Non-Photorealistic Rendering (NPR)
Motivation
- Much of the graphical imagery created is not photographic in nature
- Art
- Drawing Styles: cross-hatching, outlines, line art, etc.
- Painting Styles: impressionist, expressionist, pointillist, etc.
- Cartoons
- Characteristics: cartoon shading, distortion, etc.
- Technical Illustration
- Characteristics: Matte shading, edge lines, etc.
- Diagrams
- Characteristics: splatting, hedgehogs, etc.
- Architecture
- Characteristics: imprecise end points, sketched lines, etc.
- As late as 1990, computer graphics research was almost entirely focused on
realism
Based on Artistic Principles
- Abstract away some details, emphasize others
- Examples
- pen and ink
- sketching
- painting
- water color
Common Techniques
- Combines 2D and 3D principles
- Find silhouettes and contours
- Where surface normal is perpendicular to the view direction
- Edge detection for images
- Find image gradient and principle directions
- Maximal and minimal directions from 3dß models
- Standard methods for photos
- Find highlights
- Randomly distribute points
- Clip lines or regions to edges
Issues
- How to judge stylized rendering for visualization
- How to make more interactive (potentially many more polygons generated)
- What to do about animation?
- How to keep artifacts from wiggling during animation
- Animation of painterly rendering has no historical counterpart
- What are the Ÿstyles÷?
- Non-Physically-Based simulation for animation
Examples
References
