Rear Projection TVs

Digital Light Processing (DLP) is a technology used in projectors and video projectors. It was originally developed at Texas Instruments, in 1987 by Dr. Larry Hornbeck. more...

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One application is DLP front projectors (small standalone projection units). DLP, along with LCD and LCoS are the current display technologies behind rear-projection television, having supplanted CRT projectors. These rear-projection technologies compete against LCD and Plasma flat panel displays in the HDTV market.

Digital micromirror device

In DLP projectors, the image is created by microscopically small mirrors laid out in a matrix on a semiconductor chip, known as a Digital Micromirror Device (DMD). Each mirror represents one or more pixels in the projected image. The number of mirrors corresponds to the resolution of the projected image (often half as many mirrors as the advertised resolution due to wobulation). 800x600, 1024x768, 1280x720, and 1920x1080 (HDTV) matrices are some common DMD sizes. These mirrors can be repositioned rapidly to reflect light either through the lens or on to a heatsink (called a light dump in Barco terminology).

Rapidly toggling the mirror between these two orientations (essentially on and off) produces grayscales, controlled by the ratio of on time to off time.

Color in DLP projection

There are two primary methods by which DLP projection systems create a color image, those utilized by single-chip DLP projectors, and those used by three-chip projectors. A third method, sequential illumination by three colored light emitting diodes, is being developed.

Single-chip projectors

In a projector with a single DMD chip, colors are produced by placing a spinning color wheel between the lamp and the DMD, much like the "CBS field-sequential-color television" system that was briefly the U.S. standard for color television in 1950. The color wheel is usually divided into four sectors: the primary colors: red, green, and blue, and an additional clear section to boost brightness. Since the clear sector reduces color saturation, in some models it may be effectively disabled, and in others it is omitted altogether. Some projectors may use additional colors (for example, yellow).

The DMD chip is synchronized with the rotating motion of the color wheel so that the green component is displayed on the DMD when the green section of the color wheel is in front of the lamp. The same is true for the red and blue sections. The red, green, and blue images are thus displayed sequentially at a sufficiently high rate that the observer sees a composite "full color" image. In early models, this was one rotation per frame. Later models spin the wheel at two or three times the frame rate, and some also repeat the color pattern twice around the wheel, meaning the sequence may be repeated up to six times per frame.

Read more at Wikipedia.org