Digital Light Processing

For political parties using this acronym, see Democratic Labour Party.

Digital Light Processing (DLP) is a technology used in projectors and video projectors. DLP ([1]) was originally developed at Texas Instruments, in 1987 by Dr. Larry Hornbeck. [2]

Texas Instruments remains the primary manufacturer of DLP technology, which is used by many licensees who market products based on T.I.'s chipsets. The Fraunhofer Institute of Dresden, Germany, also manufactures Digital Light Processors, termed Spatial Light Modulators, for use in specialized applications. For example, Micronic Laser Systems of Sweden utilizes Fraunhofer's SLMs to generate deep-ultraviolet imaging in its Sigma line of silicon mask lithography writers.

In DLP projectors, the image is created by microscopically small mirrors laid out in a matrix on a semiconductor chip, known as a Digital Micromirror Device (DMD). Each mirror represents one pixel in the projected image. The number of mirrors corresponds to the resolution of the projected image. 800x600, 1024x768, 1280x720, and 1920x1080 (HDTV) matrices are some common DMD sizes. These mirrors can be repositioned rapidly to reflect light either through the lens or on to a heatsink (called a light dump in Barco terminology).

The rapid repositioning of the mirrors (essentially switching between 'on' and 'off') allows the DMD to vary the intensity of the light being reflected out through the lens, creating shades of grey in addition to white (mirror in 'on' position) and black (mirror in 'off' position). There are two primary methods by which DLP projection systems create a color image, those utilized by single-chip DLP projectors, and those used by three-chip projectors.

Single-chip projectors

In a projector with a single DMD chip, colors are produced by placing a color wheel between the lamp and the DMD where it is reflected out through the optics. The color wheel is usually divided into four sectors: the primary colors: red, green, and blue, and an additional clear section to boost brightness. Since the clear sector reduces color saturation, in some models it may be effectively disabled, and in others it is omitted altogether.

File:DLP projector rainbow effect DLP Projektor Regenbogeneffekt.JPG

The DMD chip is synchronized with the rotating motion of the color wheel so that the green component is displayed on the DMD when the green section of the color wheel is in front of the lamp. The same is true for the red and blue sections. The red, green, and blue images are thus displayed sequentially at a sufficiently high rate that the observer sees the composite "full color" image. In early models, this was one rotation per frame. Later models spin the wheel at two or three times the frame rate, and some also repeat the color pattern twice around the wheel, meaning the sequence may be repeated up to six times per frame. In fall of 2006, HDTV Manufacturers NuVision and Samsung will be releasing HDTVs that replace the color wheel and single light source with a red, green and blue LED trio, which will completely eliminate the rainbow effect described below.

The DLP "Rainbow Effect"

This visual artifact is best described as brief flashes of perceived red, blue, and green "shadows" observed most often when the projected content features bright/white objects on a mostly dark/black background (the scrolling end credits of many movies being a common example). Some people perceive these rainbow artifacts all of the time, while others say they only see them when they let their eyes pan across the image. Yet others do not notice the artifact at all. The effect is likely rooted in the concept of the flicker fusion threshold.

The image to the right shows how a white circle looks to a camera while panning horizontally, using a long exposure. The white light is visibly split into its colored components. The rainbow effect occurs when this is visible to the naked eye. The multiple images of the circle represent the individual frames of video, and are unrelated to the rainbow effect.

The "Rainbow Effect" is unique to single chip DLP projectors. Since a single chip DLP projector uses a color wheel, as described above, only one color is actually displayed at any given moment. As the eye moves across the projected image, these separate colors become visible, resulting in a perceived "rainbow". The manufacturers of single-chip DLP projection systems use color wheels rotating at higher speeds, or with more color segments in order to minimize the appearance of the artifacts. These are referred to as 2x, 3x or 4x wheels. For example, a six segment wheel(RGBRGB) rotating at 2x speed would be a 4x wheel. Another way is to replace a segmented wheel with a wheel whose colors are in an archimedian spiral. This forms bands of color that move down (or up) the screen. Normally with segmented wheels there is a pause between colors while the wheel transitions from one color to another. This means the more segments there are, the darker the display will be (all else being equal). With a spiral wheel the mirrors can display more than one color at a time, each moving down (or up) as the wheel turns.

Three-chip projectors

A three-chip DLP projector uses a prism to split light from the lamp, and each primary color of light is then routed to its own DMD chip, then recombined and routed out through the lens. Single-chip DLP systems are capable of displaying 16.7 million (24-bit) colors, whereas three-chip DLP systems can display up to 35 trillion colors.

Market place

File:DLP LOGO.jpg

DLP logo found on many products

DLP is rapidly becoming a major player in the rear-projection TV market, having sold two million systems and achieved a 10% market share. Over 50 manufacturers offered models during the 2004 holiday season, up from 18 the previous year. DLP chips currently constitute 5% of Texas Instruments' total sales. Small standalone projection units (also called front projectors) using DLP technology have become very popular for office presentation and home theater duties.

Pros

Smooth, jitter-free images.
Great contrast.
No possibility of phosphor burn-in.
Less of the screen door effect than with LCD projectors.
DLP rear projection TVs are smaller, thinner, and lighter than CRT projectors.
The use of a replaceable light source means a potentially longer life than CRTs and plasma displays.
The light source is more-easily replaceable than the backlights used with LCDs and is often user-replaceable.
The light source in certain newer models (release date: Fall 2006) uses LEDs that will last up to 60,000 hours before replacement is required.

Cons

In single chip designs, some viewers are bothered by the "rainbow effect," explained above. (Eliminated in LED models)
Not as thin as LCD or plasma displays (although approximately comparable in weight).
Fan noise. (Little to no noise, less heat, on LED Models)
The picture dims as the lamp deteriorates with time. (LED models dim very little over time)
Today's current TI based systems work exceptionally well with consoles such as the XBOX360 even in HDTV resolutions. However, older DLP displays have lag time between input and display with video consoles such as the PlayStation 2, making online video game play nearly impossible on early models.
Color accuracy can be off, especially the bright reds and yellows when at maximum brightness.
More mechanical than traditional CRT, LCD, plasma, and LCoS displays. (Mechanical color wheel is eliminated in LED models)
Replacement lamps can be expensive (USD$200-$500). However some manufacturers overcome this problem by using LEDs as a light source.

DLP and LCoS

The most similar competing system to DLP is known as LCoS (Liquid Crystal on Silicon), which creates images using a stationary mirror mounted on the surface of a chip, and uses a liquid crystal matrix, to control how much light is reflected.

External links

DLP Overview by Texas Instruments