Non-Photorealistic Computer Graphics Library

Image Precision Silhouette Edges

Author(s): Ramesh Raskar, Michael F. Cohen.
Proceedings: Symposium on Interactive 3D Graphics (I3D'99), pp. 135--140, Atlanta, Georgia, United States, 1999.
[BibTeX] [DOI]

Abstract:
Finding and displaying silhouette edges is important in applications ranging from computer vision to nonphotorealistic rendering. To render visible silhouette edges of a polygonal object in a scene from a given viewpoint, we must first find all silhouette edges, i.e. boundaries between adjacent front facing and back-facing surfaces. This is followed by solving the partial visibility problem so that only those parts of silhouette edges, which are not occluded by interior of any front facing surface, are rendered. The scene may optionally be rendered with a lighting model. This paper describes a simple general-purpose method to combine all three operations for any scene composed of objects that can be scan-converted. Using a depth buffer, the rendering process computes the intersection of adjacent front facing and back-facing surfaces in image space at interactive rates. All operations are performed in image-precision and hence special care is taken for the limited numerical precision of the depth buffer. A solution is suggested using viewdependent modification of polygonal objects. The method does not require any preprocessing or adjacency information and hence is applicable for dynamic scenes.