Parallax is the way an object’s position or direction seems to change depending on viewing angle. To experience this phenomena, simply cover one eye and focus on an object. Then move the cover to the other eye. Because each eye provides a different viewing angle, the object will appear to move.
In 3-D imaging, this phenomena is used to create the illusion of depth. A 3-D television that doesn't require glasses, for instance, can use a filter called a parallex barrier. The filter, which is a series of slits on the LCD panel, permits each of the viewer's eyes to see a different set of pixels. The viewer's brain combines the pixels from each eye's viewing angle into one image which has the illusion of depth. The parallax barrier filter can be switched off to provide backward compatibility with 2D content.
See also: auto 3-D
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