Impossible Pictures

Impossible pictures have proved to be an important source of geometric constraints which can be applied by a computer program when interpreting line drawings. Although this is our main motivation, there are several other reasons why impossible pictures have been studied. M.C. Escher raised the study of impossible pictures to an art form by incorporating them into his etchings. Psychologists and cognitive scientists have used pictures of impossible objects to investigate human visual processing and memory. Figure 2.1 shows the kind of impossible pictures used in psychological experiments to determine how shapes are represented in the brain [113, 172]. Certain odd-looking pictures appear to represent impossible objects but can, in fact, be realized as the projection of a polyhedron. Sugihara [156] suggested using the unfolded surface of such a polyhedron as a toy so that children could play at constructing the ‘impossible’ object.