Stereoscopy (also called stereoscopic or 3-D imaging) refers to a technique for creating or enhancing the illusion of depth in an image by presenting two offset images separately to the left and right eye of the viewer. These two-dimensional images are then combined in the brain to give the perception of 3-D depth. Besides the technique of free viewing, which must be learned by the viewer, three strategies have been used to mechanically present different images to each eye: have the viewer wear eyeglasses to combine separate images from two offset sources, have the viewer wear eyeglasses to filter offset images from a single source separated to each eye, or have the light source split the images directionally into the viewer’s eyes .
Stereoscopy creates the illusion of three-dimensional depth from images on a two-dimensional plane. Human vision uses several cues to determine relative depths in a perceived scene. Some of these cues are: