The Visual Computer

, Volume 34, Issue 3, pp 443–457 | Cite as

Approximations for the distribution of microflake normals

Original Article
  • 104 Downloads

Abstract

Scenes in computer animation can have extreme complexity, especially when high resolution objects are placed in the distance and occupy only a few pixels. A useful technique for level of detail in these cases is to use a sparse voxel octree containing both hard surfaces and a participating medium consisting of microflakes. In this paper, we discuss three different methods for approximating the distribution of normals of the microflakes, which is needed to compute extinction, inscattering of attenuated direct illumination, and multiple scattering in the participating medium. Specifically, we consider (a) k means approximation with k weighted representatives, (b) expansion in spherical harmonics, and (c) the distribution of the normals of a specific ellipsoid. We compare their image quality, data size, and computation time.

Keywords

Microflake Sparse voxel octree Volume rendering Distribution of normals 

Notes

Acknowledgements

We thank Mark Meyer, Tony DeRose, Eric Heitz, Wojciech Jarosz, Derek Nowrouzezahrai and Ted Kim for helpful discussions, and the SIGGRAPH, Pacific Graphics, and Visual Computer reviewers for useful suggestions. Nelson Max thanks the University of California, Davis for sabbatical salary.

Supplementary material

Supplementary material 1 (mov 12458 KB)

A rotation cycle around a forest, generated by path tracing using ellipsoid method (c) for the distribution of microflake normals.

Supplementary material 2 (mov 12401 KB)

The camera moves away from the forest, with continuously changing octtree levels used in the rendering. Generated using method (b) for the distribution of microflake normals, with the 15 even-ordered spherical harmonics terms for L = 4.

Supplementary material 3 (mov 12361 KB)

A rotation cycle around a forest, generated by path tracing using the k-means method (a) for the distribution of microflake normals, with k = 3.

Supplementary material 4 (mov 1912 KB)

A rotation cycle around a forest, generated by path tracing using method (b) for the distribution of microflake normals, with the 15 even-ordered spherical harmonics terms for L = 4.

371_2017_1352_MOESM5_ESM.mov (6.8 mb)
Supplementary material 5 (mov 6943 KB) A rotation cycle around a beech tree, generated by path tracing using method (b) for the distribution of microflake normals, with the 15 even-ordered spherical harmonics terms for L = 4.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2017

Authors and Affiliations

  1. 1.Pixar Animation StudiosEmeryvilleUSA
  2. 2.University of CaliforniaDavisUSA
  3. 3.University of CaliforniaBerkeleyUSA
  4. 4.Washington University in St. LouisSt. LouisUSA

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