| .jpeg | In computing, JPEG (pronounced JAY-peg) is a commonly used method of compression for photographic images. The name JPEG stands for Joint Photographic Experts Group, the name of the committee that created the standard.
The JPEG standard specifies both the codec, which defines how an image is compressed into a stream of bytes and decompressed back into an image, and the file format used to contain that stream. The compression method is usually lossy compression, meaning that some visual quality is lost in the process, although there are variations on the standard baseline JPEG that are lossless. There is also an interlaced "Progessive JPEG" format, in which data is compressed in multiple passes of progressively higher detail. This is ideal for large images that will be displayed whilst downloading over a slow connection, allowing a reasonable preview after receiving only a portion of the data. However, progressive JPEGs are not as widely supported. |
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| Ampere (amp) | The unit of measure for the rate of electrical current flow characterized by the symbols l(in Ohm's law formulas) and A. One ampere is the current flowing through one ohm of resistance at one volt potential. |
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| Analog backlight compensation (BLC) | Automatically adjusts picture brightness depending on lighting conditions. This helps overcome strong backlighting which normally results in silhouettes or shadows. |
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| Annunciator | An audible and visual signaling device. |
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| Aperture | The lens opening that controls the amount of light that reaches the image sensor. |
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| Aspheric: | A type of lens in which the spherical surface has been slightly altered to reduce spherical aberration. This type of lens generally allows wide angle viewing with relatively low distortion. |
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| Auto tracing white balance (ATW) | Automatically adjusts the white balance in response to varying light conditions. |
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| Automatic gain control (AGC) | Amplifies existing video to help camera create an enhanced video signal at low light levels. |
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| Automatic iris | A device in the lens that self-adjusts to light level changes. The iris opens or closes to control the amount of light passing through the lens. |
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| AWG | American Wire Guage is the measurement of the metal part of the wire diameter. The AWG number is inversely related to size, meaning as the number gets larger the size gets smaller and visa-versa. |
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| Back focus | The distance from the final glass surface of a lens to the focused image. |
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| Backlight Compensation | A feature that compensates for bright backgrounds so foreground objects aren't silhouetted. |
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| BNC Connector | A type of connector used for industrial and broadcast video or audio signals. Has a locking bayonet post that twist locks into position to prevent accidental removal. |
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| C mount | Type of camera mount which measures 17.5mm from the camera's CCD to the rear mounting surface of the lens. |
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| CCD | Charged Coupled Device. A sensor that collects light and turns it into an electrical signal. |
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| Coaxial Cable | A single wire centered inside a shield, separated by a insulated material and covered by an insulating jacket. |
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| Compression (in video storage) | The removal of redundant information to minimize storage requirements. |
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| Conductor | Material with the ability to carry electric current. The term is also used for an electirc wire. |
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| Covert surveillance | Using hidden cameras to observe a scene without being seen. |
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| CS mount | Type of camera mount which measures 12.5mm from the camera's CCD to the rear mounting surface of the lens. CS mount lenses can be used with C mount cameras by adding a 5mm spacer. |
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| Digital Recording | Technology that enables images from a camera to be stored on a hard drive. A digital recorder provides clearer images that video tape and faster access to them. |
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| Digital Signal Processing (DSP) | Conversion of the analog signal from a CCD image sensor into a digital signal through an analog to digital converter. This enables many digital features such as backlight compensation or sensitivity up. |
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| Distribution Amplifier | A DA or distribution amplifier boosts an incoming video and/or audio signal and sends the signal to several other video and/or audio signals simultaneously. |
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| Door Status Switch | A DSS is a switch used to monitor whether a door is in an opened or closed position. |
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| Duplex multiplexer | Type of multiplexer that allows playback or live viewing while images are simultaneously being recorded. |
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| Electronic Shutter | A camera feature that compensates for changes in light conditions, from bright sunlight to dim outdoor lighting. |
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| Fiber Optics | A medium using light for transmitting either an analog or digital signal. The signal loss is lower than that of coax cables and has a higher immunity to electromagnetic and static interference. |
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| Field of View | The image area produced by any camera and lens combination. |
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| Flickerless | Flicker:
The result of the differences between the frequencies (60Hz) of the ionization of the gas in a fluorescent light fixture with that of the vertical frequency (59.94Hz) in a color camera. The difference is very small, but the result is a slight flicker at the top of the monitor scene or, to a digital circuit, it would appear as movement. Flickerless:
A flickerless mode of operation of a camera eliminates flicker (see above definition), and therefore potential "movement" detected by a camera or DVR. |
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| Focal length | The distance from the center of a lens to a point where it focuses light. The combination of the focal length and the CCD format determines a camera's field of view. The shorter the focal length, the wider the field of view. |
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| Genlocking | An electronic synchronization of two or more video signals to the same timing and color phase so they can be mixed and or switched through appropriate other equipment. |
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| Ground Loop | An interference in the video signal that shows up as a vertical crawling of the picture or an oscillating hum in the audio. |
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| JPEG/MPEG | Both the Joint Photographic Experts Group and the Motion Picture Experts Group represent standards for the storage and retrieval of compressed video and still pictures. |
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| Lock Status Sensor (LSS) | Relay type to operate the LED wth an SPDT switch to indicate low voltage and tampering of the lock face locally or to a remote monitoring location. |
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| Looping | The chaining of video equipment so the signal can be looped through to several pieces of equipment. |
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| Lux | A unit measuring the intensity of light. The light of a full moon is about 0.1 lux, while bright sunlight is about 100,00 lux. |
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| Manual iris lens | A lens with a manual adjustment to set the iris opening (F-stop) to a given position. Generally used for relatively constant lighting applications. |
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| Matrix Switcher | Routes multiple audio/video signals to multiple outputs allowing you to have the ability to switch from any input signal to any output signal whenever needed. |
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| Monochrome | Black and white. |
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| Noise | Random spurts of interference. |
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| NTSC | Standard of broadcasting color television in the US and Japan formulated by the National Television Standards Committee. |
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| Passive | A non powered element of a system. |
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| PIR | Passive Infrared. A motion detector that senses body heat to detect motion. |
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| Plenum | An open space or air duct above a drop ceiling that is part of the air distribution system. Plenum rated cables have an approved fire code rating so it can be used in CL2P installations. |
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| Regulated Power Supply | A power supply provides a constant output regardless of voltage variations. |
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| Relay | An electrically controlled device that opens and closes electrical contacts to effect the operation of other devices in the same or another electrical circuit. |
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| Resolution | A measure of the ability of a camera, recorder or monitor to reproduce detail. The bandwidth of the video signal relating to the amount of detail that determines the overall quality of the picture. |
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| Roll | A loss of vertical sync which causes the picture to move up or down on the monitor. |
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| RS-232/RS-422 | A serial control standard that allows the linking of two pieces of hardware, using software from the computer, so that the equipment can communicate with one another. |
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| S-Video | A video signal where the luminance and chrominance are separated from one another when the signal is processed so they can be processed more effectively. |
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| S/N (Signal to noise) Ratio | Measured in Decibels, this is the ratio between a useful video signal and unwanted noise. The higher the value the better. |
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| Serial Port | The computer input/output (I.O.) which is RS-232 based and allows communication in both directions between the computer and the other component. |
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| Shield | A covering put between cables to prevent interference caused by signal leakage. |
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| Simplex multiplexer | Type of multiplexer that allows either playback, live viewing or recording at any one given time. |
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| Spot filter | A supplement to the iris which allows very sensitive cameras to view bright scenes easily. The iris of a lens without a spot filter would not be able to close down enough in bright light without creating an image degradation. |
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| Strike | A plate motised into or mounted on the the door jamb to accept and restrain bolt when the door is closed. In some metal installations of deadlock, the strike may simply be an opening into the jamb. (Synonym: keeper) |
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| Switcher | A device that routes video and or audio signals to different sources. |
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| Synchronization | Allows roll-free switching from camera to camera in multi-camera installations. An important part of the video signal that keeps the picture stable so it is watchable on the display device. |
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| Transformer | An electric device that changes voltage in direct proportion to currents and in inverse proportion to the ratio of the number of turns of primary and secondary windings. The input side of transformer is the primary side. The output low-voltage side is called the transformer secondary. |
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| Twisted Pair | A cable composed of two small, insulated conductors twisted together. Since both wires have nearly equal exposure to any interference, unwanted noise is substantially reduced. |
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| Varifocal lens | Contains several movable elements to permit manual adjustment of the effective focal length. This type of lens allows you to adjust the size of your field of view. |
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| Video Motion Detection | A system that detects motion in the video signal and generates a corresponding alarm. This can be accomplished by some cameras, multiplexers and digital recorders. This feature maximizes recording space by only recording while motion is detected. |
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| Volt/Amp (VA) Rating | The product of rated input voltage multiplied by the rated current. This establishes the apparent energy available to accomplish work. |
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| Voltage Drop | Voltage loss experienced by electric circuits due to two principal factors: (1) wire size and (2) length of wire runs. |
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| Watt | A common unit of electrical power. A watt is dissipated by a resistance of one ohm through which one ampere flows. |
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| White Balance | A process used in video cameras to retain true colors. |
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| Y/C | Luminance and Chrominance. Another term for S-Video where the luminance and chrominance are separate from one another so they can be processed more effectively. |
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