The Orientation: Digital Light Processing

This week’s Orientation will be focused on digital light processing aka DLP. The technology has been around for 21 years, but it hasn’t hit the mainstream until the last couple years. It’s a trademark owned by Texas Instruments. Its main purpose, in the beginning, was a way to project images from a monitor onto a large screen, which doesn’t stray too far from what we use it for today. What makes DLP so special are the tiny mirrors that are housed on an optical semiconductor called Digital Micromirror Device, which is also known as a DMD chip. That’s all fine and dandy, but what the heck does that mean? That’s why you’re here, so let’s get a move on.

DLP projector images are produced by the DMD chip that’s made up of hinged, microscopic electromechanical mirrors where each mirror represents a single pixel from the displayed image. Common DMD sizes include 800×600, 1024×768, 1280×720 and 1920×1080. All of these mirrors can be repositioned at the drop of a hat to reflect light through the lens or onto a heatsink, which is commonly known as light dumping. Think of DLP as a super high-end, fancy light switch. Switching the mirrors back and forth to the light source creates a grayscale, which in turn presents a light or dark pixel on the projection surface. The DLP site might make this part of it a tiny bit easier to understand.

“The bit-streamed image code entering the semiconductor directs each mirror to switch on and off up to several thousand times per second. When a mirror is switched on more frequently than off, it reflects a light gray pixel; a mirror that’s switched off more frequently reflects a darker gray pixel.”

Now that we’ve covered the grayscale, how do we get the colors? DLP is delivered in either one- or three-chip models. For the one chip-model, white light from the projector lamp travels through a color wheel that passes through red, green and then blue. From there it passes through one last stage that’s clear and basically cleans everything up and decreases any saturation that might occur before it hits the DMD chip. From there the DMD chip displays a full color image that isn’t dominated by one single color. How does that work out? Remember the color wheel I told you about? So the DMD chip is synchronized with the color wheel so that the red component is visible on the DMD and so forth. A single-chip DLP system is capable of displaying 16.7 million colors.

A three-chip DLP system is commonly found in cinemas or large venues because it creates a super high quality image or a super bright image, which is what you need in either application. The same thing basically happens on a three-chip system except red, green and blue have their own dedicated chip. It’s then combined and projected through the lamp. Three-chip systems can generate 35 trillion colors.

DLP isn’t perfect, though. One-chip systems suffer from the Rainbow Effect, which entails flashes of what you might think are shades of red/green/blue when viewing a bright/white object on a dark image. Think of the ending credits. But it’s not seen by everyone so it probably isn’t something you should worry about unless you’re weird and watch the ending credits all the way through. It does yield brighter and sharper images, but the bulbs have to be replaced every 1,000 to 6,000 hours. Picture quality might be sharper, but it doesn’t exactly produce the blackest of blacks.

DLP is making its way into more mainstream devices and CES was basically a launching pad for TI to showcase what DLP is capable of. I, for one, can’t wait to get my hands on a DLP HDTV over plasma and LCD. I hope this helped some of you and if others want to chime in and correct me or add anything then please feel free to do so in comments.