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Shadow Multiplexing for Real-Time Silhouette Extraction

Shadow Multiplexing for Real-Time Silhouette Extraction. Expertisecentrum for Digital Media / Hasselt University { firstname.lastname }@ uhasselt.be. Introduction. Interaction between real and virtual objects 3D modeling Collision detection. Previous Work.

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Shadow Multiplexing for Real-Time Silhouette Extraction

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  1. Shadow Multiplexing for Real-Time Silhouette Extraction Expertisecentrum for Digital Media / Hasselt University {firstname.lastname}@uhasselt.be

  2. Introduction Interaction between real and virtual objects • 3D modeling • Collision detection

  3. Previous Work [1] Hasenfratz et al. ESVR 2004 [2] Cuypers et al. GRAPP 2008 [3] Decker et al. GRAPP 2007 Silhouette based methods Creating Visual Hull Image Based Interaction

  4. Previous Work [1] Hasenfratz et al. ESVR 2004 [2] Smith and Blinn. Siggraph 1996 Disadvantages: • Expensive Multi- camera setups • Large amount of data • Background subtraction

  5. Previous Work [1] Savarese et al. ICCV 2001 [2] Yamazaki et al. ICCV 2007 [3] Lanman et al. Siggraph Asia 2008 Shadow Based Techniques: Shadow Carving Coplanar Shadowgrams Shield Fields

  6. Our Approach • Single Camera • Power LEDs • Diffuser

  7. Our Approach Advantages: Inexpensive setup Simple robust silhouette extraction No camera synchronization Limited amount of data to be captured and processed Full camera resolution available

  8. Types of Multiplexing Time Multiplexing Space Multiplexing Color Multiplexing Intensity Multiplexing

  9. Intensity Multiplexing X Render Equation

  10. Optimal Light Source Configuration • Intensities • Positioning (light fall-off) • Far away from surface • Similar frequency close to each other

  11. Hardware • Power LEDs ~ 2 meters • Calibration • Radiometric • Geometric [1] Yamazaki et al. ICCV 2007

  12. Problems • Soft borders • Motion -> lower shuttertime (pulse) • Diffuser -> morphological operations • Camera noise • Object Materials

  13. Results GPU implementation Nvidia GForce 8800 GTX Input 640 x 480 40 fps

  14. Results Diffuse

  15. Results Specular

  16. Results Translucent

  17. Results Low albedo

  18. Applications Visual Hull Reconstruction Image-Based Collision Detection

  19. Conclusions Efficient multiple silhouette extraction Single camera/single shot Full-resolution silhouettes No synchronization Less data acquisition / processing

  20. Future Work Automatic LED calibration Multispectral cameras

  21. Questions?

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