Last update: January 8, 2004.  Since this document was written, DLP projector prices have been falling steadily, but seemingly not fast enough for the consumer.  In the meantime, the image quality from LCD projectors has improved dramatically over the years, making them a viable alternative to their more expensive DLP counterparts.  However, when it comes to producing "inky" blacks, DLP technology still outperforms LCD technology.  And the only technology that can outperform DLP's blacks are old-fashioned and bulky CRT projectors which are far from portable and incredibly complex to set up.

DLP stands for "Digital Light Processing", and is the creation of Texas Instruments.  The device itself, known as a "Digital Micromirror Device" or DMD,  is basically a big chip with about a million individual tilting mirrors constructed on it's face depending on the actual resolution of the chip.  The mirrors are tightly packed together, almost completely reflective on their surface, and can be individually tilted in one direction or another over 1,000 times a second.  The mirrors are so efficient and tightly packed that even when looking very close to the projected image, you can only slightly see their layout and construction.

Because of the increased efficiency of the surface area of each individual pixel, projectors incorporating DLP technology produce a brighter image even when using the same lamps as LCD projectors, and eliminate the horrendous "screen door" effect which has bothered many LCD owners for so many years.

A DMD's method of operation is reasonably simple.  Tilt the mirror in one direction, and the light reflecting off the surface of the mirror will be directed through the projector's lens.  Tilt the mirror in the other direction, and the reflected light falls into a light trap where it's lost forever.  By varying the frequency at which the mirrors tilt in one direction or another, you can create varying intensities of reflected light.  By properly controlling the back-and-forth rate of those one million mirrors individually, you can actually generate a visible black & white image with the varying levels of reflected light.  If you pass the light through a color filter before it hits the chip, the image will come out in color.

By spinning a red-green-blue segmented color filter wheel in front of the light source, the DMD chip is now hit with alternating colors of light.  If you can properly synchronize the mirror tilting with the spinning action of the color wheel, the mirrors will reflect the correct amount of coloured light towards the lens depending on the original color combination assigned to each and every pixel, and produce a crystal clear full color image.  This is how most DLP projectors work.

There's also a projector design which includes three DMD chips where each chip is responsible for one of the three primary colors.  One set of prisms separates the white light coming from the lamp into it's three individual colors, and sends each color to it's assigned DMD chip.  The reflected coloured light is recombined together through a second set of prisms and is finally sent out through the lens.

There is also a two chip variation of this design where one chip is responsible for the color red, and another chip is responsible for the colors green and blue.  This unusual approach is not used that often, but it does exist.

Most DLP projectors are built around the single DMD chip principle, and it's pretty clear why it's so popular.  The number of components required to build a single chip projector is so small that a fully assembled unit can easily fit inside the average briefcase.  Alignment problems are completely eliminated because you're now dealing with a single light path and a single image generating panel, not a combined package of panels, prisms and light paths where one misaligned component can corrupt the image beyond recognition.  Even the rigors of daily travel from one worksite to another is not enough to seriously disrupt these projectors.  Even if one of the image components slides ever so slightly out of alignment, the effect on the final image will most likely be negligible and completely unnoticed since the projector is designed to be in transit and will still need to be set up at its destination.

Single DMD chip designs can be further improved by incorporating a special color wheel where each individual color filter is laid out in a spiral.  The technique, called SCR or "Sequential Color Recapture", can result in increased performance by tripling the rate at which the DMD chip is bombarded with the three primary colors without having to speed up the rotation of the color wheel itself.  This technique reduces a particular artifact which can easily be seen on non-SCR designed projectors when you pan your eyes across the screen very quickly.  What you see is the "rainbow effect", or a separation of the three colors for just a split-second.  If you move your eyes around a lot while watching a movie, this effect can become quite distracting especially on cheap projectors with very slow color wheels.  An SCR color wheel design can increase the rate of color transitions just enough so that a person many never be able to see these transitions no matter how quickly they pan their eyes across the screen.

Other color wheel options include a four segment color wheel where one of the segments is actually clear.  This design is mainly used in projectors intended for use as computer displays since the color shown the most often is white.  Another option is a six segment color wheel where the red, green and blue segments are doubled up.  This simple design change allows a projector to double the projection rate of the three colors without doubling the rotation speed of the wheel.  As a result, the six segmented wheel doesn't produce any extra noise and significantly reduces rainbow effects.

The three DMD chip projector designs are suppose to give you a better picture by managing the three colors independently and at the same time, but the complications of trying to keep three DMD chips perfectly aligned at all times may result in a highly complex and expensive projector which may or may not travel well.  Still, there could be enough technological advances in the near future to turn this design into a must-have affordable projector.  Already three-chip LCD projectors are the norm within their technology, but their design doesn't include reflecting the light off a mirror, rendering them less sensitive to misalignment problems.

The DMD chips now come in many configurations, and it's the responsibility of the projector manufacturers to determine which configuration is best suited for their needs.  For the 1.33:1 aspect ratio, there are 800x600, 1024x768 and 1280x1024 resolution DMD chips currently available.  For the 1.78:1 aspect ratio, a 1280x720 resolution chip specifically designed for HDTV is available along with a 848x480 chip designed for anamorphic DVD playback.  Hopefully, new projector models will incorporate the HDTV capable chips into their designs so that the promise of an HDTV theatre in almost every home will actually become a reality which we can afford.  Just about all of the 1.33:1 and 1.78:1 aspect ratio chip equipped projectors can handle an HDTV image source, but only the 1280x1024 and 1280x720 model DMD chips can display the full vertical resolution of a 720p HDTV signal.  1024x768 DLP chips, despite not being able to display the full resolution of HDTV, can still show more than enough of the original HDTV image's resolution to make this design an affordable alternative.

This explanation of DLP technology may have been long and possibly a bit confusing, but it's important to understand some of it right away.  Within a year or so, weak projector designs will have been eliminated from the product lines, leaving us with only the most efficient and cost-effective designs on the store shelves, hopefully with a few more models incorporating the outstanding HD-1 and HD-2 chips.  Already the 2002 edition of the Montreal HI-FI Expo has revealed that the only DLP hold-out left in the industry may be Sony which continues to sell their now seemingly outdated LCD designed projectors on the open market with no alternatives lying in the wings.

For more information on DLP technology, do consult the highly detailed official Website at http://www.dlp.com.