CCTV and Video Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


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A

Active video lines

All video lines not occurring in the horizontal and vertical blanking intervals.

AGC

Automatic Gain Control, automatically increases the video signal in low light conditions.

Alarm activated VCR

After pressing `record', a normal VCR takes about 20 seconds before it starts recording usable 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.

Analogue

The representation of numerical values by physical variables such as voltage, current, etc.; continuously variable quantities whose values correspond to the quantitative magnitude of the variables.

Aperture

The light gathering area of a lens, controlled by the iris.

Aspect ratio

The ratio of the vertical to the horizontal image size. This is usually 3:4.

Attenuation

This refers to signal loss in a transmission system.

Automatic iris

A lens that adjusts automatically to allow the right amount of light to fall on the imaging device. There is a tiny motor and amplifier built in which receives a control signal from the camera to maintain a constant one volt peak to peak (1.0 Vp-p) video level.

B

Back focus

A mechanical adjustment in a camera that moves the imaging device relative to the lens to compensate for different focal lengths of lenses. This is important when a zoom lens is fitted.

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 the cabling distance is too great.

Bandwidth

The range of signal frequencies that a piece of audio or video equipment can encode or decode; the difference between the limiting frequencies of a continuous frequency band. Video uses higher frequency than audio, thus requires a wider bandwidth.

C

C-Mount

The standard screw mounting for 2/3" and 1" camera lenses. The distance from the flange surface to the focal point is 17.526 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; It is light sensitive and forms the imaging device of most modern cameras. Size is measured diagonally and can be 1/3",1/2" or 2/3".

CCIR

Commite Consultatif International Radiotelegraphique. This is a standards committee of the International Telecommunications Union, who have made the technical recommendation for the European 625 line standard for video signals.

Composite video

The complete visual wave form of the colour video signal composed of chrominance and luminance picture information; blanking pedestal; field, line, and colour sync pulses; and field equalizing pulses.

CRT

Cathode Ray Tube. The main part of a normal monitor or television. Aka the screen.

CS-Mount

A new generation of lenses designed for 2/3",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 C-mount configuration. These lenses are smaller and cheaper than the C-mount equivalents.

D

Decibel (dB)

A logarithmic measure of the ratio between two powers, voltages, currents, sound intensities, etc. Signal-to-noise ratios are expressed in decibels.

Digital signal

An analogue signal that has been converted to a digital form so that it can be processed with less error.

E

EIA

The American 525 line standard for the video signal.

F

Field

Each video image (`Frame') is composed of two fields. One field consists of the odd numbered lines in the frame and the other field consists of the even numbered lines. Each field viewed independently forms a picture but `interlacing', where they are joined together forms a frame.

Focal length

The distance betwen 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.

Frame

The combination of two interlaced fields. The frame frequency is half the field frequency.

G

Genlocking

The process of aligning the data rate of a video image with that of a digital device to digitise the image and enter it into computer memory. The machine that performs this function is known as a genlock.

H

I

Infra red light

The wavelength of light produced above the visible part of the spectrum.

Interlace

The pattern described by two separate field scans when they join to form a complete video frame. As the video picture is transmitted, the first field picks up even-numbered scan lines - the second, odd-numbered ones. The two interleave together to form a single, complete frame..

Internal sync

The internal generation of sync pulses in a camera using a crystal controlled oscillator. This is needed on non-mains powered cameras.

Iris

The mechanism that can be adjusted to vary the amount of light falling on the imaging device.

J

K

L

Line locked

The sync pulses of cameras are locked to the AC mains frequency.

Line powered

A camera in which the power is supplied along the same coaxial cable that carries the video signal.

Loop frame store

The principle is that a series of video frames is compressed and stored in a continuous loop. This records a certain number of frames and then records over them again and again until an alarm signal is received. When this happens it carries on recording for a dozen frames or so and then stops. This means that frames before and after the incident are recorded. This eliminates the boring searching through hours of video tape and concentrates on the period of activity.

Luminance

Brightness.

M

Multiplexer

An electronic system that can accept a number of camera inputs and record them virtually simultaneously. They can also provide multi screen displays with four, nine, sixteen etc. cameras on the screen at once. Multiplexers can be used to transmit multiple pictures down a single video line whether it is a coaxial cable, microwave, infrared link etc. This requires a multiplexer at each end of the line.

N

Noise

Any unwanted signal that affects the video signal. Usually random electrical energy or interference. In video, noise can produce a random salt and pepper pattern over the picture. Heavy video noise is called snow.

NTSC

National Television Systems Committee of the Electronics Industries Association (EIA) which prepared the NTSC format specifications approved by the Federal Communications Commission, for US commercial colour broadcasting. `NTSC' also refers to a colour television format having 525 scan lines, a field frequency of 60 Hz, a broadcast bandwidth of 4 MHz, line frequency of 15.75 KHz, frame frequency of 1/30 of a second, and a colour subcarrier frequency of 3.58 MHz.

O

Overscanning

A technique used in consumer display products that extends the deflection of a CRT's electron beam beyond the physical boundaries of the screen to ensure that images will always fill the display area. See also underscanning.

P

PAL

Phase Alternation Line; the European standard colour television system, except for France. PAL's image format is 4:3, 625 lines, 50 Hz and 4 MHz video bandwidth with a total 8 MHz of video channel width.

Pan Tilt Zoom (PTZ)

A device that can be remotely controlled to provide both vertical and horizontal movement for a camera, with zoom.

Peak to peak

The measurement of any signal from the lowest value to the highest. In a composite or full video signal, this should be 1 Volt.

Pixel

Picture element.

Pre-set controller

A function contained within a telemetry system that, on receipt of a signal, causes a particular camera to pan, tilt and zoom to a predetermined field of view. Most systems can accommodate up to sixteen preset positions for each camera. This is an especially useful feature on larger systems with alarmed areas.

Q

Quad screen

Display where 4 cameras are viewed on the same screen, each camera image occupying a quarter of the display area. Other `multi screen' modes are possible such as 9, 16 and 25 way. The splits do not always have to be equal and other configurations can be possible.

R

Real time recording

Refers to the top speed of a video recorder; governed by the monitor - pictures are available as fast as the video can accept them.

Remote switcher

A video switcher which is connected to the camera cables and which contains the switching electronics. This unit may be remotely located and connected to a desk top controller by a single cable for each monitor.

Resolution

Number of pixels per unit of area. A display with a finer grid contains more pixels and thus has a higher resolution, capable of reproducing more detail in an image.

S

Scene illumination

The density of light 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.

Screen splitter

A term usually used for a device that can combine the views from two cameras on a single screen. Normally the camera syncs need to be locked together.

SECAM

Sequential Couleur A Memoire (sequential colour with memory), the French colour TV system also adopted in Russia. The basis of operation is the sequential recording of primary colours in alternate lines. The image format is 4:3, 625 lines, 50 Hz and 6-MHz video bandwidth with a total 8 MHz of video channel width.

Signal to Noise Ratio (SNR)

A measurement of the noise level in a signal expressed in dB (decibels). The higher the Signal to Noise ratio, the better the quality of the signal.

SVHS or Super VHS

A higher quality extension of the VHS home videotape format, featuring higher luminance and the ability to produce better copies.

S-Video

Type of video signal used in the Hi8 and SVHS videotape formats. S-video transmits luminance and colour portions separately, using multiple wires, thus avoiding the colour encoding process and its inevitable loss of picture quality.

T

Tecton

THE company for CCTV, multiplexers, video transmission, video switchers, antennae, precision time, text overlay and much more. See our Home Page.

Telemetry

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

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 at 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.

Touch screen control

A system by which all the camera controls are displayed on the screen of a special monitor. To control any function simply requires the screen to be touched at the appropriate symbol which can be to select a camera or pan, tilt and zoom. The system is computer driven and can include maps, diagrams etc. that are automatically displayed according to the alarm received.

U

Underscanning

A technique generally used by some TV and video systems as a way of ensuring that the complete image is always visible within a display area; the opposite of overscanning.

V

VCR

Video Cassette Recorder aka video, video recorder.

Video Motion Detection

A method of detecting movement in the view of the camera by the electronic analysis of the change in picture contrast.

W

White level

The brightest part of a video signal corresponding to approximately 1.0 Volt.

X

Y

Y/C Video

See S-video.

Z