The Technograph

The technique used to make a movie three-dimensional is called stereoscopic 3D. The idea is to present each of your eyes with a slightly different image that, when the two are put together, trick your eyes into thinking the image has depth. This means a 3D movie shows two different images on the same screen but sends each one to a different eye.

There are a few ways to accomplish this. Older 3D movies use something called anaglyph, involving special red-and-blue (technically, red-and-cyan) glasses worn by the viewer. The red lens allows only red light through, and the cyan lens allows only cyan light through. Both a red image and a cyan image are projected onto the movie screen, so the red image goes to one eye, and the cyan image to the other.

This technique messes up the colors of the movie, though, so modern movies theaters employ glasses and images that rely on different polarizations of light rather than different colors.

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