the lit sphere:
DESCRIPTION
The Lit Sphere:. A Model for Capturing NPR Shading from Art Peter-Pike J. Sloan William Martin Amy Gooch Bruce Gooch. Motivation. Interactive shading of 3D characters Artists shading study on the sphere. Motivation. Acquire reflectance from real world - PowerPoint PPT PresentationTRANSCRIPT
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The Lit Sphere:
A Model for Capturing NPR Shading from Art
Peter-Pike J. SloanWilliam MartinAmy Gooch
Bruce Gooch
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Motivation
• Interactive shading of 3D characters
• Artists shading study on the sphere
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Motivation
• Acquire reflectance from real world– Use to illuminate and
place synthetic objects in scene
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Previous Work
• NPR– Lake2000 – Cartoon Shading– Gooch98 – Technical Illustration– Praun2001 – Real time hatching
• Acquiring Shading Models– Environment Maps
• Blinn76,Miller84,Green86– More general models
• Yu98, Yu99, Sato99
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Simple Idea
• “Paint by normals”– Surface parameterized by normal field– Store shading model in a environment
mapped indexed by surface normal (not reflection vector)
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Simple Examples
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Simple Demo
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Creating the Environment Map
• Could just paint it– requires artistic ability
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Extracting EMap
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Creating the Environment Map
• “Extract” from source artwork– Map triangles from
source onto sphere– Simple control over
parameterization
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Creating The Environment Map
• Fill in gaps– Render at multiple
scales– Blend into final image
• (1-dest,1)
– Could solve for colors by minimizing some high pass filter (ala Hakura99 and McCool01)
– Texture synthesis
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Simple Demo 2
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More Examples
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Issues
• Texture “crawls” when view changes• Texture as a function of curvature – seems odd
but works better then one would expect, flat regions have no variation
• Could attach texture to the surface, or at least separate it from shading– Probably want texture anchored on the surface, but
able to respond to shading changes – kind of like Praun2001 but not just for hatching
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Simple Hacks
• Have separate “texture sphere” that rotates with the object– Really should just live on the surface, bad
parameterization for something very coherent– Just use cube maps
• Modulate final results with “canvas” image– Kind of like detail textures, sometimes can
make the “swimming” less objectionable
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Conclusions
• Simple way to interactively shade objects based on source artwork
• Works ok if you aren’t trying to transfer something that has strong texture
• Probably should factor the model into more then 1 term…
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Acknowledgments
• University of Utah Computer Graphics groups
• Louise Bell, Grue, Susan Ashurst• Michael Cohen, Adam Finkelstein, James
Mahoney, Wolfgang Heidrich• DARPA, NSF STC for CG&SV