Glossary of Terms

Glossary of Common CCTV Terms

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Aliasing - In sound and image generation, aliasing is the generation of a false (alias) frequency along with the correct one when doing frequency sampling. For images, this produces a jagged edge, or stair-step effect. For sound, it produces a buzz.

AGC - Automatic gain control.  A section in an electronic circuit that has feedback and regulates a certain voltage level to fall within predetermined margins.

Anti-aliasing is the smoothing of the image or sound roughness caused by aliasing. With images, approaches include adjusting pixel positions or setting pixel intensities so that there is a more gradual transition between the colour of a line and the background colour. With sound aliases are removed by eliminating frequencies above half the sampling frequencies.

Aperture - The opening of a 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.  By increasing the F-stop number (F/1.4, F/1.8, F/2.8, etc.) less light is permitted to pass to the pickup device.

Auto iris (AI) - An automatic method of varying the size of a lens aperture in response to changes in scene illumination.

AWB – Auto White Balance – See White Balance.

BLC - Backlight Compensation – A method to compensate for bright spots in a picture.

It is also important to consider whether there are bright spots in the picture such as car headlights which can make identification of the vehicle registration or model impossible.

This can also be a major problem where it is necessary to identify a person who is moving from bright daylight into artificial light. This could result in the subject becoming an unidentifiable silhouette.

Bandwidth - The complete range of frequencies over which a circuit or electronic system can function with minimal signal loss, usually measured to the point of less than 3 dB.  In PAL systems the bandwidth limits the maximum visible frequency to 5.5 MHz, in NTSC to 4.2 MHz.  The ITU 601 luminance channel sampling frequency of 13.5 MHz was chosen to permit faithful digital representation of the PAL and NTSC luminance bandwidths without aliasing.

Bit - A contraction of binary digit.  Elementary digital information that can only be 0 or 1.  The smallest part of information in a binary notation system.  A bit is a single 1 or 0.  A group of bits, such as 8 bits or 16 bits, compose a byte.  The number of bits in a byte depends on the processing system being used.  Typical byte sizes are 8, 16 and 32.

BNC - BNC stands for Bayonet-Neil-Concelman connector and it is the most popular connector in CCTV and broadcast TV for transmitting a basic bandwidth video signal over a coaxial cable.

Byte - A digital word made of 8 bits (zeros and ones).

CCD - Charge-coupled device.  The new age imaging device, replacing the old tubes.  When first invented in the 1970s, it was initially intended to be used as a memory device.  Most often used in cameras but also in telecine, fax machines, scanners, etc..

CCD aperture - The proportion of the total area of a CCD chip that is photosensitive.

CCIR - Committée Consultatif International des Radiocommuniqué or, in English, Consultative Committee for International Radio, which is the European standardisation body that has set the standards for television in Europe.  It was initially monochrome’ therefore, today the term CCIR is usually used to refer to monochrome cameras that are used in PAL countries.

CCTV - Closed circuit television.  Television system intended for only a limited number of viewers, as opposed to broadcast TV.

CCTV camera - A unit containing an imaging device that produces a video signal in the basic bandwidth.

Coaxial cable - The most common type of cable used for copper transmission of video signals.  It has a coaxial cross-section, where the centre core is the signal conductor, while the outer shield protects it from external electromagnetic interference.

Composite video signal - A signal in which the luminance and chrominance information has been combined using one of the coding standards NTSC, PAL, SECAM, etc..

dB - Decibel. A logarithmic ratio of two signals or values, usually refers to power, but also voltage and current.  When power is calculated the logarithm is multiplied by 10, while for current and voltage by 20.

Duplex - A communication system that carries information in both directions is called a duplex system. In CCTV, duplex is often used to describe the type of multiplexer that can perform two functions simultaneously, recording in multiplex mode and playback in multiplex mode.  It can also refer to duplex communication between a matrix switcher and a PTZ site driver, for example.

Encoder - A device that superimposes electronic signal information on other electronic signals.

External synchronisation - A means of ensuring that all equipment is synchronised to the one source.

Field - Refers to one-half of the TV frame that is composed of either all odd or even lines.  In CCIR systems each field is composed of 625/2 = 312.5 lines, in EIA systems 525/2 = 262.5 lines.  There are 50 fields/second in CCIR/PAL, and 60 in the EIA/NTSC TV system.

F-number - In lenses with adjustable irises, the maximum iris opening is expressed as a ratio (focal length of the lens)/(maximum diameter of aperture).  This maximum iris will be engraved on the front ring of the lens.

Focal length - The distance between the optical centre of a lens and the principal convergent focus point.

GB - Gigabyte.  Unit of computer memory consisting of about one thousand million bytes (a thousand megabytes).  Actual value is 1,073,741,824 bytes.

GND - Ground (electrical).

Grey scale - A series of tones that range from true black to true white, usually expressed in 10 steps.

HAD - Hole accumulated diode.  A type of CCD sensor with a layer designed to accumulate holes (in the electronic sense), thus reducing noise level.

HDD - Hard disk drive.  A magnetic medium for storing digital information on most computers.

Hyper-HAD or Super HAD- An improved version of the CCD HAD technology, utilising on-chip micro-lens technology to provide increased sensitivity without increasing  the pixel size.

IDE - Interface device electronics.  Software and hardware communication standard for interconnecting peripheral devices to a computer.

I/O - Input/Output.

I/P - Input.  A signal applied to a piece of electrical apparatus or the terminals on the apparatus to which a signal or power is applied.

Iris - A means of controlling the size of a lens aperture and therefore the amount of light passing through the lens.

KHz - Kilohertz.  Thousand Hertz.

LED - Light Emitting Diode.  A semiconductor that produces light when a certain low voltage is applied to it in one direction.

Lumen [lm] - The light intensity produced by the luminosity of 1 candela in one radian of a solid angle.

Lux [lx] - Light unit for measuring illumination.  It is defined as the illumination of a surface when luminous flux of 1 lumen falls on an area of 1 m2.  It is also known as lumen per square meter, or meter-candelas.

Matrix switcher - A device for switching more than one camera, VCR, video printer and similar, to more than one monitor, VCR, video printer and similar.  Much more complex and more powerful than video switchers.

MB - Megabyte.  Unit of measurement for computer memory consisting of approximately one million bytes.  Actual value is 1,048,576 bytes.  Kilobyte × Kilobyte = Megabyte.

MHz - Megahertz.  One million hertz.

Monochrome - Black-and-white video.  A video signal that represents the brightness values (luminance) in the picture, but not the colour values (chrominance).

NTSC - National Television System Committee.  American committee that set the standards for colour television as used today in the US, Canada, Japan and parts of South America.  NTSC television uses a 3.57945 MHz sub-carrier whose phase varies with the instantaneous hue of the televised colour and whose amplitude varies with the instantaneous saturation of the colour.  NTSC employs 525 lines per frame and 59.94 fields per second.

OSD – On Screen Display. A method  of displaying set-up information or instructions on to a display monitor.