Everything on Global Illumination

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Everything onGlobal Illumination
Xavier Granier - IMAGER/UBC
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Overview

• Introduction
• Radiosity Methods
• Stochastic Methods
• Conclusion

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Overview

• Introduction
• Local Illumination
• Global Illumination Effects
• Rendering Equation
• Light Paths
• Radiosity Methods
• Stochastic Methods
• Conclusion

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Local Illumination

• Equation
• Example
• OpenGL
• Simple Ray-Tracing

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Colour Bleeding
Debevec
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Indirect Lighting
Granier
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Soft Shadows
Herf
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Caustics
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Caustics
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Rendering Equation Kajiya86

• Assumptions
• Light exchange equilibrium
• One wavelength
• Emitted energy (W.m-2.sr-1)
• Self emitted
• Reflected

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The Rendering Equation (2)

• Based on radiance value only

ds
d?
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Light Paths Heckbert90

• Regular expression
• L light source
• D diffuse reflection
• S directional reflection (specular) 
• E view-point

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Diffuse assumption Goral84

• Independent of the direction of reflection
• Radiosity value (W.m-2)
• New equation

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Matrix equation

• Matrix equation Goral84
• Form factor

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Colour Bleeding
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Gathering

• Solve as an Axb
• MB Bp
• Jacobi
• Bi(k1) Bpi Sj?i Mij Bj(k)
• Gauss-Siedel
• Bi Bpi Sj?i Mij Bj

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Shooting/Progressive

• Progressive refinement
• Distribute extra radiosity DBi
• Bj(k1) Bj(k) rjFji DBi
• Extra unshot radiosity
• DBi Bj(k) Bj(k-1)
• Energy starts at emitters
• Distributes progressively
• Ambiant term

Cohen
Bi
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Hierarchical Radiosity Hanrahan91
?

• Exchanges computed at different levels
• Clustering Smith94,Silllion95,Christensen97,Willm
  ot99

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Links

• Exchange representation
• Stored on receptor
• Stored information
• Visibility
• Form Factor
• Emitter
• Exchanges partitionning

F,V,S
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One Iteration

• Refinement
• Link Creation at correct level
• Visibility and Form factor computation
• Energy transfer
• For each link
• IRS FRSVRSBS
• Push-pull
• Hierarchical update

S
R
IR IR IRS
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Push-Pull

• Energy sum on leaves
• Reflection
• Hierarchical update

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Advantages / Drawbacks

• View-independent solution
• Deal with complex scenes
• Exchanges partitioning
• Interactive updates Shaw97,Drettakis97

• Memory cost (Links/Hierarchy)
• Only diffuse
• Mesh

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Probabilistic Methods

• Based on the Rendering Equation Kajiya86
• Estimations based on samples
• Light paths, rays, particles
• Probabilistic Propagation
• Material property ? probability density function

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From a viewpoint
Kaj86, Shi90
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Propagation

• Choose p ? ? x cos
• Russian Roullette
• Propability of non-reflection p(0)
• If(Ranlt p(0)) then stop
• Else reflect in direction ? using p

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Bi-directional
Lafortune,Veach
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Particle Tracing
Walter,Jensen
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Particle Tracing

• Emission choose p ? Lp x cos
• Propagation
• Same as previous
• Reconstruction Irradiance

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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

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Photon Map Jensen

• Separate particle emission
• Diffuse
• Caustics
• BSP-tree storage
• Efficient particule representation
• Simple Kernel (n1-Cone n2-Epanechnikov)

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Advantages / Drawbacks

• Independent geometry, materials
• High directional cases
• Simple

• Noise slow convergence (diffuse)
• Dynamic case
• Solution updates (moving objects)
• Temporal continuity

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Biblio

• http//www.helios32.com/resources.htm
• Stochastic method
• Bidirectionnal (Lafortune-Veach)
• Particle Tracing (Walter)
• Photon Map (Siggraph course 2001, book)
• Radiosity Method
• Sillion/Puech Book

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Software

• http//radsite.lbl.gov/radiance/HOME.html
• http//www.cs.kuleuven.ac.be/cwis/research/graphic
  s/RENDERPARK/
• blender (radiosity)/povray(photon-map)
• http//www.mentalimages.com/p101.html
• Mental Ray (Maya)