Non-Photorealistic Rendering


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

Combines 2D and 3D principles

Common Techniques

  • 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 3d▀ 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 čstyles¸?
    • Non-Physically-Based simulation for animation

Examples

References



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