ELECTRONIC IMAGING 14.2 Download, Please Go to MAY 2004

Some of the photos and figures here are available in color in the electronic version of the newsletter. To ELECTRONIC IMAGING 14.2 download, please go to http://spie.org/web/techgroups/ei/pdfs/ei14-2.pdf MAY 2004

MAY 2004 VOL. 14, NO. 2 ELECTRONIC IMAGING

LCoS microdisplays SPIE International for projection television Technical Group Newsletter LCoS (liquid crystal on silicon) microdisplays are, mination system that generates white light, typically unlike the active-matrix liquid-crystal displays from a metal halide arc lamp. Next, the light is bro- (LCDs) found on notebooks, reflective. As shown ken up into red, green, and blue bands, pre-polar- in Figure 1, they are built on a Si backplane with a ized, after which the polarization beam splitters Special Issue on: near-standard CMOS process and include the driv- (PBSs) dump each into a separate color channel. ing circuitry that delivers the appropriate voltages The way the LC manipulates polarization de- Displays to the Al electrodes that define the pixels. There pends on the mode in which it is operating, as shown are also layers above the aluminium for in Figure 4. On the left is shown a vertically-aligned Guest Editor planarization, reflection enhancement, and liquid- nematic (VAN) mode. In the unpowered state, the Gabriel Marcu, Apple Computer crystal (LC) alignment. Above the backplane lies LC molecules stand up and the retardation of the the LC layer, followed by an anti-reflection coat- crystal is nearly zero. In this case, the polarization ing, then a common transparent electrode of indium state is unchanged. In the powered state, the LC tin oxide (ITO), both on a sheet of glass. (The de- molecules are forced into the plane of the display, tails of the electro-optical operation of the LCoS and the design is such that in this state the retarda- NEWSLETTER NOW display is beyond the scope of this article, but see tion is about 1/4 wave. This causes the polarization AVAILABLE ON-LINE Reference 1.) All of this is inserted into a package at the mirror to be circularly polarized. Upon re- Technical Group members are being for mechanical and electrical connection to the rest flection, the handedness of the circular state is re- offered the option of receiving the of the system (see Figure 2). versed (just as a clock face is reversed when seen Electronic Imaging Newsletter Figure 3 shows the architecture for a typical in a mirror). This has the effect that the outgoing electronically. An e-mail is being sent three-LCoS projection system. There are three polarization is rotated 90 with respect to the input to all group members with advice of ° the web location for this issue, and major components to this system. First is the illu- asking members to choose between Continues on page 8. the electronic and printed version for future issues. If you are a member and have not yet received this message, then SPIE does not have your correct e-mail address. To receive future issues electronically please send your e-mail address to: [email protected] with the word EI in the subject line of the message and the words electronic version in the body of the message. If you prefer to receive the newsletter in the printed format, but want to send your correct e-mail address for our database, include the words print version preferred Figure 1. Schematic of the basic structure of an LCoS microdisplay. in the body of your message.

SPIE International Technical Group Newsletter 1 ELECTRONIC IMAGING 14.2 MAY 2004

ing market for HDTV receivers were the main Is the CRT’s obsolescence imminent? forces driving improvements in not only guns and deflection yokes, but also in screens, magnetic shielding, and glass technologies. Then, in the In the 1970s, when a young engineer, fresh out the screen, used parallax to make sure each beam early 1990s, TDK developed the RAC deflection of school, started work at a Toshiba CRT (cath- only struck its corresponding colored phosphors. yoke and tube system for Toshiba. RAC systems ode ray display tube) factory in Japan, his man- In the early 1970s, guns shifted from the delta have rectangular-shaped CRT necks and yokes, ager told him that he was making a big mistake. to the inline configuration, in which the three guns which results in an impressive 30% reduction in “This is a sunset industry,” his manager said. were side-by-side. This resulted in a reduction in deflection power. As with the COTY gun, RAC “Soon, CRTs will be obsolete.” Now, more than the number of adjustments needed to align the red, and RAC-like systems are becoming pervasive, 30 years later, LCD, plasma, Digital Light Pro- green, and blue images with respect to one-an- having since been adopted by Matshita, Philips, cessing™, and their variants are eroding CRT other, and eventually allowed the shipment of pre- LGE, and others. markets at a surprising pace, and it appears that aligned tube-yoke combinations to receiver and LCDs will dominate most high-volume applica- monitor assembly factories. To the future tion areas. So we find ourselves wondering: is The ability to systematically model electron Modern-day CRTs can inexpensively provide that manager’s prediction finally about to come behavior in the electric and magnetic fields of a large, bright images with a large color gamut. true? color CRT has been the most powerful enabler Resolution has reached 0.125mm, new cathodes of the development of the technology. Early mod- deliver brighter pictures with lower-cost circuitry, CRT vs. LCD eling techniques were borrowed from early par- and bulbs have become wider and their depths Unlike LCDs, CRTs can directly generate images ticle accelerator work in the 1950s and 1960s and, shorter. Although those working in CRT research in a variety of formats, and do so without digital in 1975, a paper from Zenith articulated the prin- and development agree that there will not be any image scaling and the problems that go with it. ciples of CRT electron gun optimization. By the more big-budget projects on the scale seen in the They also currently enjoy superiority over LCDs early 1980s, computer-modeling tools had been past, innovation continues. A recent example is a in the areas of cost, viewing angle, and smooth developed—thus reducing the need for physical set of technologies for television, known collec- presentation of motion. prototypes—and the pace of innovation quick- tively as ‘slim’ CRTs, which are in pilot produc- Chief among the reasons the CRT is more cost ened. tion. One is Philips’ new 32" wide-screen effective than LCDs are the CRT’s ability to ad- Around 1982-1983, RCA started production on RealFlat™ tube for HDTV, with a depth of only dress millions of pixels sequentially with only the COTY (cost-optimized tube and yoke) gun. 35cm. three analog video signals, and the lower cost and The COTY made a tremendous improvement in The CRT will be still be around for a very long longer lives of CRT production lines. the tradeoff between deflection power and beam time because of its low cost compared to other distortion and was quickly adopted by CRT manu- technologies. Perhaps, as that manager in the Mature progression factures the world over. In the late 1980s, the dy- 1970s said, the CRT industry is a ‘sunset indus- Mass production of television receivers follow- namic quadrupole yoke was introduced. This al- try’: but it’s taking a very long time for that sun ing World War II established CRTs as mature dis- most completely compensates for deflection to slip below the horizon. play components. Advancements in the technol- defocusing of the beams from self-convergence The author wishes to acknowledge contribu- ogy came more slowly after the introduction of yokes used with inline guns. Though it took nearly tions to this article from: Roger Alig, Hsing- color tubes in 1950s. Those tubes used a ‘delta 10 years to perfect, it made 110° display tubes Yao Chen, Chris Curtin, Basab Dasgupta, gun’: three electron guns mounted in a triangular and, thus, thinner displays practical: it was the last Carlo Infante and Seyno Sluyterman. configuration in the neck of the CRT. The red, great breakthrough in gun design. green, and blue guns emited electron beams, which The emergence of a market for high-resolution Dick Cappels were scanned over the screen by a deflection yoke. personal computer displays in the late 1980s, a Mesa, AZ, USA A sheet of steel inside the tube, mounted close to sense of competition with LCDs, and the burgeon- E-mail: [email protected]

C 2004 2005 A XVII International Conference on Optical Imaging IS&T/SPIE’s Electronic Imaging Photoelectronics and Night Vision Devices Optical Diagnostic Imaging from Bench 23 - 27 January 25-28May to Bedside at the National Institutes of Health San Jose, California USA L Moscow, Russia 20 - 22 September Call for Papers • Abstracts Due 5 July 2004 Sponsored by SPIE Russia Chapter. Washington, D.C. USA Exhibition http://electronicimaging.org/call/05/ E SPIE International Symposium Organized by NIH, managed by SPIE Optical Science and Technology http://spie.org/conferences/calls/04/nih/ SPIE International Symposium N SPIE’s 49th Annual Meeting Smart Imagers and Their Applications Medical Imaging 2-6August 6-8October 13-18February Denver, Colorado USA Moscow, Russia San Diego, California USA D Includes technology track on: Signal and Image Processing and Sensors • Algorithms, Architectures, and Devices A • Mathematical Methods For More Information Contact • Detectors and Imaging Devices SPIE ¥ PO Box 10, Bellingham, WA 98227-0010 R http://spie.org/conferences/calls/04/am/ Tel: +1 360 676 3290 ¥ Fax: +1 360 647 1445 ¥ E-mail: [email protected] ¥ Web: www.spie.org

2 SPIE International Technical Group Newsletter ELECTRONIC IMAGING 14.2 MAY 2004

LCDs get up to TV speed

LCDs enabled the notebook computer mechanisms and rates are different. application, have greatly reduced the Depending on the direction of the tran- weight and volume of monitors, and are sition, the purpose of the applied com- in everything from PDAs to fish find- pensation is to either over- or ers. Now, the technology stands poised underdrive the display. The mecha- to take on the biggest display market of nism to implement these strategies, all: television. However, TV requires however, is the same in both directions much more than simply scaling existing of compensation. LCD-monitor panels to wider (for 16:9 Figure 1. General block diagram of the RTC (response-time compensa- HDTV) and larger sizes. A number of tion) overdrive function. Theory of response-time compen- TV requirements exceed the state of the sation (RTC) art of today’s monitors—such as bright- The basic theory of operation is simple ness, contrast, color envelope, color tem- and shown in Figure 1. The RTC block perature, and progressive scan—and re- intercepts the digital video stream and quire a re-engineering of the monitor so- compares the previous grey-level (GL) lution. In particular, one fundamental command to each pixel with the cur- deficiency of LCDs must be overcome rent grey-level command. It then before they can be widely applied to TV: chooses a predetermined alternative LCDs respond too slowly for TV video grey level from a look-up table (LUT). applications. This alternate is applied by this mecha- Computer applications are very for- nism for only one frame. In the next, a giving of slow pixel-response times. The new comparison between previous and same is even somewhat true for DVD current grey level will take place. If movies. Compared with the typical LCD the LUT’s surrogate grey level is cor- refresh rate of 60 frames per second, rect, it will have the effect of DVD movies are typically filmed at a transitioning the transmission of the slow 24 frames-per-second, resulting in Figure 2. An example of RTC overdrive. A surrogate GL is substituted pixel from the previous to the current moving objects being blurred in the for the intended GL that causes the output to meet the intended grey level in this one frame. Figure 2 original content. luminance by the end of just one frame. illustrates the over-drive concept in Broadcast TV is another story. Each terms of this grey-level signal. Be- frame—or field in the case of interlac- cause every combination of previous ing—is captured in less than 1/60th or and current commands is accounted 1/50th of a second depending on the for in the LUT, both directions of com- broadcast standard. The original moving pensation are provided. Figure 3 illus- component of the image is captured in trates a typical RTC block as the last sharper detail, and, in addition, must be stage of the panel’s timing-controller rendered on the display screen at faster ASIC. This keeps the display panel rates than movie frames. Response time and the LUT that characterizes it in the is much more of an issue for television same module allowing the RTC LUT than for most other video sources, and it contents to be specific to the particu- is particularly important for high defini- lar display characteristics. tion TV (HDTV). How well does RTC work? Why optical response lags the Success in forcing the LCD to reach voltage command the target brightness value in one The light transmission through a liquid- Figure 3. An example of RTC overdrive in the system. Highlighted is frame depends, at least in part, on the crystal pixel is controlled directly and the added function of the timing controller in the LCD module. An quality of the LUT contents. The RTC- immediately by the orientation of the liq- external RAM is used as frame FIFO (first in, first out) memory. boost values are predetermined based uid-crystal molecules to the propagating on a particular frame interval and also light wave. But it takes time to move the mol- i.e., the one that makes it move, is the momen- on a particular temperature. A LUT of values ecules from one position to another, and this tary imbalance of two competing torques—the pre-selected for 60Hz will not be optimal for transition entails the response time that is char- restoring torque that tries to pull the molecule 50- or 75Hz operation. And higher tempera- acteristic of an LCD. The transition time be- back to its resting position and the exciting ture results in faster transitions. Thus, tables tween any two grey levels in an LCD depends torque that is induced by the voltage applied to calibrated at one temperature are not good for on two factors: the net torque on the molecule, the LC which tries to align the molecule in its another. It is clear that RTC is the key enabling and the resistance to movement arising from electric field. This field-induced torque varies technology for helping LCD monitors make the material properties and geometries such as flow with the square of the applied voltage, but the transition into the consumer-television market. dynamics, cell thickness, and viscosity. restoring torque is not field-dependent. In other Equipped with RTC, LCD TVs have the re- The net forcing torque on the LC molecule, words, the LCD optical rise- and fall-time quired sharp, bold, moving images needed to Continues on page 8.

SPIE International Technical Group Newsletter 3 ELECTRONIC IMAGING 14.2 MAY 2004

Projection displays

A projection display consists of a pro- Projection systems designed for rear jector and a screen, or—for the largest projection are brightest in the center of displays—multiple projectors tiled to- the field, and high-end systems may fall gether on a single screen. The color char- off as little as 15% in the corners (less acteristics of a projection display are than a typical CRT display). Most pro- determined primarily by those of the jectors, however, create a pattern that is projector. The screen contributes to the brightest at the center of the bottom image appearance by affecting bright- edge. This is the result of keystone cor- ness, viewing angle, and sharpness.1 rection, where the lens is offset with re- The first color projectors consisted of spect to the imaging element. The re- three monochrome CRTs filtered to cre- sult is a projection path whose bottom ate three separate red, green, and blue edge is nearly stationary with respect to images, each projected through its own distance from the lens. This makes it lens. These images were recombined at possible to set the projector on a table the screen, resulting in a system that was without clipping the bottom edge of the difficult to align and images that were image. For small, commodity projectors, not very bright. Modern CRT systems the brightness in the top corners may be produce higher-quality images, but have 65% or less of the brightest point. Figure 1. Non-uniform brightness distribution typical of a digital been replaced in most applications by Contrast for projection displays is de- projector. That the brightest area is near the bottom of the image, projectors based on digital imaging tech- scribed as a ratio, such as 300:1, which rather than in the center, is typical of projection optics with keystone nology. represents the relative brightness of the correction. A digital projector contains a digital brightest white and the darkest black imaging element such as a small liquid projected. The advertised contrast num- crystal display (LCD) or an array of bers, which can exceed 1000:1, are of- micro-mirrors (such as the Digital Mi- ten extreme, rather than typical values, cro Display or DMD™) that modulate and as such are not good predictors of the light from a high-intensity bulb. image quality. “Black” on projection Most digital projectors contain three im- displays is usually a visible gray, caused aging elements and a dichroic mirror that by light leaking through the lens. Only splits the white light from the bulb into CRT projectors can produce an invis- its red, green, and blue components. ibly dark black. These are recombined and displayed, si- The native resolution for a digital pro- multaneously, through a single lens. The jector is defined by its imaging element. quality of the optics for the splitting and Displaying other resolutions is imple- recombining strongly affects the image mented by electronic resampling the in- quality: color, uniformity, sharpness, put image. The most common resolu- and convergence.2 tion is XGA (1024×768), especially for The smallest projectors use a single portable projectors. However, some imaging element and a color wheel of high-end systems are providing UXGA filters, displaying the red, green, and (1600×1200) resolutions, and higher. A blue images sequentially. The small large digital cinema system has a reso- DMD projectors based on the Digital lution of 2048×1080. Figure 2. Chromaticity diagram comparing the gamuts of a five Light Processing (DLP™) technology different digital projectors to the sRGB display gamut and that of a from Texas Instruments include a clear Color properties typical laptop LCD display. filter in the color wheel that is used to Color projectors are additive color sys- add white light to the brighter colors. tems, where the color at each pixel value This increases the brightness and contrast of ther out of the lens, or into a black cavity, de- is defined by the RGB primary colors the system, but only for a limited set of colors pending on the angle of the mirror. To vary the and the transfer function that maps pixel to near white.3 intensity, the mirrors are flickered to create a brightness values. In an LCD projector, the liquid-crystal pan- stream of light pulses. The primary colors for a projection system els act as light valves, modulating the amount are defined by the bulb and filter colors. There of light displayed by varying the opacity of the Imaging properties is variation in both, as well as variation in the pixel. Normally, light shines through the LCD. The imaging properties for a projector are its bulb due to aging. Even projectors of the same An LCoS (liquid crystal on single-crystal sili- brightness, contrast, and resolution. Brightness model can have visibly different color gamuts, con) imaging element, however, combines the is usually specified in ANSI lumens, which are although this can be minimized by carefully liquid-crystal light valve with a reflective sili- measured by averaging nine readings sampled matching the red, green, and blue transfer func- con surface. Light is modulated by the liquid across a uniform white field. This value will tions. The primaries chosen for digital projec- crystal and reflected out the lens. be much lower than the maximum brightness, tors are often visibly different than those for In a DMD projector, each pixel is defined as projectors do not produce a uniformly-bright by a tiny, tiltable mirror. Light is directed ei- image, as shown in Figure 1. Continues on page 8.

4 SPIE International Technical Group Newsletter ELECTRONIC IMAGING 14.2 MAY 2004

Colorimetric characterization of projection displays

In recent years, rapid advancements on background, and lack of temporal have been made in the area of pro- stability.1,5 There have been relatively jection display systems. Improved few reports of the successful colori- image quality—especially higher metric characterization of LCD pro- resolution and luminance—along jection displays.4-6 with size and weight reduction have For Digital Light Projectors widened the areas of application to (DLP™) based on the Digital include areas such as cinema, home Micromirror Device (DMD™) tech- and public entertainment, advertis- nology, it is common to employ a ing, simulation, and information dis- transparent segment in addition to the play. red, green, and blue portions of the It is well known that different color wheel in order to increase the color imaging devices reproduce projector’s brightness. This presents color differently. While this is quite a challenge for colorimetric charac- obvious when comparing funda- terization; especially since the exact mentally different devices such as algorithm for adding the fourth white printers and monitors, it is also true channel is generally not known.4,5 for devices of exactly the same type. Recently, Wyble and Zhang proposed Even two projection displays of the an approach to solving this problem.7 same make and model will have different colorimetric characteristics: Results for example, due to variations in the In our study5 two projector systems characteristics of the lamp. were characterized, one based on To achieve consistent reproduc- LCD technology, the other on DLP tion of color it is therefore neces- technology. The LCD projector sary to perform some sort of color showed fairly good inter-channel in- correction for each individual pro- dependence, especially when ac- jector. The theory and practice of counting for the black level. The color management, a concept well method proposed1 for calculation of known in the graphic arts, provides inter-channel dependency does not a framework that allows for such seem to be directly applicable to the corrections. Color consistency is tested DLP projector due to the non- achieved by mapping the color filtering segment. space of each individual device into The two projectors showed power- a device-independent color space function-like and S-shaped tone re- such as CIEXYZ. sponses for the LCD and DLP pro- Generally, an exact mapping does jector, respectively (Figure 1). The not exist, and therefore different intrinsic responses of the projectors analytical characterization models are S-shaped for the former and lin- are employed to different devices to ear for the latter. The actual responses best approximate this mapping. This therefore seem to be deliberately process of determining a suitable Figure 1. Output response of the primary colors as a function of the R, G, manufactured by internal processing. mapping function and optimizing its and B input levels for the LCD (top) and DLP projector (bottom). The chromaticity changes of the parameters for a given device is primaries resulting from changes in called colorimetric characterization. the input signal were found to be sig- The substantial increase in use of projection simple characterization model that predicts the nificant. The relatively high black level is the displays makes color management of different displayed-color tristimulus values CIEXYZ dominant reason for these changes. types of projectors an important issue. In order from the device-input RGB using non-linear Measurements of 25 spots over the images to achieve this, consistent and standardized gamma calculations followed by a 3×3 matrix revealed poor spatial luminance uniformity for methods of characterization should be estab- operation. This model is typically known as the both projectors. The intensity of the dimmest lished. The International Electrotechnical Com- gain-offset-gamma (GOG) model.2 spot relative to the brightest was only about mission (IEC) has made an effort to standard- In recent years. liquid crystal display (LCD) 20% for the DLP and 30% for the LCD projec- ize the characterization of projection systems, technology is increasingly replacing traditional tor. Somewhat unexpectedly, the LCD showed but little progress has been made since the CRT display technology, both for desktop significantly better spatial color uniformity than completion of a working draft in 1998.1 monitors and projectors. The colorimetric char- the DLP projector. acterization of these devices presents several Tests showed that both the intensity and the Display characterization models difficulties compared to that of CRTs because color of the background influenced the dis- For cathode-ray-tube (CRT) projectors it is of issues like high black level, inter-channel played color. A set of nine color patches, each common to assume that they can be described dependency, imperfect color-tracking charac- as an ideal additive RGB system, and to use a teristics, spatial non-uniformity,3,4 dependency Continues on page 9.

SPIE International Technical Group Newsletter 5 ELECTRONIC IMAGING 14.2 MAY 2004

Active-matrix liquid-crystal displays (AMLCD)

Active-matrix liquid-crystal displays ecules in the center of the cell, which is very ing process. The MVA mode is popular in desk- (AMLCDs) have enjoyed rapid growth in the different for positive and negative vertical top monitors and, as well as a wide viewing past decade. In the last few years, while the viewing. A typical viewing cone for the TN angle, has a high contrast ratio (up to 1000:1). global high-tech industry has been in slow mo- LCD has a 90° horizontal- and just 45° verti- tion, huge investments have continued to pour cal angle. For the typical single-person usage Conclusion into the manufacture of LCDs. It is now a of most notebook and hand-held applications, TFT LCDs have enjoyed tremendous growth US$50 billion business, and is still growing this TN optical characteristic is sufficient. How- recently as a result of image-quality improve- rapidly. Besides the established of these devices ever, for high-end portables or monitors, people ments and large cost reductions. The image in notebook PCs and flat-panel monitors, usually apply wide-viewing films (retardation quality is now similar to that of CRTs, while emerging applications include cell phones, films) onto the TN cell. Retardation films are power consumption is about 50% lower. After handheld devices and LCD TV. The process attractive because they do not require any successful application in notebook panels and of replacing the CRT by AMLCD has begun change in processing up to the final lamination desktop monitors, the next big additional mar- in earnest and, leading the way, are amorphous of the polarizers. Retardation films compen- ket for AMLCDs appears to be in cell phones, silicon-based thin-film-transistor (TFT) LCDs. sate for the retardation in the LC layer and im- handheld devices and television. TFT LCDs of prove horizontal and, to a lesser degree, verti- up to 57" and high-resolution displays with over Twisted-nematic (TN) LCDs cal viewing angle. The wide-viewing films can 200 pixels per inch have been demonstrated and There are various liquid-crystal technologies enlarge the viewing cone to up to 140° hori- are now slated for production. Both IPS and involved in different LCD operations with dif- zontal and 100° vertical. This technology can MVA wide-viewing-angle technologies are ferent viewing-angle requirements. The three be found in Apple 15.2" and 17" PowerBooks fiercely battling for application to LCD TV. leading modes are twisted-nematic (TN), in- and almost all 15" and 17" LCD monitors. While IPS needs further improvement of its plane switching (IPS), and multi-domain ver- contrast ratio, MVA must reduce the angular tical alignment (MVA). Most LCDs are still In-plane switching (IPS) LCDs dependence of its grey scale. using the twisted nematic (TN) liquid crystal The best viewing angle is achieved in the IPS cell that was invented in the early 1970s. The mode. Here, the electric field is applied paral- John Zhong* and Willem den Boer† 4-5µm-thick LC layer is sandwiched between lel to the glass plates by applying a voltage *Apple Computer, Cupertino, CA transparent conductors on two glass plates. between electrodes on the TFT array. The lat- E-mail: [email protected] These each have an alignment layer, which eral electric field causes the LC molecules to †ScanVue Technologies, LLC, Portland, OR causes the elongated LC molecules to twist by rotate parallel to the plates and leads to a very E-mail: [email protected] 90° from front to back plate. Perpendicular wide viewing cone. The viewing angles can be polarizers are attached outside the assembly. extended to 170° both horizontally and verti- Without an applied electric field, the linearly- cal, with a very consistent grey-scale behavior polarized light transmitted through the first and a minimal color shift. This is particularly polarizer is rotated 90° by the TN cell and will important for professional uses of an LCD Tell us about your news, be transmitted by the second polarizer. When monitor. The response time has also been im- an AC voltage of about 2-4V is applied across proved to be comparable to TN by employing ideas, and events! the LC cell, the molecules align along the elec- an over-driving approach. Drawbacks are a tric field and the polarization direction is no generally a lower pixel aperture ratio to accom- If you're interested in sending in an longer rotated by the LC. As a result, the sec- modate the multiple electrodes on the pixel. article for the newsletter, have ideas ond polarizer blocks the light. This operation There are also some manufacturing yield chal- for future issues, or would like to is called the normally-white mode. At interme- lenges. All Apple Cinema Displays employ IPS publicize an event that is coming up, diate voltage levels, a continuous grey scale can technology. we'd like to hear from you. Contact be achieved. The LC cell needs to be operated with an AC voltage without a DC component Multi-domain vertical alignment (MVA) our technical editor, Sunny Bains in order to prevent degradation of the LC-cell LCD ([email protected]) to let her know structure. Another successful approach is to use the MVA what you have in mind and she'll The best way to address the display pixels is mode, in which the LC molecules are aligned work with you to get something through an active-matrix of TFT devices. This perpendicular to the glass plates in the absence ready for publication. adds a switch at each TN-LCD pixel to control of an electric field. The LC fluid in the MVA voltage independently and obtain the intended mode has a negative dielectric anisotropy. This Deadline for the next edition, grey level. Since most TFT-LCDs are backlit, means that when a voltage is applied between 15.1, is: their luminance is proportional to the backlight the transparent electrodes on the two plates, the intensity. Peak brightness of 150-400Cd/m2 is molecules rotate to become parallel to the 30 July 2004: Suggestions for spe- typical. The white luminance is the sum of the plates. In order to obtain a symmetrical view- cial issues and guest editors. ing angle, the pixel is subdivided in domains, red, green, and blue luminance components. 20 August 2004: Ideas for articles The contrast ratio, which is defined as the ratio in which rotation starts with different initial of maximum to minimum luminance, can ex- tilts. Great efforts have been made to improve you'd like to write (or read). ceed 500:1. MVA, so much so that its viewing cone and 22 October 2004: Calendar items for The transmission-voltage curves of TN cells angular color behavior are now fairly compa- the twelve months starting June vary significantly with viewing angles, espe- rable to those in IPS. The mode also eliminates cially at intermediate grey levels. This can be a rubbing process required for alignment in TN 2004. explained by the orientation of the LC mol- and IPS cells, resulting a simpler manufactur-

6 SPIE International Technical Group Newsletter ELECTRONIC IMAGING 14.2 MAY 2004

High-resolution liquid-crystal displays: image quality and bandwidth requirements

In the late 1990s, 200-300 present a bandwidth prob- pixels-per-inch (ppi) proto- lem common to all displays type liquid-crystal displays and image capture devices. (LCDs) were produced. At a video frame rate of 30 Viewed from approxi- fps, HD (1920×1080) for- mately 17", a 200ppi screen mat requires a data rate of provides 30 line pairs per 1.5Gb/s. There is a funda- degree of visual angle and mental tradeoff between matches the spatial resolu- pixel count and data frame tion required for 20/20 vi- rate for a given channel sual acuity. Advances in bandwidth. This is illus- liquid-crystal optical per- trated in Figure 1, assum- formance, pixel-array pro- ing noise-free graphics- cess, drive electronics, card operation at the maxi- backlights, and manufac- mum DVI clock rate of turing yields have com- 165MHz and with little or bined to allow high-perfor- no blanking time. For each mance eye-matched large- DVI clock period, one area displays to enter the 24bit pixel is transmitted. marketplace. High prices, Although there have been combined with a general several recent digital video malaise in the information camera products an- technology sector during nounced with 4×HDTV 2000-2003, slowed the resolution, most video data adoption of this technol- is limited to 1920×1080: ogy. However, recent inter- well-handled by a single est in flat-screen HDTV, Figure 1. Data frame-rate limitations of DVI channels providing 165Mpixel/sec. DVI channel. coupled with price reduc- However, digital-still- tions, has renewed interest camera, computer-gener- in the benefits of high-resolution LCDs for a excellent value9 and performance10 for medi- ated-graphics, medical-imaging and geo- broad range of applications. Improved image cal applications. For color applications, the 10- graphic-information systems often produce quality, equivalent to transparency film or high- bit LUT allows much finer control of color and very large images. The display of these images quality print, has stimulated interest in projec- luminance than can be achieved with a stan- can require rapid pan, zoom, and rotation with- tion and direct-view high-end display products dard 8-bit-graphics-card LUT. out artifacts. This presents a challenge for both for entertainment, medical, and computer ap- The number of screen pixels and the screen the software application and graphics card hard- plications. refresh rate determine the data rate to the dis- ware acceleration. Most graphics card devel- Examples of high-end LCD monitor prod- play. The high pixel count of large-area, high- opment is oriented toward acceleration of 3D ucts include IBM (3840×2400, 22.2", resolution LCDs challenges the graphics card effects, not 2D functionality. For computer 204ppi),1,2 Apple (1920×1200, 23", 98ppi), and application to provide this data. The IBM generation of large moving images, parallel Samsung (1920×1200, 24", 94ppi) and Sharp T221 contains a built-in frame buffer to rendering by a cluster of computers is required. (2560×2048, 28", 116ppi). Human-factors decouple the screen refresh rate and input data LCD manufacturers have improved moving- studies have confirmed that improved task per- rate. Although it is possible to drive well-de- image quality by improving the fundamental formance can be achieved with higher pixel- signed LCDs at very-low screen refresh rates operation of the liquid-crystal light valve. Tech- density displays.3-5 The highest pixel density, without flicker, screen refresh rates are typi- niques include the use of faster switching liq- 204ppi, is obtained with the 9.2-million-pixel cally fixed in the range 40-60 frames per sec- uid crystals, signal processing to speed up IBM T221 display. This display uses the dual- ond (fps). The IBM T221 achieves excellent switching, and pulsed backlighting. If the domain in-plane-switching liquid-crystal mode static image quality at very-low full frame data screen refresh rate is not the same as the data to greatly reduce the dependence of image color rates, as low as 13fps, using any inexpensive frame rate, re-sampling artifacts will occur. and contrast on viewing angle within an 80° digital graphics card with a single digital video Such artifacts appear as a motion discontinu- viewing cone.6 The display has a built-in 10- interface (DVI) output and correct timing to ity or judder at the temporal difference fre- bit-color look-up table (LUT) that can be used support the 3840×2400 format. Good motion quency. If this is near 8Hz or lower, it will be with color calibration and management soft- rendering with typical object or camera mo- visible. ware programs.7 For medical applications, use tions requires data rates of at least 24fps. Fast- LCDs use data-polarity inversion to prevent of this LUT—combined with subpixel dither- moving objects or camera pans can require chemical changes in the liquid-crystal cell and ing techniques—have enabled extremely accu- 60fps or higher. The IBM T221 supports 1-4 to suppress crosstalk and flicker effects. For rate luminance precision8 for DICOM calibra- DVI input channels and can accept up to 48fps many LCDs, the screen refresh rate is fixed at tion. Compared to a monochrome multi-moni- full-resolution video. tor configuration, a single-color T221 provides Formats beyond HD resolution for video Continues on page 9.

SPIE International Technical Group Newsletter 7 ELECTRONIC IMAGING 14.2 MAY 2004

LCoS microdisplays for projection television Continued from cover. polarization. and blue images dur- On the right is ing each frame. shown a twisted-nem- Toshiba was showing atic (TN) mode, which an LCoS-based TV at operates somewhat dif- the Consumer Elec- ferently. There are tronics Show this year. many different varia- JVC have had a high- tions on this theme (as end digital cinema line discussed in Reference of front-screen projec- 1). The unpowered tion systems (D-ILA® state produces circular or Digital Direct Drive polarization at the mir- Image Light Ampli- ror surface, and is fier), using VAN tech- somewhat similar to Figure 2. Aurora Systems liquid-crystal-on-silicon nology, on the market Figure 3. Typical three-color projection optical the powered state of (LCoS) packaged imagers displayed on a for quite some time. system for LCoS. the VAN, although in backplane wafer. They have also been this mode the change demonstrating a con- in polarization is due to a complex combina- sumer-level TV, also VAN-based, but on the tion of birefringence and optical activity. The Aurora backplane. Some of these products are powered state is likewise similar to the expected to hit the shelves this year. Intel have unpowered state of the VAN mode, although announced their entry into the LCoS projec- in this case, there is always a small amount of tion market, but they are being very tight- residual twist left: this is why the optical per- lipped about both technology and production formance of the VAN mode is preferred. schedules. An LCoS display is a spatial, reflective light modulator that manipulates the polarization state of light on a pixel-by-pixel basis. When a Mark Flynn pixel’s reflection polarization state is rotated Senior Display Engineer 90° with respect to its entry state, the PBS trans- Aurora Systems mits the light through the projection system and San Jose, USA onto the screen, producing a bright pixel. If the E-mail: [email protected] pixel reflects in the same polarization state in Figure 4. Representation of vertically-aligned which it entered, the PBS will reflect the light nematic and twisted-nematic LC modes in the Reference powered and unpowered states. 1. S. T. Wu and D. K. Yang, Reflective Liquid back into the illumination system, producing a Crystal Displays, John Wiley & Sons, Chichester, dark pixel on the projection screen. England, 2001. LCoS projection products are at long last production began. Philips now has the first real making it into the marketplace. Thompson/ product line, called Cineos, in the stores. This RCA had a short-lived product a couple of uses a single-panel design, and produces color years back, but it was withdrawn before real images through showing sequential red, green, Projection displays LCDs get up to TV speed Continued from page 4. Continued from page 3. displays, creating substantial color shifts when trast to produce a smooth transfer function. This stand head-to-head and toe-to-toe with the en- colors designed on a display are projected. Fig- increases the often dramatic difference between trenched alternatives on the TV-showroom ure 2 shows the primaries for five different digi- the displayed colors on the speaker’s laptop and floor. tal projectors plotted together with the gamuts the projected colors on the screen. of an sRGB CRT and a laptop LCD display. Dick McCartney The native transfer function for a projector Maureen Stone Principal Display Technologist is defined by the imaging element. DMD ele- Stonesoup Consulting Displays Group ments pulse to encode the grayscale, making E-mail: [email protected] National Semiconductor them naturally linear, whereas LCD elements http://www.stonesc.com Santa Clara, USA are identical to liquid crystal displays. How- E-mail: dick.mccartney @nsc.com ever, most projectors contain image-process- References ing hardware that induces a transfer curve com- 1. M. C. Stone, Color and Brightness Appearance Issues in Tiled Displays, IEEE Computer patible with CRTs and video (a gamma curve). Graphics & Applications 20 (5) pp. 58-66, Digital projectors include brightness and September 2001. contrast controls like those on a desktop color 2. E. Stupp and M. Brennesholtz, Projection display. Unfortunately, many projection sys- Displays, John Wiley & Sons, New York, NY, 1999. tems used for presentation are installed with- 3. W. Kunzman and G. Pettitt, White Enhancement for out carefully adjusting the brightness and con- Color Sequential DLP, Proc. SID Conf., 1998.

8 SPIE International Technical Group Newsletter ELECTRONIC IMAGING 14.2 MAY 2004

High-resolution liquid-crystal displays: Colorimetric characteriza- image quality and bandwidth requirements tion of projection displays Continued from page 7. Continued from page 5. 60fps, pushing the residual low-contrast lumi- Steven L. Wright* and James Larimer† displayed on the same set of backgrounds, gave nance flicker well outside the eye’s window of *IBM TJ Watson Research Center a significant average DeltaE color difference visibility. For moving images, the least amount Yorktown Heights, NY of 4.83 for the LCD, and a more moderate dif- of flicker and crosstalk is achieved with input E-mail: [email protected] ference of 2.94 for the DLP projector. data rates exactly half the screen-refresh rate, †NASA Ames Research Center The characterizations showed that, with mi- with each frame presented in both polarities. Moffett Field, CA nor modifications to account for the black level, To render fast object or camera motions, higher E-mail: [email protected] a conventional display model may be employed screen-refresh rates are required and can lead for the LCD projector for color management, to flicker artifacts. There remains considerable References giving an accuracy that is acceptable for most disagreement among experts over required 1. Y. Hosoya and S. L. Wright, High Resolution applications. An average color difference of LCD Technologies for the IBM T220/T221 sampling rates to capture and render motion. Monitor, SID Int. Symp. Tech. Digest, pp. 83-85, 3.66 between prediction and measurement was The success of 24fps cinema, and the use of 2002. found for a set of 20 random colors. time expansion and contraction by cinematic 2. S. L. Wright, IBM 9.2-megapixel flat-panel artists for dramatic effect, suggests that—for display: technology and infrastructure, Proc. Jon Y. Hardeberg SPIE 4712, pp 24-34, 2002. many applications—lower rates will be suffi- 3. S. L. Wright, et al., Resolution and Legibility: A The Norwegian Color Research Laboratory, cient. Comparison of TFTLCDs and CRTs, SID Journal Gjøvik University College, Norway, and The IBM T221 model DG5 has a screen re- 7, p. 253 1999. SINTEF, Department of Information and fresh rate of 48fps, ideal for input source data 4. J. Gille et al., Very High Resolution Displays: Communication Technology Productivity gains in word-processing and at 24 or 48fps and compatible with both mo- spreadsheet tasks, SID Int. Symp. Tech. Digest, Norway tion-vector interpolation and fade filtering paper 49-3, 2004. E-mail: [email protected] schemes designed to reduce apparent judder.11 5. M. Powers, Very High Resolution Displays: The DG5 is capable of latching at different Reading Performance, SID Int. Symp. Tech. References Digest, paper 49-2, 2004. screen-refresh and input-data rates. When mul- 1. International Electrotechnical Commission, Color 6. K. C. Ho et al., Colorimetric Characterization of measurement and management in multimedia tiple DVI channels are used to render full- Wide-Viewing Angle Technologies, SID Int. systems and equipment - Part 6: Equipment used screen moving images, it is necessary to syn- Symp. Tech. Digest, p. 184, 2000. for digital image projection, IEC Committee chronize the DVI channels to avoid tearing ar- 7. S. L. Wright et al., Color and Luminance Draft 61966-6, 1998. Management for High-Resolution Liquid-Crystal tifacts. 2. R. S. Berns, R. J. Motta, and M. E. Gorzynski, Displays, SID Int. Symp. Tech. Digest, pp. 940- CRT colorimetry. Part I: Theory and practice, To address bandwidth constraints, IBM Re- 943, 2003. Color Research and Application 18, pp. 299–314, search is developing task-dependent hardware 8. S. L. Wright and E. Samei, Liquid-crystal 1993. solutions. For multi-monitor environments with displays for medical imaging: a discussion of 3. J. Y. Hardeberg, Lars Seime, and Trond Skogstad, monochrome versus color, Proc. SPIE 4367-49, predominantly static imagery, a new VESA Colorimetric characterization of projection 2004. displays using a digital colorimetric camera, (Video Electronics Standards Association) digi- 9. D. Hirschorn, T221 Flat Panel Monitor: Review, Projection Displays IX, Proc. SPIE 5002, pp. 51- tal packet video link (DVPL)12 protocol stan- 2003. http://www-1.ibm.com/industries/ 61, 2003. dard has been established. DPVL takes advan- lifesciences/doc/content/resource/insight/ 4. M. C. Stone, Color Balancing Experimental 940975121.html. tage of new developments in ‘intelligent’ digi- Projection Displays, Proc. IS&T/SID Ninth Color 10. E. L. Seigel et al., Clinical comparison of CRT Imaging Conf., pp. 342-347, 2001. tal display hardware to allow selective screen and LCD monitors in the evaluation of non- 5. Lars Seime and Jon Y. Hardeberg. Colorimetric refresh to lower data rates within a digital com- displaced fractures, Proc. SPIE 5371-24, 2004. characterisation of LCD and DLP projection munications architecture. Some tasks, such as 11. J. Larimer et al., Judder-induced edge flicker in displays, J. of the Society of Imaging Display 11 moving objects. SID Int. Symp. Tech. Digest 32, surveillance, are compatible with new sampling (2), 2003. pp. 1094-1097, 2001; J. Larimer et al., Judder- 6. Y. Kwak and L. W. MacDonald, Characterisation and compression techniques that can be com- induced edge flicker at zero spatial contrast, SID of a desktop LCD projector, Displays 21, pp. 179- bined to reduce transmission bandwidth re- Int. Symp. Tech. Digest 34, pp. 1042-1043, 194, 2000. quirements. IBM, under support of the US 2003. 7. David R. Wyble and Hongqin Zhang. Colorimetric 12. S. Millman, Update to VESA Digital Packet Video Army, and in collaboration with NASA and the characterization model for DLP projectors. Proc. Link (DPVL) Proposed Standard, SID Int. Symp. IS&T and SID’s 11th Color Imaging Conf., pp. US Navy, recently demonstrated new capabili- Tech. Digest, Late News paper LP-5, 2004. 346-350, 2003. ties in this area13,14 using digital, modular com- 13. K. Schleupen, A High Resolution, Reconfigurable ponents for image conversion, compression, Video System Efficient in Power and Bandwidth, USDC High Information Content Workshop, and transmission. Arlington, VA, October 2003. A net-centric architecture for communicat- 14. K. Schleupen, High Resolution Video Imaging ing video data to displays is needed to accom- and Display- Quad HDTV, DarpaTech, Anaheim, modate the potential for eye-matched large-area CA, March 2004. display monitors. The need for this new architecture will become increasingly apparent as more applications emerge to take advantage of the opportunities to displace older display technologies, such as film and printing, with high- resolution flat-panel displays.

SPIE International Technical Group Newsletter 9 ELECTRONIC IMAGING 14.2 MAY 2004

C a l l f o r P a p e r s

IS&T/SPIE 17th Annual Symposium

Submit your abstract today! 16–20 January 2005 San Jose Marriott and San Jose Convention Center San Jose, California USA Conferences • Continuing Education • Technical Exhibitions Symposium Chairs: Thrasyvoulos N. Pappas, Northwestern Univ. Andrew J. Woods, Ctr. for Marine Technology/Curtin Univ. of Australia 3D Imaging, Interaction, and Measurement Imaging, Visualization, and Perception Image Processing Digital Imaging Sensors and Applications Multimedia Processing and Applications Image and Video Communications and Processing