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Importance sampling of products from Illumination and BSDF using SRBF

Importance sampling of products from Illumination and BSDF using SRBF. Valentin JANIAUT KAIST (Korea Advanced Institute of Science and Technology). Overview. Preliminary notions BSDF Light scattering for human fiber SRBF Problem Idea Results And after? References.

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Importance sampling of products from Illumination and BSDF using SRBF

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  1. Importance sampling of products from Illumination and BSDF using SRBF Valentin JANIAUT KAIST (Korea Advanced Institute of Science and Technology)

  2. Overview • Preliminary notions • BSDF • Light scattering for human fiber • SRBF • Problem • Idea • Results • And after? • References

  3. Preliminary notion > Problem > Idea > Results > And After ? > References BSDF: Bidirectional Scattering Distribution Function BRDF BTDF BSDF

  4. Preliminary notion > Problem > Idea > Results > And After ? > References BSDF For Hair Rendering • In 2003 Stefan Marschner proposed a new model for the light scattering for Human Fiber which has been widely used until today.

  5. Preliminary notion > Problem > Idea > Results > And After ? > References BSDF For Hair Rendering

  6. Preliminary notion > Problem > Idea > Results > And After ? > References Rendering Equation for the Hair • Transmittance replace the visibility. • Single Scattering • Different optimization to handle the large amount of data. Diameter of the hair fiber Bidirectional scattering function Transmittance Environment Lighting

  7. Preliminary notion > Problem > Idea > Results > And After ? > References SRBF Number of SRBF to use for the approximation Spherical Coordinate of the Spherical Function Spherical Coordinate of the center of the SRBF Bandwidth of the center of the SRBF Coefficient depending of the problem SRBF with actually 5 parameters

  8. SRBF Viewer

  9. Preliminary notion > Problem > Idea > Results > And After ? > References Advantage of SRBF • The function can be approximate using just a row of vector: [c,ξ,λ]j • The product of different SRBF is also an SRBF. • Integration of SRBF is simple (sampling of the center of each SRBF)

  10. Preliminary notion > Problem > Idea > Results > And After ? > References Problem

  11. Preliminary notion > Problem > Idea > Results > And After ? > References Problem Pre-computation of the following integral: How to improve the offline data ?

  12. Preliminary notion > Problem > Idea > Results > And After ? > References Idea • Approximation using SRBF. • Two possible ways to solve this. • Approximating the BSDF: • Using a SRBF for each ωo • Approximating the integral: • Using a SRBF for each ωo Smooth data  efficient approximation Easy computation of the integral using SRBF sampling. Need to compute the integral. Can be used for other computation. Too much specific. Too smooth for the BSDF ? One SRBF

  13. Product of two SRBF • What if we approximate the BSDF using SRBF?

  14. Preliminary notion > Problem > Idea > Results > And After ? > References How to check my idea? • Implementation of Marschner model in Python with SciPy. • Solving SRBF with SciPy and L-BFGS-B.

  15. Preliminary notion > Problem > Idea > Results > And After ? > References Results • Approximating the BSDF: • Using a SRBF for each ωo • Approximating the integral: • Using a SRBF for each ωo • Computation of integration too slow with SciPy • The code need more optimization to work with this approach. cos (θi) cos (θ0) • Encouraging result with 8 SRBF. • Need to be tested with larger number of SRBF and real data. 16 h to obtain the image! (on a Mac Mini Intel Core 2 Duo 2GHz 1GB Ram)

  16. Preliminary notion > Problem > Idea > Results > And After ? > References And after? • Optimizing the code to validate my idea. • How to merge geometric and scattering data? • How to create a common method for all kind of hair?

  17. References • 2003: Light Scattering from Human Fiber [Marschner et al.] • 2007: Practical Global Illumination for Hair Rendering [Cem Yuksel] • 2008: Dual scattering approximation for fast multiple scattering in hair. [Zinke] • 2008: Efficient multiple scattering in hair using spherical harmonics. [Moon et .al] • 2010: Interactive hair rendering under environment lighting. [Zhong Ren] • http://hairrendering.wordpress.com/tag/marschner/ (C# implementation of Marschner Scattering model) • http://www.scipy.org/ (Scientific Computing in Python) • http://project.valeuf.org/projects/marschner/ (Website with my source code, and my PPT)

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