“Mental Holography”: Stereograms Portraying Ambiguously Perceivable Surfaces
Béla Julesz, S. C. Johnson · Bell System Technical Journal · 1968
An algorithm has been devised that can generate the same stereogram for two (or more) selected surfaces. Prior to this development the only known ambiguous stereograms have been periodic grid patterns that could be perceived at various parallel depth planes. The new algorithm, however, can portray two (or more) selected surfaces of general shapes and the observer can perceive each of these surfaces, but only one at a time. The technique is an extension of random-dot stereograms and it is shown that in most cases adequate degrees of freedom remain for coloring the random-dot texture. Since these ambiguously perceivable stereograms permit the portrayal of both the visible and the hidden surfaces of objects, they are analogous to holograms. However, in the case of holograms the observer has to inspect them from various positions, while for ambiguous stereograms it is the mind of the observer that wanders around.