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How 3-D Glasses Work

What makes 3-D glasses give 2-D images depth perception

By Gabriel Gache, Science News Editor

24th of July 2008, 13:01 GMT

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Most of you might not know this, but 3-D glasses have actually been around ever since the 1920s, reaching their peak of popularity throughout the 1950s. They are still in use even today, although not as much as they used to be. 3-D glasses rely on a technique known as stereoscopic imaging, in which 2-dimensional images are combined in order to give the illusion of depth. For this however, binocular vision is required.

Humans are among a handful of living beings on Earth to have binocular vision, meaning that both eyes are used at the same time to view an object. Binocular vision has four big advantages. One is that if an eye is damaged, the other one can perform roughly the same role as if they were both functional. Second, the field of view is much wider than that of animals without binocular vision. Third, it gives the ability to better view faint objects, and fourth, because the eyes are spaced and placed on the same side of the skull, it gives a precise depth perception.

The 3-D technology exploits the advantages of binocular vision by feeding two slightly different images into each eye, to create the illusion of depth perception. Although we might not notice it in everyday life, each of our eyes actually sees two different images. Try to view an object with the right eye closed, then open the right eye and close the left one while standing still. You will notice that although you did not move, the object appears slightly to the left or to the right, depending on which eye is closed and which one is open. This gives us the ability to accurately estimate the distance to the respective object - depth perception.

One way through which 3-D glasses are able to give the illusion of depth and project two different images in each eye is to make use of one of the visual perceptions we know as color. In this case, the system projects two images, one in red and the other in blue, for example. This in turn means that the 3-D glasses must have a red filter for one eye and a blue filter for the other. The two different images are then processes by the brain, which is fooled into thinking that the image has depth, when in fact it is projected on a 2-D display.

An alternative method through which the illusion of depth can be created is using polarized lenses. Polarization is a property of the electromagnetic wave expressed through preferential oscillation direction for the electric component. The human eye is not able to make a distinction between differently polarized light, but with the proper lenses it is possible. As in the case of the previously described method, two images are projected on a screen, but this time each with different polarization.

TAGS:

binocular vision | depth perception | color | polarization | 3-D glasses

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