MIT's 3-D Projector Could Be Bridge to Holographic Video

In a technological development that may have applications in medical imaging, researchers at the MIT Media Lab's Camera Culture group have built a prototype of a glasses-free 3-D TV projector that they intend to unveil at this year's SIGGRAPH (Special Interest Group on Computer Graphics and Interactive Techniques) show.

The projector can also improve the resolution and contrast of conventional video. The researchers hope this could make it an attractive transitional technology, cheaper and more practical than holographic video, as content producers gradually learn to harness the potential of multiperspective 3-D.

The MIT researchers, research scientist Gordon Wetzstein, PhD; graduate student Matthew Hirsch; and Ramesh Raskar, PhD, associate professor of media arts and sciences and head of the Camera Culture group, built a prototype of their new system using off-the-shelf components. Raskar's group has been working on refining glasses-free 3-D since they developed their HR3D system, which they presented at SIGGRAPH Asia in 2010.

Reporting for the MIT News Office, Larry Hardesty describes the team's 3-D projector. Hardesty says that the heart of the projector is a pair of liquid-crystal modulators, like tiny liquid-crystal displays (LCDs), that are 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," Hardesty says, so that "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 problem that arises is that, for each frame of video, each modulator must display six different patterns to arrive at eight viewing angles. Hardesty explains that the key to the researchers' system is an algorithmic technique for calculating how much information overlaps between the viewing angles and can be repeated, and how much needs to be varied. Preserving as much information as possible enables the projector to produce a brighter image.

The resulting set of light angles and intensities then has to be encoded into the patterns displayed by the modulators. By tailoring their code to run on video game graphics processing units, the scientists have gotten it to run almost in real time, with a very small lag.

Whether or not the result of all this technological development ever appears in your doctor's latest medical imaging scanner or playing last summer's blockbuster at your local electronics outlet, it is certain that holographic video is one step closer... and they're still working on it.

Stephen Levy is a contributor to Qmed and MPMN.