Physically-based Animation of ‘Sticky Lips’

Producing a realistic animation of the face is challenging due to the familiarity people have with facial expressions and movements. In recent years there has been increased activity in the use of physically-based models to create realistic animations of soft-tissue structures, as well as interest in modelling more subtle effects occurring in the mouth. This thesis presents a physically-based model of the mouth. In particular, the model recreates the effect of saliva on the movement of the lips, a largely unexplored topic. The research is composed of four novel components. The first component is a physically-based model of the mouth featuring a new stickiness model, recreating the effect of the saliva on the movements of the mouth. The model is supported by a novel moisture model which controls the stickiness level over time. The stickiness model itself provides more realistic behaviour than the few other current models and reproduces complex effects which can be seen in real mouths. The second component is a perceptual evaluation of the realism of mouth animations which incorporate stickiness. The evaluation concludes that the inclusion of the stickiness model results in an improvement in perceived realism of animations of the mouth. The third component is a new analysis process for capturing information about mouth movements from video. This analysis process is used to evaluate the developed model by comparing it against videos of real mouths. The analysis demonstrates that the stickiness model provides an improvement in accuracy of animation compared to models that do not incorporate stickiness. The fourth component is a corpus of mouth videos in which utterances and actions are recorded at varying levels of lip stickiness to produce high frame rate close up mouth videos which show stickiness effects in a variety of participants. This corpus is used in the objective evaluation.