Podcast #637: Glasses-free 3D projector concept

Glasses-free 3D projector concept

Nothing says “the future of display technology” like holograms. If you’re a Star Wars or a Star Trek fan, you know that someday we’ll have holograms for real, interacting with us. But until now that notion has existing only in science fiction and our imaginations. But fueled by the same dreams you have, over the past three years, researchers in the Camera Culture group at the MIT Media Lab have steadily refined a design for a 3D video technology that doesn’t require glasses at all.

The MIT group believes their concept has the potential to provide a cheaper, more practical alternative to holographic video. And they don’t think it’ll take decades to get there. They’re using a technique called multiperspective 3D, which is quite different from the stereoscopic 3D technology common in homes and movie theaters. So this isn’t stereoscopic 3D without glasses, which some of us have seen and not been impressed with. This is a completely different approach.

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The MIT researchers have built a prototype of their system using off-the-shelf components. There’s nothing exotic about the system, so the cost shouldn’t be prohibitive in mass production. They also built a prototype of a new type of screen that widens the angle from which their projector’s images can be viewed. The technology will be unveiled at this year’s Siggraph conference in Vancouver this August (Aug. 10-14, 2014). Siggraph is the major international conference in computer graphics and interactive technologies.

Much like the holograms in your science fiction imagination, objects depicted by a multiperspective 3D display actually show different perspectives as the viewer moves about them, just as the objects would in the real world. While stereoscopic 3D tricks your brain into perceiving depth that isn’t there, multiperspective 3D draws a visual representation of the object from multiple angles, providing more of a “floating” image than a perceived depth. Next step: the Holodeck.

How it works

We encourage you to read the full news release at mit.edu for all the details. We’ll do our best to present a summary of what they have put together, but we certainly aren’t MIT researchers, nor do we try to play them on the podcast.

The projector uses two liquid-crystal modulators, which are essentially tiny LCD displays, positioned between the light source and the lens. The first LCD is used to adjust the angle of the light passing through it. So the video information (which is the the light passing through it) reaches the second modulator only at particular angles. The combinations of the patterns displayed by the two modulators enable a viewer to see slightly different images from different angles.

“For every frame of video, each modulator displays six different patterns, which together produce eight different viewing angles: At high enough display rates, the human visual system will automatically combine information from different images. The modulators can refresh their patterns at 240 hertz, or 240 times a second, so even at six patterns per frame, the system could play video at a rate of 40 hertz, which, while below the refresh rate common in today’s TVs, is still higher than the 24 frames per second standard in film.”.

Added bonus: Better contrast and resolution

It turns out that passing the light through the two modulators can actually improve the contrast of ordinary 2D video as well. We all know about the challenges LCD displays have had representing true black, and one of the reasons we lament the loss of plasma as much as we do. The problem stems from the fact that a little bit of light always leaks through even the darkest regions of the display.

One of the MIT researchers, Gordon Wetzstein, explains it like this. “Normally you have contrast of, let’s say, values between 0 and 1. That’s the full contrast, but in practice, all modulators have something like 0.1 to 1. So you get this ‘black level.’ But if you multiply two optically together, the black level goes down to 0.01. If you show black on one, which is 10 percent, and black on the other, which is also 10 percent, what you get through is 1 percent. So it’s much more black.”

Not only an improvement in contrast, but by changing the way the two modulators are used, you can actually heighten the resolution of the resulting image. If the patterns displayed on the modulators are slightly offset from each other, you can spread the pixels so that the the light passing through them will interfere with itself in ways that produce a higher resolution image. As you can imagine, the team at MIT has come up with a way to calculate the patterns needed on the modulators to produce that effect on the fly, in real time.

The MIT team believes these two factors could make the technology an excellent bridge for theater operators - even before there is content available to take advantage of the multiperspective 3D capabilities. They can install projection systems now that provide better contrast and add the ability to produce 4k images (using only two 1080p modulators) and then they’ll already have the multiperspective 3D technology sitting there. Sounds like a win-win.