Bo Sun

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Time-Varying BRDFs

• Bo Sun
• Kalyan Sunkavalli
• Ravi Ramamoorthi
• Peter Belhumeur
• Shree Nayar
• Columbia University

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Materials Change with Time
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Previous Work

• Time-Varying Spatial Albedo Patterns
• Paints, Wet Surfaces and Dust

J. Dorsey et al., 96
J. Dorsey et al., 99
J. Lu et al., 05
S. Enrique et al., 05
C. J. Curtis., 97
J. W. Jensen et al., 99
E. Nakamae et al., 96
S. Hsu et al., 96
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Previous Work
Time-Varying Surface Appearance J. Gu et al.
2006
Appearance Manifolds J. Wang et al. 2006
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Our Goals

• Efficient TVBRDF Acquisition
• Underlying Temporal Trend Analysis
• Developing Analytic TVBRDF Models

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Acquisition Challenges

• A Key Consideration Fine sampling in the time
  domain
• High frequency reflectance in the angular domain

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Acquisition System
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Acquisition System
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Acquisition System
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Acquisition System
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Acquisition System
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Sample Plate
before
after
desired
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Acquisition System
12 seconds / scan, 360 color images / camera,
0.232 millisec exposures
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Acquisition - Sampling
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TVBRDF Samples
41 samples and three time-varying effects
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TVBRDF Samples
41 samples and three time-varying effects
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TVBRDF Samples
41 samples and three time-varying effects
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TVBRDF Samples
41 samples and three time-varying effects
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TVBRDF Samples
41 samples and three time-varying effects
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Measurement
Top Camera
Top Camera
Top Camera
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Analytic BRDF Functions

• The Oren-Nayar diffuse model
• The Torrance-Sparrow specular model
• The Blinns dust model

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Data Fitting
Top Camera
Maximum RMS Error 3.84
Top Camera
Top Camera
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TVBRDF Database
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TVBRDF Database
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TVBRDF Database
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TVBRDF Database
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Temporal Trends
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Time-Varying Phenomena

• Paints drying on smooth surfaces
• Water drying on rough surfaces
• Dust accumulation

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Paints

• Exponential fall-off of specular albedo and
  roughness
• Diffuse color shifts in a dichromatic plane

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Paints

• Exponential fall-off of specular albedo and
  roughtness
• Diffuse color shifts in a dichromatic plane

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Paints

• Exponential fall-off of specular albedo and
  roughtness
• Diffuse color shifts in a dichromatic plane

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Paints

• Exponential fall-off of specular albedo and
  roughtness
• Diffuse color shifts in a dichromatic plane

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Paints Spatial Variations
Captured Blue Watercolor on White Surface
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Paints Effects Transfer
Synthesized Green Watercolor on White Surface
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Paints Effects Transfer
Synthesized Blue Watercolor on Red Surface
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Wet Surfaces

• Diffuse color shifts on a straight line
• Sigmoidal change of surface intensity

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Wet Surfaces

• Diffuse color shifts on a straight line
• Sigmoidal change of surface intensity

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Wet Surfaces

• Diffuse color shifts on a straight line
• Sigmoidal change of surface intensity

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Time-Varying Phenomena

• Paints drying on smooth surfaces
• Water drying on rough surfaces
• Dust accumulation

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Dust

• Analysis generalizes to other BRDF models
• Exponential fall-off of specular highlights

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Dust

• Analysis generalizes to other BRDF models
• Exponential fall-off of specular highlights

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Dust Final Example
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Summary

• Acquisition of TVBRDF database (HDR)
• Analysis of temporal parameter trends
• Analytic TVBRDF models

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Future Work

• Using more complicated BRDF models
• Generalize to other time-vayring phenomena
• Timevarying BTF, subsurface scattering

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Thanks for Listening!
http//www.cs.columbia.edu/bosun/research