Technologies that produce sharper images on monitors, projection systems and
virtual displays could transform the way people use computers
In Brief:
A prototype liquid crystal display called
Roentgen offers four times the resolution of the best
commercial computer screens. Meanwhile, chip-based "microdisplays"
bring new crispness to tiny head-mounted devices and wall-size
projection screens alike. Together, such systems may eventually
substitute for printed maps and manuals, and for the cramped digital
readouts on small devices.
If images on a computer screen looked as sharp as a printed page, the working world might seem like a different place. Think how efficient and productive you would be if you could display several legible pages at once, make out fine details in maps and diagrams, or comfortably read lengthy documents onscreen. From a normal viewing distance of 16 to 18 inches, only one display in the world achieves that goal.
The cathode-ray-tube screens on most desktop PCs achieve a resolution of 80 to 100 pixels per inch (ppi), and the best commercial liquid crystal displays resolve up to 120. But Roentgen, an active matrix LCD recently developed at IBM Research, has a resolution of 200 ppi, or 40,000 pixels per square inch. From a normal viewing distance, that's about as fine as the eye can see.
For seekers of visual perfection, there is even more good news: Roentgen is only one of a number of devices IBM researchers are working on to improve the images rendered on computer screens and other electronic products. For example, a "microdisplay" that melds LCD and silicon chip technologies may bring high resolution to projection displays, as well as usher in a new breed of tiny, lightweight and low-power virtual displays for portable electronic devices like pagers, cellular phones and wearable computers. Another emerging display technology, based on organic light-emitting diodes, promises high resolution with several advantages over LCDs.
CATCHING UP WITH PRINT
Roentgen -- named after the German physicist who discovered X-rays, because the device was first envisioned for use as a radiology display -- brings computer displays into the same league as printers. "With this achievement, we are just beginning to have a display technology that approaches the capability of the rest of the system," says researcher Robert L. Wisnieff, manager of the advanced display technology laboratory at IBM's Thomas J. Watson Research Center. Typical image scanners and laser printers, for example, with 300 or 600 dots per inch (dpi) accuracy, far exceed the resolution of ordinary displays. Images in high-quality magazines are printed with 150 lines to the inch.
With its sharp definition, Roentgen renders three- or four-point type that is perfectly readable and free of the "jaggies" that mar fine print at lower resolutions. The display also allows more precise kerning, the subtle variations in character spacing that make type more pleasing to the eye.
This heightened visual sharpness, says Wisnieff, will both enhance existing computer applications and open new avenues for tomorrow. For example, unlike present displays, which make you scroll an image to read a full page of text, Roentgen displays a fully readable page -- actually, almost two pages -- at once. "The human visual system is good at taking in an entire scene, finding what's important, and zooming in on its own," Wisnieff notes. "If I can show everything at once, without time-consuming manual pans and zooms, I improve productivity."
Thus, the early adopters of this new display will be people who need to view large volumes of complex data at high resolution. Digital libraries in hospitals and insurance companies, which store scanned images, as well as graphic design and electronic publishing houses, are all expected to embrace the new display's high resolution, as are computer-aided design and manufacturing facilities. Such high resolution would also enable aircraft mechanics to view schematics or mechanical drawings with the same level of detail as in a manual. Advertising is also fertile territory for the new display because of its rich-looking, high-quality images.
To achieve 200 ppi clarity, researchers had to pack pixels even tighter than in IBM's previous resolution record-holder, a display called Monet, which resolves 157 ppi (see Research, Number 3, 1996, p. 18). They shrank each of the three subpixels -- one each for red, blue and green -- that make up one pixel into rectangles only 42 by 126 microns in area. More than 1.6 miles
of thin-film, signal-carrying "wires," specially formulated from copper rather than the conventional molybdenum and tungsten, traverse the display. The alternative metals prevent excess electrical resistance in the ultrathin wires.
REAL-WORLD DESIGN
Manufacturability remained a key goal in designing the display. Its breakthrough technology -- developed in a research laboratory -- had to carry over into a fast-paced, high-volume factory. "Unlike in the lab, where you can take a day to set up a tool to do one thing, in a factory you have just one minute," says Wisnieff.
For the display to be suitable for the PC and workstation markets, the researchers also needed to keep down the overall system cost. That meant that the graphics adapter, the component that translates software commands into image-rendering signals that make sense to the display, had to be low-cost. So rather than develop new graphics adapter chips from scratch, researchers -- in particular, Kevin Warren, manager of flat panel display systems at Watson -- took a much more practical and innovative route.
Roentgen, with a 16.3-inch-diagonal viewing area, displays 2,560 x 2,048 pixels (a total of more than 5 million pixels). No off-the-shelf graphics adapter is available for that size. Fortunately, however, a common PC graphics standard, SXGA, governs displays that are exactly one-quarter that size: 1,280 x 1,024 pixels. By conceptually viewing Roentgen as four interconnected SXGA displays, Warren constructed a low-cost adapter from four SXGA adapter chips -- components that sell in high volumes for just tens of dollars. "What you see on the screen is a seamless pattern of the four adapter chips working together," says Wisnieff, noting that this one stroke takes Roentgen a good way down the road to commercial success. Adds Warren: "It means you don't have to focus on a special, high-end adapter. Instead, you can use something generic to make those 5 million pixels sing and dance."
So far, Roentgen, now past the research and early development phases, has appeared at IBM's Technology Fair, held in September in Tokyo. The next step for researchers is to build a small number of displays for selected customers to evaluate. When customer comments are in, says Wisnieff, Roentgen should go to market soon thereafter. According to one estimate, the display may appear in high-end ThinkPad® notebook computers in late 1999 or early 2000.
PETITE PROJECTOR
The bulky and power-hungry cathode-ray tube (CRT) behind most desktop computer displays is also at the heart of most projection systems, which shoot a computer's video output onto a screen for group presentations. Here, too, IBM researchers are forging microelectronic counterparts that promise to push the venerable picture tube into history. One such system has emerged from the work of Robert Melcher and the projection display team at Watson.
By marrying two well-understood technologies -- liquid crystals and silicon integrated circuits -- Melcher and the group have produced a light-valve microdisplay that works by reflecting light from millions of tiny mirrors. The first to achieve results melding the two technologies, Melcher says that success hinged on using a chemical-mechanical polishing process to smooth the silicon's microscopically rough surface into a mirrorlike finish. One version of the light valve -- already tapped by several projector makers for new products -- generates SXGA images.
In this device, more than 1.3 million pixels are packed into a 1.3-inch-diagonal surface. Each pixel, formed by a mirror immersed in liquid crystal material, is controlled by a transistor in the silicon substrate. The microdisplay works when a specially designed arc lamp beams an intense light, which has been polarized and divided into red, blue and green rays, toward the mirrors.
As the light passes through the liquid crystal to and from the mirrors, its polarization is modulated by the liquid crystal in response to electrical signals, which are applied to the individual mirrors and represent the image to be projected. On their way to a projection screen, the reflected red, green and blue image components are combined into a full-color image. The image enters a polarization-sensitive optical system -- which blocks or passes the light, depending on its polarization -- and is magnified by a projection lens. The composite of illuminated pixels passing through the lens paints the image on a screen.
Nor are uses for the microdisplay limited to image projection. The projection team is exploring applications in computer monitors. In fact, they have already built a prototype 4 million (2,048 x 2,048) pixel, 100 ppi monitor having a 28-inch-diagonal viewing area. In contrast, building such a large monitor using LCD technology would be quite expensive, according to Melcher.
Large, high-resolution, digital television screens are another place for microdisplays, but will require improvements in the device's color management capability. One difficulty, says Melcher, is getting the light source to hold the correct color temperature and balance. In particular, arc lamps tend to change their color balance with age. Another difficulty is achieving sufficient color depth. "But," Melcher says, "there are no physical laws that must be broken to overcome these problems. It's a matter of getting the right experience and tweaking things to get it done."
GETTING VIRTUAL
Perhaps ironically, the same combination LCD-silicon devices at the heart of emerging methods for projecting large screen images are also poised to launch tiny "virtual displays" for products where light weight is key. By shrinking the already small 1.3-inch-diagonal microdisplay to a 0.25- to 0.5-inch diagonal and adding optical magnification, researchers say they can produce a device small enough to fit a lightweight visor or serve as the viewfinder in handheld equipment. For the viewer, however, the effect is the same as watching a 15-inch-diagonal display from 24 inches away.
The tiny device offers a much lighter, less power-hungry and lower-cost approach than other miniature display technologies, including CRTs, light-emitting diodes and ordinary LCDs. "It draws very little power, yet gives a viewing experience available today only at a desk," says Paul Alt, a manager for exploratory display technology. "And when you make them as small as half an inch, they are inexpensive."
Other candidates for virtual displays are special light-emitting diodes (LEDs) made from organic materials that offer more colors and lower manufacturing costs than conventional LEDs. Unlike LCDs, these organic LEDs (OLEDs) require no backlighting or other separate illumination source. "With OLEDs," says Alt, "a big advantage is that much of the optics and the depth added to provide illumination go away." OLEDs also respond faster than conventional LCDs -- important for motion video. However, he cautions, the technology is less mature than that of LCDs, and its efficiency, manufacturability and long-term stability need improvement.
Regardless of the approach, virtual displays will meet the stringent size and power restrictions of forthcoming wearable computers. At its recent Technology Fair in Tokyo, in fact, IBM demonstrated just such a system. It combined a palm-sized computer -- a reconfiguration of a complete ThinkPad 560 -- with a virtual display designed and built by Russell Budd, a senior engineer in the display group at Watson.
Virtual displays will have many other applications, as well. They will be
ideal for digital still cameras and camcorders. And they will replace the
limited and sometimes hard-to-read LCDs found on personal digital assistants,
cellular phones and pagers. While such devices today show just a few lines
of characters, future versions with virtual displays could be used to present
faxes, browse the Internet or show very long messages. In short, with research
advancing on these and other fronts, display technology promises to transform
our view of computers, figuratively and literally.
Gil Bassak is a freelance technical journalist who lives in Ossining, New York.
