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Introduction Assembling Completion Results ConclusionSkull Assembly and Completion usingTemplate-based Surface MatchingLi Wei, Wei Yu, Maoqing Li 1 Xin Li* 21 School of Information Science and TechnologyXiamen University2 Department of Electrical and Computer EngineeringCenter for Computation and TechnologyLouisiana State University*EMail: xinli@lsu.edu3DIMPVT 20111 / 17

Introduction Assembling Completion Results ConclusionIntroductionGoalTo assemble and repair fragmented skulls tocomplete models.MotivationSkull Completion is important in forensicand anthropological facial reconstruction.The traditional state-of-the-art approach:Time consumingDomain expertise requiredSubjective when large regions are missingProposed Approach:Computer-aided completion in digitalenvironment2 / 17

Introduction Assembling Completion Results ConclusionRelated Work3 / 17

Introduction Assembling Completion Results ConclusionAlgorithm Pipeline4 / 17

Introduction Assembling Completion Results ConclusionFragmented Skull AssemblingIn: A set of fragments M i and template S.Out: A set of rigid transformations T i (applied on M i ), so that thearrangement of all fragments in world coordinates wellapproximates S.5 / 17

Introduction Assembling Completion Results ConclusionFeature ExactionFeature ExtractionSlippage Feature on each Fragment M i .SignatureSpin Image [Johnson et al. 1999].Why Spin Image?Comparing the GeometricProperties of regions.Our Modified Spin-ImageSignatureResolution-InvarianceDirection Filtering6 / 17

Introduction Assembling Completion Results ConclusionFinding Coarse CorrespondenceI/OIn: 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.7 / 17

Introduction Assembling Completion Results ConclusionFragment-Template MatchingOptimal CorrespondenceExact a most isometric sub-set[Tevs et al. 2009].Local RegistrationCompute rigid transform by optimal corresponding.8 / 17

Introduction Assembling Completion Results ConclusionInter-Fragment RefinementAvoid Intersection Between FragmentsRefinement:Taking the computed transformations as starting variables, tominimize the objective function composed of three terms:E(T 1 , . . . , T n) = αE I + βE F + γE T ,whereE I = ∑ i,j∈n,i

Introduction Assembling Completion Results ConclusionSkull CompletionI/OIn: The assembled skull with damage regions, and a template.Out: A repaired skullThe completion is based on the surface matching between thethe template and subject skull .10 / 17

Introduction Assembling Completion Results ConclusionTemplate-based CompletionNon-rigid Template/Subject MappingIn: A template model, and the assembled skull.Out: Affine transformations on each template vertexMinimizing the following matching energy:E = λ 1 E data + λ 2 E shapewhereE data = ∑ Dis 2 (T i + v i , M)v i ∈SE shape =∑e i,j ,v i ,v j ∈S|T i − T j | 2 11 / 17

Introduction Assembling Completion Results ConclusionTemplate-based CompletionI/OIn: Deformed template and assembled object skull.Out: Repaired object skullCut and paste.Filling small holes/gaps[Liepaet al. 2003]Smoothing[Kobbelt et al.1998]12 / 17

Introduction Assembling Completion Results ConclusionExperimental Results13 / 17

Introduction Assembling Completion Results ConclusionCompletion in Various Cases14 / 17

Introduction Assembling Completion Results ConclusionConclusionSkull 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.15 / 17

Introduction Assembling Completion Results ConclusionAcknowledgementsThe Skull Data are provided by the Forensic Anthropology andComputer Enhancement Services (FACES) Laboratory atLouisiana State UniversityThis 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.html16 / 17

Introduction Assembling Completion Results ConclusionOn-going and Future WorkAssemblyIncrease accuracy by analyzingbreak curves.CompletionIntergrate the completion usingsymmetry.Facial reconstructionDigital face modeling on completed skull17 / 17