies lower than visible red light used for covert surveillance or as low cost wireless video link.

The pre-positioning of pan/tilt and zoom cameras by the use of potentiometers in the moving parts of the camera head. These allow the control equipment to store and move to set reference point when an alarm exists. Special telemetry equipment is required.

Are a term used in Dome cameras that refer to a specific path of movement

Patrols see also Tours
Patrols are a term used in dome cameras that signify a periodical change to a fixed camera position that covers the available range of the dome camera.


SAN Storage area network
This is a dedicated network that is separate from Lanís or WANS and it serves

Scene Illumination
the amount of light (in LUX) falling on the area to be viewed. For best results the ratio of the lightest to the darkest areas should not be more than a factor of two.

SIF (Standard Interchange Format) See also CIF.
SIF resolution, on the other hand, measures 352x288 pixels for PAL cameras but 352x240 for NTSC cameras. (You may also see it in other literature expressed as 320x240 pixels Ė this is also a valid SIF resolution).

Signal to Noise Ratio
The ratio expressed in dB of the signal voltage to the noise voltage in an electronic circuit.

An electronic circuit available on many CCD cameras. Allowing the light gathering period (1/50th of a second) of the camera to be stopped prematurely (as little as 1/100,000th of a second.

A Subnet is an identifiably separate part of an organisation's IP network.

SVHS (Super Video Home System)
New format, high-resolution VHS video recorders, capable of giving greatly improved picture quality when all features are used. It is also compatible with VHS.

SNMP (Simple Network Management Protocol)
A network management protocol originally designed for TCP/IP networks, which is now used in a wide variety of networking environments.

A computer that maintains circuits by matching an input port to an output port for each connection. The switch contains switching tables to track this information.

Switched Ethernet
LAN protocol that provides a 10-Mbps dedicated Ethernet connection to each desktop, providing non-contested bandwidth to each user.


The system by which the signal is transmitted to a remote location in order to control CCTV equipment e.g. to control pan and tilt and zoom functions, switch on lights, move to preset positions, etc. The controller and 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.

Time Lapse VCR
A type of video recorder that can be set to record continuously over long periods. This can be anything from three hours to 480 hours, achieved by the tape 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. On receipt of an alarm signal these machines can be automatically switched to real-time mode.

TCP (Transmission Control Protocol)
Networking protocol providing end-to-end transport through a connectionless IP network. TCP includes controls for security, reliability, and performance.

TDM (Time Division Multiplexing)
A network transmission method assigning transmission facility bandwidth among users through time slots. TDM is the traditional method of sharing physical bandwidth resources.

Token Ring
LAN protocol to connect desktop computers and other computers equipment over a shared ring that provides a total of 4 or 16 Mbps of bandwidth.

Tours see also patrols
Tours are a term used in PT cameras that signify a periodical change to a fixed camera position that covers the available range of the cameras movement.

Traffic Management
Disciplines and methodologies for controlling traffic load and balance across the network.

TVL (Television Lines Resolution)
The maximum number of changes between light and dark on a picture across 3/4 of the width dictates the resolution of a CCTV product, measured in TVL.


Update Rate
The rate which equates to the number of field updates that a VCR and multiplexer would make when connected together in a standard application, e.g. a standard VCR will use a 3hour videotape, recording 50 fields a second. However, when a VCR is configured to a 24 hour time-lapse mode, the updates are slowed by a factor of 8, recording 6.25 fields a second (which on playback gives a slight stroboscopic effect).


VHS (Video Home System)
Name given to tape format domestic video recorders

Video Cassette Recorder

VEXT (Head Pulse Switching)
A multiplexer feature that uses a pulse generated by the VCR so that the multiplexer automatically adjusts to the VCR time-lapse speed.

VLAN (Virtual LAN)
Provides LAN communications between end users that are logically grouped because of shared interests instead of defining LANs based on physical location.

A View is method of recalling a camera along with a preset position from a matrix.


WAN Wide Area Network
A WAN is a geographically dispersed telecommunications network.


A method of sending video pictures in 2 separate parts down 2 separate cables. The components parts are Y (the monochrome portion) and C (the colour portion).