Terms & Definitions Used in the CCTV / Security Industry
This guide will familiarize you with the common terms used in the CCTV / Security industry. Terms used for product specifications are also included for DVRs, CCTV Cameras, CCTV Monitors, Time lapse VCRs, and other CCTV Equipment.
Automatic Gain Control. A circuit for automatically controlling amplifier gain in order to maintain a constant output voltage with a varying input voltage within a predetermined range of input-to-output variation.
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.
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 IRIS LENS
A lens that automatically adjusts the amount of light reaching the imager.
The number of cycles per second (Hertz) expressing the difference between the lower and upper limiting frequencies of a frequency band; also, the width of a band of frequencies.
BAR TEST PATTERN
Special test pattern for adjusting color TV receivers or color encoders. The upper portion consists of vertical bars of saturated colors and white. The power horizontal bars have black and white areas and I and Q signals.
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 cathode-ray picture tube. In a camera, sensor element saturation and excess which causes widening of the spatial representation of a spot light source.
The attribute of visual perception in accordance with which an area appear to emit more of less light. (Luminance is the recommended name for the photo-electric quantity which has also been called brightness.)
In television system use, a device having a bandpass greater than the band of a single VHF television channel.
Also called burn. An image which persists in a fixed position in the output signal of a camera tube after the camera has been turned to a different scene or, on a monitor screen.
See Charge Coupled Device
A television camera lens mount of the 16 mm format, 1 inch in diameter with 32 threads per inch.
Common abbreviation for Closed-Circuit Television.
CCD. For imaging devices, a self-scanning semiconductor array that utilizes MOS technology, surface storage, and information transfer by shift register techniques.
A particular type of cable capable of passing a wide range of frequencies with very low signal loss. Such a cable in its simplest form, consists of a hollow metallic shield with a single wire accurately placed along the center of the shield and isolated from the shield.
That portion of the composite color signal, comprising a few cycles of a sine wave of chrominance sub carrier frequency, which is used to establish a reference for demodulating the chrominance signal. Normally approximately 9 cycles of 3.579545 MHz.
The degree to which a color is free of white light.
COMPOSITE VIDEO SIGNAL
The combined picture signal, including vertical and horizontal blanking and synchronizing signals.
The reduction in gain at one level of a picture signal with respect to the gain at another level of the same signal.
The range of light to dark values in a picture or the ratio between the maximum and minimum brightness values.
Basically, a measure of the power ratio of two signals. In system use, a measure of the voltage ratio of two signals, provided they are measured across a common impedance.
The circuitry in a color TV receiver which transforms the detected color signals into a form suitable to operate the color tube.
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 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.
The deviation of the received signal waveform from that of the original transmitted waveform.
The difference between the maximum acceptable signal level and the minimum acceptable signal level.
One of the two equal but vertically separated parts into which a television frame is divided in an interlaced system of scanning. A period of 1/60 second separates each field start time.
FIELD OF VIEW
The maximum angle of view that can be seen through a lens or optical instrument.
Of a lens, the distance from the focal point to the principal point of the lens.
A plane (through the focal point) at right angles to the principal point of the lens.
The point at which a lens or mirror will focus parallel incident radiation.
The total area, occupied by the television picture, which is scanned while the picture signal is not blanked.
An increase in voltage or power, usually expressed in dB.
A numerical value, or the degree of contrast in a television picture, which is the exponent of that power law which is used to approximate the curve of output magnitude versus input magnitude over the region of interest.
A spurious image resulting from an echo.
Electrical disturbance at the power supply frequency or harmonics thereof.
Extraneous energy which tends to interfere with the reception of the desired signals.
An adjustable aperture built into a camera lens to permit control of the amount of light passing through the lens.
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 so curved (usually Spherical), that they serve to converge or diverge the transmitted rays of an object, thus forming a real or virtual image of that object.
Refers to the ability of a lens to transmit light, represented as the ratio of the focal length to the diameter of the lens. A fast lens would be rated f/8. The larger the f number, the slower the lens.
Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm.
Also called looping. The method of feeding a series of high impedance circuits (such as multiple monitor/displays in parallel) from a pulse or video source with a coax transmission line in such a manner that the line is bridged (with minimum length stubs) and that the last unit properly terminates the line in its characteristic impedance. This minimizes discontinuities or reflections on the transmission line.
A reduction in signal level or strength, usually expressed in dB. Power dissipation serving no useful purpose.
International System (Sl) unit of illumination in which the meter is the unit of length. One lux equals one lumen per square meter.
A unit of equipment that displays on the face of a picture tube the images detected and transmitted by a television camera.
Abbreviation for National Television Systems Committee. A committee that worked with the FCC in formulating standards for the present day United States color television system.
The signal level at the output of an amplifier or other device.
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).
PAN/TILT PRESET POSITIONING
Follower pots are installed on pan/tilt unit to allow feedback to the controller and provides information relevant to horizontal and vertical positioning, allowing the controller to quickly adjust to a pre-selected scene automatically.
Short for Picture Element. A pixel is the smallest area of a television picture capable of being delineated by an electrical signal passed through the system of part thereof. The number of picture elements (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.
Three colors wherein no mixture of any two can produce the third. In color television these are the additive primary colors red, blue and green.
The amount of resolvable detail in the horizontal direction in a picture. It is usually expressed as the number of distinct vertical lines, alternately black and white, which can be seen in a distance equal to picture height.
The amount of resolvable detail in the vertical direction in a picture. It is usually expressed as the number of distinct horizontal lines, alternately black and white, which can theoretically be seen in a picture.
A loss of vertical synchronization which causes the picture to move up or down on a receiver or monitor.
In color, the degree to which a color is diluted with white light or is pure. The vividness of a color, described by such terms as bright, deep, pastel, pale, etc. Saturation is directly related to the amplitude of the chrominance signal.
Ability to control the integration (of light) time to the sensor to less than 1/60 second; e.g: stop motion of moving traffic.
The ratio between useful television signal and disturbing noise or snow.
Heavy random noise.
A transient of short duration, comprising part of a pulse, during which the amplitude considerably exceeds the average amplitude of the pulse.
STANDARD MINIMUM SIGNAL
1000 microvolts at 75 ohms (0dB mV) in RF systems; 0.7-VPP non-composite, 1-VPP composite in video systems.
A term used to describe a picture condition in which groups of horizontal lines are displaced in an irregular manner.
A chart especially prepared for checking overall performance of a television system. It contains various combinations of lines and geometric shapes. The camera is focused on the chart, and the pattern is viewed at the monitor for fidelity.
The number of horizontal lines that can be seen in the reproduced image of a television pattern.
To enlarge or reduce, on a continuously variable basis, the size of a televised image primarily by varying lens focal length.
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