Rendering Silhouettes with Virtual Lights Domingo Martin Juan Carlos Torres

Purpose Producing Images with a 2D appearance Classical Animation and Illustration Automated Images that look handmade User Interaction

Idea Use “Lights” to determine silhouettes “Lights” will only select the silhouettes, not change the color Each object owns its own set of “Lights”

Results

Advantages Separates the location of the observer and the lighting process from the selection of silhouettes Provides a familiar paradigm User Control Automation

Shortcomings Flashing (Temporal Discontinuity) Staircases (Spatial Discontinuity) May require a large number of Lights Doesn’t account for material properties

The Algorithm Definitions Types of Silhouettes Types of Lights Implementation

Definitions Curvature Function of orientation of W Geometrical condition C(c 1, c 2 ) If c 1 = c 2  curvature is deemed “fixed”  Else deemed “relaxed”

Types of Lights Standard illumination model I = I a + I d + I s Homogenous coordinates (x, y, z, w) Diffuse Reflection = 0, curvature within C(c 1, c 2 ) Specular Reflection = R (R  0), curvature within C(c 1, c 2 )

Types of Silhouettes Normal Outline Interior Outline Convex zones Concave zones

Occlusion and Priority

Implementation Selection Choosing Virtual Lights Virtual Lights own edge sets Extraction Priority Silhouette edge chains Silhouette Intersections

Example