Glasses-free 3-D projector

Christine Daniloff/MIT

New design could also make conventional 2-D video higher in resolution and contrast.

Over the past three years, researchers in the Camera Culture group at the MIT Media Lab have steadily refined a design for a glasses-free, multiperspective, 3-D video screen, which they hope could provide a cheaper, more practical alternative to holographic video in the short term.

Now they’ve designed a projector that exploits the same technology, which they’ll unveil at this year’s Siggraph, the major conference in computer graphics. The projector can also improve the resolution and contrast of conventional video, which could make it an attractive transitional technology as content producers gradually learn to harness the potential of multiperspective 3-D.

Multiperspective 3-D differs from the stereoscopic 3-D now common in movie theaters in that the depicted objects disclose new perspectives as the viewer moves about them, just as real objects would. This means it might have applications in areas like collaborative design and medical imaging, as well as entertainment.

The MIT researchers — research scientist Gordon Wetzstein, graduate student Matthew Hirsch, and Ramesh Raskar, the NEC Career Development Associate Professor of Media Arts and Sciences and head of the Camera Culture group — built a prototype of their system using off-the-shelf components. The heart of the projector is a pair of liquid-crystal modulators — which are like tiny liquid-crystal displays (LCDs) — positioned between the light source and the lens. Patterns of light and dark on the first modulator effectively turn it into a bank of slightly angled light emitters — that is, light passing through it reaches the second modulator only at particular angles. The combinations of the patterns displayed by the two modulators thus ensure that the viewer will see slightly different images from different angles.

The researchers also built a prototype of a new type of screen that widens the angle from which their projector’s images can be viewed. The screen combines two lenticular lenses — the type of striated transparent sheets used to create crude 3-D effects in, say, old children’s books.

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As content creators move to so-called “quad HD,” video with four times the resolution of today’s high-definition video, the combination of higher contrast and higher resolution could make a commercial version of the researchers’ technology appealing to theater owners, which in turn could smooth the way for the adoption of multiperspective 3-D. “One thing you could do — and this is what actual projector manufacturers have done in the recent past — is take four 1080p modulators and put them next to each other and build some very complicated optics to tile them all seamlessly and then get a much nicer lens because you have to project a much smaller spot and bundle that all up together,” Hirsch says. “We’re saying you could take two 1080p modulators, stick them in your projector one after the other, then take your same old 1080p lens and project through it and use this software algorithm, and you end up with a 4k image. But not only that, it’s got even higher contrast.”

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