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SIGGRAPH 2010

Single Scattering in

Heterogeneous Participating media

Cyril Delalandre Pascal Gautron Jean-Eudes Marvie Guillaume FrançoisTechnicolor Research & Innovation The Moving Picture Company

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Real Light Scattering

• Light interaction with heterogeneous participating media

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Participating Media• Characterized by:

– σa: absorption coefficient

– σs : scattering coefficient

– σt : σa + σs , extinction coefficient

– D(s) : medium density at the point s

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Single Scattering in participating media

in

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Explicit ray-marching

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Outline

• Introduction• Previous works• Our algorithm• Results• Conclusion

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Outline

• Introduction• Previous worksPrevious works• Our algorithm• Results• Conclusion

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Previous works

[Zhou08][Gautron09] [Jansen10]

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Volumetric Shadow Mapping[Gautron09], Siggraph Talk 2009

+ Real-time rendering- Homogeneous medium

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Real-time smoke rendering by using compensed ray marching, [Zhou08], Siggraph 2008

+ Real-Time rendering+ Single and Multiple scattering+ Heterogeneous medium- Heavy precomputation

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Fourier Opacity Map, [Jansen10] , I3D 2010

+ Real-time rendering+ Heterogeneous medium- No scattering computation

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Outline

• Introduction• Previous works• Our algorithmOur algorithm• Results• Conclusion

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Goals• Single scattering • Volume shadows• Dynamic Viewpoint and

Lighting• Generic and Dynamic Medium• Scalable • Without pre-computation

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• Acceleration of the light reduced intensity computation

• Small memory footprint

Contributions

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Attenuation Function MapAttenuation Function Map

Algorithm

Light Depth MapAttenuation function

map

View Depth & radiance

Map

Scattering Computation

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Attenuation Function Map

C0 = 0C1 = 0.Cn = 0

C0 += att1 xC1 += att1 x.Cn += att1 x

C0 += att2 xC1 += att2 x.Cn += att2 x

C0 += attn xC1 += attn x.Cn += attn x

• Light Point of View1. Opaque objects Depth Map

2. For each pixel:a. Bounding box Intersection

b. Coefficient Computation by ray-marching

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Attenuation Function Map• Light Point of View

1. Opaque objects Depth Map

2. For each pixel:a. Bounding box Intersection

b. Coefficient Computation by ray-marching

c. Store in Multi Render Targets

C0-n(0,0)

C0-n(K,0) C0-n(K,L)

C0-n(0,L)

C0-n(i,j)

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Scene Rendering

• In User point of view:1. Compute the depth and reflected radiance

of opaque objects

(R,G,B) (Alpha)19

Compute Scattering

C0-n(0,0)

C0-n(K,0) C0-n(K,L)

C0-n(0,L)

C0-n(i,j)

2. Intersection of the medium bounding box20

Depth Map

Attenuation Function Map

Compute Scattering

C0-n(0,0)

C0-n(K,0) C0-n(K,L)

C0-n(0,L)

C0-n(i,j)

3. Perform a ray-marching21

Depth Map

Attenuation Function Map

Compute Scattering

C0-n(0,0)

C0-n(K,0) C0-n(K,L)

C0-n(0,L)

C0-n(i,j)

For each ray sample:a.Check the sample visibilityb.Check the light visibilityc.Lri computation using the coefficients

Lri = c0 x + c1 x + … + cn x

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Depth Map

Attenuation Function Map

Results

Comparison between our algorithm and an explicit ray-marching algorithm100 samples per ray / 16 DCT coefficients 23

Speed-up 30x

• Ringing artifacts

High Density Medium

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• Add a scale factor to avoid ringing artifacts

High Density Medium

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Transformed Signal

scalen

scalerinri inin wPLwPL )),((),(

Reconstructed Signal

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High Density Medium

Without scale factor With scale factor

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Explicit ray-marching

Demos – GTX 480 – 720p

27500 samples / view ray, 16 DCT coefficients, 2563 medium size, 10 FPS

Demos – GTX 480 – 720p

28100 samples / view ray, 16 DCT coefficients, 1283 medium size, 19 FPS

Conclusion

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• Single Scattering• Volume Shadows• Fast Lri computation• Scalable• Generic• No pre-computation

• Large medium• Multiple Scattering• Particle representation• Image Lighting

Future Works

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• Thanks to A. W. Bargteil and C. Thompson (University of Utah) for the fluid simulation

• Thanks to K. Bouatouch for his research supervision

Acknowledgements

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Questions ?