# spherical harmonic lighting of wavelength-dependent phenomena

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

Spherical Harmonic Lighting of Wavelength-dependent Phenomena

Clifford Lindsay, Emmanuel AguWorcester Polytechnic Institute (USA)

IntroductionModeling of Light Interference As A BRDFCompactly Store Surface Response and Hemispheric Light Contribution In Terms Of Spherical Harmonic CoefficientsEvaluation of Light And Reflection Is Done on GPUWorking With Spectral Color Space Instead of RGB

Spherical HarmonicsWe can then use these coefficients to reconstruct an approximation to the original signalWe can use spherical harmonics to approximate the original, where ci is a vector of SH coefficientSpherical harmonics is a set of basis functions defined in spherical coordinates

InterferenceFactors that Affect Light Interference:Refractive index and thickness of the thin filmRefractive indices of the media 1 & 2Incident Angle and incident SPD (Spectral Power Distribution)

Spectral BRDFJust Like Regular BRDFs (but different)Rendering equationFunction of 4 angles (incident, reflection)Conservative

Whats Different?Different Color InteractionDifferent Material InteractionDifferent Viewer Interaction (non-reciprocal)

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

Our ApproachTwo Stage Approach:1. Pre-computation2. Render

Pre-computationTotal Light Contribution:BRDF Response: Texture map based all possible view vectors Set of coefficients approximating total light contribution

GPURendering:Index Texture Map Based on view VSumming the coefficients for final contributionAdd ambient, diffuse, Fresnel for additional realism

ConclusionReal-time rendering of complex materials previously available to offline renderers (ray tracers)Data and Data structures that are GPU friendlyEvaluation of Spherical Harmonics is a linear operationIncreased realism with Image Based Lighting and accurate BRDFs with GPU acceleration

Results

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