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Acronym Attack - IBM's 3D HDTV

3dSorry I’m a bit late posting this, but here is the first of some interesting tidbits from last week’s Flat Information Displays conference in San Francisco:

IBM gave its first public demonstration of a new technology that allows projectors or rear-projection TVs to switch into a 3D mode. The system requires that users wear glasses with polarizing lenses, as viewers do for modern 3D movies, such as Spykids 3D: Game Over or Aliens of the Deep. The big deal is that IBM representatives say the technology can be implemented on projectors for a small amount of money - about $50 or less, and that the TVs could be set up to switch from 2D to 3D mode at the push of a button.

The IBM rep wouldn't tell me exactly how it works, but here’s my theory:

  • The system uses filters to produce polarized light output that alternates in rapid succession. One frame of video, representing the right-eye view, is polarized in a way that it can pass only through the filter on the right side of the glasses. Then comes a frame of video with the left-eye perspective, polarized so that it passes through only the left-eye filter. Because the images flash in such rapid succession, and because all images persist in the mind for a split second, you “see” the alternating right- and left-side perspectives at the same time, creating the illusion of depth.
  • This system can be easily implemented using off-the-shelf graphics hardware. 3D games and graphics cards have long-supported the ability to create stereoscopic (right- and left-side) views. One old-time application is in LCD shutter glasses, which alternately darken to block the left and right eyes. The alteration is synched to the refresh rate of a computer monitor, so that it displays the left-eye image when the right eye is blocked and the right-eye image when the left eye is blocked. This helps explain why the IBM solution is so cheap, and also why it’s easy to switch from 2D to 3D. Their main innovation is simply to use glasses with polarizing filters in place of LCD shutters. And graphics cards have the built-in ability to switch between the shutter-glass setup and a standard “2D” monitor setup.
  • IBM may be using a spinning wheel made up of polarizing filter segments. As it spins through the light path of the projector, it alternately polarizes the light waves in one direction, then another. I originally thought that IBM had modified the color wheel of a DLP projector, which (in its simplest implementation) has segments of red, green, and blue color filters that allow a DLP projector with a single imaging chip to produce the three primary colors in such rapid succession that the mind sees them all at once. I envisioned a new, six-segment color wheel with a red left-eye polarizing filter, a red right-eye polarizing filter, a green left-eye polarizing filter, etc… My suspicion was heightened when the IBM rep told me that their system does not work with LCD projectors, which have separate chips for red, green, and blue and therefore don’t use color wheels. But the vague, one-page handout that IBM provided states that “The light engine based data projector has not been changed in any way.” So that would rule out installing a new color wheel and recalibrating its timing. My new theory is that IBM has some type of switching polarizing filter that goes on the front of the projector. So why won’t it work with LCD projectors? LCDs control light output through the liquid crystals by using polarizing filters. The light coming out of an LCD is already polarized, with the light waves all aligned in one plane. So you can’t re-polarize it in a second plane to create an image for the other eye.

Does anyone care about a 3D TV?

Probably not, but you never know. IBM (which is seeking to license the technology, not produce actual products) is initially targeting use with video games, which already contain 3D video information. Otherwise, there isn’t much content. Nearly all movies are produced for 2D, although big-time directors such as Steven Spielberg and James Cameron are taking an interest in 3D. The other option is to “upconvert” regular movies to 3D by analyzing the video, guessing at the depth information, and converting it into left- and right-eye images. A company called Dynamic Digital Depth in fact has created software to do this in realtime. I tried it out earlier this year on a Sharp Actius AL3D notebook equipped with a 3D LCD screen. It wasn’t perfect. The images sometimes blurred or went double, what a representative of the company calls “tearing.” But it worked a lot better than I would have expected.

3D has been around since the invention of stereoscopic photography in 1838. And many companies are working on modern 3D technologies using LCDs, plasmas, projection sets, and headgear. Some products require glasses, others don’t. So far, 3D has caught on only with researchers and designers who need to view complex items such as airplane designs or organic molecules in 3D. It could catch on for entertainment, but only if it works so smoothly that people don’t perceive it as some kind of dorky kludge. We’re not there yet.

November 17, 2005 in Future Tech |

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