How 3-D TV Works

You have probably looked at 3-D images before with those goofy red and blue glasses. You may have even watched something in 3-D before. Maybe in a movie theater, maybe a TV broadcast from past years. I have done all of these things, but I still thought of 3-D movies or TV shows as a clunky gimmick. So it's a surprise to me as I keep seeing news stories about 3-D TV's. I wanted to know why, all of a sudden, everything needs to be watched in 3-D. As I figured, it comes down to technology.

How This Stuff Works

3DTV's - Not really like this. (MarkWallace)

Most 3-D technologies work by giving the viewer a different image for each eye. Differences in the images give an illusion of depth and make objects appear to be popping out from the screen. 3-D content is easy to produce, just by recording the same thing with two camera lenses in slightly different positions. It is easy enough to be used for many sporting events now. The trick is getting separate images from the screen to each eye of the viewer.

The old red and blue glasses did this by tinting the two images, so the eye with the blue lens could not see the blue parts of the image, and vise-verse. But this messes with the colors and everything ends up seeming blurry, so it didn't catch on. Polarization is another method, used today in movie theaters. Read more here about light polarization. Put simply, two different projectors show images with different types of light, and filters on your glasses block one type of light for each eye. This method requires special coatings on the screen and technology to project two images at the same time, but general consensus is that polarization is the current technology with the best viewing experience.

A Collection of Technologies

The method used in the new home 3-D TV sets is neither of these, and unlike the previous methods, does not put two images on the screen at the same time. Instead, a different type of glasses are used, just as goofy looking as anything else. These glasses have battery-powered LCD lenses that quickly flicker between clear and opaque, blocking half of alternating images on the screen for the right and left eyes, producing the 3-D effect. A few pieces of technology are needed. First, the glasses, which must contain a small battery and be cheap. Not difficult, but ten years ago it would not have been possible. Next, twice as much information needs to be stored and transferred for the video signal. It just happens that blu-ray movies and digital HD TV broadcasting recently allowed for a huge increase in how much information can be put into video signals.

The big one is refresh rate, the number of images per second that the TV displays. Old TV's displayed at 30 frames-per-second, the way video is still recorded. To add images for right and left eyes, double that, to 60 fps. But going from bright image to blackness 30 times per second makes a noticeable and nauseating flicker. So the systems must switch the image twice for each recorded frame, at 120 fps or higher. This is what is really enabling all 3-D TV's. For the last few years, TV manufacturers have been building sets with higher possible frame rates, because regular video looks smoother and cleaner that way. As TVs easily display 120 fps, it is almost trivial to set them up for 3-D. The last piece is to add a transmitter, like the one on a TV remote, to tell the glasses when to open and shut. That, and some extra programming is all that separates a 3-D TV from a regular HDTV.

Problems and (some) Solutions

There are some problems with the chosen method of 3-D display. Aside from being goofy looking and annoying, the glasses are blocking light to your eye for half of the time, so the picture will appear half as bright as without the glasses. The other is that the illusion of depth is difficult for our eyes to process, so any method of 3-D will cause eye strain after enough time. There are methods for displaying 3-D without glasses, including a TV set already built and Nintendo's new portable video game system, but you may have watch from a specific spot.

I think we will see many TV's with the capability for 3-D in the next few years. You can buy a 3-D TV now in many electronics stores, and they work just fine with 2-D. ESPN has already launched a 3-D channel. I don't know if we will all be wearing funny glasses in our living rooms to watch TV, but I thought you might be interested in how it would work.

Additional Links

3-D TV at Wikipedia

How Stuff Works: 3-D TV