stereogram

A stereogram is an image designed to evoke a three-dimensional perception from a two-dimensional pattern when viewed with both eyes in proper alignment. The depth is produced by binocular disparity: each eye receives a slightly different image, and the brain fuses them to compute depth.

There are two broad classes. Random-dot stereograms present two offset patterns of random dots that, when fused, reveal a 3D shape defined by a depth map. Autostereograms, or single-image stereograms, encode depth within a single picture by repeating a texture and shifting it according to depth information, so the 3D scene appears without any separate image pair.

Viewing requires relaxing the eyes or using cross-eyed or parallel free-viewing techniques. With practice, the hidden depth can be seen as the eyes converge at a distance behind the image. Some viewers may experience eye strain or headaches if they force fusion.

History and development: The concept rests on the 1838 Wheatstone stereoscope. Bela Julesz popularized random-dot stereograms in the 1950s, demonstrating depth from disparity. Autostereograms gained popularity in the 1990s with books and computer graphics, notably the Magic Eye series, enabling depth perception from a single image.

Applications include entertainment, visual perception research, and novelty displays. They are also used to study binocular depth processing and can be employed in tests of stereo vision. The effectiveness depends on viewer distance, image resolution, and individual stereo acuity.

See also: stereopsis, binocular disparity, autostereogram, random-dot stereogram, 3D display, depth map.