1. Bo Sun Kalyan Sunkavalli Ravi Ramamoorthi Peter Belhumeur Shree Nayar Columbia University Time-Varying BRDFs

2. Materials Change with Time

3. Previous Work Time-Varying Spatial Albedo Patterns Paints, Wet Surfaces and Dust [J. Dorsey et al., 96][J. Dorsey et al., 99][J. Lu et al., 05][S. Enrique et al., 05] [C. J. Curtis., 97][J. W. Jensen et al., 99][E. Nakamae et al., 96][S. Hsu et al., 96]

4. Previous Work Time-Varying Surface Appearance [J. Gu et al. 2006] Appearance Manifolds [J. Wang et al. 2006]

5. Our Goals Efficient TVBRDF Acquisition Underlying Temporal Trend Analysis Developing Analytic TVBRDF Models

6. Acquisition Challenges A Key Consideration: Fine sampling in the time domain High frequency reflectance in the angular domain

7. Acquisition System

12. Sample Plate before after desired

13. Acquisition System 12 seconds / scan, 360 color images / camera, 0.2~32 millisec exposures

14. Acquisition - Sampling

15. TVBRDF Samples 41 samples and three time-varying effects

16. TVBRDF Samples 41 samples and three time-varying effects

17. TVBRDF Samples 41 samples and three time-varying effects

18. TVBRDF Samples 41 samples and three time-varying effects

19. TVBRDF Samples 41 samples and three time-varying effects

20. Measurement Top Camera

21. Analytic BRDF Functions The Oren-Nayar diffuse model The Torrance-Sparrow specular model The Blinn’s dust model

22. Data Fitting Maximum RMS Error 3.84% Top Camera

23. TVBRDF Database

27. Temporal Trends

28. Time-Varying Phenomena Paints drying on smooth surfaces Water drying on rough surfaces Dust accumulation

29. Paints Exponential fall-off of specular albedo and roughness Diffuse color shifts in a dichromatic plane

30. Paints Exponential fall-off of specular albedo and roughtness Diffuse color shifts in a dichromatic plane

31. Paints Exponential fall-off of specular albedo and roughtness Diffuse color shifts in a dichromatic plane

32. Paints Exponential fall-off of specular albedo and roughtness Diffuse color shifts in a dichromatic plane

33. Paints – Spatial Variations Captured Blue Watercolor on White Surface

34. Paints – Effects Transfer Synthesized Green Watercolor on White Surface

35. Paints – Effects Transfer Synthesized Blue Watercolor on Red Surface

36. Wet Surfaces Diffuse color shifts on a straight line Sigmoidal change of surface intensity

37. Wet Surfaces Diffuse color shifts on a straight line Sigmoidal change of surface intensity

38. Wet Surfaces Diffuse color shifts on a straight line Sigmoidal change of surface intensity

39. Time-Varying Phenomena Paints drying on smooth surfaces Water drying on rough surfaces Dust accumulation

40. Dust Analysis generalizes to other BRDF models Exponential fall-off of specular highlights

41. Dust Analysis generalizes to other BRDF models Exponential fall-off of specular highlights

42. Dust – Final Example

43. Summary Acquisition of TVBRDF database (HDR) Analysis of temporal parameter trends Analytic TVBRDF models

44. Future Work Using more complicated BRDF models Generalize to other time-vayring phenomena Time–varying BTF, subsurface scattering

45. Thanks for Listening! http://www.cs.columbia.edu/~bosun/research