June 2004 — Product Watch
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Glossary of Audiovisual Terms
Inverted Image: A feature enabling many video projectors to flip an image from top to bottom to compensate for mounting a projector upside down on the ceiling.
Letterbox: A format to display widescreen films as originally intended in which the image is shrunk to fit the width of the available screen - leaving blank space on the top and bottom of the screen.
Liquid Crystal Display (LCD): A video display process based on liquid crystals sandwiched between two polarizing transparent layers of glass. The crystals, charged by transistors, open or close to block or let light pass. In a projection format, light from an internal lamp passes through the LCD panel onto the screen. Each crystal represents one pixel.
Long-Throw Lens: A lens designed for projection from a long distance, typically 50-100 feet, such as might be found in a projection booth in the rear of an auditorium.
Lumen: A measurement unit for the amount of light emitted by a projector. The higher the lumen rating, the brighter the image.
Metal Halide Lamp: A very bright projection lamp used in many medium-end and all high-end portable models that emits a lot of light relative to the power it consumes. Metal halide lamps usually last between 400-600 hours and slowly lose brightness as they age.
NTSC: The traditional color video standard established in 1953 by the National Television Standards Committee in the United States, and subsequently adopted by Canada and many other countries. It consists of a 525-line image in which frames are displayed at 30 per second.
Overhead Projector: A display device designed to project images from transparencies onto a screen. It typically consists of a light, a transmitting or reflective platform, and an adjustable-lens assembly.
Pixel: Short for picture element, a pixel is the smallest data component in a video display. It is represented as a point with specified color and intensity.
Plasma: A flat-panel display technology that uses phosphor stripes painted in ribs - one stripe per color - which are then charged to create an image on a flat surface. Most plasma displays range in size from 40-61 inches, measured diagonally.
Reverse Image: A feature on many video projectors that enables them to flip an image horizontally. This is necessary for rear projection.
Short-Throw Lens: A projection lens designed to display the largest possible image from a short distance, such as in a rear-projection system where space behind the screen is limited.
SVGA: Super video graphics array is the computer-video graphics standard with resolutions as high as 2,000 x 1,620 pixels and 24-bit color (16 million colors).
VGA: Video graphics array is the basic computer-video graphics standard, offering a resolution of 640 x 480 pixels (16 colors) or 320 x 200 pixels (256 colors).
Viewing Angle: The widest, or maximum, angle at which viewers can clearly see an image projected onto a screen.
Zoom Lens: A projection lens with a variable focal length, making it possible to enlarge or shrink the image on a screen by adjusting the lens instead of moving the projector or the screen.
This glossary of terms was compiled by the International Communications Industries Association, with reference assistance from Kayye Consulting. ICIA is the premier trade association for the professional AV communications industry and founder of InfoComm, the annual tradeshow for AV communications professionals. InfoComm '04 will be held in Atlanta from June 5-11. For more information, visit www.infocomm.org.
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