Creating a Picture
Before any of the mirrors switch to their on or off positions, the chip rapidly:
- Decodes the incoming signal
- Converts interlaced data to progressive data
- Sizes the picture to fit the screen
- Makes any necessary adjustments to the picture, including brightness, sharpness and color quality
- Converts color information to red, green and blue (RGB) format
- Removes gamma correction, which is part of most television signals and adjusts for the signal-to-noise ratio of a cathode ray tube (CRT)
It then digitally relays all the information to the mirrors. If the size of the image contains fewer pixels than the DMD supports, then the chip simply ignores the unneeded mirrors.
When the set is off, all of the mirrors are flat. When someone turns the set on and the chip begins transmitting the signal, the mirrors flip back and forth thousands of times per second. They move between +10° and -10° in older DMDs, or between +12° and -12° in newer DMDs. The increase of the angle from 10° to 12° DMDs allows more light to reach the screen, producing a brighter picture. Newer DMDs also use "dark metal" on the aluminum mirrors to absorb stray light and create a clearer picture.
Photo courtesy Texas Instruments
A lens projects the light from the DMDs onto a screen. The configuration shown has separate DMDs for red, green and blue.
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Mirrors in the on position reflect the light through a projection lens and onto the screen. The longer a mirror is in the on position, the lighter the pixel it creates. Mirrors that are off for longer periods create darker pixels, and mirrors that are always off create black pixels. By varying the length of time that the mirrors point toward the projection lens, the DMD creates up to 1,024 shades of gray.
The grey pixels combine on the screen to create a progressive, fully digital monochrome image. In the next section, we will see how DLP televisions add color to the monochrome images.
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Attractive TV
DLP screens fill nearly every inch of the TV's front surface, so you can display your favorite digital photos and backgrounds like works of art. Check it out.
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