We present a new approach to the analysis of dynamic facial images for the purposes of estimating and resynthesizing dynamic facial expressions. The approach exploits a sophisticated generatire model of the human face originally developed for realistic facial animation. The face model, which may be simulated and rendered at interactive rates on a graphics workstation, incorporates a physics-based synthetic facial tissue and a set of anatomically motivated facial muscle actuators. We consider the estimation of dynamic facial muscle contractions from video sequences of expressive human faces. We develop an estimation technique that uses deformable contour models (snakes) to track the nonrigid motions of facial features in video images. The technique estimates muscle actuator controls with sufficient accuracy to permit the face model to resynthesize transient expressions.

Most of today's medical simulation systems are based on geometric representations of anatomical structures that take no account of their physical nature. Representing physical phenomena and, more speci cally the realistic modeling of soft tissue will not only improve current medical simulation systems but will considerably enlarge the set of applications and the credibility of medical simulation, from neurosurgery planning to laparoscopic surgery simulation. In order to achieve realistic tissue deformation, it is necessary to combine deformation accuracy with computer e ciency. On the one hand, biomechanics has studied complex mathematical models and produced a large amount of experimental data for representing the deformation of soft tissue. On the other hand, computer graphics has proposed many algorithms for the real-time computation of deformable bodies, often at the cost of ignoring the physics principles. In this paper, we survey existing models of deformation in medical simulation and we analyze the impediments to combining computer-graphics representations with biomechanical models. In particular, the di erent geometric representations of deformable tissue are compared in relation to the tasks of real-time deformation, tissue cutting and force-feedback interaction. Finally, we inspect the potential of medical simulation under the development ofthiskey technology. 1

This paper develops a highly automated approach to constructing realistic, working models of human heads for use in animation. These physics-based models are anatomically accurate and may be made to conform closely to specific individuals. We begin by scanning a person with a laser sensor which circles around the head, acquiring detailed range and reflectance information. Next, an automatic conformation algorithm adapts a triangulated face mesh of predetermined topological structure to these data. The generic mesh, which is reusable with different individuals, reduces the range data to an efficient, polygonal approximation of the facial geometry and supports a high-resolution texture mapping of the skin reflectivity. The conformed polygonal mesh forms the epidermal layer of a new, physics-based model of facial tissue. An automatic algorithm constructs the multilayer synthetic skin and estimates an underlying rigid "skull" substructure with a jointed jaw. Finally, the algorithm inserts synthetic muscles into the deepest layer of the facial tissue. These contractile actuators, which emulate the primary muscles of facial expression, generate forces that deform the synthetic tissue into meaningful expressions. To increase realism, we include constraints to emulate tissue incompressibility and to enable the tissue to slide over the skull substructure without penetrating into it. The resulting animate models appear significantly more realistic than our previous physics-based facial models. Keywords: Physics-Based Facial Modeling, Facial Animation, Cylindrical Facial Scanning, Feature-Based Facial Adaptation, Texture Mapping, Discrete Deformable Models. 1

ion Signal Level Semantic Level Figure 13: Multimodal Design Space (adapted from [224]) system in the design space is the pivotal center of its features. According to the characterization of an interaction along the two dimensions, fusion, and use of modalities, four basic types of multimodal interactions can be distinguished: alternative, synergistic, exclusive, and concurrent multimodal interaction, as shown in Figure 13. Obviously, synergistic systems subsume the other three classes of multimodal systems. Therefore, architectural models of multimodal integration (as presented in the next subsection and in Section 9) are sufficient if they are able to model synergistic cooperation of modalities. 6.2.2 Fusion of Multimodal Input Fusion of multimodal input events can occur on different levels, ranging from signal-level to semantic-level. Signal-level fusion (or lexical fusion [224]) performs the combination of multimodal input at the level of the input signal. Signal-level fusion has...

Abstract. Realistic deformation of computer-simulated anatomical structures is computationally intensive. As a result, simple methodologies not based in continuum mechanics have been employed for achieving real-time deformation of virtual anatomy. Since the graphical interpolations and simple spring models commonly used in these simulations are not based on the biomechanical properties of tissue structures, these “quick and dirty ” methods typically do not accurately represent the complex deformations and force-feedback interactions that can take place during surgery. Finite Element (FE) analysis is widely regarded as the most appropriate alternative to these methods. Extensive research has been directed toward applying this method to modeling a wide range of biological structures, and a few simple FE models have been incorporated into surgical simulations. However, because of the highly computational nature of the FE method, its direct application to real-time force-feedback and visualization of tissue deformation has not been practical for most simulations. This limitation is due primarily to the overabundance of information provided by the standard FE approaches. If the mathematics are optimized through pre-processing to yield only the information essential to the simulation task, run-time computation requirements can be drastically reduced. We are currently developing such methodologies, and have created computer demonstrations that support real-time interaction with soft tissue. To illustrate the efficacy and utility of these fast “banded matrix ” FE methods, we present results from a skin suturing simulator which we are developing on a PC-based platform. 1.

In this paper a method for the objective assessment of burn scars is proposed. The quantitative measures developed in this research provide an objective way to calculate elastic properties of burn scars relative to the surrounding areas. The approach combines range data and the mechanics and motion dynamics of human tissues. Active contours are employed to locate regions of interest and to find displacements of feature points using automatically established correspondences. Changes in strain distribution over time are evaluated. Given images at two time instances and their corresponding features, the finite element method is used to synthesize strain distributions of the underlying tissues. This results in a physically based framework for motion and strain analysis. Relative elasticity of the burn scar is then recovered using iterative descent search for the best nonlinear finite element model that approximates stretching behavior of the region containing the burn scar. The results from the skin elasticity experiments illustrate the ability to objectively detect differences in elasticity between normal and abnormal tissue. These estimated differences in elasticity are correlated against the subjective judgments of physicians that are presently the practice.

this paper we present a framework for facial surgery simulation which is based on volumetric finite element modeling. We contrast conventional procedures for surgical planning against our system by accompanying a patient during the entire process of planning, medical treatment and simulation. In various preprocessing steps a 3D physically based facial model is reconstructed from CT and laser range scans. All geometric and topological changes are modeled interactively using Alias.^TM Applying fully 3D volumetric elasticity allows us to represent important volumetric effects such as incompressibility in a natural and physically accurate way. For computational efficiency, we devised a novel set of prismatic shape functions featuring a globally C -continuous surface in combination with a C interior. Not only is it numerically accurate, but this construction enables us to compute smooth and visually appealing facial shapes

Facial modeling and animation are increasingly receiving attention in the graphics and artificial intelligence (AI) research communities, both of which share the common goal of synthesizing believable, simulated agents. While computer graphics researchers have been primarily concerned with physical and anatomical aspects of facial movements, AI researchers and cognitive scientists have focused on understanding and modeling the motivation behind those movements and expressions. The combination of these two avenues of research may eventually lead to agents that can interact autonomously, with humans or with each other, bearing faces that believably model the underlying meaning of the interactions. While such synthetic speaking faces are undoubtedly useful for cognitive research, their practical applications are also vast in number, encompassing such diverse fields as medicine, education, telecommunications and the entertainment industry. Facial expressions have fascinated mankind for ce...

ix Chapter 1. Quantum Field Theory: No Gauge Group 1 1.1

A mathematical model for computing stresses in sutured human skin wounds is presented. The model uses the incremental law of elasticity and elastic constants valid for in vivo orthotropic skin. The model is applied to compute the principal stress and displacements resulting from suturing small elliptical and circular wounds in a large flat sheet of skin, in order to determine the optimal suturing patterns. It is observed that the average stress index for a circular wound sutured toward the center is almost double that of a wound sutured perpendicular to a diameter. Thus, the latter type of suturing pattern is preferable. Similarly, suturing an elliptical wound perpendicular to its major axis produces a lower average stress index than a circular wound of the same area. It is also found that the optimal ratio of semi-major to semi-minor axis of an elliptical wound is near 3 (for abdomenal wounds), i.e., this ratio produces the most uniform stresses along the wound edges, where wound healing is the lowest.