Transcript Slide 1
Precomputed Radiance Transfer Field for Rendering Interreflections in Dynamic Scenes
Minhao Pan, Rui Wang, Xinguo Liu, Qunsheng Peng and Hujun Bao State Key Lab of CAD&CG, Zhejiang University, P.R. China
23/7/2007
Related works
Traditional global illumination methods Based on ray-trace or radiosity Realistic but slow Precomputed light transport Static scene —— PRT[Sloan, 2002] Shadow in dynamic Scene ——[Zhou, 2005] Interreflections in dynamic scene ——[Iwasaki, 2007] Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field
Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field
Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field Interreflection Transfer Function (ITF)
I q
p p
p
)
ds q
p
Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field Interreflection Transfer Function (ITF)
q p
1
p
2
p I q I q
p p
p
)
ds
Environment Lighting
L p
j m
1
l y j j
[Sloan, 2002]
i n
1
T p i I q
l i
i n
1
T p
1
i
i n
1
M q i p l i
l i
i n
1
i T p
2
p l i
...
Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field Interreflection Transfer Function (ITF)
q M q i I q I q
p p
p
)
ds
Environment Lighting
L p
j m
1
l y j j
[Sloan, 2002]
i n
1
p i
i I q
i n
1
T p
1
i
i n
1
M q i l p i
l i
i n
1
i T p
2
l p i
...
M q ij
M q i
y i
M q ij
Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field Interreflection Transfer Function (ITF)
q I q
p
Local lighting
p
p
)
ds p
1
p
2
p I q
i n
1
T p i l i
i n
1
T p
1
i
p l i
i n
1
i T p
2
p l i
...
Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field Proxy-based incidient light approximation
Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field Proxy-based incidient light approximation
L m L p X m X k X
2
L k X
1
L
2 1 The incident light to
p L p
Precomputed Radiance Transfer Field
k m
1
w L k
State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field Proxy-based incidient light approximation
q
I q
p
Local lighting
p
p
)
ds X m X k X
2
X
1 Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field Proxy-based incidient light approximation
q p
1
p
2
I q
p p
p
)
ds
Local lighting
X
1
L
1
I
,
n
1
n i i
T X i T X i
1 , 1 1
n
i
1 ...
n
i
1
i T X
1
M
,
i
,
p
1
p
2 ,
p
w X
1
p p
,
w X w X p
1
l
1
l
, ,
X
1
p
1
p
2
l
, ,
l i
Precomputed Radiance Transfer Field , , State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field Proxy-based incidient light approximation
q p
1
p
2
I q
p
Local lighting
p
p
)
ds X
2
L
2
I X
2 ,
q
i
1 ...
n i i i n
1
n
1
n
1
T X i T X i T X i M
2
i
2 2
X
, , , 2
p p
1
p
2 ,
q w X
p p
2 ,
p l i w X w X
l i
2 2 , ,
p
1
l i p
2
l i
State Key Lab of CAD&CG, Precomputed Radiance Transfer Field Zhejiang University
Radiance Transfer Field Proxy-based incidient light approximation
I q
p p
p
)
ds q L m X m X k
Local lighting
X
2
L k X
1
L
1
L
2
I q
I
,
I X
2 ,
q
...
M n
i
m
1
M k n
1
i
1
i M ij X k
,
q
,
i X M k
,
q i X k
,
q
l y i
,
l X i k i n
1
M i X
2 ,
q q
M ij
, ,
M ij
,
l X
2 ,
i
...
M ij X k
,
q
} Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Radiance Transfer Field
Precomputed Radiance Transfer Field {
M ij
, ,
M ij
, ,...
} State Key Lab of CAD&CG, Zhejiang University
Precomputation
Compute radiance transfer on each vertex Compute radiance transfer on samples in field Compress the radiance transfer field Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Precomputation Compute radiance transfer on vertices
X m X k X
2
X
1 Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Precomputation Compute radiance transfer on samples in field
q M q i
Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Precomputation Compression
The raw RTF data is quite large 4th-order SH, 8 - 24 proxies, 16 concentric spheres with 1536(6 × 16 × 16) directions.
——192 ∼ 576MB CPCA (Clustered Principle Component Analysis) The compression ratio is about 40-50:1 Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Rendering Overview
A two-level scheme Bouncing Step accumulate interreflections between objects Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Rendering Overview
A two-level scheme Bouncing Step accumulate interreflections between objects Shading Step compute the final shadings on vertices.
Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Rendering Bouncing Step
Iterative bouncing strategy In one iteration: For proxy q in bunny 1. compute the interreflections
q k q
from proxy
q k k
q
) TripleProduct(
L V q k bird
,
M ij
)
k
2. sum all interreflections from other proxies
k k
q
) Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Rendering Shading Step
One pass.
For each vertex:
q k
1. compute the illumination from proxy
q k k
p
) TripleProduct(
L V q k bird
,
ij M q k
,
p
) 2. sum all illumination from proxies
L p
k
p
)
k
3. standard PRT process
I p
TripleProduct(
p self
Precomputed Radiance Transfer Field
p
State Key Lab of CAD&CG, Zhejiang University
Rendering Caching strategies
Caching RTF samples Store incident light at samples. Caching RTF eigens By using CPCA, we can store the product of eigens and the incident light of proxies. ——hit rate > 95% and reduce the cost > 90% Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Results Comparison
Our approach Precomputed Radiance Transfer Field Reference State Key Lab of CAD&CG, Zhejiang University
Results
A PC with Intel Core 2 Duo 1.8GHz, 2G RAM and a nVidia 7800 graphics card.
Cornell-box Cornell-box dynamic Table Objects 7 8 4 Brick game 10 Verts RTF size 22K 44.1MB
40K 40K 86K Precomputed Radiance Transfer Field 50.0MB
FPS 8-12 10-16 32.8MB
63.5MB
8-10 5-8 State Key Lab of CAD&CG, Zhejiang University
Conclusion and future work
Contributions: 1. Radiance transfer field 2. A proxy-based approximation method for precomputed RTF 3. An efficient interreflection rendering algorithm using precomputed RTF There are also some limitations.
1. only handle low-frequency interreflections and illumination.
2. only limited to rigid objects.
Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University
Thank you!