Interactive hair rendering under environment lighting

ABSTRACT

We present an algorithm for interactive hair rendering with both single and multiple scattering effects under complex environment lighting. The outgoing radiance due to single scattering is determined by the integral of the product of the environment lighting, the scattering function, and the transmittance that accounts for self-shadowing among hair fibers. We approximate the environment light by a set of spherical radial basis functions (SRBFs) and thus convert the outgoing radiance integral into the sum of radiance contributions of all SRBF lights. For each SRBF light, we factor out the effective transmittance to represent the radiance integral as the product of two terms: the transmittance and the convolution of the SRBF light and the scattering function. Observing that the convolution term is independent of the hair geometry, we precompute it for commonly-used scattering models, and reduce the run-time computation to table lookups. We further propose a technique, called the convolution optical depth map, to efficiently approximate the effective transmittance by filtering the optical depth maps generated at the center of the SRBF using a depth-dependent kernel. As for the multiple scattering computation, we handle SRBF lights by using similar factorization and precomputation schemes, and adopt sparse sampling and interpolation to speed up the computation. Compared to off-line algorithms, our algorithm can generate images of comparable quality, but at interactive frame rates.

References

1. Agarwal, S., Ramamoorthi, R., Belongie, S., and Jensen, H. W. 2003. Structured importance sampling of environment maps. ACM Trans. Graph. 22, 3, 605--612.
2. Annen, T., Dong, Z., Mertens, T., Bekaert, P., Seidel, H.-P., and Kautz, J. 2008. Real-time, all-frequency shadows in dynamic scenes. ACM Trans. Graph. 27, 3, 34:1--8.
3. Cook, R. L., Halstead, J., Planck, M., and Ryu, D. 2007. Stochastic simplification of aggregate detail. ACM Trans. Graph. 26, 3, 79.
4. Fernando, R. 2005. Percentage-closer soft shadows. In SIGGRAPH 2005 Sketches, 35.
5. Harris, M., Sengupta, S., and Owens, J. 2007. Parallel prefix sum (scan) in CUDA. GPU Gems 3, Chapter 39.
6. Hensley, J., Scheuermann, T., Coombe, G., Singh, M., and Lastra, A. 2005. Fast summed-area table generation and its applications. Computer Graphics Forum, 547--555.
7. Kajiya, J. T., and Kay, T. L. 1989. Rendering fur with three dimensional textures. In Proceedings of ACM SIGGRAPH9, 271--280.
8. Kim, T.-Y., and Neumann, U. 2001. Opacity shadow maps. In Eurographics Workshop on Rendering, 177--182.
9. Lokovic, T., and Veach, E. 2000. Deep shadow maps. In Proceedings of ACM SIGGRAPH, 385--392.
10. Marschner, S. R., Jensen, H. W., Cammarano, M., Worley, S., and Hanrahan, P. 2003. Light scattering from human hair fibers. ACM Trans. Graph. 22, 3, 780--791.
11. Mertens, T., Kautz, J., Bekaert, P., and Reeth, F. V. 2004. A self-shadow algorithm for dynamic hair using density clustering. In SIGGRAPH 2004 Sketches, 44.
12. Moon, J. T., and Marschner, S. R. 2006. Simulating multiple scattering in hair using a photon mapping approach. ACM Trans. Graph. 25, 3, 1067--1074.
13. Moon, J. T., Walter, B., and Marschner, S. 2008. Efficient multiple scattering in hair using spherical harmonics. ACM Trans. Graph. 27, 3, 31:1--7.
14. Ng, R., Ramamoorthi, R., and Hanrahan, P. 2003. Allfrequency shadows using non-linear wavelet lighting approximation. ACM Trans. Graph. 22, 3, 376--381.
15. NVIDIA, 2007. CUDA homepage. http://developer.nvidia.com/object/cuda.html.
16. Ramamoorthi, R., and Hanrahan, P. 2001. An efficient representation for irradiance environment maps. In Proceedings of ACM SIGGRAPH, 497--500.
17. Sintorn, E., and Assarsson, U. 2008. Real-time approximate sorting for self shadowing and transparency in hair rendering. In Proceedings of I3D, 157--162.
18. Sintorn, E., and Assarsson, U. 2009. Hair self shadowing and transparency depth ordering using occupancy maps. In Proceedings of I3D, 67--74.
19. Sloan, P.-P., Kautz, J., and Snyder, J. 2002. Precomputed radiance transfer for real-time rendering in dynamic, low-frequency lighting environments. In Proceedings of ACM SIGGRAPH, 527--536.
20. Tsai, Y.-T., and Shih, Z.-C. 2006. All-frequency precomputed radiance transfer using spherical radial basis functions and clustered tensor approximation. ACM Trans. Graph. 25, 3, 967--976.
21. Ward, K., Bertails, F., Kim, T.-Y., Marschner, S. R., Cani, M.-P., and Lin, M. 2007. A survey on hair modeling: Styling, simulation, and rendering. IEEE Transactions on Visualization and Computer Graphics (TVCG) 13, 2, 213--234.
22. Yuksel, C., and Keyser, J. 2008. Deep opacity maps. Computer Graphics Forum 27, 2, 675--680.
23. Zinke, A., and Weber, A. 2007. Light scattering from filaments. IEEE Trans. Vis. Comp. Graph. 13, 2, 342--356.
24. Zinke, A., Yuksel, C., Weber, A., and Keyser, J. 2008. Dual scattering approximation for fast multiple scattering in hair. ACM Trans. Graph. 27, 3, 32:1--10.
25. Zinke, A. 2008. Photo-Realistic Rendering of Fiber Assemblies. PhD thesis, University of Bonn.

Index Terms

• Computing methodologies

  • Artificial intelligence

    • Computer vision

      • Image and video acquisition

        • 3D imaging

  • Computer graphics

    • Animation

    • Image manipulation

    • Rendering