We present a novel algorithm for physics-based real-time facial animation driven by muscle deformation. Unlike the previous works using 3D finite elements, we use a 2D shell element to avoid inefficient or undesired tessellation due to the thin structure of facial muscles. To simplify the analysis and achieve real-time performance, we adopt real-time thin shell simulation of [Choi et al. 2007]. Our facial system is composed of four layers of skin, subcutaneous layer, muscles, and skull, based on human facial anatomy. Skin and muscles are composed of shell elements, subcutaneous fatty tissue is assumed as a uniform elastic body, and the fixed part of facial muscles is handled by static position constraint. We control muscles to have stretch deformation using modal analysis and apply mass-spring force to skin mesh which is triggered by the muscle deformation. In our system, only the region of interest for skin can be affected by the muscle. To handle the coupled result of facial animation, we decouple the system according to the type of external forces applied to the skin. We show a series of real-time facial animation caused by selected major muscles that are relevant to expressive skin deformation. Our system has generality for importing new types of muscles and skin mesh when their shape or positions are changed.

ABSTRACT This paper proposes a practical approach for real‐time simulation of large deformation and ductile fracture. We adopt the oriented particles approach for robust and efficient simulation of large deformation and develop a practical model for plastic flow and fracture. The proposed method finds the optimal rotation and the optimal stretch in shape matching. The newly introduced optimal stretch leads to a material strain that can be employed in the plastic flow and fracture criteria. We also propose a graphics processing unit skinning method for real‐time rendering of a deformed, fractured visual mesh. Experimental results show that the proposed method can robustly simulate large, elastoplastic deformation and ductile fracture of large visual meshes in real time. Copyright © 2014 John Wiley & Sons, Ltd.

We present a physically based controller that simulates the flapping behavior of a bird in flight. We recorded the motion of a dove using marker-based optical motion capture and high-speed video cameras. The bird flight data thus acquired allow us to parameterize natural wingbeat cycles and provide the simulated bird with reference trajectories to track in physics simulation. Our controller simulates articulated rigid bodies of a bird's skeleton and deformable feathers to reproduce the aerodynamics of bird flight. Motion capture from live birds is not as easy as human motion capture because of the lack of cooperation from subjects. Therefore, the flight data we could acquire were limited. We developed a new method to learn wingbeat controllers even from sparse, biased observations of real bird flight. Our simulated bird imitates life-like flapping of a flying bird while actively maintaining its balance. The bird flight is interactively controllable and resilient to external disturbances.

The radiometric resolution of a motion-induced synthetic aperture radiometer (MISAR) is analytically obtained from the standard deviation of a baseline response, an observation scenario, and the imaging method of the MISAR. The intrinsic long integration time given by the whole dwell time on moving platforms improves the radiometric resolution compared with the snapshot resolution of other nominal synthetic aperture radiometers. In addition, it is illustrated that the MISAR imaging holds the tradeoff relationship between the radiometric and spatial resolutions.

Abstract This paper proposes a real‐time simulation technique for thin shells undergoing large deformation. Shells are thin objects such as leaves and papers that can be abstracted as 2D structures. Development of a satisfactory physical model that runs in real‐time but produces visually convincing animation of thin shells has been remaining a challenge in computer graphics. Rather than resorting to shell theory which involves the most complex formulations in continuum mechanics, we adopt the energy functions from the discrete shells proposed by Grinspun et al. [ GHDS03 ]. For real‐time integration of the governing equation, we develop a modal warping technique for shells. This new simulation framework results from making extensions to the original modal warping technique [ CK05 ] which was developed for the simulation of 3D solids. We report experimental results, which show that the proposed method runs in real‐time even for large meshes, and that it can simulate large bending and/or twisting deformations with acceptable realism.

Abstract Color quantization replaces the color of each pixel with the closest representative color, and thus it makes the resulting image partitioned into uniformly‐colored regions. As a consequence, continuous, detailed variations of color over the corresponding regions in the original image are lost through color quantization. In this paper, we present a novel blind scheme for restoring such variations from a color‐quantized input image without a priori knowledge of the quantization method. Our scheme identifies which pairs of uniformly‐colored regions in the input image should have continuous variations of color in the resulting image. Then, such regions are seamlessly stitched through optimization while preserving the closest representative colors. The user can optionally indicate which regions should be separated or stitched by scribbling constraint brushes across the regions. We demonstrate the effectiveness of our approach through diverse examples, such as photographs, cartoons, and artistic illustrations.

Video taken from a single monocular camera is the most common means of recording human motion. In this article, we present a practical, semiautomatic method for synthesizing a human motion that is guided by such video. After preprocessing an input video, we select a precaptured motion clip called a reference motion from a motion library. We then compute the sequence of body configurations of a virtual character by deforming this motion, according to spacetime constraints derived from a sequence of 2D features in the input video. Experimental results show that our method can synthesize highly dynamic motions, such as kicking and header motions of soccer players. We also showed the potential of our scheme as a new paradigm for motion capture, that is, capturing motions from videos taken with a monocular camera, even outside a motion capture studio.

This paper proposes a real-time simulation technique for large deformations. Green's nonlinear strain tensor accurately models large deformations; however, time stepping of the resulting nonlinear system can be computationally expensive. Modal analysis based on a linear strain tensor has been shown to be suitable for real-time simulation, but is accurate only for moderately small deformations. In the present work, we identify the rotational component of an infinitesimal deformation and extend traditional linear modal analysis to track that component. We then develop a procedure to integrate the small rotations occurring at the nodal points. An interesting feature of our formulation is that it can implement both position and orientation constraints in a straightforward manner. These constraints can be used to interactively manipulate the shape of a deformable solid by dragging/twisting a set of nodes. Experiments show that the proposed technique runs in real-time, even for a complex model, and that it can simulate large bending and/or twisting deformations with acceptable realism.

Typical high-level directives for locomotion of human-like characters are useful for interactive games and simulations as well as for off-line production animation. In this paper, we present a new scheme for planning natural-looking locomotion of a biped figure to facilitate rapid motion prototyping and task-level motion generation. Given start and goal positions in a virtual environment, our scheme gives a sequence of motions to move from the start to the goal using a set of live-captured motion clips. Based on a novel combination of probabilistic path planning and hierarchical displacement mapping, our scheme consists of three parts: roadmap construction, roadmap search, and motion generation. We randomly sample a set of valid footholds of the biped figure from the environment to construct a directed graph, called a roadmap, that guides the locomotion of the figure. Every edge of the roadmap is associated with a live-captured motion clip. Augmenting the roadmap with a posture transition graph, we traverse it to obtain the sequence of input motion clips and that of target footprints. We finally adapt the motion sequence to the constraints specified by the footprint sequence to generate a desired locomotion.