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Structured Light in Scattering Media

Structured Light in Scattering Media. Srinivasa Narasimhan Sanjeev Koppal Robotics Institute Carnegie Mellon University. Shree Nayar Bo Sun Computer Science Columbia University. Sponsor : ONR. Natural illumination in Scattering Media.

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Structured Light in Scattering Media

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  1. Structured Light in Scattering Media Srinivasa Narasimhan Sanjeev Koppal Robotics Institute Carnegie Mellon University Shree Nayar Bo Sun Computer Science Columbia University Sponsor : ONR

  2. Natural illumination in Scattering Media [ Narasimhan and Nayar, 99 - 03, Schechner et al, 01, 04 ]

  3. Active illuminationin Scattering Media [Levoy et al., Narasimhan-Nayar, Kocak-Caimi, Jaffe et al., Schechner et al., Negahdaripour et al. ]

  4. Floodlighting is Bad in Scattering Media Structured Light Critical for Good Visibility

  5. Light Stripe Range Finding in Scattering Media Light Stripe Range Finding in Clear Air Light plane Light plane Light plane Source Source Camera Camera Surface Surface

  6. Light Striping Model in Scattering Media • Irradiance due to Medium: Surface Light plane Phase Function Extinction coefficient D x s α y Source D • Irradiance due to Surface: v Camera Radiance • Final Image Irradiance:

  7. Light Striping Algorithm in Scattering Media Surface Intersection from Brightness Profile: No Scattering Moderate Scattering Significant Scattering 3D by Triangulation or Temporal Analysis : Same as in clear air. Medium from Fall-off : “Clear-Air” Scene Appearance:

  8. Experimental Setup Calibration technique similar in spirit to [Grossberg-Nayar 01 ]

  9. VIDEO

  10. Floodlit Image Computed Appearance

  11. Smoke and Mirrors Milk and Mirrors Planar Mirror seen through Dilute Milk Light Striping of Mirrors (Dark Intersections) Reconstruct surfaces with any BRDF if light plane visible [Discussions with Marc Levoy]

  12. Photometric Stereo in Clear Air Pure Air Distant Source Orthographic s Camera n P Surface Image Irradiance: Surface normal Three images required. Albedo Source direction [ Woodham 80, Horn 86 ]

  13. Photometric Stereo in Scattering Media Scattering Parallel Rays from Medium Distant Source D s Orthographic s n Camera α P Surface D v Image Irradiance: Optical Thickness + Phase Function

  14. Photometric Stereo in Scattering Media Scattering Parallel Rays from Medium Distant Source D s Orthographic s n Camera α P Surface D v 5 Parameter Non-linear Optimization (4 per pixel, 1 global) : Five Non-degenerate Sources are Necessary and Sufficient

  15. Simulations: Error Histograms Trials Trials Trials Trials 300 ( x 10 ) 300 ( x 10 ) 300 ( x 10 ) 300 ( x 10 ) 250 250 250 250 200 200 200 200 150 150 150 150 100 100 100 100 50 50 50 50 0 0 0 0 0 0.05 0.1 0 0.05 0.1 0 0.05 0.1 0 0.05 0.1 Angular Error Fractional Error for Fractional Error Fractional Error for for Normals Optical Thickness forAlbedo Phase Function, g Zero error with zero noise. Robust estimation with 5% uniform noise.

  16. Experiments: Teapot in Pure Water

  17. Experiments: Teapot in Dilute Milk Low Contrast, Flat Appearance

  18. Results: Traditional Photometric Stereo 3D Shape from NormalsToo Flat AlbedosScattering effects present

  19. Results: Our Five-Source Algorithm 3D Shape from Normals Albedos

  20. Milk Concentration 3 ml 4 ml 5 ml 6 ml 12 ml 15 ml % RMS Error 2.0 2.5 3.0 3.3 5.8 6.3 Results: Depth from Photometric Stereo 3D Shape from Normals Depth mapImpossible using traditional method

  21. Summary • Structured light improves visibility • Physics of scattering crucial • Surprising results possible • because of scattering

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