Stereoscopy, stereoscopic imaging or 3-D (three-dimensional) imaging is any technique capable of recording three-dimensional visual information or creating the illusion of depth in an image.
Human vision uses several cues to determine relative depths in a perceived scene. Some of these cues are:
* Stereopsis * Accommodation of the eyeball (eyeball focus) * Occlusion of one object by another * Subtended visual angle of an object of known size * Linear perspective (convergence of parallel edges) * Vertical position (objects higher in the scene generally tend to be perceived as further away) * Haze, desaturation, and a shift to bluishness * Change in size of textured pattern detail
All the above cues, with the exception of the first two, are present in traditional two-dimensional images such as paintings, photographs, and television. Stereoscopy is the enhancement of the illusion of depth in a photograph, movie, or other two-dimensional image by presenting a slightly different image to each eye, and thereby adding the first of these cues (stereopsis) as well.