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Pictures only a computer could love: new lenses create distorted images for digital enhancement

Science News, March 29, 2003 by Peter Weiss

Two thousand years ago, Roman Emperor Nero peered through an emerald monocle to better see his gladiators in combat. Twelve hundred or so years later, eyeglasses started to adorn faces. Up to the present, lenses have primarily served one purpose: to render the world more visible--to people, that is. Now, there are inanimate observers that can also benefit from lenses. More and more, computers are being tasked with making sense of the visual world in ways that people can't.

With a new generation of optics, engineers are recasting visual scenes for computers' consumption. To the human eye, these pictures are visual gibberish, hardly worth a single word, let alone a thousand. To computers, such data can be worth more words than you'd care to count.

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Central to it all are new styles of lenses. Instead of the familiar concave and convex disks, optical engineers are making oddly shaped, radically different lenses tailored to the strengths of computers.

"Once you break away from thinking that the optics have to form something [people] recognize as an image, there are many things that you can do," says Joseph N. Mait of the Army Research Laboratory in Adelphi, Md., and the National Defense University in Washington, D.C.

"There's no reason to go ahead and form an image," agrees Eustace L. Dereniak of the University of Arizona in Tucson. Even in nature, there are beetles that navigate by detecting certain colors or the polarization of light in space without making an image out of the data. People have been slow to explore such alternatives, however, because we've modeled optical instruments such as cameras after our own, image-making eyeballs, says Dereniak.

By weaning themselves away from conventional optics, some researchers are bestowing microscopes and other optical instruments with extraordinarily crisp focusing powers across their entire field of view--a characteristic known as extended depth of field. The lenses under development for these purposes point to many other promising prospects, optics developers say, including cameras no thicker than business cards and improved iris-scanning devices for detecting terrorists in airports.

Other optical engineers are developing novel lenses to help computers sense motion and the physical properties of remote objects.

Going beyond optical phenomena, engineers anticipate making similar lenses that can process other portions of the electromagnetic spectrum, David J. Brady of Duke University Durham, N.C. "It's a general change in the way you think about sensing," he says. Among the technologies that may be strengthened are radar, computerized axial tomography (CAT) X-ray scanners, and magnetic resonance imaging (MRI) systems.

GETTING THE POINT Using computers to manipulate images is old hat. Anybody with a copy of Photoshop or other image-processing programs can do it routinely on his or her desktop. However, what's new is the strategy of modifying images first to make them better suited for the computer mind.

When Edward R. Dowski Jr. arrived at the University of Colorado in Boulder as a Ph.D. candidate in 1990, he already was thinking along those lines. A radar engineer, Dowski was coming from a stint at the Japanese photography firm Konica. For his dissertation topic, he decided to see what it would take to devise a new type of lens that would make autofocusing work better.

Conventional cameras, microscopes, and other optical instruments use sets of convex and concave lenses to focus light onto flat pieces of film or electronic detectors. An autofocus camera typically shifts the positions of some of those optical elements forward and backward until a sensor that monitors contrast differences in the field of view detects sufficient detail.

Dowski's idea was to do away with that little dance by inserting an additional lens between the camera's built-in set of lenses and the detector. It would generate a computer-readable pattern of light that indicated how far out of focus the camera's subject was. The in-camera computer could then calculate how far to move the motor-driven lens.

The idea worked, and Dowski earned his Ph.D. But camera companies didn't show any interest. Dowski's graduate advisor, W. Thomas Cathey then realized that there might be more promise in doing just the opposite of what Dowski had done. He suggested this surprising turn of thought to Dowski, and they decided to give it a whirl.

Cathey and Dowski began by imagining any scene observed through a lens as a mosaic of tiny points of illumination. Ironically, to eliminate autofocusing systems, they devised a defocusing lens. Rather than having to rely on a movable lens to focus light, they came up with a saddle-shaped lens that stays put. It presents what appears to be a blurry image to a computer, which then runs an algorithm that can reconstruct the image point by point. The result is an image in sharp focus in both the foreground and background--that is, with great depth of field.

Cathey confesses that the extended depth of field, which he claims is at least 10 times greater than it is for conventional lenses, does have its tradeoffs. As the computer removes the overall blurring introduced by the ray-altering lens, it introduces a smattering of random errors, or noise, which may show up as subtle roughening of smooth surfaces. However, the improvement in overall focus far outweighs the effect of that misinformation, Cathey says. Moreover, additional computer processing can remove that noise, Dowski adds.

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Pictures only a computer could love: new lenses create distorted images for digital enhancement

Science News, March 29, 2003 by Peter Weiss

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