A comparison of linear skinning techniques for character animation

ABSTRACT

Character animation is the task of moving a complex, artificial character in a life-like manner. A widely used method for character animation involves embedding a simple skeleton within a character model and then animating the character by moving the underlying skeleton. The character's skin is required to move and deform along with the skeleton. Research into this problem has resulted in a number of skinning frameworks. There has, however, been no objective attempt to compare these methods.

We compare three linear skinning frameworks that are computationally efficient enough to be used for real-time animation: Skeletal Subspace Deformation, Animation Space and Multi-Weight Enveloping. These create a correspondence between the points on a character's skin and the underlying skeleton by means of a number of weights, with more weights providing greater flexibility. The quality of each of the three frameworks is tested by generating the skins for a number of poses for which the ideal skin is known. These generated skin meshes are then compared to the ideal skins using various mesh comparison techniques and human studies are used to determine the effect of any temporal artefacts introduced. We found that Skeletal Subspace Deformation lacks flexibility while Multi-Weight Enveloping is prone to overfitting. Animation Space consistently outperforms the other two frameworks.

REFERENCES

• 1: Marc Alexa, Linear combination of transformations, Proceedings of the 29th annual conference on Computer graphics and interactive techniques, July 23-26, 2002, San Antonio, Texas
• 2: Dragomir Anguelov , Daphne Koller , Hoi-Cheung Pang , Praveen Srinivasan , Sebastian Thrun, Recovering articulated object models from 3D range data, Proceedings of the 20th conference on Uncertainty in artificial intelligence, p.18-26, July 07-11, 2004, Banff, Canada
• 3: Yizong Cheng, Mean Shift, Mode Seeking, and Clustering, IEEE Transactions on Pattern Analysis and Machine Intelligence, v.17 n.8, p.790-799, August 1995 [doi>10.1109/34.400568]
• 4: Cheung, G. K., Baker, S., and Kanade, T. 2003. Shape-from-silhouette of articulated objects and its use for human body kinematics estimation and motion capture. CVPR 01, 77.
• 5: Dorin Comaniciu , Peter Meer, Mean Shift: A Robust Approach Toward Feature Space Analysis, IEEE Transactions on Pattern Analysis and Machine Intelligence, v.24 n.5, p.603-619, May 2002 [doi>10.1109/34.1000236]
• 6: Doug L. James , Christopher D. Twigg, Skinning mesh animations, ACM Transactions on Graphics (TOG), v.24 n.3, July 2005
• 7: Ladislav Kavan , Jiří Žára, Spherical blend skinning: a real-time deformation of articulated models, Proceedings of the 2005 symposium on Interactive 3D graphics and games, April 03-06, 2005, Washington, District of Columbia [doi>10.1145/1053427.1053429]
• 8: Paul G. Kry , Doug L. James , Dinesh K. Pai, EigenSkin: real time large deformation character skinning in hardware, Proceedings of the 2002 ACM SIGGRAPH/Eurographics symposium on Computer animation, July 21-22, 2002, San Antonio, Texas [doi>10.1145/545261.545286]
• 9: J. P. Lewis , Matt Cordner , Nickson Fong, Pose space deformation: a unified approach to shape interpolation and skeleton-driven deformation, Proceedings of the 27th annual conference on Computer graphics and interactive techniques, p.165-172, July 2000 [doi>10.1145/344779.344862]
• 10: Nadia Magnenat Thalmann , Frederic Cordier , Hyewon Seo , George Papagianakis, Modeling of Bodies and Clothes for Virtual Environments, Proceedings of the 2004 International Conference on Cyberworlds, p.201-208, November 18-20, 2004 [doi>10.1109/CW.2004.47]
• 11: Bruce Merry , Patrick Marais , James Gain, Animation space: A truly linear framework for character animation, ACM Transactions on Graphics (TOG), v.25 n.4, p.1400-1423, October 2006 [doi>10.1145/1183287.1183294]
• 12: Alex Mohr , Michael Gleicher, Building efficient, accurate character skins from examples, ACM Transactions on Graphics (TOG), v.22 n.3, July 2003
• 13: Mohr, A., and Gleicher, M. 2003. Deformation sensitive deformation. Tech. Rep. 4/7/2003, University of Wisconsin, Madison.
• 14: Alex Mohr , Luke Tokheim , Michael Gleicher, Direct manipulation of interactive character skins, Proceedings of the 2003 symposium on Interactive 3D graphics, April 27-30, 2003, Monterey, California [doi>10.1145/641480.641488]
• 15: Samuel Silva , Joaquim Madeira , Beatriz Sousa Santos, POLYMECO " A Polygonal Mesh Comparison Tool, Proceedings of the Ninth International Conference on Information Visualisation, p.842-847, July 06-08, 2005 [doi>10.1109/IV.2005.98]
• 16: Peter-Pike J. Sloan , Charles F. Rose, III , Michael F. Cohen, Shape by example, Proceedings of the 2001 symposium on Interactive 3D graphics, p.135-143, March 2001 [doi>10.1145/364338.364382]
• 17: Xiaohuan Corina Wang , Cary Phillips, Multi-weight enveloping: least-squares approximation techniques for skin animation, Proceedings of the 2002 ACM SIGGRAPH/Eurographics symposium on Computer animation, July 21-22, 2002, San Antonio, Texas [doi>10.1145/545261.545283]

INDEX TERMS

Primary Classification:
  I. Computing Methodologies
  I.3 COMPUTER GRAPHICS
      I.3.7 Three-Dimensional Graphics and Realism
          Subjects: Animation

Keywords:
animation, comparison, real-time, skinning