Autostereogram

An autostereogram is a two-dimensional image that creates the illusion of a three-dimensional scene using only a single image, unlike a traditional stereogram, which requires two separate images and a viewing device such as a stereoscope. Viewing an autostereogram to see its hidden 3D effect requires the viewer to either diverge the eyes as though looking at a distant point beyond the page (wall-eyed viewing) or cross the eyes as though looking at a near point in front of the page (cross-eyed viewing); doing so causes repeating patterns in the image to be matched up differently by each eye, and the brain's normal process of combining the two eyes' views to judge depth then reads those mismatches as objects floating at different distances. Giambattista della Porta experimented with a related idea, viewing two different pages with each eye separately, as early as 1593, but the modern autostereogram is much more recent: Bela Julesz invented the random dot stereogram, still requiring two images and a stereoscope, in 1959, and Christopher Tyler combined the random dot stereogram with the older wallpaper stereogram technique to create the first black and white random dot autostereogram, viewable without any special equipment, in 1979. The colorful, widely sold autostereogram books published under the Magic Eye name followed in 1991. Not everyone can see the three-dimensional effect: people with visual impairments that affect binocular vision, including amblyopia or lazy eye, often cannot perceive the illusion at all.