The big picture


By Charles Seife in Washington DC A THREE-dimensional computer image of a plastic dinosaur might be the first step towards bringing viewers television in true 3D. Unlike holography, which requires coherent laser light to generate a picture, the new technique works with ordinary light—which could eventually make it possible to record a live event and transmit the information to a 3D viewing system. In an ordinary camera the lens acts as a kind of analogue computer, running a “program” that transforms the information (light) from the outside world into an image on a flat medium, usually a piece of film. Now David Brady, an electrical engineer at the University of Illinois at Urbana-Champaign and his colleagues are using a digital computer instead of a lens, and in the process, are extracting enough information from the light to create a 3D image. To do this the team are using mathematical techniques that help radio astronomers map the sky. The team illuminated a small plastic dinosaur with light from a halogen lamp, and split the light coming from the dinosaur into two beams (Science, vol 284, p 2164). When the beams were recombined, they interfered with each other—albeit more weakly than with coherent light, where all the waves are “in step”. As the model dinosaur rotated, the scientists recorded 128 interference patterns. Taken together, these patterns contained all the 3D information about the object, which a computer program could turn back into a 3D facsimile of the dinosaur. “It’s a simple, really efficient algorithm,” says Brady. One big advantage of this technique is that it remains perfectly in focus over an infinite depth of field, unlike conventional lenses, which trade the quality of an image for the volume which is in focus. The resolution of the interferometric image depends only upon the distance you are from the camera. This would make the technique particularly useful for 3D microscopy. Brady envisages his technique producing high-resolution images of cells as they interact. “There’s nothing to keep you away from micron resolution,” he says. Since confocal microscopy uses a scanning technique—the focal plane is moved back and forth to get “slices” of cells to make a true 3D image. This makes it difficult to make a movie of a cell as it moves about. With the interferometric technique, a recorder could use an array of light sensors arranged in a circle to produce the same effect, allowing a researcher to record real-time 3D data. “Most 3D imaging systems require structured illumination and scanning, which is not suitable for temporal three-dimensional images,” says Brady. “If you’d like to create movies of cells, you can do it with this technique.” Even when the object being imaged is far away from the detectors—such as players in a sports arena—the technique is still useful. “If you want to capture a basketball game in 3D, these kind of systems are appropriate,” says George Barbastathis, an electrical engineer at MIT. “If you had a 3D viewer at home, you could watch the basketball game in virtual reality—the viewer could have the feeling that he’s actually in the middle,
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