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Modeling Anisotropic Surface Reflectance with Example-Based Microfacet Synthesis Jiaping Wang 1, Shuang Zhao 2, Xin Tong 1 John Snyder 3, Baining Guo 1.

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Presentation on theme: "Modeling Anisotropic Surface Reflectance with Example-Based Microfacet Synthesis Jiaping Wang 1, Shuang Zhao 2, Xin Tong 1 John Snyder 3, Baining Guo 1."— Presentation transcript:

1 Modeling Anisotropic Surface Reflectance with Example-Based Microfacet Synthesis Jiaping Wang 1, Shuang Zhao 2, Xin Tong 1 John Snyder 3, Baining Guo 1 Microsoft Research Asia 1 Shanghai Jiao Tong University 2 Microsoft Research 3

2 Surface Reflectance satin metal wood

3 Anisotropic Surface Reflectance anisotropicisotropic

4 Our Goal modeling spatially-varying anisotropic reflectance

5 Surface Reflectance in CG 4D BRDF ρ(o,i) – Bidirectional Reflectance Distribution Function – how much light reflected wrt in/out directions o i

6 Surface Reflectance in CG 4D BRDF ρ(o,i) – Bidirectional Reflectance Distribution Function – how much light reflected wrt in/out directions 6D Spatially-Varying BRDF: SVBRDF ρ(x,o,i) – BRDF at each surface point x

7 Related Work I parametric BRDF models – compact representation – easy acquisition and fitting – lack realistic details ground truth parametric model [Ward 92]

8 Related Work II tabulated SVBRDF – realistic – large data set – difficult to capture lengthy process expensive hardware image registration light dome [Gu et al 06]

9 Related Work II tabulated SVBRDF – realistic – large data set – difficult to capture lengthy process expensive hardware image registration light dome [Gu et al 06]

10 Microfacet BRDF Model [Cook & Torrance 82] surface modeled by tiny mirror facets

11 Microfacet BRDF Model surface modeled by tiny mirror facets shadow term fresnel term normal distribution [Cook & Torrance 82]

12 Microfacet BRDF Model based on Normal Distribution Function (NDF) – NDF D is 2D function of the half-way vector h – dominates surface appearance

13 Challenge: Partial Domains samples from a single viewing direction i – cover only a sub-region h Ω of NDF – How to obtain the full NDF? partial region ? partial NDF complete NDF

14 Solution: Exploit Spatial Redundancy similar but differently rotated NDFs find surface points with similar but differently rotated NDFs material sample partial NDF at each surface point

15 Example-Based Microfacet Synthesis Align + + = partial NDF to complete completed NDF rotated partial NDFs partial NDFs from other surface points

16 ComparisonComparison isotropic Ward model anisotropic Ward model ground truth our model

17 Overall Pipeline BRDF Slice Capture Partial NDF Recovery Microfacet Synthesis

18 Overall Pipeline BRDF Slice Capture Partial NDF Recovery Microfacet Synthesis

19 Device Setup Camera-LED system, based on [Gardner et al 03]

20 Capturing Process

21 Overall Pipeline BRDF Slice Capture Partial NDF Recovery Microfacet Synthesis

22 NDF Recovery invert the microfacet BRDF model [Ashikhmin et al 00], Unknown NDF Shadow Term Measured BRDF

23 NDF Recovery (cont) Ngan et al 05 iterative approach [Ngan et al 05] – solve for NDF, then shadow term – works for complete 4D BRDF data [Ashikhmin et al 00], Ngan et al 05 [Ngan et al 05]

24 Partial NDF Recovery biased result on incomplete BRDF data ground truth NDF shadow term [Ngan et al. 05] NDF shadow term

25 Partial NDF Recovery (cont) minimize the bias – isotropically constrain shadow term in each iteration before constraint after constraint

26 Recovered Partial NDF ground truth [Ngan et al. 05] our result

27 Overall Pipeline Capture BRDF slice Partial NDF Recovery Microfacet Synthesis

28 partial NDF to complete Merged partial NDFs completed NDF

29 Microfacet Synthesis (cont) straightforward implementation: For N NDFs at each surface point Match against (N-1) NDFs at other points In M rotation angles for alignment number of rotations/comparisons: N 2 *M 5×10 11 (N 640k, M 1k )

30 a straightforward implementation: For N NDFs in each surface point Match with (N -1) NDFs in other location In M rotation angles for alignment times of spherical function rotation and comparison N 2 * M 5×10 11 ( N 640k ) Synthesis Acceleration Clustering [Matusik et al 03] – complete representative NDFs only (1% of full set) N' 2 * M 5×10 7 ( N' 6.4k )

31 a straightforward implementation: For N NDFs in each surface point Match with (N -1) NDFs in other location In M rotation angles for alignment times of spherical function rotation and comparison N 2 * M 5×10 11 ( N 640k ) Synthesis Acceleration Clustering [Matusik et al 03] – complete representative NDFs only (1% of full set) Search Pruning – precompute all rotated candidates – prune via hierarchical searching N' 2 * M 5×10 7 ( N' 6.4k ) N'* log(N'* M) 5×10 5

32 Performance Summary 5-10 hours for BRDF slice acquisition in HDR – 1 Hour for acquisition in LDR 2-4 hours for image processing 2-3 hours for partial NDF recovery 2-4 hours for accelerated microfacet synthesis On a PC with Intel Core TM 2 Quad 2.13GHz CPU and 4GB memory

33 Model Validation full SVBRDF dataset [Lawrence et al. 06] – data from one view for modeling – data from other views for validation

34 Validation Result

35 LimitationsLimitations visual modeling, not physical accuracy single-bounce microfacet model – retro-reflection not handled spatial redundancy of rotated NDFs – easy fix by rotating the sample

36 Rendering Result: Satin

37 Rendering Result: Wood

38 Rendering Result: Brushed Metal

39 ConclusionsConclusions model surface reflectance via microfacet synthesis – general and compact representation – high resolution (spatial & angular), realistic result – easier acquisition: single-view capture cheap device shorter capturing time

40 Future Work performance optimization – capturing and data processing extension to non-flat objects extension to multiple light bounce

41 AcknowledgementsAcknowledgements Le Ma for electronics of the LED array Qiang Dai for capturing device setup Steve Lin, Dong Xu for valuable discussions Paul Debevec for HDR imagery Anonymous reviewers for their helpful suggestions and comments

42 Thank you!


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