Isophote Distance: A Shading Approach to Artistic Stroke Thickness

Abstract This paper presents an approach for determining stroke thickness in computer-generated illustrations of smooth surfaces. We assume that dark strokes are drawn to approximate the dark regions of the shaded surface. This assumption leads to a simple formula for thickness of contours and suggestive contours; this formula depends on depth, radial curvature, and light direction in a manner that reproduces aspects of thickness observed in hand-made drawings. These strokes convey local shape and depth relationships, and produce appealing imagery. Our method is simple to implement, provides temporally-coherent strokes, and runs at interactive rates.		Paper Isophote Distance: A Shading Approach to Artistic Stroke Thickness T. Goodwin, I. Vollick, A. Hertzmann. NPAR 2007. PDF~3.2M Slides NPAR 2007. PDF~7.0M
Results Bone

Rendering based on a comic illustration (left) from Bone (BONE® is ©2007 Jeff Smith). Based on the drawing, we constructed a 3D model by hand (top center), and then rendered the model using our algorithm (bottom center). Several qualitative properties captured by our algorithm are also shown: inverse dependence on radial curvature (top right), selective stroke tapering (middle right), and inverse dependence on depth (bottom right). An animated version of the result is available here » GIF~1.1M / XviD~1.6M. The 3D model can be downloaded here » PLY~1.2M / OBJ~1.0M.
Results Beetle

Rendering based on a tonal drawing (top left) and a hand-drawn technical illustration (bottom left) of a dung beetle (William L. Brudon, University of Michigan Museum of Zoology, Misc. Publication No. 54). Based on the drawing, we constructed a 3D model by hand (top center), and then rendered the model using our algorithm (bottom center). Results for alternative lighting directions are also shown (right). An animated version of the result is available here » GIF~1.5M / XviD~2.2M. The 3D model can be downloaded here » PLY~1.1M / OBJ~0.9M.
Results Styles

Three rendering styles using isophote distance strokes: a graphic ink style (left), a pen overdraw style (center), and brushed ink style (right). Corresponding stroke details are also shown (bottom).
Support This research was supported in part by the Alfred P. Sloan Foundation, the Canada Foundation for Innovation, Microsoft Research, the National Sciences and Engineering Research Council of Canada, the Ontario Ministry of Research and Innovation, and the Ontario Graduate Scholarship Program.