DLP

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This article is about Digital Light Processing. For other uses, see DLP (disambiguation).

The DLP Logo

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

Modern applications include DLP rear-projection television, which competes against LCD and Plasma flat panel displays, and DLP front projectors (small standalone projection units).

[edit] Digital Micromirror Device

Main article: Digital Micromirror Device

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).

[edit] Color in DLP projection

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.

[edit] Single-chip projectors

Chip DLP

In a projector with a single DMD chip, colors are produced by placing a spinning color wheel between the lamp and the DMD, much like the "CBS field-sequential-color television" system that was briefly the U.S. standard for color television in 1950.[1] 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. Some projectors may use additional colors (for example, yellow).

A single-chip projector alternates between colors and produces separate red, green, and blue images when displaying a moving image, or in this case, illuminating a moving hand.

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 a 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 some recent high-end models, the spinning color wheel and the white bulb have been replaced with a package containing super-bright LEDs in the three primary colors (red, green, and blue). Since LEDs can be switched on and off very quickly, this design allows even higher rates of sequential single-color image projection. Bulb life is also much longer (and light intensity more consistent over the life of the bulb) with the LED pack than with earlier lighting technologies.

[edit] 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 "Rainbow Effect" is unique to single-chip DLP projectors. 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 have used 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 two revolutions per frame would be a 4x wheel.

Another way to reduce the rainbow effect is to replace a segmented wheel with a wheel whose colors are in an Archimedean spiral. This forms bands of color that move down (or up) the screen. With segmented wheels, the DMD must "go black" while the wheel transitions from one color to another. Not only can this interfere with persistence of vision and thus accentuate the rainbow effect, it means that 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.

The LED light packs now being introduced in DLP projectors may eliminate rainbow effect for all but a few very sensitive viewers thanks to their high switching frequency and a complete lack of "black" segments as described above. Additionally, the LED pack can display any color of light at any intensity, a capability which, if exploited, provides the potential for increased color gamut and improved contrast compared to displays employing color wheels with fixed-color segments.

[edit] 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. Three-chip DLP projectors can resolve finer gradations of shade and color than one-chip projectors, because each color has a longer time available to be modulated within each video frame; furthermore they have a reduced potential for flicker and rainbow effect.

[edit] Manufacturers and market place

DLP logo found on many products

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.

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.

[edit] Pros

• Smooth (at 1080p resolution), jitter-free images.
• Perfect geometry and excellent grayscale linearity achievable.
• Usually great ANSI contrast.
• No possibility of phosphor burn-in.
• Less "screen door effect" than with LCD projectors.
• DLP rear projection TVs are smaller, thinner, and lighter than CRT projectors.
• DLP rear projection TVs are considerably cheaper than LCD or plasma flat-panel displays and can still offer 1080p resolution
• 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.

[edit] Cons

• In single-chip designs, some viewers are bothered by the "rainbow effect," explained above.
• Not as thin as LCD or plasma flat-panel displays (although approximately comparable in weight), so they cannot be wall-mounted.
• Does not come in sizes under 42 inches.
• Fan noise.
• Silk screen effect
• "Screen door effect" (SDE) may be visible at close distance and/or with lower resolution models (720p resolution and lower). SDE can also be perceived as artificially sharp looking (due to dark gaps between mirrors/pixels which are high frequency content, not part of the image displayed) and not film-like.
• Dithering noise may be noticeable, especially in dark image areas. Newer chip generations have less noise than older ones.
• Error-diffusion artifacts caused by averaging a shade over different pixels, since one pixel cannot render the shade exactly.
• Mediocre on-off contrast compared to CRT reference.
• Response time in video games may be affected by upscaling lag. While all HDTVs have some lag when upscaling lower resolution input to their native resolution, DLPs are commonly reported to have noticeably longer delays. Newer consoles such as the Xbox 360 and Playstation 3 do not have this problem as long as they are connected with HD-capable cables. [2]
• Color rendition can be off, especially the bright reds and yellows when at maximum brightness.
• More mechanical than traditional CRT, LCD, plasma, and LCoS displays.
• Replacement lamps can be expensive (USD $200 or more).

[edit] 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 (similar to a Liquid Crystal Display) to control how much light is reflected.

[edit] See also

• Flat panel display
• LCD projector
• CRT projector
• Plasma display
• OLED
• SED-tv
• Comparison of display technology

[edit] External links

• www.dlp.com, website about the technology by Texas Instruments
• DLP Overview by Texas Instruments