Non-Photorealistic Computer Graphics Library

Art-based Rendering with Continuous Levels of Detail

Author(s): Lee Markosian, Barbara J. Meier, Michael A. Kowalski, Loring S. Holden, J.D. Northrup, John F. Hughes.
Proceedings: 1st International Symposium on Non-Photorealistic Animation and Rendering (NPAR'00), pp. 59--66, Annecy, France, June 05 - 07, 2000.
[BibTeX]

Abstract:
In previous work [6], we presented an algorithm for rendering virtual scenes using art-based styles. We demonstrated the ability to render fur, grass, and trees in a stylized manner that evoked the complexity of these textures without representing all their components explicitly. We achieved this with stroke-based procedural textures that generated detail elements, or graftals, just as needed. Our implementation had several drawbacks. First, each new graftal texture required a procedural implementation that included writing code. Also, graftals were regenerated in each frame in a way that led to excessive introduction and elimination of graftals even for small changes in camera parameters. Lastly, our system provided no way to continuously vary the properties of graftals, including color, size, or stroke width. Such an ability could be used to achieve better frame-to-frame coherence, or more generally to animate graftals. In this paper, we present a new framework for graftal textures that addresses these issues. Our new framework allows all major decisions about graftal look and behavior to be specified in a text file that can be edited by a designer. We have achieved greater frameto- frame coherence by using graftals that remain in fixed positions on the model surface. The look and behavior of graftals as they appear or disappear can now be animated to create smooth transitions. Finally, we introduce the concept of tufts which manage the multiresolution behavior of graftals according to the specifications of the scene designer.