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Lighting and Shadows: Applications Lecture #10

Lighting and Shadows: Applications Lecture #10. Thanks to Li Zhang, Yoav Schechner, Steve Seitz, Bouguet, Perona, Ravi Ramamoorthi. Is there a unified representation for light sources?. How do we compare the light from a street lamp to that from an overcast sky?

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Lighting and Shadows: Applications Lecture #10

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  1. Lighting and Shadows: Applications Lecture #10 Thanks to Li Zhang, Yoav Schechner, Steve Seitz, Bouguet, Perona, Ravi Ramamoorthi

  2. Is there a unified representation for light sources? How do we compare the light from a street lamp to that from an overcast sky? It is important to unify source representation so that algorithms may be developed for all sources instead of one per type of source. Consider the SPACE of LIGHT RAYS!

  3. 4D Hypercube of Rays (p,q)-plane (x,y)-plane • Assumes vacuum (no absorption • or scattering) • No fluorescence, phosphorescence Langer and Zucker, CVPR 97

  4. Representation of Sources Langer and Zucker, CVPR 97 (x,y)-plane (x,y)-plane (p,q)-plane (x,y)-plane (p,q)-plane (p,q)-plane Laser beam – 0D Point source – 2D Distant Source (Sun) – 2D Area source (Sky) with a crack in the door – 3D Area source (Sky) with door completely open – 4D

  5. Corners of the 4D Hypercube Langer and Zucker, CVPR 97

  6. Examples of sources (p,q)-plane (x,y)-plane

  7. What is a Light Source? Is sky a source? If so, why not a white piece of paper? Is a translucent object a source? How to differentiate between source rays and non-source rays? Define a minimum set of absorbants at the ends of rays so that the whole ray space is dark.

  8. Structured Light • Any spatio-temporal pattern of light projected on a surface (or volume). • Cleverly illuminate the scene to extract scene properties (eg., 3D). • Avoids problems of 3D estimation in scenes with complex texture/BRDFs. • Very popular in vision and successful in industrial applications (parts • assembly, inspection, etc).

  9. Stereo Triangulation I J Correspondence is hard!

  10. Structured Light Triangulation I J Correspondence becomes easier!

  11. Light Stripe Scanning • Single light stripe • Spatially gray coded light striping • Spatially Color coded light striping • Spatio-temporally coded light striping

  12. Light Stripe Scanning – Single Stripe Light plane Source Camera Surface Need lots of Images

  13. Laser scanner Cyberware® face and head scanner + very accurate < 0.01 mm − more than10sec per scan

  14. Triangulation

  15. Structured Light – More complex patterns Works despite complex appearances Works in real-time and on dynamic scenes Need very few images Zhang et al

  16. Illumination Multiplexing Easier setup to capture several lighting directions.

  17. Illumination Multiplexing

  18. Illumination De-Multiplexing

  19. Illumination De-Multiplexing Better signal to noise ratio using Hadamard Codes:

  20. Illumination De-Multiplexing Better signal to noise ratio.

  21. Shadows

  22. Attached and Cast Shadows Attached shadow Cast shadow

  23. Sen, Cammarano, Hanrahan, 2003 Sloan, Kautz, Snyder 2002 Very hard shadows Very soft shadows

  24. All-Frequency Lighting and Shadows Teapot in Grace Cathedral

  25. Sharper and Softer parts of Shadows Point source model not good for rendering scenes.

  26. 3D Acquisition from Shadows Bouguet-Perona, ICCV 98

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