Automatic gain control. An electronic circuit in the 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.
In digital signal processing, anti-aliasing is the technique of minimizing aliasing (jagged or blocky patterns) when representing a high-resolution signal at a lower resolution
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. Example: A 15” monitor (measured diagonally) is 12” wide and 9” tall. The width is four increments of 3” and the height is 3 increments of 3” therefore the ratio is 4 to 3.
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.
An automatic sequential video switcher which has manual switches or buttons which allow a single camera to be displayed on screen without sequential switching.
A lens with a mechanical iris which is controlled by a motor or other electrical device and responds to the changing video levels produced by a 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. The lens automatically adjusts the amount of light reaching the imager.
The range of light, e.g., sunlight to moonlight, over which a TV camera is capable of automatically operating at specified output.
Any action initiated or controlled by an electronic circuit without manual intervention.
In display devices, the self-acting mechanism which controls brightness of the device as a function of ambient light.
A process by which gain is automatically adjusted as a function of input or other specified parameter.
The process by which the illumination incident upon the face of a pickup device is automatically adjusted as a function of scene brightness.
This is a device used to match or transform an unbalanced coaxial cable to a balanced twisted pair system. Lets one run a video signal over (cat 5) computer networking cable.
When dealing with frequencies it is the area between the boundary of lower and upper limits of specific frequencies. Example: a bandwidth of 800 Mhz (Megahertz) would be 800 Mhz wide starting from any point (100 Mhz) and ending 800 Mhz above (900 Mhz). Specific to television technology bandwidth can be related to system resolution or lines of resolution. Where 1 Mhz of bandwidth is equal to 100 lines of resolution.
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.
Video connector, the most commonly used in CCTV.
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 camera inputs on the “bridged” monitor. There are two methods of bridging a second monitor. The first is passive where the video signal is “T”ed off the incoming line and sent to the second monitor, in this case the “bridged” monitor must be unterminated. The second method is active where the video signal is regenerated by a distribution amplifier in the switcher and sent to the “bridged” monitor in which case the monitor must be terminated. The bridging switchers are not always marked as being active or passive so attention must be given to the video signal on the “bridged” monitor to be sure if the termination must be set to on or off.
The attribute of visual perception in accordance with which an area appears to emit more or less light (Luminance is the recommended name for the photo-electric quantity which has also been called brightness.)
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.
A specific style of mount used to connect a lens to a camera body. This style is the standard in the CCTV industry. Specifically it is 1” in diameter with 32 threads per inch, of the 16 mm format.
Refers to the image pick-up device size (1”, 2/3”, &Mac189;” and 1/3”). The format of the camera determines the type and size of lens used for the desired scene.
Twisted pair wire with data rate to 100Mbps (1000 Mbps with 4 pair). No longer supported replaced by CAT 5E (1000 Mbps).
An environmental protective enclosure for a cctv camera. Can include a heater for winter and blower for summer.
“Charged Coupled Device” is a solid state device that converts an optical image into an electrical current which is processed into a video signal. Also known as a “Chip” camera.
Common abbreviation for Closed-Circuit Television.
See CCD. For imaging devices, a self-scanning semiconductor array that utilizes MOS technology, surface storage, and information transfer by shift register techniques.
In the CCTV industry, refers to a solid state camera (e.g. CCD).
A color term defining the hue and saturation of a color. Does not refer to brightness.
That portion of the NTSC color television signal which contains the color information.
A special type of wire used to carry low voltage signals. It gets its name from having two conductors configured in concentric circles or two conductors having the same axis. The center conductor is a solid or stranded wire running the full length of the cable. The second conductor is constructed in a braided fashion around a separating non-conductive material. This material is called the dielectric. Coaxial cables have a rating called impedance which is a measurement of resistance and capacitance, the rating for cable used in the CCTV industry is 75 Ohm.
The degree to which a color is free of white or any other color. In reference to the operation of a tri-color picture tube it refers to the production of pure red, green or blue illumination of the phosphor dot face plate.
The transmission of a signal which represents both the brightness values and the color values in a picture.
A video signal comprised of all elements which make up a standard NTSC video signal, including sync, horizontal and vertical timing pulses, black level and video level from reference black to peak white. If color is a factor then color burst will also be present in the composite video signal.
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 monitor’s ability to reproduce good contrast.
The ratio between the whitest and blackest portions of television image.
“Special” C-Mount. Same physical characteristics except it places the back plane of a lens 5mm nearer to the image device. Auto Iris versions of this format are made in two main varieties. The main distinction between them is one has the electronics to control the iris in the lens and other relies on the camera to supply varying voltages to the lens.
A specific “window” of distance in which objects remain in focus. Example – a camera’s field of view will present a picture encompassing a distance of 200 feet from the camera; objects in the picture are in focus at a distance of 10 feet to 90 feet within the picture. The window or depth of field is 80 feet for this example. The depth of field will change in relation to the change in F-stop where the depth of field increase as the F-stop increases (F-numbers get larger).
The range of sensor-to-lens distance for which the image formed by the lens is clearly focused.
This is the latest form of recording and as a result is not the most economical method however it does have several advantages over the VCR analogue tape recorders. First of all it enables quick access to the desired event and does not require swapping of tapes.
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.
A device that provides several isolated outputs from one looping or bridging input, and has a sufficiently high input impedance and input-to-output isolation to prevent loading of the input source.
The length of time a picture from a single camera stays on the screen. Usually associated with automatic sequential switchers.
Digital Video Recorder
Electronic Industry Association. US TV standard 525 lines 60 fields.
An electronic circuit that introduces compensation for frequency discriminative effects of elements within the television system, particularly long coaxial transmission systems.
“Light Factor (f)”. The ability of a camera lens to pass light. A value used to indicate the speed of a lens where the smaller the number the better the lens “a fast lens”, the normal f stop in CCTV lenses is f/1.4 or f/1.2. Each increase in f-stop decreases the amount of light passed through the lens by 50%. The normal f-stops are: f/1.0 – f/1.4 – f.
Flexible glass fibers drawn from the highest quality pure glass used to conduct light energy. The term has come to mean any and all equipment associated with the use of these fibers such as the light power transmitters and receivers, the connecting technology and various cabling systems.
The width and height or area desired to be covered by one 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.
The distance from the focal point or center of the 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.
A measure of light intensity. A unit of illuminance on a surface that is everywhere one foot from a uniform point source of light of one candle and equal to one lumen per square foot.
Frames per second
In video it is one still picture with a duration or dwell time of 1/30th of a second made up of 525 horizontal lines. A frame is made from two fields each having 262 &Mac189; horizontal lines which are interlaced. The video frame is similar to one still picture of a motion picture film.
A CCD imager where an entire matrix of pixels is read into storage before being output from the camera. Differs from Interline Transfer where lines of pixels are output.
An increase in voltage or power, usually expressed in dB.
A numerical value used to express contrast levels in television pictures. A value of one (1) indicates a linear characteristic. Less than one indicates a curve or less contrast levels represented by a softer looking picture. The standard for a camera is .45 and for monitors is .55.
To provide for a linear transfer characteristic from input to output device.
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.
A pattern of vertical bars with shades of gray starting with white and gradually getting darker gray until ending at black. Most gray scales used in television have 10 steps or bars. The pattern is used to test the ability of a camera to reproduce true white, black and the varying steps of gray in-between.
Caused by different earth potentials clearly seen as interference or humbars on a video signal.
A term used to describe a type of automatic sequential switcher which will stop sequencing and remain on a single camera input displayed on the monitor when a switch or button is depressed which is identified with the desired camera to be displayed. This switcher has only one monitor output.
A number used to measure the ability of a camera or monitor to accurately reproduce a picture with many small picture elements. A resolution chart is used when testing a camera. The chart has several circles one large one in the center with lines in a fan shape converging in the center. The lines are marked with resolution numbers which increase as the lines become closer to each other and the center. The maximum resolution displayed on the chart is 800 lines. The more common CCTV cameras are capable of producing from 350 to 500 lines of resolution.
Corresponds to colors such as red, blue, etcetera.
An electronic device which is used to amplify small amounts of light into usable amounts of light to produce a video picture. The device uses very high voltages to accelerate photons in a vacuum tube. The device is placed between a lens mount and an image device such as a vidicon or CCD. The lenses used on cameras with intensifiers must have special attributes with f-stops of up to f/1200.
Impedance is a value of a circuit expressed in ohms, but is arrived at by the combination of resistance, capacitance and inductance. The symbol for impedance is “Z”. This term is used with reference to cable as well as electronics, example: RG59 coaxial cable has an impedance of 75 ohms. The input or output characteristic of a system component that determines the type of transmission cable to be used. The cable used must have the same characteristic impedance as the component. Expressed in ohms. Video distribution has standardized on 75-ohm coaxial and 124-ohm balanced cable.
The light that falls directly on an object.
Extraneous energy which tends to interfere with the reception of the desired signals.
In television theory the method of placing horizontal scan lines in between each other during the period of one frame. The first field lays down 262 &Mac189; horizontal lines and then the second field lays down 262 &Mac189; horizontal lines in between the first set of lines in field number one.
A scanning process for reducing image flicker in which the distance from center to center of successively scanned lines is two or more times the nominal line width, and in which the adjacent lines belong to different fields.
A technology of CCD design, where rows of pixels are output from the camera. The sensor’s active pixel area and storage register are both contained within the active image area. This differs from “frame transfer” cameras that move all active pixels to a storage register outside of the active area.
The Internet Protocol address; a unique numeric address such as 188.8.131.52 Also see Static IP and Dynamic IP.
Infrared light, invisible to the human eye. It usually refers to wavelengths longer than 700 nm. Monochrome (B/W) cameras have extremely high sensitivity in the infrared region of the light spectrum.
An adjustable aperture built into a camera lens to permit control of the amount light passing through the lens.
Local Area Network. A computer network that is housed within a single building.
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.
Follower Pots are installed on lens that allows feedback to the controller information relevant to zoom and focus positioning allowing the controller to quickly adjust to a preselected scene and arrive in focus at the proper focal length automatically.
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/1.4; a much slower lens might be designated as >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.
An amplifier for audio or video signals that feeds a transmission line; also called program amplifier.
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.
Referring to the video inputs on a device such as a switcher or quad. The input is not terminated and has provisions to continue the video line, normally two BNC connectors are present on the rear of the device making it possible to connect the video signal to additional devices. The looping of a video signal should be limited to a few devices depending on distance between devices.
A reduction in signal level or strength, usually expressed in dB. Power dissipation serving no useful purpose.
Distortion effects which occur at low frequencies. In television, generally considered as any frequency below the 15.75-kHz line frequency.
Luminous intensity (photometric brightness) of any surface in a given direction per unit of projected area of surface as viewed from that direction, measured in footlamberts (fl).
That portion of the NTSC color television signal which contains the luminance or brightness information.
A measure of light intensity (1 Foot Candle – approximately 10 Lux). International System (S1) unit of illumination in which the meter is the unit of length. One lux equals one lumen per square meter.
A term used with regard to lenses and has evolved to be the same with “power” when describing the size of a zoom lens. A 16 to 160 mm lens is said to be a 10X or ten power zoom lens. It has a magnification of 10. The other standard is a 6X lens like a 12.5-75 mm. The largest mm is divided by the shortest mm to give the power or magnification.
(1) Referring to a type of video switcher, which can be passive or active, with multiple cameras in and one monitor out, which requires buttons or switches to be pressed to change the camera displayed on the monitor.
(2) Referring to types of lenses, meaning non-auto iris but manual adjust iris; also describing the zoom function of non-motorized zoom lenses.
The process, or results of the process, whereby some characteristic of one signal is varied in accordance with another signal. The modulated signal is called the carrier. The carrier may be modulated in three fundamental ways: by varying the amplitude, called amplitude modulation; by varying the frequency, called frequency modulation; by varying the phase, called phase modulation.
A unit of equipment that displays on the face of a picture tube the images detected and transmitted by a television camera.
Black and white with all shades of gray.
In monochrome television, a signal wave for controlling the brightness values in the picture. In color television, that part of the signal wave which has major control of the brightness values of the picture, whether displayed in color or in monochrome.
The transmission of a signal wave which represents the brightness values in the picture, but not the color (chrominance) values.
A unit that can accept a number of camera inputs and almost simultaneously display them on a single monitor and/or record them to a single video tape. Multixplexers can also be used to transmit multiple cameras over the same transmission medium.
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.
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”.
(National Television Systems Committee). The standard television format (signal specifications) arrived at by this committee and the Federal Communications Commission to guide manufacturers and broadcasters so that all products in this country would be compatible, whether the signal was black and white or color. This system has 525 horizontal scan lines with 30 frames per second, commonly used in the United States and Japan. Some of the other formats of the world include PAL, CCIR, and SECAM.
The signal level at the output of an amplifier or other device.
Phase alternating line. Describes the color phase change in a PAL color signal. PAL is a European color TV system featuring 625 lines per frame, 50 fields per second and a 4.43361875-MHz sub-carrier.
A device upon which a camera can be mounted that allows movement in both the azimuth (pan) and in the vertical plane (tilt).
Same as Pan Tilt but includes a camera with zoom functionality.
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.