The difference-stereogram

In simple hypothetical experiments for producing random stereograms by ster eo-photographic means together with a pattern projection technique, we arri ve at the concept of difference-stereogram showing changes on a surface rat her than the surface itself. After the analysis of projector-camera arrange ment, an algorithmic definition of difference-stereogram is given, revealin g several of its structural properties. The related concept of difference s urface is introduced to describe the percept induced by difference-stereogr am. A two-way mapping between a surface and its difference surface is deriv ed, proving that the difference-stereogram is the autostereogram of the dif ference surface. It is also proved and demonstrated that a difference-stere ogram placed beside its basic pattern is forming a stereopair that shows th e original surface.