Digital 3-D uses images to trick your vision as well. But instead of using color to filter out the right image for each eye, most systems use polarization. Polarized lenses allow only light waves that are aligned in the right direction to pass through. In a pair of digital 3-D glasses, each lens is polarized differently. In some glasses, there is a 90-degree difference in polarization. Others use different alignments of circular polarization. The screen is specially designed to maintain the correct polarization when light from the projectors bounces off of it. Rather than looking like a mesh of red and green, movies that use this technology look normal, but blurry, when viewed without glasses.
A digital 3-D movie uses one or two digital projectors to display the picture on the screen. Setups with two projectors use one to display the picture for the left eye and the other for the right. The light that creates each image is polarized to match the corresponding lens. Most one-projector systems use a special polarization switch mounted over the projector lens. This switch is a polarized plate that allows the light for only one of the two images through at a time. In one-projector systems, each eye sees its image for each frame of the movie two or three times in extremely fast succession. Your brain blends these into a seamless, moving, three-dimensional image. A few systems use active glasses that synchronize themselves with the projectors using radio waves, but these tend to be heavier and more expensive than ordinary polarized glasses.
This technology doesn't corrupt the color of the finished image, and it doesn't cause as many unpleasant side effects as anaglyph images. For this reason, some movie makers have started making new movies with 3-D projection in mind. One example is "Meet the Robinsons," which opens March 30. According to director Steve Anderson, the use of digital 3-D helped them tell the story rather than providing a lot of visual gimmicks. "We did want to be conscious of not manufacturing those typical 3-D moments, where things are artificial," says Anderson. "We really wanted to use it more to tell the story...in the quiet emotional scenes between Lewis and Midred, the depth is scaled way back, and you're just concentrating on the characters. In the dinosaur chase...as the kids are hanging inside his mouth, you're seeing enormous amounts of depth."
It's hard to predict exactly what will happen with this technology in the future. However, children's movies that show on 3-D screens tend to perform better at the box office, so more movies may begin to include 3-D projection as time goes on.
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