Space perception in pictures

A “picture” is a flat object covered with pigments in a certain pattern. Human observers, when looking “into” a picture (photograph, painting, drawing, . . . say) often report to experience a three-dimensional “pictorial space.” This space is a mental entity, apparently triggered by so called pictorial cues. The latter are sub-structures of color patterns that are pre-consciously designated by the observer as “cues,” and that are often considered to play a crucial role in the construction of pictorial space. In the case of the visual arts these structures are often introduced by the artist with the intention to trigger certain experiences in prospective viewers, whereas in the case of photographs the intentionality is limited to the viewer. We have explored various methods to operationalize geometrical properties, typically relative to some observer perspective. Here “perspective” is to be understood in a very general, not necessarily geometric sense, akin to Gombrich’s “beholder’s share”. Examples include pictorial depth, either in a metrical, or a mere ordinal sense. We find that different observers tend to agree remarkably well on ordinal relations, but show dramatic differences in metrical relations.