The Free-form Light Stage

1. The Free-form Light Stage Vincent Masselus Philip Dutré Frederik Anrys Department of Computer Science

2. The Free-form Light Stage • Capture appearance of an object • With hand–held light source • Relight real objects The Free-form Light Stage

3. Related work • Image-based relighting • Combination of Basis Images [Nimeroff et al.1994] • Light Stage [Debevec et al. 2000] The Free-form Light Stage

4. Illuminant direction estimation Take pictures and move hand-held light source Basis images · W1 + · W2 + · Wn + … Create weighted sum Relit object Incident light map The Free-form Light Stage

5. Taking the pictures The Free-form Light Stage

6. · W2 + · Wn · W1 + + · Wn-1 + … = Relighting The Free-form Light Stage

7. Illuminant direction estimation Basis images Take pictures and move hand-held light source The Free-form Light Stage

8. Illuminant direction estimation Diffuse white spheres The Free-form Light Stage

9. Lamberts Law Ii = ρ IL ( Ni · L) L N3 I3 L N1 L I1 I2 N2 Illuminant direction estimation The Free-form Light Stage

10. Illuminant direction estimation The Free-form Light Stage

11. Illuminant direction estimation The Free-form Light Stage

12. … A direction per basis image The Free-form Light Stage

13. Accuracy of estimation The Free-form Light Stage

14. Illuminant direction estimation Basis images · W1 + · W2 + · Wn + … Incident light map Create weighted sum Take pictures and move hand-held light source The Free-form Light Stage

15. use an angular Voronoi diagram Weight computation • Weight is based on incident light in neighborhood of light source direction • Non-uniform sampling of light source directions The Free-form Light Stage

16. … Plot directions on a hemisphere The Free-form Light Stage

17. Plot directions on hemisphere 30 light directions The Free-form Light Stage

18. Create an angular Voronoi Diagram 30 light directions The Free-form Light Stage

19. Choose a parameterization The Free-form Light Stage

20. Filter each Voronoi cell Filter the incident light map Overlay incident light map with angular Voronoi diagram The Free-form Light Stage

21. 400 light directions Using all illuminant directions 30 light directions The Free-form Light Stage

22. · W1 + · W2 + · W3 + · Wn Relighting … The Free-form Light Stage

23. Relighting · W1 + · W2 + = · W3 + … · Wn The Free-form Light Stage

24. · W1 + · W2 + · Wn + … Create weighted sum Relit object Illuminant direction estimation Take pictures and move hand-held light source Basis images Incident light map The Free-form Light Stage

25. Results 400 basis images The Free-form Light Stage

26. Results 400 basis images The Free-form Light Stage

27. Results 500 basis images The Free-form Light Stage

28. Results 500 basis images The Free-form Light Stage

29. Results 500 basis images The Free-form Light Stage

30. Results The Free-form Light Stage

31. Results The Free-form Light Stage

32. Augmented virtuality The Free-form Light Stage

33. Conclusion • Relighting real objects • Easy and cheap data acquisition • Portable • Scalable • Future work • Test BIG objects • Alternative filters • Sampling density accuracy in illuminant direction estimation • For more info: see the EGWR ’02 paper The Free-form Light Stage

34. Acknowledgements • Frank Suykens and Pieter Peers • Environment maps from: • http://www.debevec.org/Probes • http://www.cs.kuleuven.ac.be/~graphics • FWO Grant #G.0354.00 The Free-form Light Stage

35. The Free-form Light Stage