Digital Light Processing

When one first hears about digital light processing (DLP), it seems almost impossibly complex, even magical —— millions of tiny mirrors on a chip the size of your thumbnail, each of them capable of moving thousands of times per second to create a digital image. In fact, DLP gives new meaning to the phrase “smoke and mirrors” as it applies to computer-related technology.

How DLP Works

In essence, DLP is a nanotechnology implementation of the old survival technique of using a mirror to signal for help ——its purpose is to shine a controlled series of light flashes on a target to send a message. The mirror in this case is part of an optical semiconductor called a digital micromirror device, or DMD. The DMD chip contains not one but an array of up to 2.1 million microscopic mirrors, each just 16 micrometers square (less than one-fifth the size of a human hair) and 1 micrometer apart.

The DMD chip is driven by a digital video or graphic signal in which each digital pixel corresponds to a single mirror on the DMD. Add a light source and a projection lens, and the mirrors can reflect a digital image onto a viewing screen or other surface. Each mirror is mounted on tiny hinges, so it can be tilted 12 degrees toward or away from the light source.

The control electronics direct each mirror to tilt——in other words, to switch on and off——up to 5,000 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 often reflects a darker-gray pixel. This lets DLP project up to 1,024 shades of gray.

To get color, such as for a TV set, a rotating color wheel (with red, green and blue filters) is put between the white light source and the DMD. The control input delivers separate signals for each of the three colors, and each mirror (i.e., each pixel) is switched on and off as the filter rotates each color between the lamp and DMD.

For example, to project a yellow pixel, a mirror will reflect only red and green light to the projection surface. To project a purple pixel, that mirror will be switched off while the blue filter is in position, and the blue and yellow flashes will alternate so rapidly, our brains will blend them together and we'll see purple. This process allows a DLP system to produce up to 16.1 million colors. Older DLP systems also included a clear segment to bump up overall brightness at the expense of color saturation.

Consumer-grade television monitors use the system described above. For very large projection, such as in movie theaters and auditoriums, a more sophisticated system uses three DMD chips, one for each color, plus an optical prism. The prism splits white light into colors and then recombines the three images before sending them through the projection lens. This system, called DLP Cinema, can produce 35 trillion colors.

In most applications, DLP competes directly with LCD projection. DLP typically offers greater contrast (up to 5,000-to-1 vs. LCD's 800-to-1), with better blacks, while LCD produces greater color saturation. Side by side, an LCD display looks slightly sharper than a DLP in text display applications, but DLP has the edge with moving video, reducing pixelation, or the “screen-door effect.”

The brightest projectors still use LCD technology, which is slightly more efficient, but the smallest, lightest projectors use DLP. In 2003, DLP systems accounted for 13% of the market for large-screen televisions (over 40 inches). In the past year, the number of models of DLP TVs has tripled.

時文選讀

數(shù)字光處理

當(dāng)?shù)谝淮温牭綌?shù)字光處理(DLP)時，它似乎是無法想象的復(fù)雜，甚至不可思議——在大拇指指甲大小的芯片上有數(shù)以百萬計(jì)的鏡子，為了生成數(shù)字圖像，它們能每秒轉(zhuǎn)動數(shù)千次。事實(shí)上，當(dāng)DLP應(yīng)用于計(jì)算機(jī)有關(guān)的技術(shù)時，它給“欲蓋彌彰”這個成語賦予了新的意義。

DLP是如何工作的?

從本質(zhì)上講，DLP是用納米技術(shù)實(shí)現(xiàn)了一種利用鏡子發(fā)求救信號的古老求生術(shù)——其目的是將受控的閃光照亮目標(biāo)以發(fā)送消息。在這里，鏡子是被稱做數(shù)字微鏡器件(DMD)的光半導(dǎo)體的一部分。DMD芯片包含了不是單個而是多達(dá)210萬個微鏡子組成的陣列，每個鏡子只有16平方微米(小于人的頭發(fā)的五分之一)，間隔1微米。

DMD芯片由數(shù)字視頻或圖形信號驅(qū)動，其中每個數(shù)字像素對應(yīng)于DMD芯片上的一面鏡子。加上一個光源和投影鏡頭，這些鏡子就能將數(shù)字圖像反射到觀看屏幕或其他表面。每面鏡子安裝在微型鉸鏈上，所以它能對著光源傾斜正負(fù)12度。

控制電路指揮每面鏡子傾斜——換言之進(jìn)行開關(guān)，速度可高達(dá)每秒5000次。當(dāng)鏡子開的頻率大于關(guān)的頻率時，它反射淺灰色的像素，鏡子關(guān)的狀態(tài)更多時，就反射深灰色像素。這就讓DLP投影高達(dá)1024級的灰度。

為獲得色彩，如為電視機(jī)等，在白光源和DMD之間放置一個旋轉(zhuǎn)的色彩輪(上有紅、綠和藍(lán)三種濾色鏡)?？刂戚斎霝槿N顏色分別提供信號，當(dāng)濾色鏡旋轉(zhuǎn)燈泡和DMD之間的每種顏色時，每個鏡子(即每個像素)就開關(guān)。

例如，要投射黃色像素，鏡子只向投影面反射紅光和綠光。為投射紫色像素，藍(lán)濾色鏡在位的同時鏡子處于關(guān)，藍(lán)色和黃色交替地快速閃光，我們的大腦會將它們混合起來，我們就看到紫色。此處理方式允許DLP系統(tǒng)產(chǎn)生1610萬種顏色。陳舊一些的DLP系統(tǒng)還含有透明片，以犧牲色彩飽和度為代價來提升亮度。

消費(fèi)級的電視監(jiān)視器采用上述的系統(tǒng)。對于非常大的投影，如電影院和大禮堂中的投影，系統(tǒng)更復(fù)雜一些，采用三個DMD芯片，一個芯片對應(yīng)一種顏色，外加一個光學(xué)棱鏡。棱鏡先將白光分成單色光，然后在將圖像發(fā)送出去之前，通過投影透鏡將三種圖像合并起來。此系統(tǒng)叫做DLP影院，能產(chǎn)生35萬億種顏色。

在大多數(shù)應(yīng)用中，DLP直接與LCD(液晶)投影競爭。通常DLP提供更高的對比度(高達(dá)5000∶1，而LCD只有800∶1)和更好的黑色，而LCD的色彩飽和度更好一些。將兩者并排放在一起，LCD顯示器在文本顯示應(yīng)用中看上去稍微比DLP清晰一些，但對于活動的視頻圖像，DLP擁有邊緣，減輕了像素化，即“屏幕門效應(yīng)”。

目前最亮的投影機(jī)使用的是LCD技術(shù)，它的效率也稍為高一些，但最小、最輕的投影機(jī)使用DLP。在2003年，DLP系統(tǒng)在大屏幕電視(超過40英寸)市場上的份額為13%。在過去的一年里，DLP電視的型號多了3倍。