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SMPL: A Skinned Multi-Person Linear Model

Matthew Loper, Naureen Mahmood, Javier Romero, Gerard Pons-Moll, Michael J. Black

SIGGRAPH AsiaAcademic4356 cites45 descendantsSkinningRetargeting

SMPL body model factoring shape and pose-dependent deformations for efficient synthesis of realistic human body shapes and animations.

Abstract

We present a learned model of human body shape and pose-dependent shape variation that is more accurate than previous models and is compatible with existing graphics pipelines. Our Skinned Multi-Person Linear model (SMPL) is a skinned vertex-based model that accurately represents a wide variety of body shapes in natural human poses. The parameters of the model are learned from data including the rest pose template, blend weights, pose-dependent blend shapes, identity-dependent blend shapes, and a regressor from vertices to joint locations. Unlike previous models, the pose-dependent blend shapes are a linear function of the elements of the pose rotation matrices. This simple formulation enables training the entire model from a relatively large number of aligned 3D meshes of different people in different poses. We quantitatively evaluate variants of SMPL using linear or dual-quaternion blend skinning and show that both are more accurate than a Blend-SCAPE model trained on the same data. We also extend SMPL to realistically model dynamic soft-tissue deformations. Because it is based on blend skinning, SMPL is compatible with existing rendering engines and we make it available for research purposes.

How to read this

Category
Method / model: learned parametric body model (SMPL)
Contributions
  • Presents a skinned vertex-based human body model that factors identity-dependent and pose-dependent shape variation and is compatible with existing graphics pipelines.
  • Makes pose-dependent blend shapes a linear function of the elements of the pose rotation matrices, enabling training the whole model (template, blend weights, blend shapes, joint regressor) from many aligned 3D meshes.
  • Shows SMPL with linear or dual-quaternion blend skinning is more accurate than a Blend-SCAPE model on the same data, and extends to dynamic soft-tissue deformation.
Context
A blend-skinning successor to deformation-based body models such as Anguelov et al.'s SCAPE, designed to stay compatible with standard rendering engines.Builds on: SCAPE: Shape Completion and Animation of People
Correctness
Accuracy claims are relative to a Blend-SCAPE baseline trained on the same data and depend on the quality and coverage of the aligned mesh training set; the linear pose-blendshape formulation is a deliberate simplification that trades some expressiveness for trainability and pipeline compatibility.
Clarity
Accessible given a skinning background; a first pass conveys the factored model, a careful second pass for the blend-shape parameterization and training.
How to read it
First pass for the shape/pose factorization and why linear pose blendshapes matter; second pass on the formulation and training if using or extending SMPL.

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