General Information, Projection TV technology
What are the technologies available for projection systems. How to get the most for your exhibit dollar. Where to turn for more information.
Choosing Projection Television Technologies
If you need to show video or digital media you will need to consider various means of exhibiting your project. The maximum size of CRT screens is about 40" (101 cm): at that size, they are extremely heavy. Another option is the Plasma screen -- they run larger, and are more manageable, but they are prohibitively expensive. Projection TV technology can give you a large screen size for a reasonable price.
Besides their use in exhibitions, and trade shows, projection TV technology is often used in classrooms or conference rooms, for multimedia presentations with a large audience. A projection TV gives you a lot of flexibility and can be used to project from a computer, thereby allowing both interactive and linear media. Be aware however that if your project is computer-driven, you need a special type of projector. Computer graphics require a higher horizontal scan frequency (which affects image resolution) than video. (Scan frequency is the rate at which an image is "refreshed" or reproduced - affecting image resolution.) The type of projector must be able to accommodate the scan frequency requirements of the input source.
Front projection needs a darkened theater because images fade when exposed to ambient light. In a rear projection system, light is thrown upon a translucent screen from behind. The images are less affected by ambient light, so images are brighter. The disadvantage is that images viewed from the sides tend to look washed out--the best viewing angle for this format is directly in front of the screen. This is why in-booth presentations at trade shows often uses the rear projection system.
CRT projectors have tubes in them just like conventional TVs. These tubes are small, expensive and very bright. One or more CRT tubes form the images onto a lens which magnifies the image and projects it onto the screen. To get a crisp, clear picture, the three images must be precisely aligned or converged to form a single image. Some CRT systems offer an automatic convergence feature, which aligns the three images in a matter of minutes. Of course, you’ll pay more for this convenience, because they produce a brighter image (up to 10 times brighter than CRT systems).
Two disadvantages of CRT projectors are that they are very heavy (due to the tubes and lenses) and they do not achieve the detail and resolution of LCD technology. There are three basic types of CRT projectors:
One color CRT tube (RGB) uses one projection lens to display the image.
One black-and-white CRT uses red, green, blue filters on a rapidly rotating wheel that is located between the CRT tube and the projection lens. Using a trick from film technology -- persistence of vision --the color images are projected so rapidly that the brain is tricked into seeing only one image. Three CRT tubes -- sometimes called "guns" (red, green, blue) with three lenses are aligned to converge into a single image on screen.
LCD technology has created larger and lighter projectors. Transmitted LCD projectors use a bright light to illuminate the LCD panel, and a lens projects the image formed by the LCD onto a screen. The LCD acts very much like a color slide in a slide projector. The advantage of this approach is that the projector can be very small (example LCDs used in PDA;s). LCD light-valve systems need less adjustment each time they’re moved or when the screen size or projection distance changes. This may not be a consideration with a permanent exhibition, but may be an issue with a commercial trade show.
Information and Links on Video Projector Technology (including Virtual Reality)
Abstract on Interactive exhibit Design Technologies and methods for interactive exhibit design: from wireless object and body tracking to wearable computers: by Flavia Sparacino, Kent Larson, Glorianna Davenport, Alex Pentland
Howstuffworks "How Projection Television Works"
The Fully Immersive Spherical Projection System for Virtual Reality Applications
Dave's CAVE pages The CAVE is a projection based virtual reality system developed at the Electronic Visualization Lab; it was created by Carolina Cruz-Neira, Dan Sandin, and Tom DeFanti, along with other students and staff of EVL.
Virtual Reality and Interactive Immersive Virtual Reality Systems from Themekit.
Natural Language Interfaces to Virtual Reality Systems
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