Skeleton-based linear blend skinning (LBS) remains the most popular method for real-time character deformation and animation. The key to its success is its simple implementation and fast execution. However, in addition to the well-studied elbow-collapse and candy-wrapper artifacts, the space of deformations possible with LBS is inherently limited. In particular, blending with only a scalar weight function per bone prohibits properly handling stretching, where bones change length, and twisting, where the shape rotates along the length of the bone. We present a simple modification of the LBS formulation that enables stretching and twisting without changing the existing skeleton rig or bone weights. Our method needs only an extra scalar weight function per bone, which can be painted manually or computed automatically. The resulting formulation significantly enriches the space of possible deformations while only increasing storage and computation costs by constant factors.
accompanying video (with narration)
We are grateful to Ofir Weber and Ilya Baran for illuminating discussions. We thank the United States Library of Congress for its collection of public domain photographs including the half-portrait of Max Schmeling. Special thanks to Felix Hornung for beautifying the teaser image. This work was supported by an SNF award 200021_137879.