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)