scape: shape completion and animation of...
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SCAPE: Shape Completion SCAPE: Shape Completion and Animation of Peopleand Animation of People
By Dragomir Anguelov, Praveen Srinivasan, By Dragomir Anguelov, Praveen Srinivasan, Daphne Koller, Sebastian Thrun, Jim Daphne Koller, Sebastian Thrun, Jim Rodgers, James DavisRodgers, James Davis
From SIGGRAPH 2005From SIGGRAPH 2005
Presentation for CS468 by Emilio AntPresentation for CS468 by Emilio Antúúneznez
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MotivationMotivation
It is difficult to get highresolution body It is difficult to get highresolution body scansscans
It is even harder at video ratesIt is even harder at video rates By building up a human model, you By building up a human model, you
could synthesize a highresolution could synthesize a highresolution scan from sparse/incomplete datascan from sparse/incomplete data
Accurate model is most easily created Accurate model is most easily created by learning from sample scansby learning from sample scans
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Preexisting Work in Preexisting Work in Deformable Human Models IDeformable Human Models I Deformations described relative to a Deformations described relative to a
template shapetemplate shape Pose deformations given relative to Pose deformations given relative to
local joints in an articulated modellocal joints in an articulated model Bodyshape deformations described Bodyshape deformations described
using displacement vectors from PCAusing displacement vectors from PCA
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Preexisting Work in Preexisting Work in Deformable Human Models IIDeformable Human Models II Pose and shape deformations rarely Pose and shape deformations rarely
addressed togetheraddressed together Most similar work by Sumner and Most similar work by Sumner and
PopoviPopovićć– Retargets pose deformation to another Retargets pose deformation to another
meshmesh– Does not learn a modelDoes not learn a model
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Paper ContributionsPaper Contributions
Learning an affine deformation model Learning an affine deformation model for both pose and shapefor both pose and shape
Shape completion for scan of an Shape completion for scan of an arbitrary human targetarbitrary human target
Body shape manipulation for motion Body shape manipulation for motion capture animationcapture animation
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Presentation OverviewPresentation Overview
Data AcquisitionData Acquisition Learning the Human ModelLearning the Human Model ApplicationsApplications
– Shape CompletionShape Completion– Motion Capture AnimationMotion Capture Animation
LimitationsLimitations
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Data Format / AssumptionsData Format / Assumptions
Each input model is a deformation of a Each input model is a deformation of a fixedtopology triangle meshfixedtopology triangle mesh
Models divided into three categoriesModels divided into three categories– One template modelOne template model– Template subject in different posesTemplate subject in different poses– Different people in (roughly) same poseDifferent people in (roughly) same pose
Articulated skeleton assigned to each Articulated skeleton assigned to each meshmesh
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Data Acquisition and Data Acquisition and ProcessingProcessing
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Learning the Human ModelLearning the Human Model
Pose and shape deformations Pose and shape deformations described pertriangle using linear described pertriangle using linear transformationstransformations
Pose transformations learned from Pose transformations learned from template subject in different posestemplate subject in different poses
Body shape transformations learned Body shape transformations learned by comparing different subjects to by comparing different subjects to templatetemplate
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Pose Deformation IPose Deformation I
Rigid (skeletal) Rigid (skeletal) deformations are deformations are represented separately represented separately from nonrigid onesfrom nonrigid ones
Transformations are Transformations are given in relative given in relative coordinate system coordinate system where one of the where one of the corners is fixed at the corners is fixed at the origin origin
O Qk
Rl[k]
template triangle
final triangle
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Pose Deformation IIPose Deformation II
Triangle edges are not Triangle edges are not forced to be consistentforced to be consistent
Final synthesized Final synthesized mesh reduces the mesh reduces the leastsquares error leastsquares error between mesh points between mesh points and triangle and triangle deformationsdeformations
O Qk
Rl[k]
template triangle
final triangle
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Learning Pose Deformation Learning Pose Deformation Model IModel I Rigid rotation is known from skeletonRigid rotation is known from skeleton Nonrigid transformation is Nonrigid transformation is
underdefinedunderdefined Q matrix is computed by requiring Q matrix is computed by requiring
adjacent triangles’ nonrigid adjacent triangles’ nonrigid transformations to be similartransformations to be similar
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Learning Pose Deformation Learning Pose Deformation Model IIModel II Nonrigid deformation modeled as an Nonrigid deformation modeled as an
affine function of adjacent joint anglesaffine function of adjacent joint angles
In practice, some of the degrees of In practice, some of the degrees of freedom are removed for constrained freedom are removed for constrained joingsjoings
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Pose Deformation Learning Pose Deformation Learning ResultsResults
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BodyShape DeformationBodyShape Deformation
Body shape is modeled as an additional Body shape is modeled as an additional linear transform, Slinear transform, S
S is underdetermined (like Q)S is underdetermined (like Q) Again, solved using a smoothness Again, solved using a smoothness
constraintconstraint
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Learning the Shape Learning the Shape Deformation ModelDeformation Model The matrix coefficients for all body The matrix coefficients for all body
shape transformations are vectorizedshape transformations are vectorized Principal component analysis is used Principal component analysis is used
to parameterize the shape transform to parameterize the shape transform vectorsvectors
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Shape Deformation Shape Deformation Learning ResultsLearning Results
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Shape Completion IShape Completion I
Assuming you know some of the node Assuming you know some of the node positions, estimate the otherspositions, estimate the others
Must estimate pose and body shapeMust estimate pose and body shape This optimization is highly nonlinear in the This optimization is highly nonlinear in the
posepose Empirically found that optimizing over all Empirically found that optimizing over all
variables at once produces bad resultsvariables at once produces bad results Instead, SCAPE iterates solving Instead, SCAPE iterates solving
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Shape Completion IIShape Completion II
Empirically found that optimizing over all Empirically found that optimizing over all variables at once produces bad resultsvariables at once produces bad results
Instead, SCAPE iterates, solving each of Instead, SCAPE iterates, solving each of these in order:these in order:– PosePose– Mesh estimateMesh estimate– Body shapeBody shape
Results in a “completed” mesh and a Results in a “completed” mesh and a “predicted” mesh“predicted” mesh
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Partial View CompletionPartial View Completion
Skeletal and pointcorrespondences Skeletal and pointcorrespondences may be off if too much data is missingmay be off if too much data is missing
Iterate between the shape completion Iterate between the shape completion algorithm previously described and algorithm previously described and remapping the point correspondencesremapping the point correspondences
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Partial View Completion Partial View Completion ResultsResults
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Motion Capture AnimationMotion Capture Animation
Motion capture data provides the pose Motion capture data provides the pose datadata
Body shape parameters can be set Body shape parameters can be set arbitrarilyarbitrarily
Since markers are generally placed on Since markers are generally placed on body surface (not in the bones), mesh body surface (not in the bones), mesh is constrained to lie in the space of is constrained to lie in the space of body shapes encoded by the modelbody shapes encoded by the model
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Motion Capture Animation Motion Capture Animation ResultsResults
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LimitationsLimitations
Assumes that pose deformation and Assumes that pose deformation and body shape are mostly independentbody shape are mostly independent
Models only pose deformations from Models only pose deformations from skeletal motionskeletal motion
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ConclusionConclusion
SCAPE learns simple body model SCAPE learns simple body model which distinguishes pose and body which distinguishes pose and body shape deformationsshape deformations
Creates reasonable shape Creates reasonable shape completions, even when large features completions, even when large features are missingare missing
Allows for flexible reconstruction of Allows for flexible reconstruction of moving model from motion capture moving model from motion capture data data