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Spherical Harmonic Lighting of Wavelength-dependent Phenomena

Spherical Harmonic Lighting of Wavelength-dependent Phenomena. Clifford Lindsay, Emmanuel Agu Worcester Polytechnic Institute (USA). Introduction. Modeling of Light Interference As A BRDF.

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Spherical Harmonic Lighting of Wavelength-dependent Phenomena

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  1. Spherical Harmonic Lighting of Wavelength-dependent Phenomena Clifford Lindsay, Emmanuel Agu Worcester Polytechnic Institute (USA)

  2. Introduction • Modeling of Light Interference As A BRDF • Compactly Store Surface Response and Hemispheric Light Contribution In Terms Of Spherical Harmonic Coefficients • Evaluation of Light And Reflection Is Done on GPU • Working With Spectral Color Space Instead of RGB

  3. Spherical Harmonics Spherical harmonics is a set of basis functions defined in spherical coordinates We can use spherical harmonics to approximate the original, where ciis a vector of SH coefficient We can then use these coefficients to reconstruct an approximation to the original signal

  4. Interference Factors that Affect Light Interference: • Refractive index and thickness of the thin film • Refractive indices of the media 1 & 2 • Incident Angle  and incident SPD (Spectral Power Distribution)

  5. Spectral BRDF Just Like Regular BRDFs (but different) • Rendering equation • Function of 4 angles (incident, reflection) • Conservative What’s Different? • Different Color Interaction • Different Material Interaction • Different Viewer Interaction (non-reciprocal)

  6. Previous Work in S.H. • Diffuse Reflection Maps, Hanrahan, Ramamoorthi, 2001 • Physically Based BRDFs, Westin 1992 • Isotropic BRDFs with SH Maps, Hanrahan, Ramamoorthi, 2002 • Arbitrary BRDFs, Kautz et al, 2002 • Radiance Transfer, Glossy Surfaces, Self-shadow, and Interreflection, Sloan et al, 2002

  7. Our Approach Two Stage Approach: 1. Pre-computation 2. Render

  8. Pre-computation Total Light Contribution: • Set of coefficients approximating total light contribution BRDF Response: • Texture map based all possible view vectors

  9. V,T,B Vertex Processor Texture Map, fi Fragment Processor Uniform Var, Li GPU Rendering: • Index Texture Map Based on view V • Summing the coefficients for final contribution • Add ambient, diffuse, Fresnel for additional realism

  10. Conclusion • Real-time rendering of complex materials previously available to offline renderers (ray tracers) • Data and Data structures that are GPU friendly • Evaluation of Spherical Harmonics is a linear operation • Increased realism with Image Based Lighting and accurate BRDFs with GPU acceleration

  11. Results

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