Glasses-free 3-D TV looks near

As striking as it is, the illusion of depth now routinely offered by 3-D movies is a paltry facsimile of a true three-dimensional visual experience. In the real world, as you move around an object, your perspective on it changes. But in a movie theater showing a 3-D movie, everyone in the audience has the same, fixed perspective - and has to wear cumbersome glasses, to boot.

Despite impressive recent advances, holographic television, which would present images that vary with varying perspectives, probably remains some distance in the future. But, in a new paper featured as a research highlight at this summer's Siggraph computer-graphics conference, the MIT Media Lab's Camera Culture group offers a new approach to multiple-perspective, glasses-free 3-D that could prove much more practical in the short term.

Instead of the complex hardware required to produce holograms, the Media Lab system, dubbed a Tensor Display, uses several layers of liquid-crystal displays (LCDs), the technology currently found in most flat-panel TVs. To produce a convincing 3-D illusion, the LCDs would need to refresh at a rate of about 360 times a second, or 360 hertz. Such displays may not be far off: LCD TVs that boast 240-hertz refresh rates have already appeared on the market, just a few years after 120-hertz TVs made their debut.

''Holography works, it's beautiful, nothing can touch its quality,'' says Douglas Lanman, a postdoc at the Media Lab and one of the new paper's co-authors. ''The problem, of course, is that holograms don't move. To make them move, you need to create a hologram in real time, and to do that, you need … little tiny pixels, smaller than anything we can build at large volume at low cost. So the question is, what do we have now? We have LCDs. They're incredibly mature, and they're cheap.''

Layers of research

The Nintendo 3DS - a portable, glasses-free 3-D gaming device introduced last year - uses two-layered LCD screens to produce the illusion of depth, with the bottom screen simply displaying alternating dark and light bands. Two slightly offset images, which represent the different perspectives of the viewer's two eyes, are sliced up and interleaved on the top screen. The dark bands on the bottom screen block the light coming from the display's backlight in such a way that each eye sees only the image intended for it.