Bicep deformed with smooth skinning Bicep deformed using our approach Bicep showing underlying musculature

Outside-In Anatomy Based Character Rigging

Michael Pratscher, Patrick Coleman, Joe Laszlo, and Karan Singh

ACM SIGGRAPH / Eurographics Symposium on Computer Animation 2005


For believable character animation, skin deformation should communicate important deformation effects due to underlying muscle movement. Anatomical models that capture these effects are typically constructed from the inside out. Internal tissue is modeled by hand and a surface skin is attached to, or generated from, the internal structure. This paper presents an outside-in approach to anatomical modeling, in which we generate musculature from a predefined structure, which we conform to an artist-sculpted skin surface. Motivated by interactive applications, we attach the musculature to an existing control skeleton and apply a novel geometric deformation model to deform the skin surface to capture important muscle motion effects. Musculoskeletal structure can be stored as a template and applied to new character models. We illustrate the methodology, as integrated into a commercial character animation system, with examples driven by both keyframe animation and recorded motion data.

Here are some videos (avi) of our results:

Location Smooth skinning only With our deformation With our deformation (X-ray)
Forearm forearm_NoDef.avi forearm_Solid.avi forearm_Xray.avi
Lower leg lowerLeg_NoDef.avi lowerLeg_Solid.avi lowerLeg_Xray.avi
Upper arm (angle view) upperArm_AngleView_NoDef.avi upperArm_AngleView_Solid.avi upperArm_AngleView_Xray.avi
Upper arm (top view) upperArm_TopView_NoDef.avi upperArm_TopView_Solid.avi upperArm_TopView_Xray.avi

Here are some videos (avi) demonstrating the deformation model:

Deformation model type Front closeup Back cross section Miscellaneous
Simple defSimpleCloseup.avi defSimpleProfile.avi  
Stretch defStretchCloseup.avi defStretchProfile.avi defStretchCloseupWireframe.avi - wireframe on surface
Trajectory defTrajectoryCloseup.avi defTrajectoryProfile.avi defTrajectoryFur.avi - using fur to visualize slippage
Arbitrary defArbitraryCloseup.avi defArbitraryProfile.avi  


DKP Effects provided one of the character models, as well as motion data. Alias provided the Maya animation software for research.

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