Glossary of Terms
ABERRATION - Any inherent deficiency of a lens or optical system. Aberrations are responsible for imperfections in shape or sharpness of the image.
ActiveX - ActiveX is a standard that enables software components to interact with one another in a networked environment, regardless of the language(s) used to create them. Web browsers may come into contact with ActiveX controls, ActiveX documents, and ActiveX scripts. ActiveX controls are often downloaded and installed automatically as required.
AF (Autofocus) - A system by which the camera lens automatically focuses on a selected part of the subject.
AGC - Automatic Gain Control, an electronic circuit that amplifies the video signal when the strength of the signal falls below a given value.
ALC - Photometric control, measures light intensity. Determines the iris reaction sensitivity. Sensitivity is increased when the potentiometer is turned towards PEAK, and decreased when turned towards AVERAGE.
Angle - The field of view, relative to a standard lens in a 35mm still camera, expressed in degrees, e.g. 30°. For practical purposes, this is the area that a lens can cover, where the angle of view is determined by the focal length of the lens. A wide-angle lens has a short focal length and covers a wider angle of view than standard or telephoto lenses, which have longer focal lengths.
ANGLE OF VIEW - May be expressed in Diagonal, Horizontal, or Vertical. Smaller focal lengths give a wider angle of view.
APERTURE - The opening of the lens that controls the amount of light reaching the surface of the pickup device. The size of the aperture is controlled by the iris adjustment.
APERTURE SCALE - The aperture scale is referred to as an F-number. The international aperture scale is: F1, F1.4, F2, F2.8, F4, F4.6, F8, F11, F16, etc.
ARP(Address Resolution Protocol) - This protocol is used to associate an IP address to a hardware MAC address. A request is broadcast on the local network to discover the MAC address for an IP address.
ARTPEC (Axis Real Time Picture Encoder) - A chip designed by Axis for image compression. ARTPEC supports a range of CCD and CMOS sensors, built-in functionality for sharpening, backlight compensation, noise reduction and white balance, support for multiple Motion-JPEG streams, support for MPEG-4 part 2, up to 30 frames/second from 4 simultaneous video sources and real-time compression of up to 45 Megapixels/second.
ASIC (Application Specific Integrated Circuit) - A circuit designed for a specific application, as opposed to a general purpose circuit, such as a microprocessor.
Aspect ratio - A ratio of width to height in images. A common aspect ratio used for television screens and computer monitors is 4:3. High-definition television (HDTV) uses an aspect ratio of 9:16.
ASPHERICAL LENS - A lens one or more of whose elements has a non-spherical surface. Aspherical surfaces are shaped to reduce the spherical and other aberrations.
AUTO-IRIS LENS - A lens with an electronically controlled iris. This allows the lens to maintain one light level throughout varying light conditions.
BACK FOCUS - A term used to describe the relationship of the distance of the lens to the image device. This distance is critical to maintaining the proper depth of field through changing focal lengths and varying light conditions. The correct back focus is normally achieved by adjusting the image pick-up device on the camera itself.
Bitmap - A bitmap is a data file representing a rectangular grid of pixels. It defines a display space and color for each pixel (or “bit”) in the display space. This type of image is known as a “raster graphic.” GIF’s and JPEG’s are examples of image file types that contain bitmaps.
Because a bitmap uses this fixed raster method, it cannot easily be rescaled without losing definition. Conversely, a vector graphic image uses geometrical shapes to represent the image, and can thus be quickly rescaled.
Bit rate - The bit rate (in kbit/s or Mbit/s) is often referred to as speed, but actually defines the number of bits/time unit and not distance/time unit.
BLC - Back light compensation. A function of the camera that compensates for excessive light directed at the camera, which causes the video to bloom or the images in front of the light to be unusable.
Bluetooth - Bluetooth is an open standard for wireless transmission of voice and data between mobile devices (PCs, handheld computers, telephones and printers).
Bonjour - Also known as zero-configuration networking, Bonjour enables automatic discovery of computers, devices, and services on IP networks. Bonjour allows devices to automatically discover each other without the need to enter IP addresses or configure DNS servers. Bonjour is developed by Apple Computer Inc.
BOOTP (Bootstrap Protocol) - A protocol that can automatically configure a network device (give it an IP address).
Broadband - In network engineering terms, this describes transmission methods where two or more signals share the same carrier. In more popular terminology, broadband is taken to mean high-speed data transmission.
CAMERA FORMAT - The approximate size of a camera image pickup device. This measurement is derived from the diagonal line of a chip or the diameter of the tube. Currently there are five format sizes in the CCTV industry: 1", 2/3", ?", 1/3" and, ?"
C-MOUNT - An industry standard for mounting a lens to a camera where a 1? x 32 thread is employed and the distance from the image plane is 17.52mm from the shoulder of the lens. A C-mount lens may be used CS-mount camera with the use of a 5mm-adapter ring.
CCD (Charged Coupled Device) - This light-sensitive image device used in many digital cameras is a large integrated circuit that contains hundreds of thousands of photo-sites (pixels) that convert light energy into electronic signals. Its size is measured diagonally and can be 1/4", 1/3", 1/2" or 2/3".
CGI (Common Gateway Interface) - A specification for communication between a web server and other (CGI) programs. For example, a HTML page that contains a form might use a CGI program to process the form data once it is submitted.
CIF (Common Intermediate Format) - CIF refers to the analog video resolutions 352x288 pixels (PAL) and 352x240 pixels (NTSC). See also Resolution.
Client/server - Client/server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the server, which fulfils the request. Typically, multiple client programs share the services of a common server program. A web browser is a client program that requests services (the sending of web pages or files) from a web server.
CMOS (Complementary Metal Oxide Semiconductor) - A CMOS is a widely used type of semiconductor that uses both negative and positive circuits. Since only one of the circuit types is on at any given time, CMOS chips require less power than chips using just one type of transistor. CMOS image sensors also allow processing circuits to be included on the same chip, an advantage not possible with CCD sensors, which are also much more expensive to produce.
Coaxial cable - Coaxial cable is the standard means of transmitting analog video in a CCTV system. Coaxial is also used by cable companies to distribute television in residential buildings.
Codec - In communications engineering, a codec is usually a coder/decoder. Codecs are used in integrated circuits or chips that convert e.g. analog video and audio signals into a digital format for transmission. The codec also converts received digital signals back into analog format. A codec uses analog-to-digital conversion and digital-to-analog conversion in the same chip.
Codec can also mean compression/decompression, in which case it is generally taken to mean an algorithm or computer program for reducing the size of large files and programs.
Composite video - A type of video signal in which the red, blue and green signals (sometimes audio signals too) are mixed together.
Compression - See Image Compression.
Contrast - Defines the degree of difference between the lightest and darkest parts of an image or video stream.
Control unit - If a CCTV system has more than one camera, there must be a way to control the video signals going to recorders and monitors. There are three basic types of Video Control Unit: Multiplexer, Switch and Quad.
CS-MOUNT - A relatively new industry standard for mounting a lens to a camera where a 1" X 32 thread is employed and the distance from the image plane from the shoulder of the lens is 12.52mm. A CS-mount lens may NOT be used on a C-mount camera.
DC TYPE AUTO-IRIS - Auto-iris lenses where the iris is controlled by the circuitry of the camera.
DC-Iris - This special type of iris is electrically controlled by the camera, to automatically regulate the amount of light allowed to enter.
Decoder - See video decoder.
De-interlacing - See interlacing.
DEPTH OF FIELD - The regions in front of and behind the focused distance where the image remains in focus. With a greater the depth of field, more of the scene near to far is in focus. Lens aperture and scene lighting will greatly influence the D.O.F.
DHCP (Dynamic Host Configuration Protocol) - DHCP is a protocol that lets network administrators automate and centrally manage the assignment of Internet Protocol (IP) addresses to network devices in a network.
DHCP uses the concept of a "lease" or amount of time that a given IP address will be valid for a computer. The lease time can vary, depending on how long a user is likely to require the network connection at a particular location.
DHCP also supports static addresses for e.g. computers running web servers, which need a permanent IP address.
DNS (Domain Name System) - DNS is used to locate and translate Internet domain names into IP (Internet Protocol) addresses. A domain name is a meaningful and easy-to-remember name for an Internet address. For example the domain name www.example.com is much easier to remember than 188.8.131.52. The translation tables for domain names are contained in Domain name servers.
Domain server - Domains can also be used by organizations that wish to centralize the management of their (Windows) computers. Each user within a domain has an account that usually allows them to log in to and use any computer in the domain, although restrictions may also apply. The domain server is the server that authenticates the users on the network.
EXTENSION TUBES - Various size spacers used between the camera and lens to reduce the Minimum Object Distance. Not recommended for use with zoom lenses due to the loss of tracking ability.
ENCODER - See video encoder.
ETHERNET - Ethernet is the most widely installed local area network technology. An Ethernet LAN typically uses special grades of twisted pair wires. The most commonly installed Ethernet systems are 10BASE-T and 100BASE-T10, which provide transmission speeds up to 10 Mbps and 100 Mbps respectively.
ETRAX (Ethernet Token Ring AXIS) - The ETRAX chip is the cornerstone of Axis technology and the 'brain' in nearly all Axis products. A multipurpose Linux chip with integrated Ethernet networking and extremely flexible I/O options.
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.
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.
Factory default settings - These are the settings that originally applied for a device when it was first delivered from the factory. If it should become necessary to reset a device to its factory default settings, this will, for many devices, completely reset any settings that were changed by the user.
FIELD OF VIEW - The horizontal or vertical scene size at a given length from the camera to the subject.
FIREWALL - A firewall works as a barrier between networks, e.g. between a Local Area Network and the Internet. The firewall ensures that only authorized users are allowed to access the one network from the other. A firewall can be software running on a computer, or it can be a standalone hardware device.
Fixed iris - See Autoiris.
FOCAL LENGTH - The distance from the center of the lens to a plane at which point a sharp image of an object viewed at an infinite position. The focal length determines the size of the image and angle of FOV seen by the camera through the lens. This is the center of the lens to the image pickup device.
FTP (File Transfer Protocol) - FTP is an application protocol that uses the TCP/IP protocols, used to exchange files between computers/devices on networks.
FRAME - A frame is a complete video image. In the 2:1 interlaced scanning format of the
Frame rate - The frame rate used to describe the frequency at which a video stream is updated is measured in frames per second (fps). A higher frame rate is advantageous when there is movement in the video stream, as it maintains image quality throughout.
Full-duplex - Transmission of data in two directions simultaneously. In an audio system this would describe e.g. a telephone system. Half-duplex also provides bi-directional communication, but only in one direction at a time, as in a walkie-talkie system. See also Simplex.
HUNTING - An industry term used to describe a auto-iris lenses inability to stabilize under certain light conditions.
LENS FORMAT - The approximate size of a lens projected image. In most cases the lens will project a 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 a 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.
LEVEL CONTROL - Used to set the auto-iris circuit to a video level desired by the user. Turning the level potentiometer towards the HIGH position will open the iris allowing more light to pass through the lens, towards the LOW will close the iris allowing less light to pass through the lens.
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.
MINIMUM OBJECT DISTANCE (M.O.D.) - The closest distance a given lens will be able to focus upon a object. Generally the smaller the focal length the shorter the M.O.D. This distance can be altered with use of extension tubes.
PINHOLE LENS - Lenses used primarily in covert applications where the camera/lens must remain out of sight.
PRE-POSITION LENSES - Pre-position lenses are specially designed lenses with extra mechanical/electrical components to allow for computer interfacing. This function allows the lens (when used with the appropriate controller) to feedback to the controller information relevant to zoom and focus propositioning allowing the controller to quickly scan to a pre-selected scene, arriving in focus at the proper zoom point without operator intervention.
SPOT FILTER - A neutral density filter paced 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.
TELEPHOTO - Telephoto is a term used to describe lenses that have a high focal number causing the reproduced image to appear larger than human eye reproduction.
VARI-FOCAL - A low cost version of a zoom lens designed to meet installers needs for versatility. This lens does not have the ability to track from wide to telephoto.
ZOOM LENS - A lens with the ability to change its focal length manually or through the use of a controller to cover a variety of needs.
ZOOM RATIO - The ratio of the starting focal length (wide) to the ending focal length (telephoto) of a zoom lens. A 10X zoom will magnify the image at the wide end by 10 times. Examples of a 10X zoom lenses; 8mm~80mm, 12mm~120mm.