The Effect of Lighting Direction on the Perception of Shape in Graphic Displays

Roger A. Browse, James C. Rodger, and Robert A. Adderley

Abstract Accurately conveying three-dimensional shape is a requirement for many computer graphic applications. The general belief that we call The Photorealism Assumption asserts that understanding of depicted object shapes improves with increasing realism of the display. We contend that parameters determining a graphic rendering vary widely in importance for accurately portraying shape. By identifying the relative contributions of rendering parameters, we provide a framework for developing cost-effective display systems. Our current work concerns the role of light direction in conveying the three-dimensional shape of depicted objects. In our experiments, we present sequences of displays that each show an elongated superquadric object. An observer attempts to reproduce the shape of the cross section orthogonal to the elongated axis by adjusting a sample contour. The object rotates continuously so that observers solve the task from an overall understanding of the shape, rather than from static two-dimensional features. We vary the shape of the superquadric objects, as well as the illumination directions. Our results indicate that the accuracy of observers' estimates is surprisingly robust to these variations.