Digital Light Processing

Or DLP. This is the technology being used in digital movie theaters and it is also seeing used in home TV sets.

The way this system works is that a color image is separated into three primary component colors of Red, Green and Blue (RGB) and each of this signals is fed to a separate device called a DMD (Digital Micro Mirror Device). This device works by mounting a small mirror for each pixel onto a board controlled by magnets and computer chips. These computer chips tell the magnets how much angle to provide and then the mirrors are tilted to allow more or less light to be reflected.

The difference between home systems and professional theatrical systems comes in how the color is created.

For lower costing home systems a single DMD is used along with a spinning color wheel with the colors Red, Green and Blue. As this wheel spins the DMD changes the mirror position for that color and projects varied amounts of white light through the filter for each pixel based on the slant of the individual mirrors. This is then projected onto a screen by either rear or front projection processes.

Some newer systems use a clear filter area or possible a dark green and yellow filter in addition to the RGB filters and few use two sets of RGB filters. All of these filter changes are utilized to improve the color saturation.

The biggest downside with the spinning wheel is a rainbow effect seen when you move your eyes from one screen area to another. This doesn’t happen with the more expensive 3 DMD processes described below.

In the far more expensive process used by movie theaters, this light comes from a source on the side that directs white light into a prism with RGB colored filters. So the white lights gets turned into red light for the DMD that decodes the Red image, and the Green light goes into the DMD that controls the Green image, etc.

The three colors of reflected light are then sent to a projection lens which focuses on the screen.

The result is a mosaic of RGB color intensities for each pixel in the matrix. That matrix can be of any size, but currently the most popular for home TV sets is 1020 x 720.

The contrast range for DLP generally exceeds LCD screen, with a 400:1 ratio for even simple spinning wheel screens to 5000:1 for some more expensive home theater systems.

As the cost for DMD chips reduces, home projection TV systems will start to see more use of DLP processes, which can actually give a better image on the screen than most other systems. Image quality rivaling digital movie theaters!



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