Random dot stereograms are composed of two arrays (or frames) of randomly scattered dots. The arrays are identical except for a certain area(s) in one of the arrays which has been horizontally shifted to introduce disparity between the two arrays. The two arrays (images) are usually displayed side by side to allow the observer to compare them. When viewed monocularly the viewer is confronted with a mass of dots and fails to make any correspondences across the images. However when the images are stereoscopically fused (by crossing the eyes then either converging or diverging them - try to gaze beyond the images) correspondences across dots are made and the shifted area(s) in the stereogram appears at a separate depth level from the unshifted area. Figure 4, below, shows a stereogram example which when fused should reveal a square area in the middle of the image at a different depth level.
Figure 4: A random dot stereogram
Figure 5: The shear surface of the stereogram
[ The stereo correspondence problem |
Panum's fusional area ]
Comments to: Sarah Price at ICBL.