Dirty Glass: Rendering Contamination on Transparent Surfaces

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Eurographics Symposium on Rendering 2007
Dirty Glass Rendering Contamination on
Transparent Surfaces
Jinwei Gu Ravi Ramamoorthi
Peter Belhumeur Shree Nayar
Columbia University
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Transparency in CG Renderings
Hakura and Synder, 01
Whitted, 80
Jensen, 01
Zongker et.al., 99
Chris Wyman, 05
Narasimhan et.al., 06
Jensen, 00
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Transparent Objects in Real World
Courtesy of many photographers from flickr.com
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Transparent Objects in Real World

• Effects
• Contrast reversal

Dirty Window
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Transparent Objects in Real World

• Effects
• Contrast reversal
• Angular dependency

Stains on Wine Glass
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Transparent Objects in Real World

• Effects
• Contrast reversal
• Angular dependency
• Lens glare and blur

Image Taken with a Dirty Lens
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Transparent Objects in Real World

• Effects
• Contrast reversal
• Angular dependency
• Lens glare and blur
• Monitor effects

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Transparent Objects in Real World

• Effects
• Contrast reversal
• Angular dependency
• Lens glare and blur
• Monitor effects
• Simply alpha-blending with a texture will NOT
  work, because contaminants will both scatter and
  attenuate light.

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Related Work

• Surface Aging Weathering
• Patina, weathered stone, flow, etc.
• Surface cracks, scratches, etc.

J.Dorsey et al., 00
T. Wong et al., 97
S. Merillou et al., 01
Weathering on opaque surfaces.

• Light Scattering in Layered Materials
• Simulation of dusty surfaces
• Reflection of layered materials
• Rendering of composite paint

J.Blinn, 82
P. Harahan and W. Kruger, 93
S. Ershov et al., 01
Additional scattering components are required for
contaminated transparent surfaces.
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Our Work

• Rendering contamination on transparent surfaces
• Modeling Analytic BRDF/BTDF Model based on
  Single Scattering
• Measurement Contaminants Patterns Scattering
  Parameter
• Rendering 3D Scenes and 2D Photographs

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Our Work

• Rendering contamination on transparent surfaces
• Modeling Analytic BRDF/BTDF Model based on
  Single Scattering
• Measurement Contaminants Patterns Scattering
  Parameter
• Rendering 3D Scenes and 2D Photographs

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Clean Transparent Surface
Li
Air, n1
Transparent Medium, n3
Snells law Fresnel equations
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Contaminated Transparent Surface
Air, n1
Li
Contaminant, n2

Transparent Medium, n3
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The BRDF/BTDF Model

• The contaminant layer is optically very thin.
• e.g., dust, lipids/ fingerprint, dirt/salt, etc.
• Single scattering dominates.
• Aggregate as a (local) BRDF/BTDF model.

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Single Scattering Events Reflection
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Single Scattering Events Transmission
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The BRDF/BTDF Model

• BRDF

• BTDF

Optical thickness of the contaminant layer
Heyney-Greenstein phase function
(Scattering) albedo of the contaminant
Refraction index of the contaminant
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The BRDF/BTDF Model
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The BRDF/BTDF Model
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The BRDF/BTDF Model
Change the incident angle
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Verification
Proposed Model
Monte Carlo
4 samples/pixel,7 seconds
2048 samples/pixel,1 hour
RMS relative difference 2.2
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Comparison with Related Work
Reflectance Lr

• Collimated beam
• Albedo 0.5
• Optical thickness 0.2
• Phase function g0.9
• Refraction index 1.0

Monte Carlo
Our Model
HK93/Blinn82
Outgoing Angle
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Our Work

• Rendering contamination on transparent surfaces
• Modeling Analytic BRDF/BTDF Model based on
  Single Scattering
• Measurement Contaminants Patterns Scattering
  Parameter
• Rendering 3D Scenes and 2D Photographs

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Measurement (1)

• Optical thickness
• Setup
• Shadow images due to attenuation

Lambertian board
Contaminants
Thin glass
Camera
Projector
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Measurement (1)

• Optical thickness
• Setup
• Shadow images due to attenuation

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Some Acquired Textures
Household Dust
Powder
Water Stripes
Soil
Fingerprints 1
Fingerprints 2
Smudges
Detergent
Salt Water Deposit
Soap Water
Oil Stain
Salt Deposit
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Measurement (2)

• Scattering parameter
• Setup

Thin glass
Camera
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Measurement (2)

• Scattering parameter
• Setup

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Results
Clean
Fingerprints
Soap Deposit
Sand
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Results
Clean
Fingerprints
Soap Deposit
Sand
g0.99
g0.94
g0.86
g0.78
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Synthesis Tool
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Our Work

• Rendering contamination on transparent surfaces
• Modeling Analytic BRDF/BTDF Model based on
  Single Scattering
• Measurement Contaminants Patterns Scattering
  Parameter
• Rendering 3D Scenes and 2D Photographs

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Clean Window of a Room
Outside the room
Inside the room
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Dirty Window View inside the Room
Contrast Reversal
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Dirty Window Viewed outside the Room
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Dirty Window in 24 hours
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Contamination on Monitor Screen
Monitor ON
Monitor OFF
Monitor Effects
Angular Dependency
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Stains on Cognac Glass
Contrast Reversal
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Stains on Cognac Glass
Vertical Shadow
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Stains on Cognac Glass
Angular Dependency
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Stains on Cognac Glass
Without Scattering
With Scattering
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Rendering on 2D Photographs
Image
Lens
Contaminant layer
Planar Light Source
(2D Photograph)
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Seawater Sprayed on Glass
Photograph
Contaminant Texture
http//www.flickr.com
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Seawater Sprayed on Glass
Photograph
http//www.flickr.com
Composition
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Dirty Camera Lens
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Making a Window Dirty
Homography camera position
Contaminant texture
Photograph
F. Durand and J. Dorsey, 02
Synthesized light probe
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Making a Window Dirty
Photograph
F. Durand and J. Dorsey, 02
Composition
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Conclusions

• Analytic BRDF/BTDF model based on single
  scattering.

• Simple measurement for various kinds of
  contaminants.

• Rendering applications on 3D scenes and 2D
  photographs.

Source code measured data available
at http//www.cs.columbia.edu/CAVE/projects/dirty
_glass/
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Future Work

• Contaminated translucent materials
• e.g., lipids on skin
• Cleaning dirty glass in photographs

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Acknowledgement

• Srinivasa Narasimhan, Stephen Marschner, Craig
  Donner, Bo Sun, Kevin Egan, Aner Ben-Artzi, Ryan
  Overbeck, Li Zhang, Kshitiz Garg for insightful
  discussions and help.
• Anonymous reviewers for detailed comments and
  suggestions.

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Thank you!

• Comments Questions?

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(No Transcript)
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Q A
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Measurement (1)

• Why only consider attenuation?
• Most contaminant are mainly forward scattering
  (ggt0.7).
• If too much blur, we use another setup below and
  scale the result accordingly.

Lambertian board
Contaminants
Thin glass
Camera
Projector
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Comparison with Related Works

• Collimated beam.
• Albedo 0.5
• Optical thickness 0.2
• Phase function g0.9
• Refraction index 1.0

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Thin Glass Slab with Contamination

• BRDF/BTDF model by similar derivation

Li
Air, n1
Contaminant, n2
Transparent Slab, n3
Air, n1
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Dusty Glass Sphere
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Dust on Cognac Glass
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Comparison with Related Works
Blinn 82 Hanrahan Kruger 93 Our Model
Derived From Geometric Inference Transport Theory Transport Theory
Fresnel No Yes Yes
Lr(1) No Yes Yes
Lr(2) No No Yes
Lr(3) Yes Yes Yes
Lr(4) No No Yes
Lt(1) Yes Yes Yes
Lt(2) Yes Yes Yes
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Derivation of the BSDF Model (1)

• Assume the contaminant layer has no interface
  between the air (e.g. dust)

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Derivation of the BSDF Model (2)

• Assume the contaminant layer has no interface
  between the air (e.g. dust)

n1
n2