Automatic Linearization of Nonlinear Skinning

Ladislav Kavan
Trinity College Dublin
Steven Collins
Trinity College Dublin
Carol O'Sullivan
Trinity College Dublin

Linear blending is one of the fastest skinning methods, but suffers from volume-collapsing artifacts (a). These artifacts can be removed by a nonlinear blending method (such as dual quaternions), but at the cost of more complex vertex processing (b). Our method automatically places virtual bones in critical parts of the model (c), so that linear blending using these virtual bones efficiently approximates the nonlinear skinning technique (d).


Linear blending is a very popular skinning technique for virtual characters, even though it does not always generate realistic deformations. Recently, nonlinear blending techniques (such as dual quaternions) have been proposed in order to improve upon the deformation quality of linear skinning. The trade-off consists of the increased vertex deformation time and the necessity to redesign parts of the 3D engine. In this paper, we demonstrate that any nonlinear skinning technique can be approximated to an arbitrary degree of accuracy by linear skinning, using just a few samples of the nonlinear blending function (virtual bones). We propose an algorithm to compute this linear approximation in an automatic fashion, requiring little or no interaction with the user. This enables us to retain linear skinning at the core of our 3D engine without compromising the visual quality or character setup costs.


Ladislav Kavan, Steven Collins, Carol O'Sullivan. Automatic Linearization of Nonlinear Skinning. Symposium on Interactive 3D Graphics and Games, 2009.  

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We wish to thank Martin Pražák and Rachel McDonnell for assistance with motion capture and Daniel Sýkora, Simon Dobbyn, Cormac O'Brien and the anonymous reviewers for their valuable comments. This work has been supported by the Higher Education Authority of Ireland and Science Foundation Ireland.