A Powell Optimization Approach for Example-Based Skinning in a Production Animation Environment

We propose a layered framework for incorporating example-based skinning algorithms such as Pose Space Deformation or Shape-by-Example into an existing character animation system. The challenge in implementing example-based skinning in an existing system lies in the fact that it is generally believed that the interpolation of the examples is best performed before doing other skinning deformations (although there has been no analysis as to why this is the case), whereas the examples are specified by the user after the other deformations are performed. It is therefore necessary to invert the operation of these skinning and deformation operators. Existing systems typically allow layering of both basic skinning methods such as Skeleton Subspace Deformation (SSD) and other deformations such as lattices, etc., and commercial systems may further allow additional proprietary deformation algorithms as part of the character skinning. Unfortunately, understanding and accessing their various parameters can be laborious at best, and we do not have access to the algorithms in the case of commercial packages. The contributions of this paper are 1) a detailed analysis showing how inverting the skinning operations leads to better example interpolation, and 2) a demonstration ∗xiao0003@ntu.edu.sg that the black-box inverse can be accomplished in practice using Powell optimization, resulting in an improved example-based skinning capability for existing large animation systems.