Surface Cues and Perceived Distortions in Pictorial Images

Ahna Girshick, University of California, Berkeley

The characteristic phenomena in viewing pictorial images (printed pictures and digital displays) can be described in terms of the perceived distortions (or lack thereof) of depicted objects. The perceived shape of an object in a pictorial image when viewed from the actual center of projection is seen as distorted despite the fact that the retinal image specifies an undistorted object. Conversely, when viewed from a point laterally displaced from the actual center of projection the depicted object is seen as undistorted, despite the distortion specified by the retinal image. Both these phenomena are due to the effect of viewing a pictorial image of an object obliquely in the presence of surface cues. These cues, binocular disparity, motion parallax, texture cues and focus cues, specify the orientation of the picture surface. Quantifying the effects of surface cues is critical for understanding the transformations that give rise to the characteristic phenomena in viewing pictorial images. We systematically controlled surface cues and obliqueness of view while measuring the perceived distortion of objects in two complementary ways. In the first experiment, subjects dynamically adjusted the dimensions of an ellipsoid whose projection was viewed obliquely on a CRT until they perceived it as a sphere. In the second experiment, subjects adjusted the orientation of a pictorial surface until the depicted objects appeared undistorted. This is equivalent to finding the correct center of projection. In both experiments, the removal of surface cues systematically reduced perceived distortions.

Abstract Author(s): Ahna Reza Girshick, Dhanraj Vishwanath, Martin Banks