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Accurate Accurate Image BasedImage Based
Relighting Relighting through through
OptimizationOptimization
Pieter PeersPhilip Dutré
Department of Computer ScienceK.U.Leuven, Belgium
What is Image Based Relighting?What is Image Based Relighting?
Basis ImagesBasis Images
Processing & Processing & RelightingRelighting
Relit ImageRelit Image
Previous WorkPrevious Work
• The Light Stage (Debevec et al. ’00)
Images: ACM SIGGRAPH ‘00
Previous WorkPrevious Work
• Environment Matting (Zonker et al. ’99, Chuang et al. ’00)
Images: ACM SIGGRAPH ’99
Previous workPrevious work
Diffuse Materials
Specular Materials
The LightStage
+ -
Environment Matting
- +
Sparse sampling of light source directionsSufficient angular sampling
Large span of incominglight directions
Bundled incominglight directions
• Matusik et al. EGWR’02
Three-step algorithmThree-step algorithm
Basis Image Basis Image RecordingRecording
Relit image = Captured reflectance + Light-mapRelit image = Captured reflectance + Light-map
1
3
2
Reflectance field Reflectance field calculationcalculation
Basis Image RecordingBasis Image Recording
Basis Image RecordingBasis Image Recording
...
Basis Image RecordingBasis Image Recording
HDR photographsHDR photographs
Practical SetupPractical Setup
• HDR photographs
• Monitor calibration
• 4x4 grid, 9 patterns per lightpatch
• ±600 basis images
Three-step algorithmThree-step algorithm
Basis Image Basis Image RecordingRecording
1
3
2
Relit image = Captured reflectance + Light-mapRelit image = Captured reflectance + Light-map
Reflectance field Reflectance field calculationcalculation
Support and reflection coefficientSupport and reflection coefficient
Support and reflectanceSupport and reflectance
…
PatternsPixel
× Rpix,patch
Reflection Coefficient
=
=
=
=
Resulting Value
……
→ Error1
→ Error2
→ Errorn-1
→ Errorn
Find and Rpix,patch that minimize: Errork
click
Support and reflectance: examplesSupport and reflectance: examples
top
left back right
Three-step algorithmThree-step algorithm
Basis Image Basis Image RecordingRecording
1
3
2
Relit image = Captured reflectance + Light-mapRelit image = Captured reflectance + Light-map
Reflectance field Reflectance field calculationcalculation
Re-lightingRe-lighting
For each pixel:
Pixel value = ∑ Filteri(LightMap) × Rpix,i
support i
ResultsResults
A
C
B
D
ResultsResults
A
C
B
D
ResultsResults
A
C
B
D
ResultsResults
A
C
B
D
ComparisonComparison
Stochastic ray tracing Relit from rendered basis images
ComparisonComparison
Stochastic ray tracing Relit from rendered basis images
ComparisonComparison
Stochastic ray tracing Relit from rendered basis images
ConclusionConclusion
• Accurate relighting:– Diffuse materials– Specular materials
• Combine strengths from:– The Light Stage– Environment matting
Future WorkFuture Work
• Alternative emitting devices
• Investigate other patterns & optimization algorithms
AcknowledgementsAcknowledgements
• Frank Suykens and Vincent Masselus
• Some environment maps from: http://www.debevec.org/Probes
Thank you…Thank you…
Questions?Questions?