CCTV & Surveillance System Glossary

This glossary contains a list of general terms and definitions related to surveillance systems, security cameras, and CCTV equipment. If you find any terms on our web site that you do not understand and can not find in this glossary, please email or call us so that we can add it.

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3-Axis Mounting Bracket / 3-Axis Gimbal
Cameras that feature a 3-axis mounting bracket (bullet cameras) or 3-axis gimbal (dome cameras) allow you to mount the camera virtually anywhere (wall or ceiling) and position the camera at any angle to achieve the field of view you desire.
Automatic Gain Control is an electronic circuit that amplifies the video signal when the strength of the signal falls below a certain value. In low brightness situation, the Auto Gain Control will be adjusted according to lighting condition for displaying a bright and clear image.
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.
AWB (Auto White Balance)
This feature automatically adjusts the colour temperature of the camera image to match the type of light available, so that white and other colours appear as natural as possible.


Back Focus
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.
Black Level
The dark parts of a video signal corresponding to approximately 0.3 volts.
BLC (Back Light Compensation)
A feature of modern CCD cameras, which electronically compensates for high background lighting, to give details that would normally be silhouetted. When light is behind the main object, the main object and background’s light and shade contrast is big, uses backlight compensation function to make both main object and background exposure level close.
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 in, 1/4 in, 1/3 in, 2/3 in and 1 in.
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 in – 1/2 in or 2/3 in. There are two types, frame transfer and interline transfer.
Determines how many cameras can be recorded at one time. For example, a four-channel DVR allows you to record and view up to 4 video cameras simultaneously.
The European 625 line standard for the video signal.
An industry standard for mounting a lens to a camera with a 1 in x 32 thread and a distance from the image plane of 17.52 mm from the shoulder of the lens. A C-mount lens may be used with a CS-mount camera with a 5 mm adapter ring.
An industry standard for mounting a lens to a camera with a 1 in x 32 thread and a distance from the image plane of 12.52 mm from the shoulder of the lens. A CS-mount lens may not be used on a C-mount camera.
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.
Concealed Cable Management
Where the camera video and power cables are fed through a built-in mounting bracket, protecting the wiring from vandals and criminals, and to provide a cleaner installation. For applications requiring external wiring, there may be a gap in the base of the camera’s mounting bracket for convenience.


Day & Night With IR Cut Filter
Day & Night – equip built- in Mechanical ICR filter perfect for 24-hour and 7 day (24/7) surveillance. It provides perfectly visible colors during daylight and IR Cut filter remove automatically at night time to give clear B/W images at night as well.
Day/Night (Digital)
Digital day/night (also referred to as electronic day/night) improves low light sensitivity, delivers a sharper image in low light conditions, and enables the camera to see in the dark without the help of external IR illuminators. Unlike true day/night cameras, which use a mechanical filter, the camera electronically adjusts colors during the day instead of using an infrared filter. This allows the digital day/night cameras to deliver similar benefits of true day/night cameras, but at a lower cost. Without the need for a physical filter, digital day/night technology can be leveraged for smaller form factors, such as bullet cameras.
Day/Night (True)
True day/night (also referred to as mechanical day/night) improves low light sensitivity, delivers a sharper image in low light conditions, and enables the camera to see in the dark without the help of external IR illuminators. To accomplish this, the camera automatically removes the infrared filter from in front of the CCD chip which enables the camera to see near infrared light, and allows more light into the imager to deliver a clearer picture and minimize distortion when in black and white mode.
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 Noise Reduction (DNR)
Digital Noise Reduction (DNR) technology offers several benefits. First, DNR delivers a cleaner signal, resulting in up to 70% disk space savings – so you can store more video evidence on your hard drive. Next, cameras equipped with DNR technology deliver a more visually appealing image, making it easier to identify suspects. Finally, DNR technology makes it easier for your camera to distinguish between true motion and image noise – allowing for your DVR to be more efficient in motion detection – especially in low light conditions. How it works: The chip in a camera is constantly picking up noise (fine static) in your images, especially in low-light modes. DNR technology compensates for this, correcting imperfections in the image by removing a large percentage of this noise. When a DVR or computer is processing the video data, it must compress and save every part of the image that is moving. The less noise in the image, the less data the DVR will save, and the more real motion it will detect.
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.
Digital Slow Shutter
Allows you to see clear images in extreme low light conditions without the need for artificial illumination. DSS technology (also known as ‘sens-up’ or ‘sense-up’) enables very low light capabilities by slowing down shutter speed to allow more light to be collected by the CCD imager. This means that the camera can capture color images in conditions of near darkness. The user can adjust these settings to specify conditions that engage this feature automatically.
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.
Frame Rate
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.
Gamma Correction
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.
Ground Loop
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.
Ground Loop Transformer
An isolation transformer. There is no direct connection between input and output.


H.264 Compression
H.264 is a stable, proven and widely used compression technology, with unbeatable recording picture quality and a small compression ratio that saves valuable hard drive storage space (5-10 times smaller than MPEG-4).
Hertz (Hz)
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.
Infrared (IR)
Infrared (IR) cameras feature built-in illuminators that project infrared light, which is nearly invisible to the human eye but very visible to IR surveillance cameras. This technology allows you to capture crystal clear, black and white video of suspects who feel protected by complete darkness. IR cameras are very effective in covering targeted areas with little or no light, ranging from exterior parking areas and entryways, to interior rooms requiring 24 hour surveillance. For coverage of wider areas, consider adding an additional external infrared illuminator.
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.
Motion Detection
DVR: Allows you to pre-define motion detection zones and sensitivity for each individual camera. When motion is detected by the DVR, this will trigger a pre-programmed event (usually a recording), or it can activate an external device, such as an alarm. This benefit allows you to save hard drive space by only recording relevant video in the areas you care about. It also saves time: you don t have to sift through countless hours of useless video where nothing is happening – you can quickly scan through the captured activity in the pre-defined area of coverage.
Camera: Allows you to integrate your cameras with external devices – to engage that device upon the detection of motion. Common devices include security lights, alarms, access control devices, and more.
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.


Optical Zoom Lens
Choice of 2.6X, 12X, 25X, 30X, optical zoom with maintain focus.
On Screen Display
A camera’s On Screen Display (OSD) allows you to fine tune virtually every setting of your camera to achieve the best possible image quality. Without OSD, you are dependent upon the factory settings of the camera, and subject to any impact to the camera experienced during delivery or installation. With the convenient design features of DIGIOP Black cameras, including 2nd video out and on-board one-finger joystick controls, you can adjust your every aspect of your camera at the point of installation – without having to run back-and-forth to your DVR or monitor. Aspects you can control include wide dynamic range, auto iris exposure settings, day/night settings, and many more.
The signal level at the output of an amplifier or other device.


Pan & Tilt
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.
Phase Adjustable
The ability to delay the line locking process so as to align cameras fed from AC voltages of different phases.
Photo Detector
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.
Privacy Zone
Privacy zone prevent objects and areas such as windows and doors which are within the camera’s viewing range but not in the scope of surveillance, 8 masking areas per screen simultaneously.


Quad Splitter
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.


Random Interlace
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.
Reflected Light
Scene illumination multiplied by reflectance. This is the amount of light returned to the camera and determines the quality of picture.
Refracted Index Profile
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’).
Remote Switcher
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.
RS-485 Controls
RS-485 controls allow camera settings to be changed remotely without the operator being physically present at the camera location. This is done by using an RS-485 controller which is typically set up at the viewing station or control room.


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.
Most cameras are not able to adjust IR output based on object distance, which often results in a washout for over-IR-exposed scenes, or a darkened image for under-IR-exposed scenes. SMART IR allows the camera to automatically adjust IR intensity as the subject moves closer to or further away from the camera, so you always have a clear image that is not washed out or too dark.
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.
Sun/Rain Shield
Some cameras come with an adjustable sun/rain shield to prevent glare and direct contact from the elements, in order to deliver the cleanest possible video signal.


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.
Telemetry Transmitter
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.
Tight Buffered
A type of cable in which the optical fibers are tightly bound.
Time Lapse VCR
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.


Unbalance Signal
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. Cameras with built-in UTP (also called video balun) allows you to send video over longer distances, allowing you to position your cameras further away from the recording device without losing quality of your video signal. While a standard analog camera can deliver signal up to approximately 300 ft over a standard CAT5 cable, UTP extends transmission capabilities up to 750 ft. UTP also allows you to use CAT5 cable (instead of coaxial cable) for longer runs, resulting in an easier installation due to the smaller wire size and a significant cost savings for larger jobs.


Varifocal Lens
A camera lens with variable focal length in which the focus changes as focal length (and, therefore, the magnification) changes. This is different to a parfocal, or “true” zoom lens, which remains in focus as the lens zooms (focal length and magnification change). Varifocal lenses offer greater flexibility over fixed lenses as they allow the lens aperture to be adjusted as needed. Varifocal lenses come in a range of apertures, including 2.8-12 mm, 3.5-8 mm, and 6-60mm. The greater the aperture size, the more magnified the image will appear with greater detail being captured. A smaller aperture size will result in a wider view with less detail being captured.
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.
White Level
The brightest part of a video signal corresponding to approximately 1.0 volt (0.7 volts above the black level).
Wide Dynamic Range (WDR)
Enables the camera to deliver video with near perfect exposure in the harshest of lighting conditions. To accomplish this, wide dynamic cameras use advanced digital processing to capture two images at different exposures, and then combine them into a single image. WDR cameras are ideal for challenging lighting situations, such as doorways or windows to the outside, looking into car headlights, or any application looking into a direct light source. They are also ideal in opposite conditions, such as looking from a well lit area into a darker area.
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.