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  1. 1. Advantages Allows a much bigger image. Wide viewing angle. Allows for Keystone correction (where the top of the image is wider than the bottom of the image, see picture below).
  2. 2. Disadvantages The room lighting for front projection must be carefully designed. The image you view, when front projection is used, consists of light from the projector reflected off the screen. This also means any light in the room will also be reflected off the screen back to you, washing out the image (this is why a cinema is generally very, very dark). Projection equipment is often located in the same room as the screen and unless carefully coordinated creates a new source of noise, glare, distraction, etc.
  3. 3. Advantages Allows for easy interaction with the projected image. Good for long, narrow rooms such as conference rooms. Can be viewed in a room with normal illumination. Excellent for taking notes and command center types of situations where individuals move around and are doing other activities. Generally provides a cleaner looking system installation appearance.
  4. 4. Disadvantages Screen size is limited to the size of transportable glass. Space is required behind the projection screen. However, this space can be utilized as the audiovisual system equipment room. The use of mirrors can further reduce the depth requirements of the room. Rear projection systems are generally a little more expensive. Rear projection screens are slightly more expensive than front projection roll down screens and the additional cost of the square footage required for the rear projection room can be an issue.
  5. 5. A CRT projector is a video projector that uses a small, high-brightness CRT (or picture tube) as the image generating element. Theimage is then focused and enlarged onto a screen using a lens kept infront of the CRT face. Most modern CRT projectors are color and havethree separate CRTs (instead of a single, color CRT), and their ownlenses to achieve color images. The red, green and blue portions of theincoming video signal are processed and sent to the respective CRTswhose images are focused by their lenses to achieve the overallpicture on the screen. Various designs have made it to production,including the "direct" CRT-lens design, and the Schmidt-CRT, whichemployed a phosphor screen that illuminates a perforated sphericalmirror, all within an evacuated "tube.“
  6. 6. Advantages Long service life; CRT tubes maintain good brightness to 10,000 hours. High-end CRT projectors can precisely display images up to 1920 x 1200 with accurate color reproduction. A few projectors can scan at even higher resolutions up to 3200 x 2560, although their ability to resolve fine detail at this resolution is greatly reduced. Superior black level compared to LCD and DLP based projectors. As with CRT monitors, the image resolution and the refresh rate are not fixed but variable within some limits. Interlaced material can be played directly, without need for imperfect deinterlacingmechanisms. Very fast response time (especially when compared to LCD-based projectors), resulting in minimal (if any) motion blur when showing video with fast motion. CRT projectors do not show a Rainbow effect seen with single chip DLP projectors.
  7. 7. Disadvantages CRT projectors are both considerably larger and heavier than comparable LCD and DLP projectors. CRT projectors require far more time to set up and adjust than LCD and DLP based projectors. Absolute ANSI brightness achievable with CRT projectors is lower than with comparable LCD and DLP projectors. Low-end or poorly tuned CRT projectors may suffer from color divergence or geometric distortion (for example, straight lines may not always appear completely straight, especially near the corners). CRT projectors use more power / cost more to run than LCD and DLP units. Unlike LCD or DLP projectors, CRT projectors are somewhat prone to burn-in. This can lead to issues in brightness uniformity on projectors that frequently use both a full 4:3 and widescreen aspect ratio.
  8. 8. An LCD projector is a type of video projector fordisplaying video, images or computer data on a screen orother flat surface. It is a modern equivalent of the slideprojector or overhead projector. To display images, LCD(liquid-crystal display) projectors typically send light froma metal-halide lamp through a prism or series of dichroicfilters that separates light to three polysilicon panels – oneeach for the red, green and blue components of the videosignal. As polarized light passes through the panels(combination of polarizer, LCD panel and analyzer),individual pixels can be opened to allow light to pass orclosed to block the light. The combination of open andclosed pixels can produce a wide range of colors andshades in the projected image.
  9. 9.  LED projectors are becoming more and more popular. LED technology is used in a wide range of products, including home theater projectors, business and education projectors, and even the emerging market of pico projectors, handheld projectors, and other mini projector systems. LED light sources have some serious advantages over conventional lamps. LED projectors require little maintenance, as there is no lamp to be changed. Furthermore, LED light sources last significantly longer than the competition. Lastly, the techonology is greener than the alternative conventional projector lamps. Between their long lives, lack of upkeep, and lower power usage, LED projectors save you money in the long run.