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CCTV Glossary

  • Angle of View:
    May be expressed in Diagonal, Horizontal or Vertical. Smaller focal lengths give a wider angle of view.

  • Aperture:
    In CCTV optics, the aperture is the diameter of the lens that controls the amount of light reaching the image sensor. It is shown by an f-number. Larger aperture lenses have smaller f-numbers. For instance, a lens with an f-number of 1.2 will allow more light to reach the sensor than a lens with an f-number of 2.0 thus producing a brighter image. The higher the f number the less light is permitted to pass into the camera.

  • Aspect Ratio:
    The ratio of width to height for the frame of the televised picture. 4:3 for standard systems

  • Auto Balance:
    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.

  • Auto electronic shutter (AES):
    Feature of a camera to adjust for light changes without the use of an auto-iris lens.

  • Auto-Iris Control:
    An automatic iris lens is a lens with a motorized iris that automatically adjusts to only allow a specific amount of light to reach the image sensor. When there is little light, the iris will open to let more light in. When there is too much light, the iris will close to reduce the amount of light let in. Auto iris lenses are primarily used in applications where light levels vary and it would be impracticable to manually adjust the lens. Automatic iris lenses are generally more efficient than the electronic shutter since they actually control the amount of light reaching the sensor as opposed to simply adjusting shutter speed.

  • Automatic Gain Control:
    Most Supercircuits cameras come with an AGC circuit. This circuit examines the brightness level of the video signal to keep it at a consistent level. For example, if the video signal is dark, it will attempt to increase the gain to bring the brightness up to a normal level.

  • Back Focus:
    A mechanical adjustment in a camera that moves the imaging device relative to the lens to compensate for different back focal lengths of lenses. An important adjustment when a zoom lens is fitted.

  • Back Light Compensation:
    Many Supercircuits cameras include a BLC circuit. This circuit is used to help correct an image with more light behind the subject being viewed. Without backlight compensation, the subject appears dark with little detail. Using the backlight compensation will reduce the brightness of the light to allow the subject to appear brighter and bring out the details.

  • BALUN:
    A transformer that levels out impedance differences, so that a signal generated on to a coaxial cable can be transferred on to a twisted pair cable.

  • Black Level:
    The dark parts of a video signal corresponding to approximately 0.3 volts.

  • BNC:
    Video connector used in CCTV installations.

  • C Mount Lenses:
    An industry standard for lens mounting. The C-Mount has a thread with a 1 inch diameter and 32 threads per inch. The distance from the lens mounting surface to the sensor surface is 0.69 inches (17.526 mm). It is possible to mount a C mount lens onto a CS mount camera with the use of a CS adapter ring.

  • Camera Formats:
    Common formats are 1/4”, 1/2”, 1/3”, 2/3”, and 1”. The size of the sensor directly affects the field of view obtained. When using the same size lens on different format sensors, different viewing areas are obtained. For example, using a 6mm lens on a 1/3” sensor will give you a 37º field of view. Using the same lens on a 1/2” sensor will increase the field of view to 56º and 74º on a 2/3” sensor.

  • CCD:
    Charge coupled device, a flat thin wafer that 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". There are two types, frame transfer and interline transfer.

  • CCIR:
    The European 625 line standard for the video signal.

  • Coaxial Cable:
    A type of cable capable of passing a wide range of frequencies with very low signal loss.

  • Compression:
    The reduction in gain at one level of a picture signal with respect to the gain at another level of the same signal.

  • CS Mount Lenses:
    An industry standard for lens mounting. The CS-Mount has a thread with a 1 inch diameter and 32 threads per inch. The distance from the lens mounting surface to the sensor surface is 0.492 inches (12.5 mm). It is not possible to use a CS mount lens on a C mount camera.

  • 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.

  • Digital video recorder (DVR):
    A special computer that converts analog computer images to digital images, compresses the images, and then stores them for later viewing. A DVR replaces the time-lapse VCR, multiplexor and switch found in analog CCTV surveillance systems.

  • Distortion:
    The deviation of the received signal waveform from that of the original transmitted waveform.

  • Duplex:
    An electronic device used to record and display camera images at the same time. A full-duplex DVR can record camera images while displaying images from a different camera at the same time.

  • EIA:
    Electronic Industries Alliance. Monochrome video signal standard used in North America and Japan: 525 lines 60Hz

  • Equalizer:
    An electronic circuit that introduces compensation for frequency discriminative effects of elements within the television system, particularly long coaxial transmission systems.

  • Ethernet:
    The most widely used LAN transmission network. Based on a bus network topology, it runs at a maximum speed over 100 meters of 10Mbit/s. It operates over conventional co-axial cable, thin wire co-axial cable and unshielded twisted pair cabling. This has several implementations - 10Base5 for use over conventional co-axial cable, 10BaseF for use over optic fibre, and 10BaseT for use over Unshielded Twisted Pair (UTP) cabling.

  • EXview HAD:
    EXview HAD CCD is a trademark of Sony Corporation. The HAD CCD dramatically improves light efficiency by including near infrared light as a basic structure of the sensor. Conventional CCD sensors are sensitive to infrared light but are unable to efficiently gather the charge. Because of this greater efficiency, HAD CCD sensors achieve sensitivities approximately 4 times that of a conventional CCD.

  • Field of View:
    The horizontal or vertical scene size at a given length from the camera to the subject.

  • F-Number:
    Indicates the brightness of the image formed by the lens, controlled by the iris. The smaller the F-number the brighter the image.

  • Framerate:
    The number of frames per second that the camera produces.

  • F-Stop:
    A term used to indicate the speed of a lens. The smaller the F-number the greater amount of light passes through the lens.

  • Gain:
    An increase in voltage or power, usually expressed in dB.

  • Galvanometric:
    This is one method used on Auto Iris and Direct Drive lenses to move the iris vanes, open and closed using a coil operation.

  • Gamma Correction:
    An electronic correction carried out by the camera circuitry to balance the brightness seen by the camera to that of the monitor.

  • GateWay:
    A node that allows connection to another network using another protocol.

  • Ground Loop Transformer:
    An isolation transformer. There is no direct connection between input and output.

  • Ground Loop:
    An alternating current (AC) that can be produced in a cable. This is usually caused by parts of the system being fed from different electrical sources resulting in different earth potentials at each end of the signal path. This results in interference of the video pictures in the form of a black shadow bar across the screen or as a tearing effect in the top comer of a picture.

  • HERTZ (Hz):
    The number of variations per second (e.g. picture frames, alternating of the current, etc).

  • Housing:
    Protective enclosure that a camera can be placed in to protect it from outside weather conditions.

  • HTTP Port 80:
    Normally this is the HTTP port address that cameras can communicate over.

  • HTTP:
    Hyper text transfer protocol.

  • Impedance (input or output):
    The input or output characteristic of a system component that determines the type of transmission cable to be used. Expressed in ohms.

  • Infrared:
    The area below the visible spectrum. B&W cameras are very sensitive to infrared light and allow the use of infrared illuminators to enhance poorly lit locations without alerting subjects during surveillance. Color cameras are also sensitive to infrared light, but require an infrared filter to filter out the red light to keep the image colors.

  • IP Address:
    The network location of an IP camera, which can be located using a Web browser on a PC. (example – 192.168.1.100)

  • Iris:
    Mechanism within a lens to regulate the amount of light that passes through, and falls upon, the image sensor. It can be controlled manually or automatically.

  • Jitter:
    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.

  • Lens Format:
    The approximate size of a lens-projected image. In most cases the lens will project an image slightly greater than the designated image size to insure the pickup device is completely covered. It is recommended that camera and lenses are the same format size. A lens larger format size can be used on a smaller format camera, however a smaller format lens should never be used with a larger format camera.

  • Lens Speed:
    Refers to the lens aperture or its ability to transmit light. This is measured in F-stops.

  • Lens:
    A transparent optical component consisting of one or more pieces of optical glass with surfaces curved (usually spherical), so that they converge or diverge the transmitted rays of an object, forming a real or virtual image of that object.

  • Line Locked :
    A camera that is synchronized to the frequency of its AC power supply.

  • Lumen/FT2:
    A unit of incident light. It is the illumination on a surface one square foot in area on which a flux of one lumen is uniformly distributed, or the illumination at a surface all points of which are at a distance of one foot from a uniform source of one candela.

  • Luminance:
    Luminous intensity (photometric brightness) of any surface in a given direction per unit of projected area of the surface as viewed from that direction, measured in footlamberts (fl).

  • Lux:
    International System (Sl) unit of illumination in which the meter is the unit of length. One lux equals one lumen per square meter.

  • Manual Iris Lens:
    A lens with a manual adjustment to set the iris opening (aperture) to a fixed position. This type lens is generally used in fixed lighting conditions.

  • Matrix Switcher:
    A combination of electromechanical or electronic switches which route a number of signal sources to one or more designations.

  • Monochrome:
    Black and white with all shades of gray.

  • MPEG4:
    Moving picture experts group, version 4. A form of compression that makes transmission and storage of images easier.

  • Multiplexer:
    An analog device found in older CCTV systems that allows multiple cameras to be displayed simultaneously on a single CCTV Monitor. Multiplexers can also be used to transmit multiple camera images at once over a single cable.

  • ND Filter:
    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.

  • Noise:
    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".

  • NTP Server:
    A central source that can set the time of all network devices.

  • NTP:
    Network time protocol.

  • NTSC:
    National Television Standards Committee. Color Video Signal standard used in North American and Japanese: 525 Lines, 60Hz.

  • Output:
    The signal level at the output of an amplifier or other device.

  • PAN & TILT:
    A device that can be remotely controlled to provide both vertical and horizontal movement for a camera.

  • Peak-TO-Peak:
    The measurement of a video signal from the base of the sync pulse to the top of the white level. For a full video signal this should be one volt.

  • Phase Adjustable:
    The ability to delay the line locking process so as to align cameras fed from AC voltages of different phases.

  • Photo Cell:
    A device that automatically switches on the infra-red lights when light levels fall to a pre-set level.

  • Photo Detetor:
    A device at the receiving end of an optical fibre link that converts light to electrical power.

  • Pin In Pic:
    An electronic device that superimposes the view from one camera over that of another.

  • Pinhole camera:
    A spy camera with a lens that can see through a tiny hole. These camera are usually hidden.

  • Power-over-Ethernet (POE):
    Device that allows one to transmit power to a security power through an Ethernet network cable.

  • PTZ:
    Stands for pan-tilt-zoom. PTZ cameras have motors that allow them to be remotely moved up-down, side-to-side, and the camera lens zoomed in or out.

  • Quad:
    Analog CCTV test monitor equipment used to display 4 camera images simultaneously on a single monitor.

  • Quad Splitter:
    A product that can display the views from 4 cameras simultaneously on one monitor. It is also possible to select any individual camera for full-screen display on real time monitoring, dependent on model.

  • Random Interlace:
    A method of combining two fields to make one frame where strict timing is not a requirement.

  • Real-time recording:
    For digital video, 30 frames-per-second per camera allows no jerkiness in the video.

  • Reflectance:
    The ratio of light returned from a surface expressed as a percentage.

  • Reflected Light:
    Scene illumination multiplied by reflectance. This is the amount of light returned to the camera and determines the quality of picture.

  • Refracted Index Profile:
    A description shown in the form of a diagram illustrating how the optical density of an optical fibre alters across its diameter.

  • Regenerators:
    Devices placed at regular intervals along a transmission line to detect weak signals and re-transmit them. These are seldom required in fibre optic systems. (Often incorrectly referred to as 'repeaters').

  • Remote surveillance:
    The ability to view a camera image that is located remotely, where the video image is transmitted over a phone line or the Internet.

  • Remote Switcher:
    A video switcher to which the cables from the cameras are connected and which contains the switching electronics. This unit may be remotely located and connected to a desktop controller by a single cable for each monitor.

  • RG-59:
    A type of coaxial cable used in CCTV systems.

  • Sensitivity:
    For a camera usually specified in lux to provide indication of light level required to gain a full video signal from the camera.

  • Shutter:
    Ability to control the integration (of light) time to the sensor to less than 1/60 second.

  • Signal-to-Noise Ratio (SNR):
    The ratio of video signal to noise. This is a measure of how much signal noise the camera can withstand and still present a good image. The higher this number is, the better the picture quality.

  • Spot Filter:
    A neutral density filter placed at the center of one of the elements (or on an iris blade) to increase the high end of the F-stop range of the lens.

  • Super HAD:
    The Super HAD CCD is a version of Sony’s high performance HAD with improved sensitivity from the use of more efficient on-chip microlenses. The Super HAD optimizes the shape of the on-chip lenses in order to minimize the ineffective area between the lenses on each pixel thereby minimizing lost light and improving the overall sensitivity per pixel.

  • Switch:
    An analog device found in older CCTV systems that takes multiple camera inputs and displays them on a monitor one at a time (unlike a quad).

  • Telemetry Transmitter:
    The unit that is at the control position of a CCTV system and contains the keys, joysticks etc. for the remote control of pan/tilt/zoom cameras.

  • Telemetry:
    The system by which a signal is transmitted to a remote location in order to control the operation of equipment. In CCTV systems this may include controlling pan, tilt and zoom functions, switch on lights, move to pre-set 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.

  • Termination:
    The video cable requires an impedance of 75 ohms at normal video signal bandwidth. This is often called 'low Z'. There is a switch on the back of the monitors to select either 75 ohm or 'high Z' (sometimes 'high/low'). If a signal is looped through more than one monitor all should be set to 'high' except at last, which should be to 'low' or 75 ohm.

  • Tight Buffered:
    A type of cable in which the optical fibres are tightly bound.

  • Time-lapse VCR:
    A special VCR found in analog CCTV systems designed to slow down the recording rate in order to store many hours of video footage on a single videotape.

  • Unbalanced Signal:
    A composite video signal, transmitted along a coaxial cable, is an example of an unbalanced signal. (See balanced signal).

  • Unterminated:
    Video input of apiece of equipment, wired so as to allow the video signal to be fed to further equipment. Does not necessarily include extra sockets for the extra cables.

  • UPS (Uninterruptible Power Supply):
    A battery, attached to a piece of hardware, for example a server, that provides back up power for conducting an orderly shutdown if the server's normal power supply fails.

  • UTP (Unshielded Twisted Pair):
    The standard cabling used for telephone lines. The standard IEEE 802.3, 10BaseT, defines use of Ethernet over UTP for rates up to 10Mbit/s. The general LAN medium of choice for the 1990s.

  • Varifocal lens:
    A camera lens in which the focus is not fixed and that can be adjusted either manually or automatically.

  • Vertical Resolution :
    The number of horizontal lines that can be seen in the reproduced image of a television pattern.

  • Video Amplifier :
    A wideband amplifier used for passing picture signals.

  • Video Band :
    The frequency band width utilized to transmit a composite video signal.

  • Video gain:
    Also called video amplification, this is the increase in video signal power by an amplifier.

  • Video Signal (Non-Composite) :
    The picture signal. A signal containing visual information and horizontal and vertical blanking (see also Composite Video Signal) but not sync.

  • WAN (Wide Area Network):
    A network that covers a larger geographical area than a LAN and where telecommunications links are implemented, normally leased from the appropriate PTO(s). Examples of WANs include packet switched networks, public data networks and Value Added Networks.

  • Watch-dog timer:
    The automatic reboot of a DVR system whenever a problem is detected.

  • WaveLet:
    Compression that is optimised for images containing low amounts of data. The relatively inferior image quality is offset against the low bandwidth demands on transmission mediums.

  • White Balance:
    Color cameras only. Different lighting sources provide different color temperatures. The white balance helps correct these differences by adjusting the color processing to bring the color temperature to a fixed level. Without this balancing feature, due to the CCD’s poor adaptability, some colors would appear different (green instead of white in sunlight).

  • White Level:
    The brightest part of a video signal corresponding to approximately 1.0 volt (0.7 volts above the black level).

  • WorkStation:
    Term used freely to mean a PC, node, terminal or high-end desktop processor (for CAD/CAM and similar intensive applications) - in short, a device that has data input and output and operated by a user.

  • Y/C:
    A colour camera producing separate luminance (Y) and chrominance (C) signals to provide greatly improved picture quality from video recorders. Can only be used with a restricted range of equipment.

  • Zoom Lens:
    An optical system of continuously variable focal length, the focal plane remaining in a fixed position.

  • Zoom:
    To enlarge or reduce, on a continuously variable basis, the size of a televised image primarily by varying lens focal length.