Monocular depth-simulation
Three-dimensional-viewing consists of two aspects: monocular viewing and binocular viewing (Stereopsis).
Pictures designed for monocular viewing are most common in arts and conventional computergraphics. The sense of depth arises from light and shadow, perspective and mutual blocking of several objects. This method of viewing is based on experience and training.
Monocular depth-simulation
The other method, binocular viewing, is physically based. We have two eyes, each viewing a slightly different image. Our brain manages to composite those two images into one picture with depth-impression. Binocular viewing consists of several parts: Accomodation, Conver-gence and Stereo-Disparity.
Accomodation is the mechanism of focusing on a picture by modifying the curve of the lens, valid for distances between 10 centimeters and 5 meters.
Convergence describes the correlation of the axes of both eyes. The axes intersect in the center of the image. Usually both mechanisms are linked together, but as we will show later, it is necessary to unlink Accomodation and Convergence for viewing Autostereograms. (In fact, the unability of doing this is the reason that some people cannot see the correct picture in the Autostereogram.)
Stereo-Disparity means that both eyes receive slightly different images, that are composited by our brain.
Stereo-Disparity and Binocular viewing