How do 3-D movies work? Use of digital projection, polarized lenses the key

http://www.chicagotribune.com/services/newspaper/printedition/friday/friday/chi-3d_movies-0905sep05,0,6113136.story

 

By Marshall Brain | McClatchy/Tribune newspapers

 

September 5, 2008

At this moment in history, we are about to see a huge transformation in the movie theater business. DreamWorks, the studio that has created animated blockbusters such as "Shrek" and " Kung Fu Panda," has stated that all its new animated films will be 3-D starting in 2009. Other studios will follow its lead.

 

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

 

Anyone who has ever used a View-Master understands the appeal of 3-D 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 3-D depth information from them. What your brain sees is a beautiful 3-D image that looks incredibly realistic.

 

Movies in 3-D 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 because 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 3-D 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 filters in front of each eye, a separate image enters each eye and your brain creates the 3-D effect. The obvious problem with this system is that it messes with the color of the images.

 

The more modern way to handle 3-D uses polarized light. This technique makes use of a 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, a polarizing filter is placed in front of the lens of the left projector. 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. Another polarizing filter is placed on the right projector that lets through only the light waves with the left-right orientation. And to complete the system, everyone in the audience wears 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 3-D effect.

 

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

 

Even more amazing is the fact that you will be able to get the 3-D effect at home as well. Some TVs already have 3-D 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 3-D images.

 

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

 

Marshall Brain is founder of HowStuffWorks.com.