Rendering Silhouettes with Virtual Lights

Domingo MartinJuan 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(c1, c2) If c1 = c2

curvature is deemed “fixed” Else deemed “relaxed”

Types of Lights

Standard illumination model I = Ia + Id + Is Homogenous coordinates (x, y, z, w)

Diffuse

Reflection = 0, curvature within C(c1, c2)

Specular

Reflection = R (R 0), curvature within C(c1, c2)

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