Using Surface Markings to Enhance Accuracy and Stability of Object Perception in Graphic Displays

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

Abstract

Effective computer graphic applications should accurately convey three dimensional shape. Previously, we investigated the contributions of shading and contour, specular highlights, and light source direction to three dimensional shape perception. Our experiments use displays of convex solid objects based on the superquadric parameterization, permitting continuous variation in their cross-sectional shapes. Our present work concerns the impact of surface markings. Rotating wireframe or uniformly shaded objects may produce perceptually distorting shapes. We investigate the idea that such distortions interfere with shape judgements, and that surface markings may either enhance perceptual accuracy by encouraging stability, or impair it by interfering with global shading patterns. Our displays include rotating objects with no surface markings, stripes, latitudinal or longitudinal stripes, each with two different scene illuminations. Observers view pairs of objects, a target shape and a second object whose shape they adjust, using mouse clicks, to match that of the target. Our principal result is that these surface patterns do not enhance performance, even though the chosen stripe intensities minimize interference with global shading, and the stripe patterns may actually encode surface curvature. We are now investigating alternatives for applying surface patterns to modelled objects, including hardware supported texture mapping. Our long term goal remains the identification of a comprehensive set of conditions for optimising shape understanding of graphic objects.