Depth Perception in Pictures/Film

Depth perception in general can be understood as a reconstructive process that interprets the retinal image in our eye such that a three-dimensional (3-D) object arises in our mind. Pictures and films can also provide vivid impressions of depth. This pictorial depth differs in nature. It is a constructive process of its own and presents an additional level of difficulty. Normal vision allows us to glean information about an object's shape and color as well as about such things as its spatial relations, its mass, and its potential danger. Normal vision typically reconstructs the real-world object which gives rise to the retinal image with admirable precision. This is possible because our visual system is able to resolve the many ambiguities present in the retinal image. Pictorial depth is both more confined and broader than normal depth. Figure 1 illustrates the nature of the (re) constructive processes in pictorial viewing compared with normal viewing. In normal viewing, a large number of 3-D objects would qualify as permissible reconstructions that could be made on the basis of one given retinal image. This is the case for the canvas. Pictorial depth is processed in addition.

Figure 1 Reconstructing Physical Depth and the Two-Layered Process of Constructing Pictorial Depth

To date, perceptual psychologists have not been able to agree about just how the mind solves this so-called underspecification problem and singles out the one reconstruction that ends up in our awareness. The reconstruction is close to the actual 3-D object that we see, most of the time. The great physiologist Hermann von Helmholtz has argued that the visual system acts like a problem solver and uses unconscious inferences and depth cues to solve the underspecification problem. This entry describes the dual nature of pictures, the limitations of pictorial depth, and violations of spatial construction rules in frozen and dynamic renditions.