for Rendering Soft Shadows

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Efficient Image-Based Methods for Rendering Soft Shadows

Efficient Image

Efficient Image - - Based Methods Based Methods for Rendering Soft Shadows

for Rendering Soft Shadows

SIGGRAPH 2001SIGGRAPH 2001 Maneesh Agrawala

Ravi Ramamoorthi Alan Heirich

Laurent Moll

Pixar Animation Studios Stanford University Compaq Computer Corporation Compaq Computer Corporation

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Hard vs. Soft Shadows Hard vs. Soft Shadows Hard vs. Soft Shadows

Hard Shadows Soft Shadows

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Shadow maps Shadow maps Shadow maps

• Image-based hard shadows [Williams 78]

• Time, memory depend on image size, not geometric scene complexity

• Disadvantage: bias and aliasing artifacts

• Soft shadows [Chen and Williams 93]

• View interpolate multiple shadow maps

• Image-based hard shadows [Williams 78]

• Time, memory depend on image size, not geometric scene complexity

• Disadvantage: bias and aliasing artifacts

• Soft shadows [Chen and Williams 93]

• View interpolate multiple shadow maps

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IBR good for soft shadows IBR good for soft shadows IBR good for soft shadows

• IBR good for secondary effects

• Artifacts less perceptible

• IBR works well for nearby viewpoints

• Shadow maps from light source

• Light source localized area

• Poorly sampled regions are also dimly lit

• IBR good for secondary effects

• Artifacts less perceptible

• IBR works well for nearby viewpoints

• Shadow maps from light source

• Light source localized area

• Poorly sampled regions are also dimly lit

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IBR good for soft shadows IBR good for soft shadows IBR good for soft shadows

• Poorly sampled regions are also dimly lit• Poorly sampled regions are also dimly lit

Attenuation only With lighting Light

Shadow map

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Contributions Contributions Contributions

• Extend shadow maps to soft shadows

• Image-based rendering especially suitable

• Two novel image-based algorithms:

• Layered attenuation maps (LAM)

• Coherence-based raytracing (CBRT)

• Extend shadow maps to soft shadows

• Image-based rendering especially suitable

• Two novel image-based algorithms:

• Layered attenuation maps (LAM)

• Coherence-based raytracing (CBRT)

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• LAM

•Display: 5-10 fps

•Some aliasing artifacts

•Interactive applications

•Games

•Previewing

• CBRT

•Render: 19.83 min

•Speedup: 12.96x

•Production quality images

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Preliminaries Preliminaries Preliminaries

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Refresher: LDIs Refresher: Refresher: LDIs LDIs

• Layered depth images [Shade et al. 98]• Layered depth images [Shade et al. 98]

Geometry

Camera

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Refresher: LDIs Refresher: Refresher: LDIs LDIs

LDI

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Refresher: LDIs Refresher: Refresher: LDIs LDIs

LDI

(Depth, Color)

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Precomputation Precomputation Precomputation

• Render views from points on light (hardware)

• Create layered attenuation map (software)

• Warp views into LDI

• Store (depth, attenuation)

• Objects in LAM visible in at least 1 view

• Render views from points on light (hardware)

• Create layered attenuation map (software)

• Warp views into LDI

• Store (depth, attenuation)

• Objects in LAM visible in at least 1 view

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Precomputation Precomputation Precomputation

1^st viewpoint

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Precomputation Precomputation Precomputation

2^nd viewpoint

Attenuation = 1/2 Attenuation = 2/2

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Precomputation Precomputation Precomputation

Warped 2^nd viewpoint

Attenuation = 1/2 Attenuation = 2/2

Not present

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Display Display Display

• Render scene without shadows (hardware)

• Project into LAM (software)

• Read off attenuation

• Attenuation modulates shadowless rendering

• Render scene without shadows (hardware)

• Project into LAM (software)

• Read off attenuation

• Attenuation modulates shadowless rendering

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Display Display Display

LAM (center of light)

Eye

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Display Display Display

Eye

Attenuation = 2/2 Color = Color * 2/2

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Display Display Display

Eye

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Display Display Display

Eye Not in LAM

Attenuation = 0 Color = Color * 0

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Precompute algorithm Precompute Precompute algorithm algorithm

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Illustration Illustration Illustration

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Rendered images from light R R endered images from light endered images from light

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Layered images Layered images Layered images

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Layered attenuation map Layered attenuation map Layered attenuation map

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Display algorithm Display algorithm Display algorithm

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Attenuation map and rendering Attenuation map and rendering Attenuation map and rendering

rendering attenuation map

one layer

2nd layer 1st layer

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•LAM size: 512 x 512

•Avg num depth layers: 1.5

•Precomp:

• 7.7 sec (64 views)

• 29.4 sec (256 views)

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•LAM size: 512 x 512

•Avg num depth layers: 2

•Precomp:

• 6.0 sec (64 views)

• 22.4 sec (256 views)

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• Layered attenuation maps – fast, aliases

• Coherence-based raytracing – slow, noise

• Layered attenuation maps – fast, aliases

• Coherence-based raytracing – slow, noise

LAM CBRT

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Coherence-based raytracing Coherence Coherence - - based based raytracing raytracing

• Hierarchical raytracing through depth images

• Time, memory decoupled from geometric scene complexity

• Coherence-based sampling

• Light source visibility changes slowly

• Reduce number shadow rays traced

• Also usable with geometric raytracer

• Hierarchical raytracing through depth images

• Time, memory decoupled from geometric scene complexity

• Coherence-based sampling

• Light source visibility changes slowly

• Reduce number shadow rays traced

• Also usable with geometric raytracer

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• Represent scene with multiple shadow maps• Represent scene with multiple shadow maps

Light

Image-based raytracing Image Image - - based based raytracing raytracing

1^st shadow map

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• Represent scene with multiple shadow maps• Represent scene with multiple shadow maps

Light

Image-based raytracing Image Image - - based based raytracing raytracing

2^nd shadow map 1^st shadow map

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• Trace shadow ray through shadow maps• Trace shadow ray through shadow maps

Light

Image-based raytracing Image Image - - based based raytracing raytracing

2^nd shadow map 1^st shadow map

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Light source visibility image Light source visibility image Light source visibility image

Light

Visibility image

s₁

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Light source visibility image Light source visibility image Light source visibility image

s₁

s₂

Vis image for s₁ Light

Visibility image

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Coherence-based sampling Coherence Coherence - - based sampling based sampling

• Compute visibility image at first point s

₁

• Loop over following surface points s

_i

• Predict visibility image at s_i from s_i-1

• Trace rays where prediction confidence low

• Compute visibility image at first point s

₁

• Loop over following surface points s

_i

• Predict visibility image at s_i from s_i-1

• Trace rays where prediction confidence low

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Predicting visibility Predicting visibility Predicting visibility

Blocker pts

s₁ s₁

s₂

Prediction

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Predicting visibility Predicting visibility Predicting visibility

Blocker pts

s₁ s₁

s₂

Prediction

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• Low confidence

Light source edges

Blocked/unblocked edges

Prediction confidence Prediction confidence Prediction confidence

Predicted visibility

• Trace rays in all X’ed cells

• High confidence: 5

• Low confidence: 31

• Total cells: 36

• Ratio: 5/36 = 0.14

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• Low confidence

Light source edges

Blocked/unblocked edges

Prediction confidence Prediction confidence Prediction confidence

Predicted visibility

• Trace rays in all X’ed cells

• High confidence: 56

• Low confidence: 88

• Total cells: 144

• Ratio: 56/144 = 0.40

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Propagating low confidence Propagating low confidence Propagating low confidence

• If traced ray = prediction trace neighbor cells

• Similar to [Hart et al. 99]

Prediction correct

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Propagating low confidence Propagating low confidence Propagating low confidence

• If traced ray = prediction trace neighbor cells

Prediction incorrect

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• Light cells: 16 x 16 (256)

• Four 1024 x 1024 maps

• Precomp: 2.33 min

• Render: 19.83 min

• Rays: 79.86

• Speedup: 12.96x

2.27x due to image-based raytracing accelerations 5.71x due to coherence-based sampling

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• Light cells: 16 x 16 (256)

• Four 1024 x 1024 maps

• Precomp: 3.93 min

• Render: 65.13 min

• Rays: 88.74

• Speedup: 8.52x

2.16x due to image-based raytracing accelerations 3.94x due to coherence-based sampling

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LAM LAM LAM

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Ray tracing Ray tracing Ray tracing

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CBRT CBRT CBRT

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LAM CBRT

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Conclusions Conclusions Conclusions

• Two efficient image-based methods

• Layered attenuation maps

• Interactive applications

• Coherence-based raytracing

• Production quality images

• IBR ideal for soft shadows – secondary effects

• Two efficient image-based methods

• Layered attenuation maps

• Interactive applications

• Coherence-based raytracing

• Production quality images

• IBR ideal for soft shadows – secondary effects