3D TV: How It Works

As the current boom in 3D movies continues—witness AVATAR, Toy Story, Despicable Me, etc.—and movie makers get an ever-larger percentage of revenues from DVD rentals and sales, TV manufacturers have been steadily introducing 3D TV technologies.

Naturally, moviegoers want the same attention-grabbing, you-are-there immersion of a movie such as AVATAR while watching movies and sports at home. But does 3D TV live up to that promise?

NowPublic describes the two major categories of 3D TV—active and passive—and they're a bit more complicated than the red/green glasses you might have worn for 3D movies in the past.

In the active category is so-called "active shutter" technology. In this case, the HDTV alternates projecting left and right images at 120 frames/second (120 Hz). Meanwhile, you're on the couch wearing special "shutter glasses" that are synchronized with the HDTV and alternate closing the left- and right-eye views, so each eye sees only the image intended for it. This happens so quickly that your brain interprets these alternating pictures as a single three-dimensional image—and suddenly you're nearly inside the movie.

In the passive category are TVs that display two slightly different images simultaneously, which you view through specially polarized glasses that resemble sunglasses. (If you saw AVATAR in 3D in theaters you probably watched it through polarized glasses.) Left and right images are projected onto the TV screen through filters polarized at 90-degree angles to one another, and since your glasses are similarly polarized, each eye receives a different image and your brain combines them into a 3D image.

Finally, two no-glasses technologies are in the experimental stages, but they're both a bit tricky. The first involves two projectors set closely behind a screen but at fractionally different angles, so one eye naturally "goes" to one set of images while the other prefers the second set. The downside of this technology is that you've got to sit precisely 4 meters (13 feet) away from the screen or risk seeing both sets of images.

The second technology involves a parallax barrier, essentially a TV screen with two sets of tiny slits in it, angled to aim each of two sets of underlying images at different eyes. Both these technologies are nearing, but not yet on, the market.

Although there's relatively little 3D content available yet, buying a 3D TV (and 3D-capable DVD player) now means you'll get an excellent 2D picture at home now and be ready as 3D content increases, especially movies and sports.

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Have you ever watched AVATAR on a 3D TV? What did you think?