Résumé: This paper reviews some image- and model- based approaches for deriving artistic sketches of terrain surfaces. Using a 3D visualization system for rendering luminance maps of different types of terrain, the project compared four common edge detectors for extracting the sketches. The Sobel, and especially the Canny, operators were more useful than other operators. The best results were obtained by combining sketches from luminance maps generated using a headlight and a vertical light, respectively. Pen, pencil and charcoal styles of sketching can be obtained by varying the grey scale and thickness of output primitives. Movies of such sketches ( posted on the web) exhibited good inter- frame coherence, which engendered the perception of the solid mass and shape of the terrain. Sample sketch frames were compared with model- based pro .le- stroke sketches to highlight some limitations of luminance map- based edge detection. The illustrations are used to provide a framework of qualitative criteria on which sketches may be evaluated. Cross- references to recent work are used to identify some themes for future research.

Langue: Anglais