Stylizing Silhouettes at Interactive Rates:� From Silhouette Edges to Silhouette Strokes

Abstract

A way to create effective stylized line drawings is to draw strokes that start and stop at visible portions along the silhouette of an object to be portrayed. In computer graphics to date, algorithms to extract silhouette edges are many, although putting these edges into a form such that stylized strokes may be applied to them has not been greatly covered, so that existing methods are either time‐consuming or presented vaguely. In this paper, we introduce an algorithm that takes a set of silhouette edges originating from polygonal meshes and efficiently computes the visible parts of the edges before connecting them to form long smooth silhouette strokes to which stylization algorithms may be effectively applied. Features of our algorithm that gain efficiency and accuracy over existing methods is that we directly exploit the analytic connectivity information of the mesh in combination with the available z‐buffer information during rendering, and filter artifacts in connected edges during the process to improve the visual quality of strokes after stylization. Categories and Subject Descriptors (according to ACM CCS): 1.3.3 [Computer Graphics]: Picture/Image Generation—Line and curve generation 1.3.7 [Computer Graphics]: Three‐Dimensional Graphics and Realism—Hidden line/surface removal

Self-similar texture for coherent line stylization

“…We use the segment atlas data-structure describe in [Cole and Finkelstein 2010] to compute the visibility of the paths and perform the final rendering of the strokes on the GPU. Nevertheless, our approach could be used with any system that renders lines as textured quads, such as [McGuire and Hughes 2004;Kalnins et al 2002;Isenberg et al 2002;Markosian et al 1997]. Our system runs at interactive framerates for scenes of moderate complexity on a commodity PC with an Intel Core 2 Duo 2.4GHz CPU and 4 GB RAM.…”

Stylized strokes for coherent line drawings

“…In order to obtain the accurate line visibility, hybrid approaches such as an ID reference buffer [15], an item buffer [16][17][18], or a depth buffer [19] are used to link adjacent paths using the connectivity of the extracted lines. However, simple heuristics based on distances and angles must be defined to solve ambiguities at line intersections, which lead to popping and overlaps in the stylized animation.…”

Depth-aware coherent line drawings

“…Rendering descriptive lines of polygonal objects was explored by Elber [1995], who proposed simple techniques to create line drawings which enhance the quality of illustrations. Silhouettes are often regarded as important shape-conveying lines and Isenberg et al [2002] introduced a technique to render them as connected stylized strokes at interactive rates. A system is presented by Kalnins et al [2002] in which users directly draw strokes on 3D models with a chosen brush style.…”