Toward RealTime Global Illumination

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Toward Real-Time Global Illumination
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Project Ideas

• Distributed ray tracing
• Extension of the radiosity assignment
• Translucency (subsurface scattering)

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Global Illumination Offline?

• Ray Tracing and Radiosity are inherently slow.
• Speedup possible by
• Brute-force more hardware, multicoreetc.
• Approximate results

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Under Simplified Assumption

• Can it become faster if
• the view is fixed?
• the scene is static?
• the lights are simple?
• if indirect lighting is limited?

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Lighting Design

• Assuming
• Static scene
• Fixed (or limited) view
• Example
• Lpics a hybrid hardware accelerated relighting
  engine for computer cinematography, SIGGRAPH 2005

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Instant Radiosity (and the Problem of Many
Lights?)

• What if we place many virtual light sources to
  represent indirect lighting?
• How do we handle a very large number of light
  sources?
• Lightcuts A Scalable Approach to Illumination,
  SIGGRAPH 2005

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Precomputed Light Transport
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Indirect Lighting

• Many indirect lighting effects are subtle, yet
  crucial for visual realism. Examples are
• Soft shadow
• Ambient occlusion

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Ambient Occlusion

• Ambient light is a very crude approximation to
  indirect reflections of surrounding objects.
• What if a point cant see much of its
  surrounding?

From Janne Kontkanen Samuli Laine ACM I3D 2005
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Soft Shadow from Environment Lighting
Sloan, Kautz, Snyder 2002
Sen, Cammarano, Hanrahan, 2003
Shadows from smooth lighting (precomputed
radiance transfer)
Shadows from point-lights (shadow maps, volumes)
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Beyond Monte Carlo Path Tracing?

• Are global illumination solvers always time
  consuming?
• What if the scene and the lights are static ? ?
  Radiosity (view can changes!)
• What if only the scene is static?

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Light Stage

• Take photos under single point light at various
  positions.
• Trivial questions how to produce new images at
• Two point lights?
• Area light?
• Environment light (captured by light probe)?

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(No Transcript)
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Precomputed Light Transport

• Three important papers to start with
• "Precomputed Radiance Transfer for Real-Time
  Rendering in Dynamic, Low-Frequency Lighting
  Environments" Sloan et al., SIGGRAPH 2002
• "All-Frequency Shadows Using Non-linear Wavelet
  Lighting Approximation" Ng et al., SIGGRAPH 2003.
• "Triple Product Wavelet Integrals for
  All-Frequency Relighting" Ng et al.  SIGGRAPH 2004

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• The following 8 slides are from Ren Ngs SIGGRAPH
  2003 presentation

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Relighting as Matrix-Vector Multiply
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Relighting as Matrix-Vector Multiply

• Output Image(Pixel Vector)

• Input Lighting(Cubemap Vector)

• TransportMatrix

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Ray-Tracing Matrix Columns
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Ray-Tracing Matrix Columns
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Light-Transport Matrix Rows
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Light-Transport Matrix Rows
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Light-Transport Matrix Rows
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Rasterizing Matrix Rows

• Pre-computing rows
• Rasterize visibility hemicubes with graphics
  hardware
• Read back pixels and weight by reflection function

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Low-Frequency vs. All-Frequency
Teapot in Grace Cathedral
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Related Work
SH PRT
SH PRT
Sloan et al. 2002
Kautz et al. 2002
Deformable
Bump mapping
Gaussians
BTFPRT
Sloan et al. 2005
Sloan et al. 2005
Green et al. 2006
Sloan et al. 2003
Subsurface
Wavelet Triple
Wavelet Double
Wavelet Double
Ng et al. 2003
Wang et al. 2005
Ng et al. 2004
Wang et al. 2006