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Quick survey about PRT

Quick survey about PRT. Valentin JANIAUT KAIST (Korea Advanced Institute of Science and Technology). Some Math before. Wavelet Spherical Harmonic Spherical Radial Basis Function. Wavelet: How to compress signal. Goal: Express a function as a set of coefficients. Sum of sinus and cosinus.

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Quick survey about PRT

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  1. Quick survey about PRT Valentin JANIAUT KAIST (Korea Advanced Institute of Science and Technology)

  2. Some Math before. • Wavelet • Spherical Harmonic • Spherical Radial Basis Function

  3. Wavelet: How to compress signal Goal: Express a function as a set of coefficients. Sum of sinus and cosinus. NO TIME (OR SPACE) RESOLUTION Fourier transform restricted to cosinus. Cut the signal into different window for better analysis.

  4. Wavelet: Intuitive approach FEATURES • Orthonormal basis • Catch the high-frequency • Quite complicate • Used in JPEG-2000 • A lot of possible kernels

  5. Spherical Harmonic FEATURES • Spherical basis • Catch large features • Quite complicate • Used in geology • Use Legendre polynomial as kernel.

  6. Spherical Radial Basis Function FEATURES • Spherical basis • Catch high and low frequency. • Fairly simple • Use Gaussian or Poison kernel Gaussian Distribution

  7. What is PRT? • A set of technique to pre-compute various function related to the Radiance Transfer. Problem How to integrate the rendering equation over large-scale lighting environment? • Monte-Carlo Ray Tracing • Radiosity • Multi-pass rendering No real-time

  8. Some key paper in this field Precomputed Radiance Transfer for Real-Time Rendering in dynamic, low-frequency lighting environment. [Sloan] Clustered principal components for precomputed radiance transfer. [Sloan] All frequency shadows using non-linear wavelet lighting approximation. [Ng] Precomputed Radiance Transfer: Theory and Practice SIGGRAPH05 Course All frequency interactive relighting of translucent objects with Single and Multiple Scattering. [Wang] Importance sampling of products from illumination and BRDF using spherical radial basis functions. [Tsai] Real-time editing and relighting of homogeneous translucent materials. [Wang] All-frequency Rendering of Dynamic, Spatially-Varying Reflectance. [Wang] 2002 2003 2005 2008 2010

  9. An example of Transfer Matrix Rendering Equation Geometry relighting Image Relighting B = TL

  10. Precomputed Radiance Transfer for Real-Time Rendering in dynamic, low-frequency lighting environment. • Use Spherical Harmonic to represent how an object scatter light. LIMITS • No High-Frequency (too many SH coeff.) • Only diffuse and glossy surface.

  11. Clustered principal components for precomputed radiance transfer • Similar than the previous approach. • Add support for diffuse multiple scattering

  12. All frequency shadows using non-linear wavelet lighting approximation • Same framework than [SLOAN02] • Approximate the environment map in a wavelet basis keeping only the largest terms (=non-linear approximation) LIMITS • Rigid scene (but relighting is OK) • Only diffuse and glossy surface.

  13. All frequency interactive relighting of translucent objects with Single and Multiple Scattering. • Add support for Diffuse Multiple Scattering in [Ng] framework. with T is precomputed into Wavelet like in [Ng].

  14. Importance sampling of products from illumination and BRDF using spherical radial basis functions. • No transfer function, use directly precomputation of BRDF and the environment map into SRBF. LIMITS • Support only BRDF. • Needs more data, but only one product at the Running time.

  15. Real-time editing and relighting of homogeneous translucent materials. • Improved version of the previous article. • Reading not done yet.

  16. All-frequency Rendering of Dynamic, Spatially-Varying Reflectance • Proposed an unified technique to represent SVBRDF using SRBF. • Using the micro-facet model.

  17. Back to our problem

  18. Current solution Implemented using marschner model. Extract the SRBF coefficient using L-BFGS-B solver like [Tsai08] DOES NOT SOLVE THE HAIR GEOMETRY DEPENDANT TERMS

  19. Better approach • Find a way to pre-compute the different terms of the equation using SRBF. • Look to the visibility map • Look to PRT techniques with support to geometry modification

  20. Papers to read • Local, deformable precomputed radiance transfer [Sloan05] • Generalized wavelet product integral for rendering dynamic glossy objects [Sun06] • Real-time soft shadows in dynamic scenes using spherical harmonic exponentiation [Ren06] • Real-time, all-frequency shadows in dynamic scenes [Annen08]

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