A continuously varying action, or movement that takes time to change from one position to another. Standard audio and video signals are analog. An analog signal has an infinite number of levels between its highest and lowest value. (Not like digital, where changes are by steps.) 

A type of lens or adapter designed to produce a wide-screen image from a condensed image on the film. 

A standard for measuring light output, used for comparing projectors.

The relationship of the horizontal dimension to the vertical dimension of a rectangle. In viewing screens, standard TV is 4:3, or 1.33:1; HDTV is 16:9, or 1.78:1. Sometimes the ':1' is implicit making TV = 1.33 and HDTV = 1.78. 

Named for J. M. E. Baudot, the inventor of the Baudot telegraph code. The number of electrical oscillations per second, called 'baud rate'. Related to, but not the same as transfer rate in bits per second, 'bps'. 

Bayonet Neill-Concelman. A cable connector used extensively in television and named for its inventor. A cylindrical bayonet connector operates with a twist-locking motion. To make the connection, align the two curved grooves in the collar of the male connector with the two projections on the outside of the female collar, push and twist. This allows the connector to lock into place without the need of tools.

Usually refers to the amount or intensity of video light produced on a screen without regard to colour. Sometimes called 'black level'.

In video display, this is a term to describe what happens when an image has been displaying too long, resulting in a permanent image being 'burned in' to the screen phosphor. 

A two-conductor wire in which one conductor completely wraps the other with the two separated by insulation. Constant impedance transmission cable. Example: 75 ohm, type RG-59u cable used for video signals. Abbreviated as 'coax'. 

The colour quality, expressed in degrees Kelvin (K), of a light source. The higher the colour temperature, the bluer the light. The lower the temperature, the redder the light. 

Our colour television system starts with three channels of information; red, green, & blue (RGB). In the process of translating these channels to a single composite video signal they are often first converted to Y, R-Y, and B-Y. Both 3-channel systems, RGB and Y, R-Y, B-Y are component video signals. They are the components that eventually make up the composite video signal. Higher quality program production is possible if the elements are assembled in the component domain. 

An all-in-one video signal comprised of the luma (black and white), chroma (colour), blanking pulses, sync pulses and colour burst. 

The range of light and dark values in a picture, or the ratio between the maximum and the minimum brightness values. Low contrast is shown mainly as shades of grey, while high contrast is shown as blacks and whites with very little grey. It is also the name of a TV monitor adjustment, which increases or decreases the level of contrast of a displayed picture. Also called 'white level'. 

The ratio of the high light output level divided by the low light output level. Ideally, the contrast ratio of the projection system should be at least 300:1. It is important to bear in mind that projectors cannot project black so the blackest black achievable is the base colour of the screen (usually white!)

A connector with rounded corners and angled ends, taking on the shape of the letter 'D'. Commonly used in computers and video, most D connectors have two rows of pins. If they have more than two rows, they are usually called HD (high density) connectors. 

Decibel. The standard unit used to express gain or loss of power. It indicates the logarithmic ratio of output power divided by input power. A power loss of 3dB is an attenuation of half of the original value. The term '3dB down' is used to describe the 'half power point'. In audio work, 0dB is the threshold of hearing. 120dB level is the threshold of pain. A change of 3dB halves or doubles the apparent loudness. 

The fidelity with which a video picture is reproduced. The clearer the picture, the higher the definition. Definition is influenced by resolution. 

A system of data or image values in the form of discrete, non-continuous codes, such as binary. When data is in a digital format, it can be processed, stored (recorded) and reproduced easily while maintaining its original integrity. 

(1) Digital video using separate colour components, such as Y'CbCr or R'G'B'. See CCIR 601. It is sometimes incorrectly referred to as D-1. (2) A digital representation of a component analog signal set, most often Y, B-Y, R-Y. The encoding parameters are specified by ITU-R BT.601-2 (CCIR 601). The parallel interface is specified by ITU-R BT.656 (CCIR 656) and SMPTE 125M. 

(1) Digital video that is essentially the digitised waveform of (M) NTSC or (B, D, G, H, I) PAL video signals, with specific digital values assigned to the sync, blank, and white levels. It is sometimes incorrectly referred to as D-2 or D-3. (2) A digitally encoded video signal, such as NTSC or PAL video, that includes horizontal and vertical synchronizing information. 

Direct Drive Image Light Amplifier. Developed by Hughes-JVC, D-ILA uses digitally addressed ILA ® instead of CRT-addressed as with earlier devices. See ILA. The D-ILA ? is a device based on the Image Light Amplifier or ILA ® developed by Hughes-JVC Technology Corporation. The new D-ILA technology is a reflective liquid crystal modulator where electronic signals are addressed directly to the device. The D-ILA device has an X-Y matrix of pixels configured on a C-MOS single crystal silicon substrate mounted behind the liquid crystal layer using a planar process that is standard in IC technology. 

An acronym for Deutsche Industrie Norm. A round connector with notches, or keys for alignment. They can be in several sizes: 4-pins, 5-pins, 8-pins, etc. A convenient way of combining all of the signal lines in one connector, 4-pin DIN connectors are often used for S-video. 

DA. A device that allows connection of one input source to multiple, isolated (buffered) output destinations such as monitors or projectors. 

Digital light processing. See DMD. 

Digital micromirror device. In 1977, it was originally called 'Deformable Mirror Device'. Texas Instruments has developed DMD microchips used in DLP (digital light processing) projector subsystems that hope to replace the 100-year old CRT technology. DMD chips use an array of mirrors and memory cells. A digital image is stored in the memory, and then projected when light is reflected onto the mirrors.

Digital Versatile Disc. An optical disc about the size of a CD-ROM, but capable of storing an entire movie. The technology uses MPEG-2 compression. Typical capacity for these discs is 4.5 GB, or about 133 minutes of digital video. Originally called 'Digital Video Disk'. 

A data communication scheme used with digital camcorders, the 1394 FireWire manages the digitisation, compression and audio synchronization processes while shooting. This puts broadcast quality video footage directly into your computer or DV (Digital Video) editing system. 

The front of a mirror. In mirrors intended for A/V applications, the first surface is coated with a reflective material to prevent double images (ghosting). 

An alternating change of light intensity, typically perceived at a rate of a few Hertz to 60 Hz when viewing static images such as text. Flicker can occur when the electron gun paints the screen too slowly, giving the phosphors on the screen time to fade before being refreshed. This may occur when the refresh rate of the video is too low, or when the persistence of the display device is too short. A fluorescent light fixture may produce the same effect.

FL. The distance between the centre of a lens and the point where the image comes into focus. In projection, a shorter focal length yields a larger image on the screen for any given projection distance. 

The act of adjusting a lens to make the image appear sharp and well defined. The best possible resolution of an image, showing the image to be sharp and well defined. 

A thin, flat lens made by cutting concentric circular grooves into its surface. The grooves act like prisms to bend and focus light. A fresnel lens is a fraction of the size and weight of a conventional lens, and the image is more distorted. Because of its lower cost and compact weight and size, the fresnel lens is often used for the condenser lens in overhead projectors and in studio spotlights. 

A light-reflecting screen used when the image is projected from a source in front of the screen. See Rear projection.

To project an image from the audience's side of a light-reflecting screen.

(1) A general term for an increase in signal power or voltage produced by an amplifier. The amount of gain is usually expressed in decibels above a reference level. Opposite of attenuation. (2) The amplification of a signal, unit or system. Expressed in the unit of measurement appropriate to the signal or system, or in a mathematical formulation (YxZ) for screens. 

A method of synchronizing video equipment by using a common, external signal. This locks the sync generators of multiple devices to a single source. 

(Also called ghosting, or 'reflections') A shadowy or weak duplication of the original image. It can be the result of transmission conditions where secondary signals are created and then displayed earlier or later than the original signal. Ghosts can also be the result of burning an image on a screen or by a mirror. 

Gigahertz. One billion cycles per second.

A high-density 'D' connector having its pins arranged close together, sometimes in three rows instead of two rows. Example: a 15- pin VGA connector (HD) vs. a Mac connector (D). 

High definition television. Any one of a variety of video formats offering higher resolution than the current NTSC, PAL and SECAM broadcast standards. Current formats generally range in resolution from 655 to 1,125 scan lines, with an aspect ratio of 9 to 16, and bandwidth of 30 to 50 MHz. 

Hz. The international term for cycles per second. 

Tint control. Hue is the parameter of colour that allows us to distinguish between colours. The hue, or tint control adjusts the amount of colour displayed.

Image light amplifier. Used in their large screen projectors, a Hughes/JVC device that uses low-intensity images to modulate high-intensity light through a liquid crystal layer. 

A reproduction or imitation of a person or thing displayed by any type of visual media. 

IR. Light waves just outside the visible spectrum; that is, waves slightly longer than those visible to the human eye. Infrared light is sometimes filtered out to reduce heat on film or slides. See Infrared control. 

A wireless medium of remote control, which sends signals to a device via pulses, transmitted in the infrared light spectrum. Its use is restricted to equipment within line-of-sight or reflections off a wall or ceiling. This is sometimes called 'IR remote'. 

A source for data or a signal to be used by another device. The physical connector or port for entering such a signal or data is called the 'input'. 

A video problem in which stair step-like lines appear where there should be straight-angled lines or smooth curves. 

A video problem in which the displayed image is unstable or appears to shake. 

Joint Photographic Experts Group. A committee formed as a joint effort between the International Standards Organization (ISO) and CCITT that developed a standard for the still digital image compression/decompression for use in computer systems. The JPEG image size may be reduced by as much as 30:1 with some loss of data. It does not work well with line art, text or vector graphics. The file extension is '.jpg'. 

A distorted picture where one edge is not the same dimension as the opposite edge, producing a tapered, or wedge shape. Typically, this results when the image is projected to the screen at an angle. In stone buildings, the tapered stone at the top of an arch is the 'key' that prevents the arch from falling. 

Liquid crystal display. A panel that utilizes two transparent sheets of polarizing material with a liquid containing rod-shaped crystals between. When a current is applied to specific pixel-like areas, those crystals align to create dark images. The dark areas are combined with light areas to create text and images on the panel. LCD panels do not emit light but are often back-lit or side-lit for better viewing. 

A device used to project video images through a liquid crystal display and an overhead projector onto a large screen. The panel is placed over the stage of an overhead projector, projecting the computer display onto a screen. 

 Utilizing the LCD technique, these projectors separate the red, green and blue information to three different LCD panels. Since LCD panels do not produce colour, the appropriate coloured light is then passed through each panel and combined to exit through the projector lens and onto a viewing screen. 

A means of moving a projector lens up, down and sometimes side to side without distorting the image. Useful for fine picture alignment and when stacking multiple projectors.

An Increased Definition Television (IDTV) feature that doubles the number of scan lines in a video picture. This fills the space between the original lines, making them less noticeable and increases the brightness of the picture. For example, the NTSC video field of 262.5 lines is doubled to 525 non-interlaced lines and the PAL field of 312.5 lines becomes 625. 

LM. A unit of measure for the amount of light emitted by a source. 0.98 Ft-c (foot-candles) of light covering a surface of 1 square foot. 

An output on a projector providing a means of connecting a monitor. Typically these are RGB (computer) only but on more advanced models can accommodate video output on to a standard PC monitor

The television standard for North America and parts of South America having 525 lines/60 Hz (60 Hz refresh), two fields per frame and 30 frames per second.

A device that produces an image on a screen by transmitting light through a transparent material placed on the stage of the projector.

Phase alternate line. A television standard in which the phase of the colour carrier is alternated from line to line. It takes four full pictures for the colour to horizontal phase relationship to return to the reference point. This alternation helps cancel out phase errors. For this reason the hue control is not needed on a PAL TV set. PAL, in many forms, is used in Australia, England, Scandinavia, South Africa, and Western Europe. PAL uses 625-line, 50-field composite colour transmission system.

A plug most often used with line level audio signals. Also known as an RCA plug.

An illustration or table that names signals, voltages, etc. that are on each pin of a connector or cable

Picture in picture. Displaying a small picture within a larger picture by scaling down one of the images to make it smaller. Each picture requires a video source (camera, VCR, channel selector, etc.). Consumer TV can use PIP for viewing two channels at the same time or for viewing taped video and a channel, etc. Videoconferencing uses PIP to display pictures from video sources at each participating site onto each screen at the same time. The large picture could be of the current speaker, while pictures from the other sites display across the bottom of the screen.

A translucent screen with a special coating that allows an image to be projected through the screen from the rear, instead of from the front.

A presentation method in which the image is projected through a translucent screen toward the audience. The slide or film must be reversed, or a mirror must be used to correct the image for rear screen presentation. In some video or computer projectors, the image can be reversed electronically.

A device for controlling the function of a device at a distance. May be wired or wireless.

The density of lines or dots for a given area that make up an image. Resolution determines the detail and quality in the image. A measure of the ability of a camera or video system to reproduce detail, or the amount of detail that can be seen in an image. Resolution is often expressed as a number of pixels, but more correctly it is the bandwidth. We say that a sharp, clear picture has high resolution.

Red, green and blue. The chroma information in a video signal. The basic components of the colour television system. They are also the primary colours of light in the "additive colour process".

A form of colour video signal (red, green and blue) distinctly different from the composite colour video used in standard television sets. RGB can be displayed only on an RGB monitor that has a separate electron gun for each of these primary colours. Some colour television sets use only one gun. RGB monitors are noted for their crisp, bright colours and high resolution. RGB video can have four different forms: RGsB (sync is on the green signal), RGBS (sync is separate from the colours), RGBHV (sync is separate from the colours, and the horizontal and vertical sync signals are separate) and RsGsBs (sync on red, green and blue).

An Electronic Industries Association (EIA) serial digital interface standard specifying the characteristics of the communication path between two devices using either DB-9 or DB-25 connectors. This standard is used for relatively short-range communications and does not specify balanced control lines. RS-232 is a serial control standard with a set number of conductors, data rate, word length and type of connector to be used. The standard specifies component connection standards with regard to computer interface. It is also called RS-232-C, which is the third version of the RS-232 standard, and is functionally identical to the CCITT V.24 standard.

Also called "video converter" or "TV converter", a scan converter is a device that changes the scan rate of a source video signal to fit the needs of a display device. Examples: computer-video to NTSC (TV), or NTSC to computer-video.

A European video-audio connector widely used in consumer equipment. The scart connector has 21 pins, carrying 2 audio channels - in and out, video channels - in and out, RGB signals, ground and some additional control pins. Simplicity is an advantage, however, the physical connection is quite weak and signal leakage is quite high.

(Sequential Couleur Avec Mémoire) Translated as 'sequential colour with memory'. A composite colour transmission system that potentially eliminates a need for both a colour and hue control on the monitor. One of the colour difference signals is transmitted on one line and the second is transmitted on the second line. Memory is required to obtain both colour difference signals for colour decoding. This system is used in France, Africa, Asia, Russia, Saudi Arabia and many Eastern European countries. It is similar to PAL, but produces colour signals in a different manner. SECAM uses 625 horizontal scan lines, 50 fields per second (625/50).

An input/output connection on the computer that allows it to communicate with other devices in a serial fashion?data bits flowing on a single pair of wires. The serial port is used with RS-232 protocol.

Super Video Graphics Array. A term used to denote resolutions higher than VGA (640 x 480). SVGA computer graphics cards have a resolution of 800 x 600 (480,000 pixels) but may be able to output resolutions of up to 1280 x 1024 and 16 million colours.

Super-video home system. A high band video recording process for VHS that increases the picture quality and resolution capability. See S-video.

The composite video signal is separated into the luma (Y, black and white information) and the chroma (C, colour information).

(1) A device which allows a selection between more than one source, such as: video cameras, VCRs, etc. In audio/video, switchers are a means of connecting an input source to an output device or a system. (2) A term often used to describe a special effects generator; a unit that allows the operator to switch between video camera signals. Switchers are often used in industrial or security applications to switch between video cameras that view certain areas for display on a monitor, or system of display devices. These kinds of switchers do not have sync generators.

Super Extended Graphics Array. A graphics standard with a resolution of 1280 x 1024 (1,310,720 pixels). This exceeds XGA (1024 x 768, at 786,432 pixels).

Synchronization. In video, sync is a means of controlling when things happen with respect to other things. This is accomplished with timing pulses to insure that each step in a process occurs at exactly the right time. For example, horizontal sync determines exactly when to begin each horizontal line (sweep) of the electron beam. Vertical sync determines when to bring the electron beam to the top left of the screen to start a new field. There are many other types of sync in a video system. (Also called 'sync signal' or 'sync pulse'.)

Universal Serial Bus. USB was developed by seven PC and telecom industry leaders (Compaq, DEC, IBM, Intel, Microsoft, NEC and Northern Telecom). The goal was easy plug-and-play expansion outside the box, requiring no additional circuit cards. Up to 127 external computer devices may be added through a USB hub, which may be conveniently located in a keyboard or monitor. USB devices can be attached/detached without removing computer power. The number of devices being designed for USB continues to grow, from keyboards, mice, and printers to scanners, digital cameras, ZIP drives, etc.

Ultra extended graphics array. A graphics standard resolution of 1600 x 1280 (2,048,000 pixels). This exceeds SXGA (1280 x 1024 = 1,310,720 pixels).

Generally defined as video cassette recorder. In Europe, however, VCR is a trademark for a particular video format developed by Philips of The Netherlands.

Video Graphics Array. Introduced by IBM in 1987, VGA is an analog signal with TTL level separate horizontal and vertical sync. The video outputs to a 15-pin HD connector and has a horizontal scan frequency of 31.5 kHz and vertical frequency of 70 Hz (Mode 1, 2) and 60 Hz (Mode 3). The signal is non-interlaced in modes 1, 2, 3 and interlaced when using the 8514/A card (35.5 kHz, 86 Hz) in mode 4. It has a pixel by line resolution of 640 x 480 with a colour palette of 16/256,000.

An amplifier for strengthening the video signal so that it can be supplied to a number of video monitors at the same time.

Extended Graphics Array Card. IBM?s graphics standard that includes VGA and extended resolutions up to 1024 x 768 (interlaced 35 kHz) with 65k colours. This card uses a 15-pin HD VGA-style connector.

A term used with cameras and video displays related to the ability to change the view anywhere between near and far. Definitions for near and far vary from one device to another.

A lens with a variable focal length providing the ability to adjust the size of the image on a screen by adjusting the zoom lens, instead of having to move the projector closer or further.