【開發故事】DLP投影儀（一）：堅持20年不放棄的男人（上） 美國德克薩斯州最大的城市達拉斯。在這個有著牧牛和牛仔 歷史的城市裡，一項技術宣告誕生。這項技術在很長時間裡“養在深閨人未識”，甚至一度處於行將消亡的境地。然而，憑借一個 男人長年累月的苦斗，成就了時至今日的一項無人不曉的核心技術…… (詳見全文) 【開發故事】DLP投影儀（二）：堅持20年不放棄的男人（下） Larry最初的工作，是制作有機械構造的微鏡陣列。這 種微鏡陣列是將金屬覆膜的薄塑料板載於硅制芯片上而成。這是Larry自己的創意。他們首先試制出了用銻對硝酸纖維素…… (詳見全文) 【開發故事】DLP投影儀（三）：對，是數字式的（上） 采用可動的微鏡來控制光的行進方向的器件。用電來控制微 鏡的角度，並將其應用到打印機上，這是在美國德州儀器（Texas Instruments，TI）進行微鏡器件研究的Larry J.Hornbeck的目標…… (詳見全文) 【開發故事】DLP投影儀（四）：對，是數字式的（下） 首先，不管怎麼說，傾斜角度是最重要的因素。例如，可在±10 度的角度內傾斜。此前的懸臂式微鏡器件無法傾斜如此大的角度。另外，此次的傾斜角度可不受周圍環境變化及時序變化影響地一直保持恆定…… (詳見全文) 【開發故事】DLP投影儀（五）：糟糕，微鏡不動了（上） 不知道是誰在小聲提醒。大原為了讓微鏡的故障不那麼明顯，開 始頻繁地切換場景進行演示。因為切換場景的話，吸附在底板上的微鏡有可能復原…… (詳見全文) 【開發故事】DLP投影儀（六）：糟糕，微鏡不動了（下） 令大原擔心的理由另外還有一個。這就是，大原剛剛回到達拉斯，他 在達拉斯的直屬上司就跳槽走了。而那是一個十分理解DMD用DSP重要性的人，大原就是在他的要求下才來到達拉斯的…… (詳見全文) 【開發故事】DLP投影儀（七）：要買請耐心等待（上） 為了開拓微鏡器件“DMD”的用途，美國德州儀器的工作 人員在美國內外四處奔忙。當然，在日本的展會上，德州儀器也大張旗鼓地進行了展示。在1995年大阪舉辦的Electronics Show上，該公司就展出了實際采用DMD的顯示器及投影儀。沖著這種投影儀，有3個男人千裡迢迢從東京趕了過來…… (詳見全文) 【開發故事】DLP投影儀（八）：要買請耐心等待（下） “這是真機？還是實物模型？”“不是在騙人吧？”“背後有 什麼機關吧？”在特設會場參觀了試制機的人，大多留下了這樣的感想。另外，很多人表示希望接觸到真機。顯然他們不相信這麼小的投影儀 真的能工作…… (詳見全文) 【開發故事】DLP投影儀（九）：哪裡不好，請告訴我（上） 憑借普樂士推出的超小型前投式投影儀，使人們對DLP技 術的認知度不斷提高。接下來美國TI的最終目標是應用在背投電視上。在這方面，聯手開發的合作方仍然是日本企業。美國TI 的工作人員走訪擁有豐富的電視機開發經驗的企業進行游說。然而，對方提出的嚴格要求卻遠遠超出了TI的預想…… (詳見全文) 【開發故事】DLP投影儀（十）：哪裡不好，請告訴我（下） 在松下電器總部的會議室裡，TI的工作人員與松下電器的 技術團隊相互對峙。TI方面的負責人是當時全權負責DLP背投電視業務開發的Dale Zimmerman。松下電器方面，則 有電視機業務的負責人及許多開發人員參加…… (詳見全文) 【開發故事】DLP投影儀（十一）：這種“白”還是初次見（上） 美國TI的Larry J. Hornbeck殫精竭慮開發出了微鏡器件“DMD”。DMD順利地在前投式投影儀上得到采用，來自日本國內電視機廠商的關注度也與 日俱增，在背投電視上的應用也逐步取得了進展。在商用多屏顯示器方面，還有一家果敢地向實用化發起挑戰的公司…… (詳見全文) 【開發故事】DLP投影儀（完）：這種“白”還是初次見（下） 自TI的Larry J. Hornbeck開始研發DMD起到現在已經過去27年了。這項技術最初只不過是眾多未來的技術之一
Wikipedia
Digital Light Processing (DLP) is a trademark owned by Texas Instruments, representing a technology used in some TVs and video projectors. It was originally developed in 1987 by Dr. Larry Hornbeck of Texas Instruments.
DLP is used in DLP front projectors (small standalone projection units) and DLP rear projection television.
DLP, along with LCD and LCoS, are the current display technologies behind rear-projection television, having supplanted CRT rear projectors. These rear-projection technologies compete against LCD and plasma flat panel displays in the HDTV market.[1]
The single-chip version of DLP and 3LCD are the two main technologies used in modern color digital projectors, with the two technologies being used in over 95% of the projectors sold in 2008.
DLP is also one of the leading technologies used in digital cinema projection.
In March 2008, TI announced the initial production of the DPP1500 chipset, which are micro projectors to be used in mobile devices. Availability for final products would show up in the market early 2009.
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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 heat sink (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
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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, and is currently used in televisions manufactured by Samsung. Yet another method, color LASERs, is currently in use by Mitsubishi in their LASERVUE products.[2]
Single-chip projectors
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| Interior view of a single-chip DLP projector, showing the light path. Light from the lamp enters a reverse-fisheye, passes through the spinning color wheel, crosses underneath the main lens, reflects off a front-surfaced mirror, and is spread onto the DMD (red arrows). From there, light either enters the lens (yellow) or is reflected off the top cover down into a light-sink (blue arrows) to absorb unneeded light. Top row shows overall components, closeups of 4-segment RGBW color wheel, and light-sink diffuser/reflection plate on top cover. | |||
In a projector with a single DLP chip, colors are produced either by placing a color wheel between a white lamp and the DLP chip or by using individual light sources to produce the primary colors, LEDs or LASERs for example. The color wheel is divided into multiple sectors: the primary colors: red, green, and blue, and in many cases secondary colors including cyan, magenta, yellow and white. The use of the secondary colors is part of the new color performance system called BrilliantColor which processes the primary colors along with the secondary colors to create a broader spectrum of possible color combinations on the screen.
The DLP 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, blue and other sections. The colors 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. Now, most systems operate at up to 10x the frame rate.
The color wheel "rainbow effect"
DLP projectors utilizing a mechanical spinning color wheel may exhibit an anomaly known as the “rainbow effect.” This is best described as brief flashes of perceived red, blue, and green "shadows" observed most often when the projected content features high contrast areas of moving bright/white objects on a mostly dark/black background. The scrolling end credits of many movies are a common example, and also in animations where moving objects are surrounded by a thick black outline. Brief visible separation of the colours can also be apparent when the viewer moves their eyes quickly across the projected image. Some people perceive these rainbow artifacts frequently, while others may never see them at all.
This effect is caused by the way the eye follows a moving object on the projection. When an object on the screen moves, the eye will follow the object with a constant motion, but the projector will display each alternating color of the frame at the same location, for the duration of the whole frame. So, while the eye is moving, it will see a frame of a specific color (red for example). Then, when the next color is displayed (green for example), although it gets displayed at the same location overlapping the previous color, the eye will have moved toward the object's next frame target. Thus, the eye will see that specific frame color slightly shifted. Then, the third color gets displayed (blue for example), and the eye will see that frame's color slightly shifted again. This effect is not perceived only for the moving object, but the whole picture.
The effect varies with the rotational speed of the color wheel and the frame refresh rate of the video signal. There is a maximum rotational speed limit for the wheel, typically 10,000 to 15,000 RPM. Video framerate is usually measured in frames per second and must be multiplied by 60 to find the wheel speed, whereas 60 frames/sec equals 3,600 frames/minute. If the color wheel spins 4 times per frame, it is rotating at a speed of 14,400 RPM. (Projector specifications often list the wheel speed at specific framerates as 2x, 3x, 4x, etc.)[3][4] Increasing the video refresh rate to 85 frames per second does not necessarily further reduce the rainbow effect since this rate would increase the wheel speed to 20,400 RPM, potentially exceeding the safe limits of wheel rotation and requiring the projector to drop back to 3x speed, at 15,300 RPM.
Multi-color LED-based and LASER-based single-chip projectors are able to eliminate the spinning wheel and minimize the rainbow effect since the pulse rate of LEDs and LASERs are not limited by physical motion.
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 DLP chip, then recombined and routed out through the lens. Three chip systems are found in higher-end home theater projectors, large venue projectors and DLP Cinema projection systems found in digital movie theaters.
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 three-chip DLP projectors are capable of displaying the entire gamut of colors we can distinguish (this is fundamentally impossible with any system composing colors by adding three constant base colors). In contrast, it is the one-chip DLP projectors that have the advantage of allowing any number of primary colors in a sufficiently fast color filter wheel, and so the possibility of improved color gamuts is available.
Light source
The main light source used on DLP-based rear screen projection TVs is based on a replaceable high-pressure mercury-vapor metal halide 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 or LASERs are used as a source of illumination.
Metal-halide lamps
For metal-halide lamps, during start-up, the lamp is ignited by a 5000 volt 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 while waste heating of the lamp increases. The mercury lamp's end of life is typically indicated via an LED on the unit or an onscreen text warning, necessitating replacement of the lamp unit.
Older projectors would simply give a warning that the lamp life had expired but would continue to operate. Newer projectors will not power up until the lamp is replaced and the lamp hours are reset. Most devices include a lamp hours reset function for when a new lamp is installed, but it is possible to reset a projector to continue to use an old lamp past its rated lifespan.
When a metal-halide lamp is operated past its rated lifespan, the efficiency declines significantly, the lightcast may become uneven, and the lamp starts to operate extremely hot, to the point that the power wires can melt off the lamp terminals. Eventually, the required startup voltage will also rise to the point where ignition can no longer occur. Secondary protections such as a temperature monitor may shut down the projector, but a thermally overstressed quartz arc tube can also crack and/or explode, releasing a cloud of hot mercury vapor inside and around the projector. 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.
LED-based DLPs
The first commercially-available LED-based DLP HDTV 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 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), Samsung electronics (SP-P400) and Casio (XJ-A series). 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.
Luminus Devices PhlatLight LEDs have also been used by Christie Digital in their DLP-based
LASER-based DLPs
The first commercially-available LASER-based DLP HDTV was the Mitsubishi L65-A90 LASERVUE in 2008, which also eliminated the use of a color wheel. Three separate color LASERs illuminate the digital micromirror device (DMD) in these projection TVs, producing a richer, more vibrant color palette than other methods. See the laser video display article for more information.
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 2008, there are over 6,000 DLP-based Digital Cinema Systems installed worldwide.[6]
DLP projectors are also used in RealD Cinema for 3-D films.
Manufacturers and market place
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 technology has quickly gained market share in the front projection market and now holds roughly 50% of the worldwide share in front projection. Over 30 manufacturers use the DLP chipset to power their projectors.
Pros
- Smooth (at 1080p resolution), jitter-free images.
- Perfect geometry and excellent grayscale linearity achievable.
- Usually great ANSI contrast.
- No possibility of screen burn-in.
- Less "screen-door effect" than with LCD projectors.
- DLP rear projection TVs generally have a smaller form factor than comparable 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 and LASER 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.
- DLP Projectors can process up to 7 separate colors giving them strong color performance
- DLP projectors do not suffer from “Color Decay” often seen with LCD projectors in which the image on the screen turns yellow after extended periods of usage.
Cons
- 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), although some models as of 2008 are becoming wall-mountable (while still being 10" to 14" thick)[7]
- Replacement of the lamp / light bulb. The average life span of a TV light source averages 2000-5000 hours 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. Newer generations units use LEDs or LASERs which effectively eliminates this issue, although replacement LED chips could potentially be required over the extended lifespan of the television.
- Some devices may have fan noise.
- 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.
- 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 longer delays. Newer consoles such as the Xbox 360 do not have this problem as long as they are connected with HD-capable cables.[8]
- Reduced viewing angle as compared to direct-view technologies such as CRT, plasma, and LCD.
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.
See also
References
- ^ a b "4 styles of HDTV". CNET.com. 2007-03-13. http://www.cnet.com/4520-7874_1-5108443-3.html. Retrieved 2007-08-13.
- ^ http://www.laservuetv.com
- ^ Discussion of color wheel speed as 2x, 3x per frame. http://www.projector.com/resources/projectordisplaytypes.php
- ^ Book cite on rainbow effect and color wheel rotations per frame, pp 217–218, Newnes Guide to Television and Video Technology, By K. F. Ibrahim, Eugene Trundle, Edition: 4, illustrated, Published by Newnes, 2007, ISBN 0750681659, ISBN 9780750681650, 586 pages, Direct link to cited material via Google Books: http://books.google.com/books?id=90GZPA-hCuMC&pg=PA218&dq=DLP+projector+wheel+4x&ei=tW80SpfFBprAM57izJ4E#PPA217,M1
- ^ "Luminus Devices’ PhlatLight LEDs Illuminate Christie MicroTile’s New Digital Canvas Display". Businesswire. http://www.businesswire.com/portal/site/home/permalink/?ndmViewId=news_view&newsId=20100609006222&newsLang=en. Retrieved 2010-63-28.
- ^ TI (2008-02-15). "“European Cinema Yearbook”". Mediasalles. http://www.mediasalles.it/yearbook.htm. Retrieved 2008-02-15.
- ^ http://www.futurelooks.com/420-CES-2007-Home-Entertainment-Products-Highlights.html?page=4
- ^ "HDTVs and Video Game Lag: The Problem and the Solution.". AVS Forum. 2005-07-11. http://www.avsforum.com/avs-vb/showthread.php?t=558125. Retrieved 2007-08-13.
External links
- DLP Demo
- BOXLIGHT Corp. DLP White Paper https://system.netsuite.com/core/media/media.nl?id=6485&c=492114&h=25551c21675d994130e9&_xt=.pdf
- DLP projectors vs LCD projectors Easy guide on DLP and LCD technology in projectors and how they compare
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