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Computer-Generated Pen-and-Ink Illustration of Trees

Computer-Generated Pen-and-Ink Illustration of Trees. Oliver Deussen Thomas Strothotte University of Magdeburg. Why pen, ink, and trees. Drawings convey visual information Illustrations in books Architecture and landscaping. Main ideas. Using existing models Drawing the foliage

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Computer-Generated Pen-and-Ink Illustration of Trees

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  1. Computer-Generated Pen-and-Ink Illustration of Trees Oliver DeussenThomas StrothotteUniversity of Magdeburg

  2. Why pen, ink, and trees • Drawings convey visual information • Illustrations in books • Architecture and landscaping

  3. Main ideas • Using existing models • Drawing the foliage • Large data • Abstract representation • Drawing styles

  4. Leaves Alvy Smith Fractals Small disks Reeves and Blau Particle system to represent leaves Sasada Tree sketch in architecture environments View facing polygons Strokes Simulate brush Tone and texture Related work

  5. Interactive Pen and Ink Illustration • 2D drawing • Tone and texture • High level cumulative effect • Randomness to the strokes • Stored stroke textures

  6. Trunk Silhouette Shading Leaves Primitive shape Foliage Well lit Half shadow Deep shadow Traditional methods

  7. Image from xfrog

  8. Input model • xfrog system • Tree skeleton • 2 levels of branches • Foliage • Particles vs. polygons • 183,000 to 8,800

  9. Tree skeleton • Silhouette • Mokosian • Rakar • Shading • Floyd Steinberg method • Difference image algorithm • Stroke area and direction

  10. Foliage • First attempt • Merging shapes into outlines • Abstractions • Depth difference • Saito and Takahashi • Enhance outlines

  11. Depth differences • Zero order difference determines outlines • z-buffer • Difference with neighbor • Threshold

  12. Using z-buffer • Parameters: • Depth value from the camera: z0, z1 • z-buffer value: d0=0, d1=65535 • Threshold: 10% of the depth of the tree

  13. Disk size and threshold a) size: 0.15, threshold: 1000 b) size: 0.7, threshold: 2000

  14. Abstract primitives • 3D impression

  15. Level of abstraction • Using z-buffer value • Primitive size

  16. Software framework • Interactive vs. high quality • Software shadows • Vectoriation of primitive polygons

  17. Results: • Interactive: 3 trees of 20,000 particles each and 25,000 ground particles at 3 fps. • 13,200 elliptic primitives - 10 seconds (SGI Octane)

  18. Results: • 200,000 leaves reduce to 16,200 particles • 90,000 tree particles, 23,000 grass particles - 1 minute

  19. Pro: Using existing models Primitive shape Level of abstraction Hand drawn style Con: Interactive speed Dealing with large models Conclusion

  20. Extensions • Trees only? • Depth difference extends to other models.

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