Digital Light Processing or DLP is a projection technology which can be used for either rear projection televisions or forward projection. A rear projection television has an internal projector projecting from the rear onto the viewing surface.

DLP, a proprietary technology from Texas Instruments (TI), is based on fabricated chips, digital micromirror devices (DMD), covered with a matrix of millions of microscopic electromechanically actuated mirrors. Each mirror corresponds to a pixel in the image with the number of mirrors determined by the resolution required. For example 1080p is 1920 x 1080 pixels requiring over 2 million microscopic mirrors on the DMD. However, sometimes for cost savings the number of mirrors is halved by using a wobulation (referred to by TI as SmoothPicture) where each mirror produces the output for two pixels by wobbling between them.

The microscopic mirrors on the chip are rotated to reflect light either into the lens or to a heatsink. Rapid toggling of the mirrors between these two orientations produces grayscales in correspondence to the ratio of time on (light directed into lens) to time off (light directed away from the lens into the heatsink). The small image created by the DLP chip is magnified by projection up to the size of the display surface.

DLP Color

Color is added to images by one of three methods.

Spinning Color Wheel

For single DMD chip projectors a color wheel is positioned between the projector bulb and the DMD chip coloring the light passing through. A color wheel commonly contains red, green, and blue primary color sectors, as well as a clear fourth sector to control brightness or a fourth color.

The DMD chip is synchronized with the rotating motion of the color wheel so that the one color component (eg. red) of an image is displayed on the DMD the same color section of the color wheel is aligned in front of the lamp. Using this method, red, green, and blue images are displayed sequentially fast enough for the viewer’s eyes combine them into a full color image. Single DMD chip DLP projection systems are prone to the rainbow effect.

Three DMD Chips

A three-chip projector uses a prism to split the projection light into three beams (red, green and blue) each directed towards its own DMD chip. The outputs of the three DMD chips are recombined and then projected. Three-chip DLP projectors are able to resolve finer gradations of shade and color than one-chip projectors due to the longer time available for modulation within each video frame.

Sequential Illumination

The spinning color wheel in the single-chip arrangement can be replaced by using red, green, and blue light-emitting diodes (LED) instead of using the traditional projection bulb. Read our article New Generation of DLP Rear Projection TVs for more details.

Texas Instrument’s BrilliantColor

The latest DMD being used by display and projector manufacturers is the DarkChip 3 which supports BrilliantColor, Texas Instruments latest trademarked technology for delivering improved brightness and a wider range of colors.

The full gamut of colors visible to the human eye cannot be reproduced using only primary colors, with the color space subset not including vivid colors such as yellow and cyan commonly seen in nature. By processing up to six color channels, TI’s BrilliantColor allows display and projector manufacturers to create multi-primary color systems by adding colors like yellow, cyan and magenta colors for color rendering. As well as increasing the color space which can be rendered with the added color filters, the system also utilizes the light source more efficiently with a 50% increase in brightness.

A further benefit of BrilliantColor technology is more accurate rendering calculations from the use of floating point arithmetic. According to TI, this results in less noise and more accurate colors with over 200 trillion color shades being possible.

Texas Instrument’s DarkChip 4

In September 2008 Texas Instruments announced the introduction of a new chipset, DarkChip™ 4. TI report that the new chipset will deliver a 30% or more increase in native contrast ratio depending upon the application. It is expected that the DarkChip4 will be available in a consumer electronics products, including televisions and projectors, in 2008.

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