Plesniak says the degree of sensation and control afforded by combining a haptic interface with holography “would provide a complete path in digital prototyping.” In one demonstration, she uses the stylus to carve a red drum-shaped object as if it were rotating on a lathe; in another, a sheetlike image becomes dimpled when prodded. In general, the image produced by the system is brilliant, seems lifelike, and looks for all the world as if it is floating in space right in front of the user. “With most 3-D systems it takes a while for the 3-D effect to come in, and you never get as much depth as the math says you should,” says Benton. “But you don’t have those problems with holograms.”The system has some way to go, though, before it’s likely to be commercialized. The biggest problem is that making a video hologram requires crunching enormous amounts of data. That may not be surprising, given that a hologram provides not just a single view of an image, but all views from any number of angles. Still the diffraction pattern from just one high-resolution hologram can easily use up more than a terabyte of data-enough to fill 1,600 compact discs. A moderately flicker-free holographic video would require at least 20 such holograms per second. Clearly, churning through 20 terabytes worth of information every second would require extraterrestrial technology: today’s fastest PCs operate at one- hundred-thousandth that rate. As a result, the Mark II accepts a number of compromises in image quality in order to bring the computing requirements down to a manageable 16 megabytes per second. The system uses a single color, makes only 10.16-by-12.7-centimeter images, and generates a flickering frame-update rate of about seven images per second. In addition, because the image is stripped of the information needed to accommodate an observer’s view of the top or bottom, the image changes only as the observer moves from side to side. “It’s amazing how few people notice that nothing changes when you look over or under it,” says Benton.
A hardware remake that is in the works should bring the system much closer to commercialization. The goals for the overhaul include switching to a parallel-microprocessor arrangement capable of churning out the high processing speeds needed to achieve larger image size, greater resolution, and a faster frame rate.
In addition, the group hopes to make the jump to an ultrahigh-resolution display screen based on microelectromechanical systems. That technology would employ thousands of tiny mirrors and laser beams-each one creating one pixel of a whole diffraction pattern. Such displays aren’t expected to exist for at least a few years, but Benton notes that his group doesn’t plan on seeing its work bear commercial fruit for at least another four years anyway. “Holography is hard,” he says with a sigh. “That’s why it’s one of the longest-range projects at the Media Lab.”