Automatic muscle generation for character skin deformation

Abstract

As skin shape depends on the underlying anatomical structure, the anatomy-based techniques usually afford greater realism than the traditional skeleton-driven approach. On the downside, however, it is against the current animation workflow, as the animator has to model many individual muscles before the final skin layer arrives, resulting in an unintuitive modelling process. In this paper, we present a new anatomy-based technique that allows the animator to start from an already modelled character. Muscles having visible influence on the skin shape at the rest pose are extracted automatically by studying the surface geometry of the skin. The extracted muscles are then used to deform the skin in areas where there exist complex deformations. The remaining skin areas, unaffected or hardly affected by the muscles, are handled by the skeleton-driven technique, allowing both techniques to play their strengths. In order for the extracted muscles to produce realistic local skin deformation during animation, muscle bulging and special movements are both represented. Whereas the former ensues volume preservation, the latter allows a muscle not only to deform along a straight path, but also to slide and bend around joints and bones, resulting in the production of sophisticated muscle movements and deformations.

Muscle pushing based skin deformation on GPU

“…As we could see, all these methods could reflect the appealing effect of muscle bulging, bumping, etc. But Yang [8], Lee [9] have to do lots of tedious preparation work, including painting bone weights to the skin, muscles. Moreover, during the calculation, each muscle would be divided into several short sections.…”

“…Yang [8] uses an extended "skeleton-driven deformation", Lee [9] adopts a "two-layer skinning approach". They are both based on adding the impact of muscle vertices on the skin vertices, but they need to do lots of preparation work, including assigning appropriate weight values to the muscle and skin vertices.…”

Shape modeling for animated characters using ordinary differential equations

“…These models usually comprise a skeleton, muscles, other tissues, and skin. The involvement of muscles and other tissues causes volumetric deformation [14][15][16].…”

Automatic cage construction for retargeted muscle fitting

“…Mimicking complicated human musculature from basic shapes depends entirely on the animator's creativity. To automate (a) Pratscher [13] (b) Yang [14] (c) 75 feature points used for Seo's method [3] (d) our result this procedure, Pratscher et al [13] presented an "outsidein" muscle modelling technique which builds muscle structures from the analysis of the skin shape. However the muscles constructed are still too simplistic (Figure 1(a)) to create realistic muscle deformation.…”

“…However the muscles constructed are still too simplistic (Figure 1(a)) to create realistic muscle deformation. Later work by Yang [14] based on Constrained Delaunay Triangulation created more complicated musculature (Figure 1(b)), but the results are still far from realistic. For each new project, an animator will typically need to model skin, skeletal and muscular structure from scratch.…”