spatial directional radiance caching václav gassenbauer czech technical university in prague...
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Spatial Directional Radiance Caching
Václav GassenbauerCzech Technical University in Prague
Jaroslav KřivánekCornell University
Kadi BouatouchIRISA / INRIA Rennes
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GoalAcceleration of Global Illumination
Computation on Glossy Surfaces
Adapt glossiness of surfaces
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Previous Work
Irradiance caching (IC) ◦ [Ward et al. 88], [Ward and Heckbert 92]
◦ Indirect illumination changes slowly → interpolate
Variants of IC◦ [Tabellion and Lamorlette 04], [Brouillat et
al. 08], [Arikan et al. 05], …
Radiance caching (SHRC) ◦ [Křivánek et al. 05]
Other techniques ◦ [Hinkenjann and Roth 07, …]
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Motivation
Radiance caching limitation◦Uniform sampling of full hemisphere
◦Low glossy surfaces
◦Conversion of the scene BRDFs into the frequency domain in preprocess
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SDRC – Overview
Caching schemeCache structureNew record computationSpatial / Directional InterpolationOutgoing radiance computation
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Spatial Cache Lookup
SpatialCacheMiss!
BRDFImportanceSampling
Spatial Directional Caching Scheme
SpatialCache
p2
iL
p1
Project Sample onto Unit Square
Store incache
iLiL
N
i
oL1
/pdfoL
Spatial Cache Lookup
iL
SpatialCache
Hit!
DirectionalCache HIT!
DirectionalCache MISS!
Directional
CacheUpdate
M
i
oL1
/pdfoL
Directional Cache
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Structure of the Two Caches
kD-tree(directional cache)
Octree (spati
al cache)
SpatialCache
iL
iL
iL
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New Record Computation
Generate N samples using BRDF importance sampling
pCompute incoming radiance using ray casting and photon mapTransform samples onto 2D domain
Build a k-D tree upon the samples
L-tree
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Spatial Interpolation
p
Collect L-trees that can be used for interpolation at p (borrowed from RC)
For all L-trees found compute the spatial weight
1
1
i
i
isi Rw nn
ppp
Spatial
Cache
Spatial Cache Lookup
p1
p2p
SpatialCache
Hit!L-tree(p2)
p2
L-tree(p1)p1
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Directional Interpolation
p2
p
L-tree(p2)
Generate M(M<<N) samples using BRDF importance sampling
For all the samples try find nearby radiance samples in L-tree(p2) in S(p)
Transform samples onto unit domain
Update L-tree(p2) if necessary
Radiance sample found
Radiance not sample found→ ray tracing
L-tree(p2)
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Which Radiance Samples Are Nearby?
i-th L-tree
dr
2d
2
1,0maxr
wjik
jdik
inin
in
Compute search radius for each radiance sample
Collect nearby radiance samples
Compute directional weights
dr inj
inik
inik
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Incoming Radiance Interpolation
Interpolate all collected radiance sample◦Sums run over all radiance samples from all
contributing L-trees.
Product of spatial and directional
weights
k-th radiance sample stored in
the i-th L-tree
Interpolated
incoming radiance
Si Tkj
dik
si
Si Tkikj
dik
si
j
i
i
ww
Lww
Lin
inin
inin
p
p
p
,~
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Outgoing Radiance Computation
Evaluate Monte Carlo Estimator
interpolated incoming radiance
# render
samples
Sampling probability ofoutin j
Estimated outgoing radiance
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M
j j
jjj BRDFL
ML
1 ,pdf
cos,,~
1,
~outin
inoutinininoutout p
p
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Results
SHRC vs. SDRC◦SHRC = Spherical harmonics caching
◦SDRC = new Spatial-Directional caching
MC vs. SHRC vs. SDRC vs. REF◦MC = Monte Carlo importance sampling
◦REF = reference solution
SDRC scalabilityAnimation
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SHRC vs. SDRC
SDRC adapts to the BRDF lobe exponent automatically
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MC vs. SHRC vs. SDRC vs. REF
SDRC produce less noise than MC SDRC produce no ringing artifacts as SHRC.
MC SDRC (new)
SHRC REF
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SDRC scalability
N=64 / t≈6.2s
N=128 / t≈13.0s N=256 / t≈23.6s
SD
RC
MC
Rendering time is O(N).
indirect lighting compu-tation time of
the detail
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AnimationWithout reusing cache
record
With reusing cache record- Flickering reduced
Side-by-side comparison
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Discussion
Interpolation◦MC performs better than SDRC for highly
glossy materialsSupported materials
◦Spatially varying ones without sudden changes
◦Availability of sampling procedureMemory consumption
◦≈ higher memory requirements than SHRC (N = 512 and SH order of 10)
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Conclusion
Indirect lighting computation on glossy surfaces
PROS:+Exploits spatial / directional coherence+No blurry / banding artifacts+Adapts automatically to the glossiness+Less noisy than MC
CONS−Higher memory requirements−Potentially difficult parallelization
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Future Work
Precise formalization of illumination coherence
Decrease flickering in animation
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Acknowledgements
Chess pieces courtesy of T. Hachisuka
Ray tracing system - PBRT
Thank you for your attention
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Cache Record Density Control