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. 

Alarm Input
Some DVRs and security cameras have alarm inputs, which can accept input from a sensor device such as a door contact or a passive infra-red motion detection which trigger the camera or DVR to take some action such as to begin recording.

Aperature - The opening of the CCTV lens.  The size of which is controlled by the iris and is measured in F numbers. Generally, the lower the F number, the larger the aperture is and consequently more light can pass through the lens.

Audio/Video Interleave (AVI) 
An AVI file is a sound and motion picture file that conforms to the Microsoft Windows Resource Interchange File Format (RIFF) specification. AVI files (which end with an .avi extension) require a special player that may be included with your web browser.

Auto Balance 
A system for detecting errors in colour 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 Iris
Security cameras with auto iris, have the ability to compensate for large variations in light levels. This is useful for security cameras that need to adjust for changes from bright sunlight to darkness or night. Auto iris circuitry is normally linked to a motorized drive that opens and shuts the iris on the camera lens. Closing a physical iris is a much better way to protect a camera from being damaged by bright sunlight then simply using electronics to reduce the signal strength.

Back Light Compensation (BLC)
This is a feature of security cameras that automatically adjusts the image to compensate for bright light to give more detail on the darker areas of the image. For example, use is to focus on the detail of a face of a person that has the sunlight shining from behind.

A Video Balun enables the transmission of video using unshielded twisted pair wire instead of coaxial cable. The word "balun" comes from combining the terms balanced and unbalanced. The function of a balun is to transform an unbalanced signal into a balanced signal. When video signal is transmitted through coaxial cable, the distance traveled by the signal is limited because the signal is in the form of an unbalanced signal that is susceptible to Radio Frequency Interference or noise. Coax cable incorporates special shielding to minimize noise. Video Baluns transform the video signal into a balanced form in which each wire in the twisted pair transmits an identical signal with opposite polarized magnetic fields. Noise affects each signal equally. When the signals are combined, the noise is cancelled out. By using a designed balun, an unshielded twisted pair wire can transmit video for much longer distances than coax cable and with a lower cable cost.

BNC Connector
BNC is a connector for coaxial cable that is most commonly used for CCTV installations.

CCD Charge Coupled Device
Charge Coupled Device, CCD, is one of the two main types of image sensors used in security cameras. When a video is recorded, the CCD is struck by light coming through the camera's lens. Each of the thousands or millions of tiny pixels that make up the CCD converts this light into electrons. The number of electrons, usually described as the pixel's accumulated charge, is measured, and then converted to a digital value. This last step occurs outside the CCD, in a camera component called an analog-to-digital converter.

C Mount Lens & CS Mount Lens
There are two main types of lenses used in security cameras. The C mount lens has a flange back distance of 17.5mm. The CS mount lens has a flange back distance of 12.5mm. C mount lenses therefore have a longer focal distance. CS mount became widely used, because it its more practical for many of today's more compact cameras. Lenses are often supplied with a 5mm spacer ring (sometimes called a C ring) that allows a C mount lens to be used on a CS camera. Most modern security cameras are CS.

Co-Axial Cable
A type of cable typically used in cctv installations that has a central conductor, surrounded by a shield sharing the same axis. The shield can be made from a variety of materials including, braided copper, or lapped foil. There are various standards for specific types of co-axial cable. The cable used for normal CCTV installations is called RG59.

Composite Video
The encoded output of a surveillance camera whereby the red, green, and blue video signals are combined with the synchronizing, blanking, and color burst signals and are transmitted simultaneously down one cable.

Complementary Metal Oxide Semiconductor. Similar to a CCD, it also detects light for conversion into a signal. Lesser image clarity than CCD, but more compact in size with lower power usage.

Digital video pictures can be compressed with a number of techniques. These include: JPEG and JPEG-2000 (for still images), M-JPEG and MPEG (for moving pictures).

DVR (Digital Video Recorder)
A Digital Video Recorder is a generic term for a device that is similar to a VCR but records television data in digital on a hard drive as opposed to a VCR tape. A DVR looks like a VCR and has all of the same functionality of VCR (recording, playback, fast forwarding, rewinding, and pausing) plus the ability to skip to any part of the program without having to rewind or fast forward the data stream.

Dwell Time Programming
The length of time a switcher or CCTV multiplexer displays one camera before sequencing to the next. Multiplexers with dwell time programming capability allow you control this length of time.

Focal Length
The distance between the center of a lens, or its secondary principal point and the imaging sensor. Lower lengths give a greater field of view and less magnification. Longer lengths give a narrower field of view and greater magnification. The table below gives an approximate value for the angle of the field of view for lenses of various focal lengths and also considering the size of the imaging device (CCD). Most CCTV cameras have one of the 3 sizes of imaging devices listed below, 1/4", 1/3" or 1/2". Almost all of CCTV Camera Pros cameras have 1/3" Sony CCD imaging devices.

Focal Length

Imaging Device Size

1/4" 1/3" 1/2"
2.8 mm 64˚ 80˚ 97˚
4.0 mm 45˚ 60˚ 74˚
6.0 mm 30˚ 38˚ 57˚
8.0 mm 23˚ 30˚ 40˚
12.0 mm 15˚ 20˚ 30˚
16.0 mm 11˚ 15˚ 22˚
50.0 mm

An increase in voltage or power, usually expressed in dB.   A piece of hardware that acts as the ‘gate’ between a LAN and the internet. The Gateway address is simply the IP address of the Gateway.

General Packet Radio Service (GPRS)  
Part of the GSM standard that delivers "always-on" wireless packet data services to GSM customers. GPRS can provide packet data speeds of up to 115 kb/s.

A spurious image resulting from an echo.

Gigabyte (GB) 
This unit is typically used to measure large data storage or data transfer capacities (by current standards). 1GB = 1024 MB = 1,048,576 KB = 1,073,741,824 bytes.

Gray Scale 
Variations in value from white, through shades of gray, to black on a television screen. The gradations approximate the tonal values of the original image picked up by the TV camera.

Gamma Correction
Gamma correction controls and adjusts the overall brightness of an image for consistency.

A quality brand of DVR Cards made for Windows based computers.

H.264 Compression 
It is generated from MPEG-4, but more advanced for video compression. It has more complex coding algorithm, lower usage of bandwidth and smaller royal fee than MPEG4. It works well on a very wide variety of applications, networks and systems (e.g., for broadcast, DVD storage, and multimedia telephony systems). 

Hard Disk Drive (HDD) 
The storage device usually fixed inside of your computer or DVR used to store information.

High Speed Circuit Switched Data (HSCSD) 
A GSM transmission standard that allows data to be transferred at up to 28.8kbps

Image Intensifier 
A device coupled by fiber optics to a TV image pickup sensor to increase sensitivity. Can be single or multi stage.

The total opposition offered by a device to the flow of an alternating current. Measured in Ohms.

Incident Light 
The light that falls directly on an object.

Infra Red Camera 
Infrared cameras (night vision cameras) have special infrared lights installed around the perimeter of the camera lens. This provides special light that the camera uses to capture a good picture even in total darkness.

Insertion Loss 
The signal strength loss when a piece of equipment is inserted into a line.

Extraneous energy which tends to interfere with the reception of the desired signals.

Internal Sync
Devices with internal sync have an internal crystal to provide sync pulses without needing reference from any external device.

Integrated Services Digital Network (ISDN) 
Digital telephony scheme that allows a user to connect to the Internet over standard phone lines at speeds higher than a 56K modem allows. Capable of speeds from 57.6 K to 128 K.

An adjustable aperture built into a camera lens to permit control of the amount of light passing through the lens.

IP (Internet Protocol) 
The TCP/IP standard protocol that defines the IP datagram as the unit of information passed across an Internet and provides the basis for connectionless packet delivery service. 

IP Address 
The numeric address of a computer on the Internet. An IP address is written as a set of four numbers separated by periods (each number can range from 0 to 255). An example of an IP address is 

IP Waterproof Rating
IP waterproof ratings are a BSi standard measurement for how waterproof something is. Many security cameras or camera housings are designed for outdoor use need to be waterproof. The IP rating number has two digits, and optional letters after them. E.G IP66 and IP68. The first number defines the protection against ingress of foreign objects. 0 is the lowest rating and means non-protected. 6 is the highest rating and means dust tight and protects against access with a wire. The second number defines the level of protection against ingress of water. 0 is the lowest rating means non-protected. 8 is the higest rating and means protects against continuous immersion in water.

JPEG is a standard for the encoding and compression of images. JPEG is used in the video surveillance systems to compress and store individual frames of video. JPEG was developed by the Joint Photographic Experts Group.

JPEG2000  JPEG2000 is image coding system and the successor of the JPEG format. Its architecture lends itself to a wide range of uses from portable digital cameras to advanced pre-press, medical imaging and other key sectors. Compared to JPEG, JPEG2000 offers higher compression without compromising quality, progressive image reconstruction. 

LAN (Local Area Network) 
A communications system that links computers into a network, usually via a wiring based cabling scheme. LANs connect PCs, workstations and servers together to allow users to communicate and share resources like hard disk storage and printers. Devices linked by a LAN may be on the same floor or within a building or campus. It is user-owned and does not run over leased lines, though a LAN may have gateways to the PSTN or other, private, networks.

Light Emitting Device  is a type of light source which generates an infrared frequency when stimulated by electricity. 

Liquid Crystal Display. Liquid crystal displays (LCDs) offer several advantages over
traditional cathode-ray tube displays that make them ideal for several applications. LCD’s are flat, and they use only a fraction of the power required by CRTs. They are easier to read and more pleasant to work with for long periods of time than most ordinary video monitors. There are several tradeoffs as well, such as limited view angle, brightness, and contrast, not to mention high manufacturing cost.

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.

Lens Preset Positioning 
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 pre-selected scene and arrive in focus at the proper focal length automatically.

Lens Speed 
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.

Line Amplifier
An amplifier for audio or video signals that feeds a transmission line; also called program amplifier.

Loop Through 
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.

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).

Unit of light illuminance used as a measure of low-light recording capacity in security cameras. Cameras with a Lux rating of 0.2 Lux or less would be considered low-light cameras. It is not possible to get good color definition in low light levels, so in general low light cameras are always black and white. Day/night cameras use electronics to switch from color during the daytime, to black/white during night or low light conditions. Many low light cameras also use infrared, which is useful in zero light conditions. The lower the LUX rating of a camera, the better it will see in low light.

Megabits Per Second (MBPS) 
A measurement of the transmission speed of data measured in 1,048,576 bits per second.

Motion Joint Photographic Experts Group (MJPEG) 
This compression standard generally refers to JPEG images shown at high frame rate, generally 25 frames per second. It gives high quality video images, but the comparatively large file sizes of each individual image does put demands on the transmission bandwidth. 

Modem (Modulate/Demodulate) 
D device for the transmission of data via dial-up networking.

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.

Monochrome Signal 
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.

Monochrome Transmission 
The transmission of a signal wave which represents the brightness values in the picture, but not the color (chrominance) values.

MPEG-4 is a graphics and video compression algorithm. It is further development of the MPEG-2. MPEG-4 resolves the picture more effectively and can thus compress sequence quicker and maybe smaller. Now, it is popularly used for Internet transmitting.

The Motion Picture Experts Group(MPEG) released MPEG-4 encoding in 1998. The basic idea behind MPEG is that compressed images are compared before being transmitted over the network. The first compressed image is used as a reference and compared to the images that follow it in the video sequence. The first image is transmitted over the network along with the parts of the following images that differ from the initial reference image. The viewing application on the receiving end of the transmission then reconstructs all images based on this information and displays the result. This is a simplified description of how MPEG-4 works.

This is a device that takes inputs from 2 or more video channels and combines them into one signal. This is often done by using time division multiplexing, which interleaves frames from each channel in such a way that they can be split out again. Frequency division multiplexing uses different frequencies to achieve the separation of the signals.

Network Camera
This refers to a camera that is designed to record pictures and transmit them directly over a computer network or internet connection. Network cameras normally do not have any analogue video outputs. The images are encoded directly in one of the standard compression techniques, such as JPEG or MPEG.

Night Vision 
Cameras that have night vision have the ability to see in low light conditions. To judge how dark it can be for your camera to work, look at the Lux rating on the camera. The lower the lux, the better it will see at night.

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`.

Non-Composite Video 
A video signal containing all information except sync.

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.

NTSC is an abbreviation for the National Television Standards Committee. The term "NTSC video" refers to the video standard defined by the committee, which has a specifically limited color gamut, is interlaced, and is approximately 720 x 480 pixels, and 30 frames per second (fps). This standard is used in North America.

OSD (On Screen Display)
A method of displaying set-up information and/or instructions on a display monitor.

The signal level at the output of an amplifier or other device

PAL is an abbreviation for Phase Alternating Line. This is the television display standard that is used mainly in Europe, China, Malaysia, Australia, New Zealand, the Middle East, parts of Africa, and other parts of the world. PAL uses 625 lines per frame and a frame rate of 25 frames per second.

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.

PCI Video Card 
A PC card that allows video from analogue cameras to be fed into a computer.

PIR  Passive Infrared.
Widely used in devices to detect motion. A special lens on the front of the PIR divides the sensor into zones. A individuals body heat radiation is detected as it moves through the sensor zones in front of the PIR

Pinhole Lens
This is a type of lens with a very small aperture. Normally used for covert applications, where it can easily hide behind or within another object.

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. Monitor resolution is measured in pixels. CCTV pictures of 640 x 480 pixels (full screen) and 320 x 240 (quad screen) are most common.

Port Re-direction 
This refers to pointing a port of a modem/router to an IP address where a PC or networked DVR can be found for viewing cameras over the internet.

When data is being transmitted between two or more devices something needs to govern the controls that keep this data intact. A protocol is a formal description of message formats and the rules two computers must follow to exchange those messages.

Proxy Server 
A server that acts as an intermediary between a user's computer and the computer they want to access. If a user makes a request for a resource from computer "A," this request is directed to the proxy server, which makes the request, gets the response from computer "A," and then forwards the response to the client. Proxy servers are useful for accessing World Wide Web resources from inside a firewall.

Quad Processor 
Is a device which uses digital video to display pictures from 4 cameras on a single monitor. 

A device that forwards data packets along networks. Typically when referred to in CCTV installations, a router is used to connect a surveillance DVR and a computer to a single internet connection. A router can also be used to connect multiple IP based security cameras to a single internet connection.

A type of telephone connector. Standard in the US.

A standard network connector, often found at the end of CAT-5 cable.

Real time video 
Is a picture with more than 24 frames per sec and therefore looks continuous

Resolution (horizontal) 
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.

Resolution, Limiting 
The details that can be distinguished on the television screen. Vertical resolution refers to the number of horizontal black and white lines that can be resolved in the picture height. Horizontal resolution refers to the black and white lines resolved in a dimension equal to the vertical height and may be limited by the video amplifier bandwidth.

Resolution (vertical) 
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. 

Retained Image 
Also called image burn. A change produced in or on the target which remains for a large number of frames after the removal of a previously stationary light image and which yields a spurious electrical signal corresponding to that light image.

is a measure of picture definition and clarity and is represented by number of lines. Greater the number of lines, higher the resolution. 

is a type of coaxial cable used for transmission of video signals up to 230m. It is the most popular cable used in CCTV.

RF (Radio Frequency) 
A frequency at which coherent electromagnetic radiation of energy is useful for communication purposes. Also, the entire range of such frequencies.

A loss of vertical synchronization which causes the picture to move up or down on a receiver or monitor.

RS-232 is a communications standard for serial communications between devices. In CCTV, this can be communication between a contoller and a surveillance camera. The RS-232 standard allows for the connection of two devices through a serial link, and is the protocal used for serial connections in computers. RS-485 allows for serial connections between more than 2 devices on a networked system and is defined below.

RS485, also referred to as EIA-485 is a communications standard for serial communication between devices. When talking about surveillance systems, RS-485 is typically used as the protocal to allow computers and remote controllers to control the activity of cameras such as pan, tilt, rotate, and zoom operations. RS485 is an updated version of the original serial protocol, RS-232.

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.

The process of moving the electron beam of a pickup tube or a picture tube across the target or screen area of a tube. Sensitivity - In television, a factor expressing the incident illumination upon a specified scene required to produce a specified picture signal at the output terminals of a television camera.

Standard European 20 pin connector used for carrying both video and audio signals in domestic TV appliances, now utilised on some CCTV equipment

Serial Port 
Also known as a communications port or COM port. The serial port is a location for sending and receiving serial data transmissions. These ports are known by the names COM1, COM2, COM3, and COM4.

Ability to control the integration (of light) time to the sensor to less than 1/60 second; eg. stop motion of moving traffic.

Signal to Noise Ratio (S/N Ratio)
This is the ratio between the signal strength and the noise levels on an audio or video signal.

A transient of short duration, comprising part of a pulse, during which the amplitude considerably exceeds the average amplitude of the pulse.

Static IP address 
An IP address which is the same every time you log on to the Internet. The alternative to a dynamic IP address. Often standard for business broadband but not for domestic broadband.

Subnet Mask 
A numeric designation, with the same format as an IP address, which determines how much of an IP address is used to partition a network using TCP/IP into smaller entities called subnets. 

Television Lines (TVL)
This is a measure of the resolution of a video device. The higher the number, the higher the resolution is. 380 TVL is considered medium resolution. 480 TVL or greater is considered high resolution.

Test Pattern 
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.

Time/date generator 
Is a device which generates time and a date superimposes it on the video signal.

Time Lapse VCR 
A video recorder, most often in the VHS format,that can slow down the recording process and create a time lapse between recorded frames. This increases the amount of recording time on an individual tape. Unlike a standard VCR which has a maximum recoding time of 8 hours, time lapse recorders can record from 2 to 960 hours on a standard VHS tape. Recording speeds available on some Time Lapse VCR.

Transmission Control Protocol/ Internet Protocol (TCP/IP) 
The protocols, or conventions, that computers use to communicate over the Internet.

TV Line Resolution 
The number of distinct horizontal lines, alternately black and white, which can theoretically be seen in a picture. Allows a buyer to judge the quality of any camera. Low resolution is between 300 and 380, medium resolution is between 400 and 480, high resolution is 480 plus. 

Universal Serial Bus (USB)  A standard port that enables you to easily connect external devices (such as digital cameras, scanners, and mice) to a PC.
Upstream  The uploading of data from your PC to the Internet. ADSL has both upstream and downstream data rates.

Varifocal (Zoom)
This refers to a type of lens that has the capability to change the focal length. This allows adjustment of the magnification and field of view of the security camera.

Varifocal lens 
is a type of manual zoom lens with a small zoom ratio (ranging between 4mm to 12mm depending on brand). It is used when the focal length of the lens needs to be fine tuned to meet the requirements of the actual scene.

VCR Activator 
A unit, when used with a PIR camera, will automatically instruct your domestic video to record. After motion has stopped, the VCR Activator will stop your video recording.

Vertical Resolution (TVL) 
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 Capture Card 
Computer cards that you can install on the motherboard of your own computer to create your own video recording computer.

Video Graphics Array (VGA) 
The display standard for PC monitors. VGA outputs are compatible with PC monitors.

Video Motion Detection (VMD) 
A method for detecting motion in a video image by checking to see if the pixels in the video image have changed.

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.

Video Server 
A video server compresses video signal from analogue cameras to allow them to be viewed over a network such as a LAN or the internet.

A mathematical codec useful in image compression. In the Internet, wavelet has been used to compress images to a greater extent than is generally possible with other methods such as JPEG or MPEG.

WDR Security Cameras
A WDR security camera (Wide Dynamic Range) is used for capturing clear images of objects surrounded by a strong back light, while still keeping the background visible.

Web Server 
A DVR or Software system with a built-in web server allows you to view cameras over an internet browser.

Wireless Camera 
Wireless cameras allow the transmission of video and audio data to be transmitted to the receiver without having to run wires (using radio waves). Wireless cameras often have an option to power the camera via mains in which case there will be a lead from camera to power point.

Wired camera 
A camera that transmits its signal via cable back to the recording/control device. Some wired cameras use composite cable (taking both the video and power signal) whilst some have separate power and video cables.

Y Signal 
A signal transmitted in color television containing brightness information. This signal produces a black and white picture on a standard monochrome receiver. In a color picture it supplies fine detail and brightness information.

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

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

Zoom Ratio 
A lens with variable elements giving adjustable magnification and differing fields of view in one, i.e. 12:1.



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