.
Isophote Distance: A Shading Approach to Artistic Stroke Thickness
Author(s): Todd Goodwin, Ian Vollick, Aaron Hertzmann.
Proceedings: NPAR '07: Proceedings of the 5th international symposium on Non-photorealistic animation and rendering, pp. 53--62, New York, NY, USA, ACM,
2007.
[BibTeX] [DOI] 
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.