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Introduction Assembling Completion Results Conclusion
Skull Assembly and Completion usingTemplate-based Surface Matching
Li Wei, Wei Yu, Maoqing Li 1 Xin Li*2
1School of Information Science and TechnologyXiamen University
2Department of Electrical and Computer EngineeringCenter for Computation and Technology
Louisiana State University*EMail: [email protected]
3DIMPVT 2011
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Introduction Assembling Completion Results Conclusion
Introduction
Goal
To assemble and repair fragmented skulls tocomplete models.
Motivation
Skull Completion is important in forensicand anthropological facial reconstruction.The traditional state-of-the-art approach:
Time consumingDomain expertise requiredSubjective when large regions are missing
Proposed Approach:Computer-aided completion in digitalenvironment
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Related Work
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Algorithm Pipeline
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Fragmented Skull Assembling
In: A set of fragments Mi and template S.
Out: A set of rigid transformations Ti (applied on Mi ), so that thearrangement of all fragments in world coordinates wellapproximates S.
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Feature Exaction
Feature Extraction
Slippage Feature on each Fragment Mi .
Signature
Spin Image [Johnson et al. 1999].Why Spin Image?
Comparing the GeometricProperties of regions.
Our Modified Spin-ImageSignature
Resolution-InvarianceDirection Filtering
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Finding Coarse Correspondence
I/O
In: Spin image signatures on fragments feature points andtemplate points.
Out: Correspondence from feature points (on fragments) to thetemplate.
The most possible many-to-manymapping (most similarcorresponding pairs of points) isthe coarse correspondence.
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Fragment-Template Matching
Optimal Correspondence
Exact a most isometric sub-set[Tevs et al. 2009].
Local Registration
Compute rigid transform by optimal corresponding.
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Inter-Fragment Refinement
Avoid Intersection Between Fragments
Refinement:Taking the computed transformations as starting variables, tominimize the objective function composed of three terms:
E(T1, . . . , Tn) = αEI + βEF + γET ,
whereEI =
∑i,j∈n,i<j Int(Ti(Mi), Tj(Mj)),
EF = ‖∑
i
∑v∈Ti (Mi )
Dis(v , S)‖2,ET =
∑i S(Ti).
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Skull Completion
I/O
In: The assembled skull with damage regions, and a template.
Out: A repaired skull
The completion is based on the surface matching between thethe template and subject skull .
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Template-based Completion
Non-rigid Template/Subject Mapping
In: A template model, and the assembled skull.
Out: Affine transformations on each template vertex
Minimizing the following matching energy:
E = λ1Edata + λ2Eshape
where
Edata =∑
vi∈S
Dis2(Ti + vi , M)
Eshape =∑
ei,j ,vi ,vj∈S
|Ti − Tj |2
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Template-based Completion
I/O
In: Deformed template and assembled object skull.
Out: Repaired object skull
Cut and paste.
Filling small holes/gaps[Liepaet al. 2003]
Smoothing[Kobbelt et al.1998]
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Experimental Results
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Completion in Various Cases
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Conclusion
Skull Assembling:Fragment-template matching —> Spatial relationship of fragments.Robust and efficient partial matching by improved spin image.Global refinement to reduce self intersection.
Skull Completion:Non-rigid registration from template to object.Robust hole-filling and smoothing algorithm.
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Acknowledgements
The Skull Data are provided by the Forensic Anthropology andComputer Enhancement Services (FACES) Laboratory atLouisiana State University
This work is supported by Louisiana Board of Regents ResearchCompetitiveness Subprogram (RCS) LEQSF(2009-12)-RD-A-06,PFund: NSF(2009)-PFund-133, and LSU Faculty ResearchGrant 2010.
Project Website:http://www.ece.lsu.edu/xinli/SkullAssembly.html
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On-going and Future Work
Assembly
Increase accuracy by analyzingbreak curves.
Completion
Intergrate the completion usingsymmetry.
Facial reconstruction
Digital face modeling on completed skull
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