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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 Oliver DeussenThomas StrothotteUniversity 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 • Large data • Abstract representation • Drawing styles
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
Interactive Pen and Ink Illustration • 2D drawing • Tone and texture • High level cumulative effect • Randomness to the strokes • Stored stroke textures
Trunk Silhouette Shading Leaves Primitive shape Foliage Well lit Half shadow Deep shadow Traditional methods
Input model • xfrog system • Tree skeleton • 2 levels of branches • Foliage • Particles vs. polygons • 183,000 to 8,800
Tree skeleton • Silhouette • Mokosian • Rakar • Shading • Floyd Steinberg method • Difference image algorithm • Stroke area and direction
Foliage • First attempt • Merging shapes into outlines • Abstractions • Depth difference • Saito and Takahashi • Enhance outlines
Depth differences • Zero order difference determines outlines • z-buffer • Difference with neighbor • Threshold
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
Disk size and threshold a) size: 0.15, threshold: 1000 b) size: 0.7, threshold: 2000
Abstract primitives • 3D impression
Level of abstraction • Using z-buffer value • Primitive size
Software framework • Interactive vs. high quality • Software shadows • Vectoriation of primitive polygons
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)
Results: • 200,000 leaves reduce to 16,200 particles • 90,000 tree particles, 23,000 grass particles - 1 minute
Pro: Using existing models Primitive shape Level of abstraction Hand drawn style Con: Interactive speed Dealing with large models Conclusion
Extensions • Trees only? • Depth difference extends to other models.