CCTV Glossary

Automatic Gain Control (AGC)
An electronic circuit in the CCTV camera which begins to amplify the video signal when it starts to fall below a given value due to lack of light on the image device.

Aspect Ratio
Ratio of picture width to height. Standard aspect ratio is 4 X 3 for standard systems, 5 X 4 for 1K x 1K, and 16 X 9 for HDTV.

Auto Balance
A system for detecting errors in color balance in black and white areas of the picture, and automatically adjusting those levels for both the red and blue signals.

Auto Homing
An automatic sequential video switcher which has manual switches or buttons, which allow a single CCTV camera to be displayed on screen without sequential switching.

Auto Iris Lens
A lens with a mechanical iris, which is controlled by a motor and responds to the changing video levels produced by a CCTV camera. The iris will be driven more open as the light hitting the image device becomes less and less and visa versa with an increase in light.

Auto Light Range
The range of light, e.g. sunlight to moonlight, over which a CCTV camera is capable of automatically operating at specified output.

Automatic Brightness Control
In display devices, the self-acting mechanism, which controls brightness of the device as a function of ambient light.

Automatic Gain Control
A process by which gain is automatically adjusted as a function of input or other specified parameter.

Automatic Light Control
The process by which the illumination upon the face of a pickup device is automatically adjusted as a function of scene brightness.

Bandwidth
When dealing with frequencies, it is the area between the boundary of lower and upper limits of specific frequencies.

Blooming
The defocusing of regions of the picture where the brightness is at an excessive level, due to enlargement of spot size and halation of the fluorescent screen of the CCTV monitor.

Bridging
A term used to describe a type of automatic sequential switcher which has the ability to send a signal to two monitors (dual output) - one continually sequencing and the second one able to display any one of the CCTV camera inputs on the "bridged" monitor.

Brightness
The attribute of visual perception in accordance with which an area appears to emit more or less light (also called luminance).

Burned-In Image
An image which persists in a fixed position in the output signal of a CCTV camera tube after the camera has been turned to a different scene or, on a CCTV monitor screen.

C Mount
A specific style of mount used to connect a CCTV lens to a camera body. This style is the standard in the CCTV industry.

Camera Format
Refers to the image pick-up device size. The format of the CCTV camera determines the type and size of lens used for the desired scene.

Charged Coupled Device (CCD)
A solid state device that converts an optical image into an electrical current which is processed into a video signal.

CCTV
Common abbreviation for Closed-Circuit Television.

Chrominance
A colour term defining the hue and saturation of a colour. Does not refer to brightness.

Chrominance Signal
The portion of the PAL colour television signal which contains the colour information.

Coaxial Cable
A special type of wire used to carry low voltage signals.

Colour Purity
The degree to which a colour is free of white or any other colour.

Colour Transmission
The transmission of a signal which represents both the brightness values and the colour values in a picture.

Composite Video Signal
A video signal comprised of all elements which make up a standard PAL video signal, including sync, horizontal and vertical timing pulses, black level and video level from Reference Black to Peak White.

Contrast
The noticeable difference between blacks and whites in a picture. If the two extremes look like gray and off-white the contrast is not good. A gray scale can be used to check the CCTV monitor's ability to reproduce good contrast.

Contrast Range
The ratio between the whitest and blackest portions of television image.

CS Mount
Same physical characteristics as a C Mount, except it places the back plane of a CCTV lens 5mm nearer to the image device.

Criminal Damage
Crimes where any person without lawful excuse intentionally or recklessly destroys or damages any property belonging to another.

Depth Of Field
A specific "window" of distance in which objects remain in focus.

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

Digital Signal Processing
An algorithm within the CCTV camera that digitises data (the image).

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

Distribution Amplifier
A device that provides several isolated outputs from one looping or bridging input, and has a sufficiently high input burden and input-to-output isolation to prevent loading of the input source.

Dwell
The length of time a picture from a single CCTV camera stays on the screen. Usually associated with automatic sequential switchers.

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

Evidence Quality
Includes specifics such as DVR recordings set at a resolution rate so that faces, number plates etc. can be identified, and accurate time and date information displayed with each recording.

Field Of View
The width and height or area desired to be covered by one CCTV camera. This area is determined by the focal length of the lens on the camera and the distance the camera is mounted from the scene.

Focal Length
The distance from the focal point or center of the CCTV lens to the focal plane or image pick-up device and usually expressed in millimeters (mm). The larger the number the longer the lens and the more telephoto the field of view.

Frame
One still picture with a duration or dwell time of 1/30th of a second made up of 525 horizontal lines. A frame is similar to one still picture of a motion picture film.

Frame Frequency
The number of times per second that the frame is scanned. The UK standard is 26 frames per second.

Frame Transfer
A CCD imager where an entire matrix of pixels is read into storage before being output from the CCTV camera. Differs from interline transfer where lines of pixels are output.

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

Gamma
A numerical value used to express contrast levels in television pictures. A value of "1" indicates a linear characteristic. Less than "1" indicates a curve or less contrast levels represented by a softer looking picture. The standard for a CCTV camera is ".45" and for CCTV monitors is ".55".

Gamma Correction
To provide for a linear transfer characteristic from input to output device.

Geometric Distortion
The warped look of objects in a television picture due to erratic scanning of the electron beam in the picture tube or vidicon tube. A circle may look egg shaped or a straight line look like a curve.

Grey Scale
A pattern of vertical bars with shades of grey starting with white and gradually getting darker grey until ending at black. The pattern is used to test the ability of a CCTV camera to reproduce true white, black and the varying steps of grey in-between.

Homing
A term used to describe a type of automatic sequential switcher, which will stop sequencing and remain on a single CCTV camera input displayed on the monitor when a switch or button is depressed. This switcher has only one monitor output.

Hue
Corresponds to colors such as red, blue, etc.

Image Intensifier
An electronic device which is used to amplify small amounts of light into usable amounts of light to produce a video picture.

Incident Light
The light that falls directly on an object.

Interference
Extraneous energy which tends to interfere with the reception of the desired signals.

Interlace
The method of placing horizontal scan lines in between each other during the period of one frame.

Interlaced Scanning
A scanning process for reducing image flicker in which the distance from centre to centre of successively scanned lines is two or more times the nominal line width, and in which the adjacent lines belong to different fields.

Interline Transfer
A technology of CCD design, where rows of pixels are output from the CCTV camera. The senso's active pixel area and storage register are both contained within the active image area. Differs from frame transfer where all active pixels are moved to a storage register outside of the active area.

Iris
An adjustable aperture built into a CCTV camera lens to permit control of the amount light passing through the lens.

Lens
A transparent optical component consisting of one or more pieces of optical glass with surfaces so curved, that they serve to converge or diverge the transmitted rays of an object, thus forming a real or virtual image of that object.

Lens Speed
Refers to the ability of a lens to transmit light, represented as the ratio of the focal length to the diameter of the lens.

Line Amplifier
An amplifier for audio or video signals that feeds a transmission line.

Looping
The method of feeding a series of high burden circuits (such as multiple CCTV monitors) from a pulse or video source in such a manner that the line is bridged and that the last unit properly terminates the line.

Loss
A reduction in signal level or strength, usually expressed in dB.

Low Frequency Distortion
Distortion effects which occur at low frequencies.

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

Luminance Signal
That portion of the PAL colour television signal which contains the luminance or brightness information.

Lux
A measure of light intensity.

Magnification
A term used with regard to lenses and has evolved to be the same as "power" when describing the size of a zoom lens.

Modulation
The process, or results of the process, whereby some characteristic of one signal is varied in accordance with another signal.

Monitor
A unit of equipment that displays on the face of a picture tube the images detected and transmitted by a CCTV camera.

Monochrome
Black and white with all shades of grey.

Monochrome Signal
In monochrome television, a signal wave for controlling the brightness values in the picture. In colour television, that part of the signal wave which has major control of the brightness values of the picture, whether displayed in colour or in monochrome.

Monochrome Transmission
The transmission of a signal wave which represents the brightness values in the picture, but not the colour (chrominance) values.

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.

Noise
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".

NTSC Format
The standard television format arrived at by the National Television Systems Committee and the Federal Communications Commission to guide manufacturers and broadcasters so that all products in the USA, Japan, Korea (Rep) and several countries in South America would be compatible, whether the signal was black and white or colour.

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

PAL Format
Phase Alternate Line is the most common system for transmission of analogue colour television signals. The system maintains the correct colour reproduction by cancelling out the effects of signal phase errors that occur during the transmission. This standard is used in the UK, China, extensively through Europe, Asia, Africa and also some countries in South America.

Pan and Tilt
A device upon which a camera can be mounted that allows movement in both the azimuth (pan) and in the vertical plane (tilt).

Peak To Peak
The amplitude (voltage difference between the most positive and the most negative excursions (peaks) of an electrical signal. A full video signal measures one volt peak to peak.

Pinhole Lens
A special lens with a very small objective lens which is able to gather light through a small opening. These lenses are generally physically longer than a normal lens of the same focal length and are available in manual and auto-iris configuration; some are also made in a right angle form.

Pixel
A pixel is the smallest area of a television picture capable of being delineated by an electrical signal passed through the system or part thereof. The number of pixels in a complete picture, and their geometric characteristics of vertical height and horizontal width, provide information on the total amount of detail which the raster can display and on the sharpness of the detail, respectively.

Primary Colours
Three colours wherein no mixture of any two can produce the third. In colour television these are the additive primary colours red, blue and green.

Remote
This word can pertain to any function that can be operated from a distance, i.e. video switching; camera motion; recording; relay action. These remote functions can be caused to happen due to direct voltage over a long cable or digital information carried by cable, light, radio frequency transmission, etc.

Resolution (Horizontal)
A number used to measure the ability of a camera or monitor to accurately reproduce a picture with many small picture elements. The more common CCTV cameras are capable of producing from 350 to 500 lines of resolution.

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

Retained Image
Also called image burn. A change produced in or on the target which remains for a large number of frames after the removal of a previously stationary light image and which yields a spurious electrical signal corresponding to that light image.

RF (Radio Frequency)
A frequency at which coherent electromagnetic radiation of energy is useful for communication purposes. Also, the entire range of such frequencies.

Roll
A loss of vertical synchronisation which causes the picture to move up or down on a receiver or monitor.

RS-170
The initials "RS" stand for "Recommended Standard". There are many standards set by the IEE pertaining to types of signals produced by an electronic circuit. This particular standard deals with a television signal parameter setting certain standards for signal level and timing.

Saturation
In colour, the degree to which a colour is diluted with white light or is pure. The vividness of a colour, described by such terms as bright, deep, pastel, pale, etc. Saturation is directly related to the amplitude of the chrominance signal.

Scanning
The movement of an electron beam from left to right and top to bottom over a target area used to produce a video signal and reproduce a visual image.

Sensitivity
In television, a factor expressing the incident illumination upon a specified scene required to produce a specified picture signal at the output terminals of a television camera.

Sequential
Relating to, or arranged in a sequence. Used in relation to switching of camera inputs to a monitor so as to display different camera scenes one at a time in a sequential manner or repetition.

Shutter
Ability to control the integration (of light) time to the sensor to less than 1/60 second; e.g: stop motion of moving traffic.

Snow
Heavy random noise.

Spot Filter
A small filter placed in the center of one of the elements of a lens to increase the ability of a camera to pass light. These filters are "neutral density" type which do not affect the colour rendition of the lens.

Sync
The part of a video signal which synchronises the scanning of a monitor to the scanning of an image device. There are vertical sync pulses and horizontal sync pulses which are used to keep the timing or start time of the electron beam in proper synchronisation.

Tearing
A term used to describe a picture condition in which groups of horizontal lines are displaced in an irregular manner.

Terminated
Used when referring to the end point of a video signal.

Vandalism
Criminal damage against households and household property only.

Video Amplifier
A wideband amplifier used for passing picture signals.

Video Tape Recorder
A device which stores video signals on magnetic tape for retrieval at a later time.

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