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When 3-D movies returned to theaters five years ago with the opening of Chicken Little,they came with new specs. The old 3-D glasses that relied on red/cyan lenses went the way of Godzilla. Instead the new eye gear used a variety of more sophisticated methods to bring a sharp, full-color, three-dimensional image to viewers’ eyes without limiting the spectrum of colors they could see. Dolby, one of the major players in the 3-D movie market, just received a patent for its glasses, which offers a close-up look at how they work.
The Dolby glasses (Patent No. 7,784,938) rely on a phenomenon called spectral separation. A projector breaks up each of the three primary colors into multiple spectra and beams two different images—one meant for the left eye, one meant for the right eye—to the screen in rapid succession, one right after the other. (The images are projected at a rate of 144 frames per second, so you don't notice the trick.) Multilayer filters on Dolby's glasses allow the left eye to see shorter wavelength bands of blue, green and red than the right eye. “Both eyes get a full spectrum of color, but it's not the exact same frequency that the other eye is getting,” says Martin Richards, a principal staff engineer in Dolby's image technology group. The filters in each lens are made up of 70 to 80 layers of titanium oxide or silicon oxide, each with a different index of refraction; they either reflect or allow light to pass through, depending on its wavelength.
Dolby designed its glasses with curved lenses to correct for cross talk (when the right eye's image leaks into the left eye's field of vision), color shift, and reflections at the edge of the field of view. It also allows for light to hit the glasses from any angle without distortion. The actual glasses are not as bug-eyed as in the original sketch and come enclosed in black frames.