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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 or more pixels in the projected image. The number of mirrors corresponds to the resolution of the projected image (often half as many mirrors as the advertised resolution due to wobulation). 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).
Rapidly toggling the mirror between these two orientations (essentially on and off) produces grayscales, controlled by the ratio of on time to off time.
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. A third method, sequential illumination by three colored light emitting diodes, is being developed.
Single-chip projectors
In a projector with a single DMD chip, colors are either produced by placing a spinning color wheel between the lamp and the DMD or by using individual light sources to produce the primary colors, LEDs for example. 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). The color wheel technique was used in the early 1950s by the original CBS color television system before the standardization of NTSC color.
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.
The DLP "rainbow effect" in single-chip systems
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 are 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. The effect is likely rooted in the concept of the flicker fusion threshold. In some viewers the effect can lead to eye strain, headaches, or migraines after as little as a few minutes of viewing. New LED based DLPs can produce the alternating images fast enough so that most people will not be affected by the rainbow effect.
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. The spiral wheel can greatly reduce these effects.
Later LED-based DLPs are equipped with red, blue and green LEDs, providing both the primary colors and illumination in one device. The LEDs, which turn on and off almost instantly, are activated in sequence to display each color channel. The use of LEDs eliminates the color wheel mechanism and metal halide lamps required by traditional DLP designs.
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, there won't be any flicker or rainbow effect like with the single chip solution. Like three-tube CRT projectors, the optics for some three-chip DLP projectors must be carefully aligned. But it's more common to use a prism which makes it necessary for only one optic, instead of three, and therefore removes the problem of color separation.
According to DLP.com, the three-chip projectors used in movie theaters can produce 35 trillion colors, which many suggest is more than the human eye can detect. The human eye is suggested to be able to detect around 16 million colors, which is theoretically possible with the single chip solution. However, this high color precision does not mean that DLP projectors are capable of displaying the entire gamut of colors we can distinguish.
Light source
The main light source used on DLP-based rear screen projection TVs is based on a replaceable mercury vapor arc lamp unit (containing a quartz arc tube, reflector, electrical connections, and sometimes a quartz/glass shield), while in some newer DLP projectors high-power LEDs are used as a source of illumination.
For mercury types, during start-up the lamp is "ignited" by a 5000V pulse from a current-regulating ballast to initiate an arc between two electrodes in the quartz tube. After warmup, the ballast's output voltage drops to approximately 60 volts while keeping the relative current high. As the lamp ages, the arc tube's electrodes wear out and light output declines somewhat; eventually, the required startup voltage will also rise to the point where ignition can no longer occur. In the rarest, most extreme situations, the quartz arc tube can crack and/or explode; however, practically all lamp housings contain heat-resistant barriers (in addition to those on the lamp unit itself) to prevent the red-hot quartz fragments from leaving the area. Any which way, the mercury lamp's end of life is typically indicated via an LED on the unit, necessitating replacement of the lamp unit.
The first commercially-available LED-based DLP screen was the Samsung HL-S5679W in 2006, which also eliminated the use of color wheel. Besides long lifetime eliminating the need for lamp replacement and elimination of the color wheel, other advantages of LED illumination include instant-on operation and improved color, with increased color saturation and improved color gamut to over 140% of the NTSC color gamut. Samsung expanded the LED model line-up in 2007 with products available in 50", 56" and 61" screen sizes. For spring 2008, the third generation of Samsung LED DLP products are available in 61" (HL61A750) and 67" (HL67A750)screen sizes.
Ordinary LED technology does not produce the intensity and high lumen output characteristics required to replace arc lamps. The special patented LEDs used in the all of the Samsung DLP TVs are PhlatLight LEDs, designed and manufactured by US based Luminus Devices. A single RGB PhlatLight LED chipset illuminates these projection TVs. The PhlatLight LEDs are also used in a new class of ultra-compact DLP front projector commonly referred to as a "pocket projector" and have been introduced in new models from LG Electronics (HS101)and Samsung electronics (SP-P400). Home Theater projectors will be the next category of DLP projectors that will use PhlatLight LED technology. At InfoComm, June 2008 Luminus and TI announced their collaboration on using their technology on home theater and business projectors and demonstrated a prototype PhlatLight LED based DLP home theater front projector. They also announced products will be available in the marketplace later in 2008 from Optoma and other companies to be named later in the year.
Digital Cinema
DLP is the current market-share leader in professional digital movie projection, largely because of its high contrast ratio and available resolution as compared to other digital front-projection technologies. As of December 2007, there are 5,827 DLP-based Digital Cinema Systems installed, of which 79% are in North America. [2]
DLP projectors are also used in Real D Cinema for 3-D films.
Manufacturers and market place
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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.citation needed
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 (this may also be a con as listed below).
- The light source is more-easily replaceable than the backlights used with LCDs, and on DLPs is often user-replaceable.
- New LED DLP TVs and projectors eliminate the need for lamp replacement.
- Using two projectors, one can project full color stereoscopic images using polarized process (because beams can be polarized).
- Lighter weight than LCD and Plasma televisions.
- Unlike their LCD and Plasma counterparts, DLP screens do not rely on fluids as their projection medium and are therefore not limited in size by their inherent mirror mechanisms, making them ideal for increasingly larger high-definition theater and venue screens.
Cons
- In single-chip designs, some viewers are bothered by the "rainbow effect," explained above.
- Some viewers experience eye strain, headaches, and migraines when viewing DLP screens.
- Not as thin as LCD or plasma flat-panel displays (although approximately comparable in weight), though newer sets are thin enough to be wall-mounted.
- Some devices may have 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 (post ~2004) 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.citation needed
- 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.[3]
- Color rendition can be off, especially the bright reds and yellows when at maximum brightness.
- Poor viewing angle on rear projection displayscitation needed compared with direct-view technologies such as CRT, Plasma, and LCD.
- Replacement of of the lamp / light bulb. The average life span of a TV light source averages 1-3 years (based upon how often the television is powered on and off and the duration of viewing) and the replacement cost for these range from $99 - $350, depending on the brand and model. After replacing the bulb a few times the cost can easily exceed the original purchase price of the television itself.
- Noise level is elevated due to two factors. The first being due to the heat of the halogen light bulb (this lighting option is in the majority of DLP sets currently on the market) a fan is necessary to dissipate the heat built up. Many consumers may hear this fan during viewing and it will run for a few minutes even after powering off the set. The second issue may be with the light engine itself (also called the color wheel), which may create a high pitched whine as it spins to create the picture on screen. Many consumers have commented that this whine is not apparent in new sets but sets in as the TV ages.
DLP, LCD, and LCoS Rear Projection TV
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.[1] DLP-based television systems are also arguably considered to be smaller in depth than traditional projection television.
Advertising campaign
Texas Instruments has aggressively marketed DLP, focusing on the microscopic mirrors which are the key to it. Texas Instruments' commercials feature a young girl, Bella Thorne, accompanied by an elephant, holding a tiny box. When the box is opened, a beam of light shines upward, and the girl replies with Texas Instruments' DLP slogan, "It's Amazing. It's The Mirrors."
Racing
DLP is the title sponsor of a NASCAR car. In the NASCAR Sprint Cup Series, DLP sponsors the #96 Hall of Fame Racing driven by J. J. Yeley
See also
External links
- DLP Demo
- Information about PhlatLight LEDs from Luminus Devices http://www.luminus.com
- LCoS, DLP, 3LCD comparison table http://www.pro-projectors.com/Lcoscompare.htm
References
- ^ a b "4 styles of HDTV". CNET.com (2007-03-13). Retrieved on 2007-08-13.
- ^ TI (2008-02-15). "“European Cinema Yearbook”", Mediasalles. Retrieved on 2008-02-15.
- ^ "HDTVs and Video Game Lag: The Problem and the Solution.". AVS Forum (2005-07-11). Retrieved on 2007-08-13.
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