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The Lit Sphere: A Model for Capturing NPR Shading from Art Peter-Pike J. Sloan William Martin Amy Gooch Bruce Gooch.

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Presentation on theme: "The Lit Sphere: A Model for Capturing NPR Shading from Art Peter-Pike J. Sloan William Martin Amy Gooch Bruce Gooch."— Presentation transcript:

1 The Lit Sphere: A Model for Capturing NPR Shading from Art Peter-Pike J. Sloan William Martin Amy Gooch Bruce Gooch

2 Motivation Interactive shading of 3D characters Artists shading study on the sphere

3 Motivation Acquire reflectance from real world –Use to illuminate and place synthetic objects in scene

4 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

5 Simple Idea Paint by normals –Surface parameterized by normal field –Store shading model in a environment mapped indexed by surface normal (not reflection vector)

6 Simple Examples

7 Simple Demo

8 Creating the Environment Map Could just paint it –requires artistic ability

9 Extracting EMap

10 Creating the Environment Map Extract from source artwork –Map triangles from source onto sphere –Simple control over parameterization

11 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

12 Simple Demo 2

13 More Examples

14 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

15 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

16 Conclusions Simple way to interactively shade objects based on source artwork Works ok if you arent trying to transfer something that has strong texture Probably should factor the model into more then 1 term…

17 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


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