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Matting and Transparency

Matting and Transparency. 15-463: Computational Photography Alexei Efros, CMU, Fall 2006. Midterm Statistics. Semi-transparent mattes. What we really want is to obtain a true alpha matte, which involves semi-transparency Alpha between 0 and 1. Matting Problem: Mathematical Definition.

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Matting and Transparency

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  1. Matting and Transparency 15-463: Computational Photography Alexei Efros, CMU, Fall 2006

  2. Midterm Statistics

  3. Semi-transparent mattes • What we really want is to obtain a true alpha matte, which involves semi-transparency • Alpha between 0 and 1

  4. Matting Problem: Mathematical Definition

  5. Why is general matting hard?

  6. Solution #1: No Blue!

  7. Solution #2: Gray or Flesh

  8. Triangulation Matting (Smith & Blinn) • How many equations? • How many unknowns? • Does the background need to be constant color?

  9. The Algorithm

  10. Triangulation Matting Examples

  11. More Examples

  12. More examples

  13. Problems with Matting • Images do not look realistic • Lack of Refracted Light • Lack of Reflected Light Solution: Modify the Matting Equation

  14. Environment Matting and Compositing slides by Jay Hetler Douglas E. Zongker ~ Dawn M. Werner ~ Brian Curless ~ David H. Salsin

  15. Environment Matting Equation • C = F + (1- a)B + F • C ~ Color • F ~ Foreground color • B ~ Background color • a ~ Amount of light that passes through the foreground • F ~ Contribution of light from Environment that travels through the object

  16. Explanation of F R – reflectance image T – Texture image

  17. Environment Mattes

  18. Performance • Calibration • Matting: 10-20 minutes extraction time for each texture map (Pentium II 400Mhz) • Compositing: 4-40 frames per second • Real-Time?

  19. How much better is Environment Matting? Alpha Matte Environment Matte Photograph

  20. How much better is Environment Matting? Alpha Matte Environment Matte Photograph

  21. Movies!

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