Today's computer-animated movies do a pretty good job of imitating three-dimensional environments. In films like "The Incredibles," "Cars" and the "Shrek" series, characters seem to exist as solid objects that can move and interact with their surroundings. It takes a lot of work and a good understanding of how people perceive images to achieve this effect. Filmmakers even make real, tangible models of their characters, known as maquettes, to help them figure out how a 3-D character would move in a 3-D space.
In the past few years, filmmakers have taken this attempt to recreate three-dimensional space on screen one step further. With digital 3-D, animators can fool your eyes and brain into thinking that they're looking into a 3-D space rather than at a 2-D screen. The end result is like looking through a window into a real, three-dimensional world or like having elements of the scene in the theater with you. While it's similar to older 3-D movies, the technology is considerably more advanced.
Both old and new 3-D movies rely on quirks of human vision to create deep, panoramic scenes or objects that seem to fly from the screen. Human beings have binocular vision -- each eye sees a different image, and the brain combines them into a single, unified picture. The brain uses the slight difference in angle between the two images, known as parallax, to help it perceive depth. This is why people who lose their sight in one eye have trouble judging distances.
Old 3-D movies used anaglyph images to take advantage of binocular vision and parallax. These images include two color layers in a single strip of film shown from one projector. One layer is predominately red, and the other is predominately blue or green. To watch the movie, you wear 3-D glasses with one red lens and one blue or green lens. These lenses force one eye to see the red part of the image and the other eye to see the blue or green part. Because of the differences between the two, your brain perceives them as one image with three dimensions. However, because of the use of color-filtering lenses, the color of the final image isn't accurate. This type of 3-D technology has also caused some people to experience headaches, eye strain and nausea.
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 [characters] 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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