Stereo grams fool your brain into thinking there is a 3D image by letting your eye see a similar but slighty different picture with each eye. This is just what happens when you see a real 3D object. For instance hold your finger in front of you and view it with each eye in turn. Notice that you see a different image with each eye. Your brain combines the two images to form a 3D object just as it tries to do with stereograms and analglyphs (see 3D glasses)
There are three basic ways of looking at 3D images . . . Normally, if you look at or read something on a page, you aim your eyes directly at the surface of the paper. If you use normal viewing to look at 3D images at this site, you just won't see 3D.
With the parallel method, the lines of sight of your eyes move outward toward parallel and meet in the distance at a point well behind and beyond the image. When you parallel-view, the muscles inside your eye that control the focusing lens relax and lengthen. You can acheive this by focussing on something beyond the stereogram.
Another method for 3D viewing is called cross-viewing or the cross-eyed method. You aim your eyes so that the lines of sight of your eyes cross in front of the image. When you cross-view, the muscles inside your eye that control the focusing lens contract strongly and shorten. If you cross-view pictures or other images intended for parallel-viewing, shapes that should pop out will look punched in.
try it out on the easy cow stereogram then have a go at the single image random dot stereo gram. Theres no hidden picture but they should appear 3-dimensional.
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