Efficient and Realistic Character Animation through Analytical Physics-based Skin Deformation

Physics-based skin deformation methods can greatly improve the realism of character animation, but require non-trivial training, intensive manual intervention, and heavy numerical calculations. Due to these limitations, it is generally time-consuming to implement them, and difficult to achieve a high runtime efficiency. In order to tackle the above limitations caused by numerical calculations of physics-based skin deformation, we propose a simple and efficient analytical approach for physicsbased skin deformations. Specifically, we (1) employ Fourier series to convert 3D mesh models into continuous parametric representations through a conversion algorithm, which largely reduces data size and computing time but still keeps high realism, (2) introduce a partial differential equation (PDE)-based skin deformation model and successfully obtain the first analytical solution to physics-based skin deformations which overcomes the limitations of numerical calculations. Our approach is easy to use, highly efficient, and capable to create physically realistic skin deformations

Automatic skeletonization and skin attachment for realistic character animation.

The realism of character animation is associated with a number of tasks ranging from modelling, skin defonnation, motion generation to rendering. In this research we are concerned with two of them: skeletonization and weight assignment for skin deformation. The fonner is to generate a skeleton, which is placed within the character model and links the motion data to the skin shape of the character. The latter assists the modelling of realistic skin shape when a character is in motion. In the current animation production practice, the task of skeletonization is primarily undertaken by hand, i.e. the animator produces an appropriate skeleton and binds it with the skin model of a character. This is inevitably very time-consuming and costs a lot of labour. In order to improve this issue, in this thesis we present an automatic skeletonization framework. It aims at producing high-quality animatible skeletons without heavy human involvement while allowing the animator to maintain the overall control of the process. In the literature, the tenn skeletonization can have different meanings. Most existing research on skeletonization is in the remit of CAD (Computer Aided Design). Although existing research is of significant reference value to animation, their downside is the skeleton generated is either not appropriate for the particular needs of animation, or the methods are computationally expensive. Although some purpose-build animation skeleton generation techniques exist, unfortunately they rely on complicated post-processing procedures, such as thinning and pruning, which again can be undesirable. The proposed skeletonization framework makes use of a new geometric entity known as the 3D silhouette that is an ordinary silhouette with its depth information recorded. We extract a curve skeleton from two 3D silhouettes of a character detected from its two perpendicular projections. The skeletal joints are identified by down sampling the curve skeleton, leading to the generation of the final animation skeleton. The efficiency and quality are major performance indicators in animation skeleton generation. Our framework achieves the former by providing a 2D solution to the 3D skeletonization problem. Reducing in dimensions brings much faster performances. Experiments and comparisons are carried out to demonstrate the computational simplicity. Its accuracy is also verified via these experiments and comparisons. To link a skeleton to the skin, accordingly we present a skin attachment framework aiming at automatic and reasonable weight distribution. It differs from the conventional algorithms in taking topological information into account during weight computation. An effective range is defined for a joint. Skin vertices located outside the effective range will not be affected by this joint. By this means, we provide a solution to remove the influence of a topologically distant, hence highly likely irrelevant joint on a vertex. A user-defined parameter is also provided in this algorithm, which allows different deformation effects to be obtained according to user's needs. Experiments and comparisons prove that the presented framework results in weight distribution of good quality. Thus it frees animators from tedious manual weight editing. Furthermore, it is flexible to be used with various deformation algorithms

Efficient ordinary differential equation-based modelling and skin deformations for character animation.

In the area of character animation, skin surface modelling, rigging and skin deforamtion are three essential aspects. Due to the different complexity of the characters, the time cost on creating corresponding skin surface model, animation skeleton in order to achieve diverse skin de- formations, fluctuates from several hours to several weeks. More importantly, the data size of skin deformations could sharply influence the efficiency of generating animation. Smaller data size can also speed up character animation and transmission over computer networks. Over years, researchers have developed a variety of skin deformation techniques. Geometric skin deformation approaches have high efficiency but low realism. Example-based skin deformation approaches interpolate a set of given example poses to improve realism and effects that cannot be easily produced by geometric approaches. Physics-based skin deformation methods can greatly improve the realism of character animation, but require non-trivial training, intensive manual intervention, and heavy numerical calculations. Due to these limitations, many recent activities have initiated the research of integrating geometric, example-based, and physics-based skin deformation approaches. The current research is to develop techniques based on Ordinary Differentical Equations (ODE) to efficiently create C2 continuous skin surfaces through two boundary curves, automatically generate skeleton to make the rigging process fast enough for highly efficient computer animation applications, and achieve physically realistic skin deformations for character animation by integrating geometric, physical and data-driven methods. Meanwhile, it is the first attempt to obtain an analytical solution to realistic physics-based skin deformations for highly efficient computation, to avoid the solving of a large set of linear equations, which largely reduces data size and computing time. The basic idea is to build ODE mechanics model, involve isoparametric curves and Fourier Series representation, develop accurate and efficient solutions to calculate physical skin deformations through interpolating input realistic reconstructed 3D models. The proposed techniques will greatly avoid tedious manual work, reduce data size, improve skin deformation realism, and raise efficiency of producing character animation