At SIGGAPH 2012, the MIT Media Lab’s Camera Culture group plans to showcase a glasses-free 3D TV featuring a third LCD layer for near-holographic 3D imagery.
Researchers in the MIT Media Lab’s Camera Culture group believe they are one step closer to true glasses-tree 3D TV thanks to a new method for producing multiple-perspective 3D images. In fact, this method could prove to be more practical in the short term than holography, they claim.
There's no question that holographic TV is a long ways off -- it's simply too expensive to sell on the market despite "impressive" recent advancements in holographic technology. There's also another problem: holograms currently don't move. They're pretty to look at, but in order to make them move, they need pixels smaller than anything the industry can currently build at large volume and at low cost.
So rather than use expensive, complex hardware to create holograms, the Media Lab system instead uses technology of today: LCDs. To produce a convincing 3D illusion, the method uses several layers of LCDs featuring a refresh rate of 360 Hz, or 360 times a second. Of course, currently there's no such thing in the mainstream market: LCDs with a refresh rate of 240 Hz have recently appeared on store shelves, just a few years after 120 Hz HDTVs made their debut.
For starters, the base technology of MIT's Media Lab system is also used in current glasses-free gadgets including the Nintendo 3DS: layered screens with the bottom screen 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.
"The bottom screen displays the same pattern of light and dark bands no matter the image on the top screen," MIT News reports. "But Lanman, graduate student Matthew Hirsch and professor Ramesh Raskar, who leads the Camera Culture group, reasoned that by tailoring the patterns displayed on the top and bottom screens to each other, they could filter the light emitted by the display in more sophisticated ways, creating an image that would change with varying perspectives. In a project they dubbed HR3D, they developed algorithms for generating the top and bottom patterns as well as a prototype display, which they presented at Siggraph Asia in 2010."
However unlike a current stereoscopic system which displays only two perspectives on a visual scene (one for each eye), the system Media Lab researchers envisioned offered hundreds of perspectives in order to accommodate a moving viewer. But to produce a convincing 3D image, the resulting display would require a 1,000 Hz refresh rate. Eventually they managed to bring that down to 360 Hz by adding a third LCD layer which displays another pattern, but this in turn made calculating the patterns exponentially more complex.
In solving this specific problem, the team used a method similar to the way CT scans are performed, only in reverse. "As it turns out, the math is similar to that behind computed tomography, or CT, an X-ray technique used to produce three-dimensional images of internal organs. In a CT scan, a sensor makes a slow circle around the subject, making a series of measurements of X-rays passing through the subject’s body. Each measurement captures information about the composition of tissues at different distances from the sensor; finally, all the information is stitched together into a composite 3D image," MIT News reports.
The Media Lab researchers plan to demonstrate this three-layer LCD panel at SIGGAPH 2012 along with a two-panel version that uses a sheet of lenses which refract light left and right. A visual explanation of both displays can be seen in the embedded video below.