Activity detection

Refers to a method built into some devices (e.g., recorders, digital cameras and multiplexers) for defecting movement within the camera’s field of view.


Alternating current/direct current.


Analogue to digital conversion; usually the very first stage of an electronic device that processes signals into digital format. The signal can be video, audio, control output and similar.


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


Automatic light control; a part of the electronics of an automatic iris lens that has a function similar to backlight compensation in photography.


An occurrence of sampled data interference. This can occur in CCD image projection of high spatial frequencies and is also known as Moiré patterning. It can be minimized by a technique known as optical low pass filtering.

Alphanumeric video generator (also text inserter)

A device for providing additional information, normally superimposed on to the picture being displayed. The information can range from one or two characters to full-screen alphanumeric text. Such generators use the incoming video signal synchronization pulses as a reference point for the text insertion position, which means if the video signal is of poor quality the text stability will also be of poor quality.


The maximum value of a varying waveform.

Analogue signal

Representation of data by continuously varying quantities. An analogue electrical signal has a different value of volts or amperes for electrical representation of the original excitement (sound, light) within the dynamic range of the system.


A procedure employed to eliminate or reduce (by smoothing and filtering) the aliasing effects.


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 Fstop number (F/1.4, F/1.8, F/2.8, etc.) less light is permitted to pass to the pick-up device.


Long-term off-line storage. In digital systems, pictures are generally archived onto some form of hard disc, magnetic tape, or optical disc.


Undesirable elements or defects in a video picture. These may occur naturally in the video process and must be eliminated in order to achieve a high-quality picture. The most common are cross-colour and cross-luminance.


American standard code for information interchange. A 128-character set that includes the upper-case and lower-case English alphabet, numerals, special symbols and 32 control codes. A 7-bit binary number represents each character. Therefore, one ASCII-encoded character can be stored in one byte of computer memory.

Aspect ratio

The ratio between the width and height of a television or cinema picture display. The present aspect ratio of the television screen is 4:3, which means four units wide by three units high. Such aspect ratio was elected in the early days of television, when the majority of movies were of the same format. The new, high-definition television format proposes a 16:9 aspect ratio.

Aspherical lens

A lens that has an aspherical surface. It is harder and more expensive to manufacture but it offers certain advantages over a normal spherical lens.


The uneven foreground and background blur that is in an image.


Lacking synchronization. In video, a signal is asynchronous when its timing differs from that of the system reference signal. A foreign video signal is asynchronous before a local frame synchronizer treats it.


Asynchronous transfer mode; a transporting and switching method in which information does not occur periodically with respect to some reference, such as a frame pattern.


The decrease in magnitude of a wave, or a signal, as it travels through a medium or an electric system. It is measured in decibels (dB).


Advanced Television System Committee. An American committee involved in creating the high-definition television Standards.

Auto iris (AI)

An automatic method of varying the size of a lens aperture in response to changes in scene illumination.

Auto pan function

A function that allows automatic panning between adjustable limits.


American wire gauge. A wire diameter specification based on the American Standard. The smaller the AWG number, the larger the wire diameter.

Back focus

The distance between the external surface of the lens, which is closest to the imaging device (last lens vertex), and the focal point.

Back-focus adjustment

A procedure for adjusting the physical position of the CCD-chip/lens to achieve the correct focus for all focal length settings (especially critical with zoom lenses).

Back porch

  1. The portion of a video signal that occurs during blanking from the end of a horizontal synchronization pulse to the beginning of active video.
  2. The blanking signal portion that lies between the trailing edge of a horizontal synchronization pulse and the trailing edge of the corresponding blanking pulse. Colour burst is located on the back porch.

Balanced signal

In the CCTV industry, this term refers to a type of video signal transmission through a twisted pair cable. It is called balanced because the signal travels through both wires, thus being equally exposed to the external interference, so when the signal gets to the receiving end the noise is cancelled out at the input of a differential buffer stage.


A device used to match or transform an unbalanced coaxial cable to a balanced twisted pair system.


On analogue systems, 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 and in NTSC systems it limits it to 4.2 MHz. The ITU BT.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. On digital streaming-based systems, bandwidth is usually equated to the bits per second rate of the link.


The frequency band occupied by the aggregate of the signals used to modulate a carrier before they combine with the carrier in the modulation process. In CCTV the majority of signals are in the baseband.


Date rate, named after Maurice Emile Baud, which is equal to one symbol per second. Baud is equivalent to bits per second only in cases where each signal event represents exactly 1 bit. Typically, the baud settings of two devices must match if the devices are to communicate with one another. Most digital links use multi-bit symbols and the Baud rate is much lower than the bit rate (for instance 56 kbps modems typically operate at 3300 Baud.


Bit error rate; the ratio of received bits that are in error relative to the total number of bits received, used as a measure of noise induced distortion in a digital bit stream. BER is expressed as a power of 10. For example, a 1 bit error in 1 million bits is a BER of 1:106.


Current or voltage applied to a circuit to set a reference operating level for proper circuit performance, such as the high-frequency bias current applied to an audio recording head to improve linear performance and reduce distortion.


A base 2 numbering system using the two digits 0 and 1 (as opposed to 10 digits [0–9] in the decimal system). In computer systems, the binary digits are represented by two different voltages or currents, one corresponding to zero and another corresponding to one. All computer programs are executed in binary form.


A signal containing both positive-going and negative-going amplitude. It may also contain a zero amplitude state.


Broadband Integrated Services Digital Network; an improved ISDN is composed of an intelligent combination of more ISDN channels and can transmit more data per second.


A contraction of binary digit. Elementary digital information that can only be 0 or 1. It is the smallest part of information in a binary notation system. A bit is a single 1 or 0. A group of 8 bits is a byte.

Bitmap (BMP)

A pixel-by-pixel description of an image. Each pixel is a separate element. Also a computer file format.

Bit rate

Bps = bytes per second; bps = bits per second. The digital equivalent of bandwidth, bit rate is measured in bits per second. It is used to express the rate at which the data bitstream is transmitted. The higher the bit rate, the more information that can be carried.

Blackburst (colour-black)

A composite colour video signal. The signal has composite sync, reference burst and a black video signal, which is usually at a level of 7.5 IRE (50 mV) above the blanking level.

Black level

A part of the video signal, close to the sync level, but slightly above it (usually 20 mV–50 mV) in order to be distinguished from the blanking level. It electronically represents the black part of an image, whereas the white part is equivalent to 0.7 V from the sync level.

Blanking level

The beginning of the video signal information in the signal’s waveform. It resides at a reference point taken as 0 V, which is 300 mV above the lowest part of the synchronization pulses. Also known as pedestal, which is the level of a video signal that separates the range that contains the picture information from the range that contains the synchronizing information.


The defocusing of regions of a picture where brightness is excessive.


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


Bidirectional predictive coded picture; an MPEG term for a picture that is coded using motion-compensated prediction from a past and/or future reference picture.


A group of textile or metallic filaments interwoven to form a tubular structure that may be applied over one or more wires or flattened to form a strap.


In NTSC and PAL video signals, the brightness information at any particular instant in a picture is conveyed by the corresponding instantaneous d.c. level of active video. Brightness control is an adjustment of set-up (black level, black reference).

Burst (colour burst)

Seven to nine cycles (NTSC) or ten cycles (PAL) of subcarrier placed near the end of horizontal blanking to serve as the phase (colour) reference for the modulated colour subcarrier. Burst serves as the reference for establishing the picture colour.


In computer architecture, a path over which information travels internally among various components of a system and is available to each of the components.


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

Cable equalization

The process of altering the frequency response of a video amplifier to compensate for highfrequency losses in coaxial cable.

Camera housing

An enclosure to provide physical and/or environmental protection of the camera, lens and ancillary equipment.

Candela [cd]

A unit for measuring luminous intensity. One candela is approximately equal to the amount of light energy generated by an ordinary candle. Since 1948 a more precise definition of a candela has become ‘the luminous intensity of a black body heated up to a temperature at which platinum converges from a liquid state to a solid’.


A range of microwave frequencies, 3.7–4.2 GHz, commonly used for satellite communications.


Charge-coupled 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 (now known as ITU-R)

Committée Consultatif International des Radiocommuniqué or, in English, Consultative Committee for International Radio (CCIR), which was the European standardization body that 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 countries where TV is broadcast in PAL.


An International Standard (renamed ITU-R BT.601) for component digital television that was derived from the SMPTE RP1 25 and EBU 3246E Standards. ITU-R BT.601 defines the sampling systems, matrix values and filter characteristics for Y, Cr, Cb and RGB component digital television. It establishes a 4:2:2 sampling scheme at 13.5 MHz for the luminance channel and 6.75 MHz for the chrominance channels with eight-bit digitizing for each channel. These sample frequencies were chosen because they work for both 525 line 60 Hz and 625 line 50 Hz component video systems. The term 4:2:2 refers to the ratio of the number of luminance channel samples to the number of chrominance channel samples; for every four luminance samples, the chrominance channels are each sampled twice. The Dl digital videotape format conforms to ITU-R BT.601.


The International Standard (renamed ITU-R BT.656) defining the electrical and mechanical interfaces for digital television equipment operating according to the ITU-R BT.601 recommendation. ITU-R BT.656 defines both the parallel and serial connector pinouts, as well as the blanking, sync and multiplexing schemes used in both parallel and serial interfaces.


Closed circuit television; a TV system intended for 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.

CCTV installation

A CCTV system, or an associated group of systems, together with all necessary hardware, auxiliary lighting, etc., located at the protected site.

CCTV system

An arrangement comprising a camera and lens with all ancillary equipment required for the surveillance of a specific protected area.


Closed circuit video equipment; an alternative acronym for CCTV.


Compact disc; a standard of media where music and data are stored in digital format.
NOTE: In 1980 Philips and Sony proposed a standard for compact discs.


Compact disk read-only memory. The total capacity of a CD-ROM when storing data is 640 MB.


Correlated double sampling; a technique used in the design of some CCD cameras that reduces the video signal noise generated by the chip.


Colour filter array; a set of optical pixel filters used in single-chip colour CCD cameras to produce the colour components of a video signal.


An integrated circuit in which all the components are micro-fabricated on a tiny piece of silicon or similar material.

Chroma crawl

An artifact of encoded video, also known as dot crawl or cross-luminance. It occurs in the video picture around the edges of highly saturated colours as a continuous series of crawling dots and is a result of colour information being confused as luminance information by the decoder circuits.

Chroma gain (chroma, colour, saturation)

In video, the gain of an amplifier as it pertains to the intensity of colours in the active picture.

Chroma key (colour key)

A video key effect in which one video signal is inserted in place of areas of a particular colour in another video signal.


The colour information of a colour video signal.

Chrominance-to-luminance intermodulatlon (crosstalk, cross-modulation)

An undesirable change in luminance amplitude caused by superimposition of some chrominance information on the luminance signal. Appears in a TV picture as unwarranted brightness variations caused by changes in colour saturation levels.


Commission Internationale de l’Eclairagé. This is the International Committee for Light, established in 1965. It defines and recommends light units.


The outer part of a fibre optics cable, which is also a fibre but with a smaller material density than the centre core. It enables a total reflection effect so that the light transmitted through the internal core stays inside.

Clamping (d.c.)

The circuit or process that restores the d.c. component of a signal. It is video clamp circuit, usually triggered by horizontal synchronizing pulses, and re-establishes a fixed d.c. reference level for the video signal. A major benefit of a clamp is the removal of low frequency interference, especially power line hum.

Clipping level

An electronic limit to avoid overdriving the video portion of the television signal.


The first Standard for CCTV lens screw mounting. It is defined with the thread of 1? (2.54 mm) in diameter and 32 threads/inch, and the back flange-to-CCD distance of 17.526 mm (0.69?). The C-mount description applies to both lenses and cameras. C-mount lenses can be put on both C-mount and CS-mount cameras. Only in the latter case is an adaptor required.


A colour encoding system used by printers in which colours are expressed by the ‘subtractive primaries’ (cyan, magenta and yellow) plus black or Key (called K). The black layer is added to give increased contrast and range on printing presses.

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.


Code/Decode. An encoder plus a decoder is an electronic device, which compresses and decompresses digital signals (e.g., video or audio).

Colour bars

A pattern generated by a video test generator, consisting of eight equal width colour bars. Colours are white, cyan, green, magenta, red, blue and black. Depending on the percentage of colour amplitude (from 0% corresponding to 0 V to 100% corresponding to 0.7 V) there are colour bars referred to as bars or bars. The first numbers refer to the maximum amplitude of an uncoloured signal (white), the second to minimum values of an uncoloured signal (black), the third to the maximum value of the coloured signal and the last to the minimum value of the coloured signal again. The colour bars are also referred to as EBU colour bars.

Colour carrier

The subfrequency in a colour video signal (4.43 MHz for PAL) that is modulated with the colour information. The colour carrier frequency is chosen so that its spectrum interleaves with the luminance spectrum with minimum interference.

Colour difference signal

A video colour signal created by subtracting luminance or colour information from one of the primary colour signals (red, green or blue). In the Beta-cam colour difference format, for example, the luminance (Y) and colour difference components (R – Y and B – Y) are derived as follows:

Y = 0.3 Red + 0.59 Green + 0.11 Blue
R – Y = 0.7 Red - 0.59 Green - 0.11 Blue
B – Y = 0.89 Blue - 0.59 Green - 0.3 Red

The G – Y colour difference signal is not created because it can be reconstructed from the other three signals. Other colour difference conventions include SMPTE, EBU-N1 0 and MII. Colour difference signals should not be referred to as component video signals. That term is reserved for the RGB colour components. In informal usage, the term ‘component video’ is often used to mean colour difference signals.

Colour field

In the NTSC system, the colour subcarrier is phase-locked to the line sync so that on each consecutive line subcarrier phase is changed 180° with respect to the synchronization pulses. In the PAL system, colour subcarrier phase moves 90° every frame. In NTSC this creates four different field types, while in PAL there are eight. In order to make clean edits, alignment of colour field sequences from different sources is crucial.

Colour frame

In colour television, four (NTSC) or eight (PAL) properly sequenced colour fields compose one colour frame.

Colour phase

The timing relationship in a video signal, measured in degrees and keeps the hue of a colour signal correct.

Colour subcarrier

The 4.43361875 MHz signal that carries colour information. This signal is superimposed on the luminance level. Amplitude of the colour subcarrier represents saturation and phase angle represents hue.

Colour temperature

Indicates the hue of the colour. It is derived from photography where the spectrum of colours is based upon a comparison of the hues produced when a black body (as in physics) is heated from red through yellow to blue, which is the hottest. Colour temperature measurements are expressed in Kelvin.

Comb filter

An electrical filter circuit that passes a series of frequencies and rejects the frequencies in between, producing a frequency response similar to the teeth of a comb. It is used on encoded video to select the chrominance signal and reject the luminance signal, thereby reducing cross-chrominance artefacts, or conversely to select the luminance signal and reject the chrominance signal, thereby reducing cross-luminance artefacts. Introduced in the S-VHS concept for a better luminance resolution.

Composite sync

A signal consisting of horizontal sync pulses, vertical sync pulses and equalizing pulses only, with a no-signal reference level.

Composite video signal (CVS)

A signal in which the luminance and chrominance information has been combined using one of the coding Standards (i.e., NTSC, PAL, SECAM, etc.).


A common term used in reference to the video picture dynamic range (i.e., the difference between the darkest and the brightest parts of an image).


Central processing unit. A common term used in computers.


Cathode ray oscilloscope (see oscilloscope).


A type of interference or undesired transmission of signals from one circuit into another circuit in the same system. It is usually caused by unintentional capacitance (a.c. coupling).


A newer standard for lens mounting. It uses the same physical thread as the C-mount, but the back flange-to-CCD distance is reduced to 12.5 mm in order to have the lenses made smaller, more compact and less expensive. CS-mount lenses can only be used on CS-mount cameras.

CS-to-C-mount adaptor

An adaptor used to convert a CS-mount camera to C-mount to accommodate a C-mount lens. It looks like a 5 mm-thick ring, with a male thread on one side and a female on the other, and with 1? diameter and 32 threads/inch. It usually comes packaged with the newer type (CS-mount) of cameras.


Composite video burst signal. In broadcast television this refers to the video signal, including the colour information and synchronization pulses.

D/A (also DA)

Opposite to A/D (i.e., digital to analogue conversion).

Dark current

Leakage signal from a CCD sensor in the absence of incident light.

Dark noise

Noise caused by the random (quantum) nature of the dark current.

DAT (digital audio tape)

A system developed initially for recording and playback of digitized audio signals, maintaining signal quality equal to that of a CD.
NOTE: Recent developments in hardware and software might lead to a similar inexpensive system for video archiving, recording and playback.


Decibel; a logarithmic ratio of two signals or values that usually refers to power, but may also refer to voltage and current. When power is calculated, the logarithm is multiplied by 10, while for current and voltage it is multiplied by 20.


Direct broadcast satellite. Broadcasting from a satellite directly to a consumer user, usually using a small aperture antenna.


Direct current. Current that flows in only one direction, as opposed to a.c.


Discrete cosine transform; a mathematical algorithm used to generate frequency representations of a block of video pixels. The DCT is an invertible, discrete orthogonal transformation between time and frequency domain. It can be either forward discrete cosine transform (FDCT) or inverse discrete cosine transform (IDCT).


A device used to recover the component signals from a composite (encoded) source.


To demagnetize.

Delay line

An artificial or real transmission line or equivalent device designed to delay a wave or signal for a specific length of time.


A device that strips the video and audio signals from the carrier frequency.

Depth of field

The area in front of and behind the object in focus that appears sharp on the screen. The depth of field increases with the decrease of the focal length (i.e., the shorter the focal length the wider the depth of field). The depth of field is always wider behind the objects in focus.


An insulating (non-conductive) material.

Differential gain

A change in subcarrier amplitude of a video signal caused by a change in luminance level of the signal. The resulting TV picture will show a change in colour saturation caused by a simultaneous change in picture brightness.

Differential phase

A change in the subcarrier phase of a video signal caused by a change in the luminance level of the signal. The hue of colours in a scene change with the brightness of the scene.

Digital signal

An electronic signal in which every different value from the real-life excitation (sound, light) has a different value of binary combinations (words) that represent the analogue signal.

Digital video recorder (DVR)

A system that allows recording of video images on a hard disk.


Deutsche Industrie-Normen. The national standards body of Germany. The designation number of German national Standards are preceded by the letters ‘DIN’.


A flat circular plate on which data may be stored. It may be a flexible floppy disc or a rigid hard disk, such as a compact disc (CD) or digital video disc (DVD).


Non-proportional representation of an original.


Digital micro-mirror device; a new video projection technology that uses chips with a large number of miniature mirrors, whose projection angle can be controlled with digital precision.


Disk operating system; a software package that makes a computer work with its hardware devices such as hard drive, floppy drive, screen, keyboard, etc.

Dot pitch

The distance in millimetres between individual dots on a monitor screen. The smaller the dot pitch the better, since it allows for more dots to be displayed and better resolution. The dot pitch defines the resolution of a monitor. A high-resolution CCTV or computer monitor would have a dot pitch of less than 0.3 mm.

Drop-frame time code

SMPTE time code format that continuously counts 30 frames per second, but drops two frames from the count every minute except for every 10th minute (drops 108 frames every hour) to maintain synchronization of time code with clock time. This is necessary because the actual frame rate of NTSC video is 29.94 frames per second rather than an even 30 frames.


Digital signal processing. It usually refers to the electronic circuit section of a device capable of processing digital signals.


Transcribing from one recording medium to another.


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


A new standard proposed by JVC for recording digital signals on a VHS video recorder.


Mini digital video; a new format for audio and video recording on small camcorders, adopted by the majority of camcorder manufacturers. Video and sound are recorded in a digital format on a small cassette (66 × 48 × 12 mm), superseding S-VHS and Hi 8 quality.


(See digital video recorder.)

Dynamic range

The difference between the smallest amount and the largest amount that a system can represent.


A point-to-point digital data link with a nominal capacity of up to 2 048 kbps. The E carrier standards for digital telecommunications form part of the synchronous digital hierarchy (SDH) where groups of E1 circuits can be bundled on to higher capacity E3 links. An E1 circuit has 32 timeslots of 64 kbps capacity, each giving a total capacity of 2 048 kbps. (In practice, two of the timeslots are unavailable as they are dedicated to data-framing and call set-up and tear down).


European Broadcasting Union.


Electronics Industry Association, which has recommended the television standard used in the US, Canada and Japan, based on 525 lines interlaced scanning. It was formerly known as RMA or RETMA.


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


The rearrangement of the bit stream of a previously digitally encoded signal in a systematic fashion to make the information unrecognizable until restored on receipt of the necessary authorization key. This technique is used for securing information transmitted over a communication channel with the intent of excluding all (other than authorized) receivers from interpreting the message. It can be used for voice, video and other communications signals.

ENG camera

Electronic news-gathering camera. Refers to CCD cameras in the broadcast industry.


Erasable and programmable read-only memory; an electronic chip used in many different security products that stores software instructions for performing various operations.


A component or circuit that allows for the adjustment of a signal across a given band, which is designed to compensate for loss and delay frequency effects within a system.


A local area network used for connecting computers, printers, workstations, terminals, etc. within the same building. Ethernet operates over twisted wire and coaxial cable at speeds of up to 10 Mbps, 100 Mbps and 1000 Mbps (gigabit ethernet). Ethernet specifies a CSMA/CD (carrier sense multiple access with collision detection). CSMA/CD is a technique of sharing a common medium (wire, coaxial cable) among several devices.

Event recording

The event-controlled recording or storing of image signals for a pre-determined time.

External synchronization

A method of feeding reference timing signals to all connected devices to ensure that their video output signals are synchronous. A means of ensuring that all equipment is synchronized to the one source.


Federal Communications Commission (US).


Fast Fourier transformation.

Fibre optics

A technology designed to transmit signals in the form of pulses of light. Fibre-optic cable is noted for its properties of electrical isolation and resistance to electrostatic and electromagnetic interference.


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.

Film recorder

A device for converting digital data into film output. Continuous tone recorders produce colour photographs as transparencies, prints or negatives.

Filter mount

The attachment point on a lens for mounting an optical filter.

Fixed focal-length lens

A lens with a predetermined fixed focal length, a focusing control and a choice of iris functions.

Flange back distance

The distance between the surface of the lens mount flange to the focal point.

Flash memory

Non-volatile, electronic digital storage medium.


An annoying picture distortion, mainly related to vertical synchronization pulses and video fields display. Some flicker normally exists due to interlacing; it is more apparent in 50 Hz systems (PAL). Flicker also shows when static images are displayed on the screen, such as computer-generated text transferred to video. Poor digital image treatment, found in lowquality system converters (going from PAL to NTSC and vice versa), creates an annoying flicker on the screen. There are several electronic methods to minimize flicker.


See ‘wow and flutter’.


In lenses with adjustable irises, the maximum iris opening, expressed as a ratio (focal length of the lens)/(maximum diameter of aperture). This maximum iris is 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.

Focusing control

A means of adjusting the lens to allow objects at various distances from the camera to be sharply defined.


An illumination light unit used mostly in American CCTV terminology. It equals 10 times (more precisely, 9.29) of the illumination value in luxes. Fourier transformation Mathematical transformation of time domain functions into frequency domain.


Refers to a composition of lines that make one TV frame. In CCIR/PAL TV systems one frame is composed of 625 lines, while in EIA/NTSC TV systems it is composed of 525 lines. There are 25 frames/second in the CCIR/PAL TV system and 30 in the EIA/NTSC TV system. (See also field.)

Frame store

An electronic device that digitizes a TV frame (or TV field) of a video signal and stores it in memory. Multiplexers, fast-scan transmitters, quad compressors and some cameras have built-in frame stores.

Frame switcher

Another name for a simple multiplexer, which can record multiple cameras on a single VCR (and play back any camera in full screen) but does not have a mosaic image display.

Frame synchronizer

A digital buffer that, by storage and comparison of sync information to a reference and timed release of video signals, can continuously adjust the signal for any timing errors.

Frame transfer (FT)

Refers to one of the three principles of charge transfer in CCD chips. The other two are interline and frame-interline transfer.

Frame-interline transfer (FIT)

Refers to one of the three principles of charge transfer in CCD chips. The other two are interline and frame transfer.


The number of complete cycles of a periodic waveform that occur in a given length of time. Usually specified in cycles per second (Hertz).

Frequency modulation (FM)

Modulation of a sine wave or carrier by varying its frequency in accordance with amplitude variations of the modulating signal.

Front porch

The blanking signal portion that lies between the end of the active picture information and the leading edge of a horizontal synchronization pulse.


Any increase or decrease in strength of an electrical signal. Gain is measured in terms of decibels or number of times of magnification.


A correction of the linear response of a camera in order to compensate for the monitor phosphor screen non-linear response. It is measured with the exponential value of the curve describing the non-linearity. A typical monochrome monitor’s gamma is 2.2, and a camera needs to be set to the inverse value of 2.2 (which is 0.45) for the overall system to respond linearly (i.e., unity).


The range of voltages allowed for a video signal, or a component of a video signal. Signal voltages outside of the range (i.e., exceeding the gamut) may lead to clipping, crosstalk or other distortions.


Gigabyte; a unit of computer memory consisting of about one thousand million bytes (a thousand megabytes). Its actual value is 1 073 741 824 bytes.


A way of locking the video signal of a camera to an external generator of synchronization pulses.


GigaHertz. One billion cycles per second.


Ground (electrical).

Grey scale

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

Ground loop

An unwanted interference in the copper electrical signal transmissions with shielded cable. It is a result of ground currents when the system has more than one ground; for example, in CCTV, when there is a different earthing resistance at the camera, and the switcher or monitor end. The induced electrical noise generated by the surrounding electrical equipment (including mains) does not discharge equally through the two earthings (since they are different) and the induced noise shows up on the monitors as interference.

Group delay

A signal defect caused by different frequencies having differing propagation delays (for example, delay at 1 MHz is different from delay at 5 MHz).


Graphical user interface.


A video compression recommended by ITU standarization body and used most often in video conferencing over ISDN lines and multiples of 64 kb/s channels. The picture format used is common intermediate format (CIF) of 352 × 288 pixels, and Quarter of it (QCIF) with 176 × 144 pixels. The term ‘common’ refers to a commonality between PAL and NTSC scanning systems as defined by ITU-R BT.601.


Expanded Standard of H.261, where picture size can be sub-QCIF, QCIF, CIF, 4CIF and 16CIF.


The latest (at time of drafting) in the range of ITU-T H video/audio compression recommendations, which is more scalable, offers substantially higher quality and, hence, is used in the emerging high-definition DVD authoring. Its full designation number is ITU-T H.264.


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


Hard disk drive; a magnetic medium for storing digital information on most computers and electronic equipment that process digital data.


High-definition digital television. The upcoming standard of broadcast television with extremely high resolution and aspect ratio of 16:9. It is an advancement from the analogue high definition and is already used experimentally in Japan and Europe. The picture resolution is nearly 2000 × 1000 pixels and uses the MPEG-2 standard.


High-definition television. It usually refers to the analogue version of the HDDTV. The SMPTE in the US and ETA in Japan have proposed a HDTV product standard: 1125 lines at 60 Hz field rate 2:1 interlace; 16:9 aspect ratio; 30 MHz RGB and luminance bandwidth.

Head end

The electronic equipment located at the start of a cable television system, usually including antennas, earth stations, preamplifiers, frequency converters, demodulators, modulators and related equipment.

Helical scan

A method of recording video information on a tape, most commonly used in home and professional VCRs.


Patterning caused by driving a colour-modulated composite video signal (PAL or NTSC) into a monochrome monitor.


Unit measurement for the number of oscillations per second.

Horizontal drive (also horizontal sync)

This signal is derived by dividing the subcarrier by 227.5 and then doing some pulse shaping. The signal is used by monitors and cameras to determine the start of each horizontal line.

Horizontal resolution

Luminance resolution (detail) expressed horizontally across an image. This is usually expressed as a number of black to white transitions or lines that can be differentiated. It is limited by the bandwidth of the video signal or equipment.

Horizontal retrace

A brief period, at the end of each horizontal line of video, when the scanning beam returns to the other side of the screen to start a new line.

Horizontal sync

The synchronizing pulse at the end of each video line that determines the start of horizontal retrace.

Housings, environmental

Usually refers to camera and lense containers and associated accessories, such as heaters, washers and wipers, to meet specific environmental conditions.


Horizontal sync.

Hue (tint, phase, chroma phase)

One of the characteristics that distinguishes one colour from another. Hue defines colour on the basis of its position in the spectrum (i.e., whether red, blue, green or yellow, etc.). Hue is one of the three characteristics of television colour. In NTSC and PAL video signals the hue information at any particular point in the picture is conveyed by the corresponding instantaneous phase of the active video subcarrier. (See also saturation and luminance.)


An unwanted induction of mains frequency.

Hum bug

Another name for a ground loop corrector.


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


Interface device