Reducing Blendshape Interference by Selected Motion Attenuation

J.P. Lewis
Jonathan Mooser
Zhigang Deng
Ulrich Neumann
Computer Graphics and Immersive Technology Lab
U. Southern California


Blendshapes (linear shape interpolation models) are perhaps the most commonly employed technique in facial animation practice. A major problem in creating blendshape animation is that of blendshape interference: the adjustment of a single blendshape ``slider'' may degrade the effects obtained with previous slider movements, since the blendshapes have overlapping, non-orthogonal effects. Because models used in commercial practice may have 100 or more individual blendshapes, the interference problem is the subject of considerable manual effort. Modelers iteratively resculpt models to reduce interference where possible, and animators must compensate for those interference effects that remain. In this short paper we consider the blendshape interference problem from a linear algebra point of view. We find that while full orthogonality is not desirable, the goal of preserving previous adjustments to the model can be effectively approached by allowing the user to temporarily designate a set of points as representative of the previous (desired) adjustments. We then simply solve for blendshape slider values that mimic desired new movement while moving these ``tagged'' points as little as possible. The resulting algorithm is easy to implement and demonstrably reduces cases of blendshape interference found in existing models.

ACM SIGGRAPH Symposium on Interactive 3D Graphcis and Games (I3D 2005):


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