Everything on Global Illumination Xavier Granier - IMAGER/UBC

2 IMAGER /UBCEverything on Global Illumination Overview  Introduction  Radiosity Methods  Stochastic Methods  Conclusion

3 IMAGER /UBCEverything on Global Illumination Overview  Introduction  Local Illumination  Global Illumination Effects  Rendering Equation  Light Paths  Radiosity Methods  Stochastic Methods  Conclusion

4 IMAGER /UBCEverything on Global Illumination Local Illumination  Equation  Example:  OpenGL  Simple Ray-Tracing

5 IMAGER /UBCEverything on Global Illumination Colour Bleeding Debevec

6 IMAGER /UBCEverything on Global Illumination Indirect Lighting Granier

7 IMAGER /UBCEverything on Global Illumination Soft Shadows Herf

8 IMAGER /UBCEverything on Global Illumination Caustics

9 IMAGER /UBCEverything on Global Illumination Caustics

10 IMAGER /UBCEverything on Global Illumination Rendering Equation [Kajiya86]  Assumptions  Light exchange equilibrium  One wavelength  Emitted energy (W.m -2.sr -1 )  Self emitted  Reflected

11 IMAGER /UBCEverything on Global Illumination The Rendering Equation (2)  Based on radiance value only d’d’ ds’

12 IMAGER /UBCEverything on Global Illumination Light Paths [Heckbert90]  Regular expression :  L = light source  D = diffuse reflection  S = directional reflection (specular)  E = view-point

13 IMAGER /UBCEverything on Global Illumination Diffuse assumption [Goral84]  Independent of the direction of reflection  Radiosity value (W.m -2 )  New equation

14 IMAGER /UBCEverything on Global Illumination Matrix equation  Matrix equation [Goral84]  Form factor

15 IMAGER /UBCEverything on Global Illumination Colour Bleeding

16 IMAGER /UBCEverything on Global Illumination Gathering  Solve as an A x=b  MB = B p  Jacobi  B i ( k +1) = B pi –  j  i M ij B j ( k )  Gauss-Siedel  B i = B pi –  j  i M ij B j BiBi

17 IMAGER /UBCEverything on Global Illumination Shooting/Progressive  Progressive refinement  Distribute extra radiosity  B i  B j ( k +1) = B j ( k ) +  j F ji  B i  Extra “unshot” radiosity   B i = B j ( k ) – B j ( k -1)  Energy starts at emitters  Distributes “progressively”  Ambiant term BiBi [Cohen]

18 IMAGER /UBCEverything on Global Illumination Hierarchical Radiosity [Hanrahan91]   Exchanges computed at different levels  Clustering [Smith94,Silllion95,Christensen97,Willmot99]

19 IMAGER /UBCEverything on Global Illumination Links  Exchange representation  Stored on receptor  Stored information  Visibility  Form Factor  Emitter  Exchanges partitionning F,V,S

20 IMAGER /UBCEverything on Global Illumination One Iteration  Refinement  Link Creation at “correct level”  Visibility and Form factor computation  Energy transfer  For each link  I RS = F RS V RS B S  Push-pull  Hierarchical update I RS I R = I R + I RS S R

21 IMAGER /UBCEverything on Global Illumination Push-Pull  Energy sum on leaves  Reflection  Hierarchical update

22 IMAGER /UBCEverything on Global Illumination Advantages / Drawbacks  View-independent solution  Deal with complex scenes  Exchanges partitioning  Interactive updates [Shaw97,Drettakis97]  Memory cost (Links/Hierarchy)  Only diffuse  Mesh

23 IMAGER /UBCEverything on Global Illumination Probabilistic Methods  Based on the Rendering Equation [Kajiya86]  Estimations based on samples  Light paths, rays, particles  Probabilistic Propagation  Material property  probability density function

24 IMAGER /UBCEverything on Global Illumination From a viewpoint [Kaj86, Shi90]

25 IMAGER /UBCEverything on Global Illumination Propagation  Choose p   x cos  Russian Roullette  Propability of non-reflection p(0)  If(Ran#< p(0) ) then stop  Else reflect in direction  ’ using p

26 IMAGER /UBCEverything on Global Illumination Bi-directional [Lafortune,Veach]

27 IMAGER /UBCEverything on Global Illumination Particle Tracing [Walter,Jensen]

28 IMAGER /UBCEverything on Global Illumination Particle Tracing  Emission : choose p  L p x cos  Propagation  Same as previous  Reconstruction : Irradiance

29 IMAGER /UBCEverything on Global Illumination Photon Map [Jensen]  Photon generation stage  Emit photons on light sources  Random walk (trace photons through scene)  Store interactions (position x, power phi, …)  Rendering : Modified distribution ray tracing  Approximate radiance by density estimation  Query k nearest photons  Radiance = sumOfEnergies/coveredArea

30 IMAGER /UBCEverything on Global Illumination Photon Map [Jensen]  Separate particle emission  Diffuse  Caustics  BSP-tree storage  Efficient particule representation  Simple Kernel (n=1-Cone n=2-Epanechnikov)

31 IMAGER /UBCEverything on Global Illumination Advantages / Drawbacks  Independent : geometry, materials  High directional cases  Simple  Noise : slow convergence (diffuse)  Dynamic case  Solution updates (moving objects)  Temporal continuity

32 IMAGER /UBCEverything on Global Illumination Biblio   Stochastic method  Bidirectionnal (Lafortune-Veach)  Particle Tracing (Walter)  Photon Map (Siggraph course 2001, book)  Radiosity Method  Sillion/Puech Book

33 IMAGER /UBCEverything on Global Illumination Software   h/graphics/RENDERPARK/  blender (radiosity)/povray(photon-map)   Mental Ray (Maya)