Normal human vision is binocular, providing us with subtle information
on depth and relief within the central part of our field of view. Stereoscopy
is the practice of presenting each eye with its own view of a scene, so
that the brain is able to combine the two images and perceive the areas
of varying depth.
There are several common methods use to achieve stereopsis. One of the oldest is to present the eyes with a stereo pair which is examined using a viewer (the stereoscope) which directs each eye at the appropriate picture. The right eye sees the right image, and the left eye the left image. Lenses usually accomplish this in the classical stereoscope. If the stereogram is not too large, it is possible with a little practice to learn the art of "free-viewing," that is, viewing in three dimensions without the use of a stereoscope. You may try this on the example below. Do not cross your eyes, but let them drift apart so that their directions of gaze are virtually parallel. It helps to concentrate your attention on the same object in both images, until you are able to make them merge into one.
The Devil's Potato Patch, a periglacial boulder field at Little Gap in
Blue Mountain, 1.3 km west of Danielsville,
Northampton County, Pennsylvania, USA
View other examples in a Stereo Slide-Show.
Visit a tutorial
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