Post on 27-Dec-2015
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A Fast Rendering Method for Clouds Illuminated by Lightning Taking into Account Multiple Scattering
A Fast Rendering Method for Clouds Illuminated by Lightning Taking into Account Multiple Scattering
Yoshinori Dobashi (Hokkaido University)Yoshihiro Enjyo (Hokkaido University)Tsuyoshi Yamamoto (Hokkaido University)Tomoyuki Nishita (The University of Tokyo)
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OverviewOverview
Introduction Previous Work Basic Idea of Our Method Precomputation of Basis Intensities Real-time Rendering Process Examples Conclusions & Future Work
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Introduction (1/3)Introduction (1/3)
Realistic Image Synthesis Visual Assessment, flight simulators, etc… Assuming under fine weather conditions
Simulation under bad weather conditions Rainfalls, windstorm, lightning, clouds, etc… Flight simulation/computer games Real-time rendering Reality
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Introduction (3/3)Introduction (3/3)
Multiple scattering Enhancing reality High computation
cost Difficult to achieve
real-time rendering
clouds
viewpoint
lightning
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Features of Proposed MethodFeatures of Proposed Method
Real-time rendering of clouds illuminated by lightning Arbitrary shapes of lightning Anisotropic multiple scattering Consisting of preprocess and real-time process Use of wavelet transform for drastically
accelerating intensity calculation
Assumption: Static clouds
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OverviewOverview
Introduction Previous Work Basic Idea of Our Method Precomputation of Basis Intensities Real-time Rendering Process Examples Conclusions & Future Work
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Previous Work on LightningPrevious Work on Lightning
Visual simulation of lightning [ Reed94] Use of random numbers to create shape of lightning strokes
Probabilistic modeling of lightning [Kruszewski99] Allowing user to control shapes
Physically-based animation of lightning [Kim04] Calculating propagation of lightning via physical simulation
Focusing on modeling shape of lightning Illumination on clouds are not considered.
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Previous Work on Fast Rendering of Clouds/SmokePrevious Work on Fast Rendering of Clouds/Smoke Rendering of clouds using GPU [Dobashi00]
Clouds/atmosphere illuminated by lightning Use of GPU for acceleration Single scattering only
Precomputed radiance transfer [Sloan02] Real-time rendering of clouds as well as glossy ob
jects Assuming light sources far from clouds Lihgtning is not considered.
[Dobashi01]
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OverviewOverview
Introduction Previous Work Basic Idea of Our Method Precomputation of Basis Intensities Real-time Rendering Process Examples Conclusions & Future Work
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Basic Idea of Our Method (1/7)Basic Idea of Our Method (1/7)
Shape of lightning Polylines generated
by Reed’s method [Reed94]
Density distribution of clouds Represented by 3D grid Use of Dobashi’s method
[Dobashi00]lightning
clouds
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Basic Idea of Our Method (2/7)Basic Idea of Our Method (2/7)
Intensity calculation of clouds Point sources on strokes Illuminations due to each
point source Multiple scattering Accumulation of illuminations
due to all point sources Preprocess and
real-time process point source
illuminate
lightning
clouds
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Basic Idea of Our Method (3/7)Basic Idea of Our Method (3/7)
simulation space
grid for clouds
grid for simulation space
Two separate grids
clouds
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Basic Idea of Our Method (4/7)Basic Idea of Our Method (4/7)
Virtual point sources at each grid point
clouds
simulation space
grid for clouds
grid for simulation space
virtual point source
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Basic Idea of Our Method (5/7)Basic Idea of Our Method (5/7)
Preprocess ： computation of basis intensities
virtual point source (intensity = 1.0)
intensity calculation taking into account multiple scattering
save
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Basic Idea of Our Method (6/7)Basic Idea of Our Method (6/7)
Preprocess ： computation of basis intensities
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Basic Idea of Our Method (6/7)Basic Idea of Our Method (6/7)
Preprocess ： computation of basis intensities
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basis intensities
Basic Idea of Our Method (6/7)Basic Idea of Our Method (6/7)
Preprocess ： computation of basis intensities
Repeating for all grid points
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Basic Idea of Our Method (7/7)Basic Idea of Our Method (7/7)
Real-time process ： rendering of cloudsbasis intensities
intensity of virtual point sources
multiplication
accumulation
generating lightning
Fast but cost proportional to number of grid points Further acceleration by using wavelets
×
×
×
×
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OverviewOverview
Introduction Previous Work Basic Idea of Our Method Precomputation of Basis Intensities Real-time Rendering Process Examples Conclusions & Future Work
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Subdivision of Simulation SpaceSubdivision of Simulation Space
Contribution of virtual point source
clouds
r
intensity due to point source
1.0r2
virtual point source
simulation space
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Subdivision of Simulation SpaceSubdivision of Simulation Space
Adaptive subdivision
clouds
rl
rl+1
2
12
11
ll rr
2
12
11
ll rrsimulation space
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Precompuation of Basis IntensitiesPrecompuation of Basis Intensities
Intensity calculation due to virtual point source
virtual source l
grid point i : intensity at grid point i due to virtual source l
bil
ncld : number of grid points for clouds
bil
calculation of multiple scattering
(b1l, b2l, …, bncld,l)
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Precompuation of Basis IntensitiesPrecompuation of Basis Intensities
Intensity calculation due to virtual point source
virtual source l
grid point i basis intensitiesdue to virtual light lbil
calculation of multiple scattering
ncld : number of grid points for clouds
(b1l, b2l, …, bncld,l)
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Precompuation of Basis IntensitiesPrecompuation of Basis Intensities
Intensity calculation due to virtual point source
virtual source l
grid point i
ncld : number of grid points for clouds
bil
calculation of multiple scattering
wavelet transform
(b1l, b2l, …, bncld,l)
(B1l, B2l, …, Bncld,l)
basis intensitiesdue to virtual light l
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cldn
kikklil Bb
1
)(x
Precompuation of Basis IntensitiesPrecompuation of Basis Intensities
basis intensity at grid point i due to virtual source l
number of basis functions (= number of grid points for clouds)
coefficient after wavelet transform
basis function (Haar basis)
Basis intensities due to virtual source l
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Basis intensities due to virtual source l
Many of Bij are nearly zero. Discarding if |Bil| < ( : threshold)
Precompuation of Basis IntensitiesPrecompuation of Basis Intensities
ln
kikklil Bb
1
)(x
cldn
kikklil Bb
1
)(x
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Basis intensities due to virtual source l
Many of Bij are nearly zero. Discarding if |Bil| < ( : threshold)
cldn
kikklil Bb
1
)(x
Precompuation of Basis IntensitiesPrecompuation of Basis Intensities
ln
kikklil Bb
1
)(x
nl << ncld
Reducing memory requirement Accelerating intensity calculation
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OverviewOverview
Introduction Previous Work Basic Idea of Our Method Precomputation of Basis Intensities Real-time Rendering Process Examples Conclusions & Future Work
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Real-time Rendering Process (1/7)Real-time Rendering Process (1/7)
Calculation of intensities of virtual source
generating lightning
placing point sources on strokes
distributing to neighboring grid points
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Real-time Rendering Process (2/7)Real-time Rendering Process (2/7)
Calculation of intensity of virtual source
virtual source l intensity el
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Real-time Rendering Process (3/7)Real-time Rendering Process (3/7)
Weighted sum of basis intensities
basis intensities
e1
e2
e3
e4
final image
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Real-time Rendering Process (4/7)Real-time Rendering Process (4/7)
Final intensity Ii at grid point i for clouds
number of virtual sources with non-zero intensities
tn
llili ebI
lg
1
intensity Iigrid point i
virtual source lintensity el
basis intensity
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Real-time Rendering Process (5/7)Real-time Rendering Process (5/7)
Intensity Ii at grid point i for clouds
tn
llili ebI
lg
1
basis intensity
ln
kikklil Bb
1
)(x
coefficient after wavelet transform
number of virtual sources with non-zero intensities
basis intensity
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Real-time Rendering Process (6/7)Real-time Rendering Process (6/7)
Intensity Ii at grid point i for clouds
tn
lkllk BeH
lg
1
lt l n
kikk
n
l
n
kikklli HBeI
11 1
)()(lg
xx
1. Calculation of Hk
2. Inverse wavelet transform
wavelet transform of intensity distribution of clouds
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with wavelet
Real-time Rendering Process (7/7)Real-time Rendering Process (7/7)
Calculation of Intensities at all grid points for clouds
without wavelet
tn
lkllk BeH
lg
1
(k = 1, 2,…, nl)
tn
llili ebI
lg
1
(i = 1, 2,…, ncld)
nl << ncld (1/10)
+inversewavelet transform
O(ncld)
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OverviewOverview
Introduction Previous Work Basic Idea of Our Method Precomputation of Basis Intensities Real-time Rendering Process Examples Conclusions & Future Work
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ExamplesExamples
Simulation condition
simulation space20x20x7
Memory requirement for basis intensities without wavelet compression ： 1137.5 MB with wavelet compression ： 86 MB
compression to 1/13
intensity calculation ： 32x32x4
cloud volume: 128x128x16
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Previous Method vs. Proposed MethodPrevious Method vs. Proposed Method
same visual quality
previous method[Max94] proposed method
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Previous Method vs. Proposed MethodPrevious Method vs. Proposed Method
0
10%
previous
proposed
difference image
(100 % = 255 difference in intensity)
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Previous Method vs. Proposed MethodPrevious Method vs. Proposed Method
Computation time Precomputation: 60 min (proposed method only) Real-time process:
computer: Pentium 3.5GHz,Ⅳ GeForece 7800 GTX
35 times faster
提案手法
0.2 秒Proposed method
0.06 sec.
Previous method
2.12 sec.
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ConclusionsConclusions
Real-time rendering of clouds illuminated by lightning Taking into account multiple scattering Precomputation of basis intensities Acceleration by using Haar wavelet transfor
m 16 frames per second on CPU