How Stuff Works: 3D Movies

Marshall Brain - Mclatchy -Tribune News Service

At this moment in history, we are about to see a huge transformation in the movie theater business. Everything is about to go 3D. While there have been a handful of 3D movies in the past, we are about to enter the golden age of 3D movies.

Dreamworks, the studio that has created animated blockbusters like "Shrek" and "Kung Fu Panda," has stated that all its new animated films will be 3D starting in 2009. Other studios will follow its lead. And there will be thousands of theaters across the United States with the equipment needed to digitally project those movies by 2009. It would not be surprising to see most of the mainstream Hollywood movies coming out in 3D in the coming years.

The obvious question is: How do these new 3D movies work? Let's take a look.

Anyone who has ever used a View Master understands the appeal of 3D images. With a View Master (or any other stereoscopic viewer) you are simultaneously looking at two still images that appear to be nearly identical. The viewer is set up so that the left eye sees one of the images, and the right eye sees the other.

But the images are not identical. When the images were taken, they were shot using two cameras that were several inches to several feet apart. Your brain is able to combine the two slightly-different images and extract 3D depth information from them. What your brain sees is a beautiful 3D image that looks incredibly realistic.

3D movies are doing exactly the same thing. They are simultaneously presenting one moving image to your left eye and another, slightly offset image, to your right eye. But since you are sitting in a movie theater looking at a single screen with both eyes, there's a problem. How do you get separate images into each eye?

In the early days of 3D movies, anaglyph glasses were the answer. These are the familiar red/blue glasses with a red filter for one eye and a blue filter for the other. Both left and right images appear on the screen at once, but one is tinted red and the other is tinted blue. Because of the colored filters in front of each eye, a separate image enters each eye and your brain creates the 3D effect. The obvious problem with this system is that it messes with the color of the images.

The more modern way to handle 3D uses polarized light. This technique makes use of a very weird property of light called polarization. Imagine two synchronized projectors. One projector is showing the images of the movie intended for the left eye, while the other is projecting the images for the right eye. Both projectors point at the same screen.

Now, in front of the lens of the left projector, we put a polarizing filter. The light coming through the projector has light waves oriented in both up-down and left-right directions. But the filter only lets through the light waves with the up-down orientation. We put another polarizing filter on the right projector that lets through only the light waves with the left-right orientation. And to complete the system, we have everyone in the audience wear glasses that also contain two polarized filters. So, the left eye can see only the light coming from the left projector, and the right eye can see only the light from the right projector. The brain puts the two separate images together and creates the 3D effect.

When you use this polarization system with digital projectors, the 3D effect is even stronger. The images are perfectly synchronized and perfectly clear. There aren't any scratches or specs as with film projectors. And animated movies can enhance the effect even more because, in an animated film, you can design the movie around the 3D theme. For example, in the new 3D animated film called "Fly Me to the Moon", the miniature characters fly through a field of 3D grass. The 3D effect is amazing.

Even more amazing is the fact that you will be able to get the 3D effect at home as well. Some TVs using DLP equipment already have 3D capability built in. The TV can display images so quickly that it can alternate images for the left eye and right eye 120 times per second. You wear a pair of electronic shutter glasses. These glasses use liquid crystal shutters to alternately block the left eye and the right eye. A box on top of the TV sends a signal to the glasses telling them when to switch from one eye to the other. Your brain sees beautiful 3D images.

We just happen to live at the moment in history when this 3D transformation is happening. We will be the first ones to see the most amazing 3D movies ever.

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