Min Gyu Choi

Planning biped locomotion using motion capture data and probabilistic roadmaps

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.

Modal warping: real-time simulation of large rotational deformation and manipulation

This work proposes a real-time simulation technique for large deformations. Greens 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.

Simulating complex hair with robust collision handling

We present a new framework for simulating dynamic movements of complex hairstyles. The proposed framework, which treats hair as a collection of wisps, includes new approaches to simulating dynamic wisp movements and handling wisp-body collisions and wisp-wisp interactions. For the simulation of wisps, we introduce a new hair dynamics model, a hybrid of the rigid multi-body, serial chain and mass-spring models, to formulate the simulation system using an implicit integration method. Consequently, the simulator can impose collision/contact constraints systematically, allowing it to handle wisp-body collisions efficiently without the need for backtracking or sub-timestepping. In addition, the simulator handles wisp-wisp collisions based on impulses while taking into account viscous damping and cohesive forces. Experimental results show that the proposed technique can stably simulate hair with intricate geometries while robustly handling wisp-body collisions and wisp-wisp interactions.

Evaluation of the Clinical Efficacy of Fractional Radiofrequency Microneedle Treatment in Acne Scars and Large Facial Pores

Background Fractional technology overcomes the problems of ablative lasers, such as inaccurate depth control and damage to the epidermis. Minimally invasive fractional radiofrequency microneedle devices allow for more‐selective heating of the dermis. Objective To evaluate the clinical efficacy of fractional radiofrequency microneedle (ERM) treatment in acne scars and large facial pores. Materials and Methods Thirty patients with acne scars and large facial pores were enrolled. Bipolar radiofrequency energy was delivered to the skin through the electrodes of the FRM device. Skin lesions were evaluated according to grade of acne scars, Investigator Global Assessment of large pores, skin surface roughness, transepidermal water loss (TEWL), dermal density, microscopic and composite image, sebum measurement, and questionnaires regarding patient satisfaction. Results The grade of acne scars and Investigator Global Assessment of large pores improved in more than 70% of all patients. Skin surface roughness, dermal density, and microscopic and composite images also improved, whereas TEWL and sebum measurement did not change. Conclusion Clinical improvement from FRM treatment appeared to be related to dermal matrix regeneration. FRM treatment may be effective in improving acne scars and facial pores.

Human motion reconstruction from inter-frame feature correspondences of a single video stream using a motion library

Videos taken from a single camera are a most common source of human motions. In this paper, we present a novel method to reconstruct the motion of a human-like figure from inter-frame feature correspondences of a single video stream. We exploit a motion library to resolve the depth ambiguity in recovering the 3D configurations from 2D features. Our reconstruction method takes three major steps: timewarping to align the reference motion with that in the video, reconstructing the joint orientations, and estimating the root trajectory. Experimental results show that our approach can reconstruct highly dynamic motions such as shooting of soccer players, which would be hard to do, otherwise.

Real‐Time Simulation of Thin Shells

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.

Data-driven control of flapping flight

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 birds 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.

Video-guided motion synthesis using example motions

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.

Increased expression of the aryl hydrocarbon receptor in patients with chronic inflammatory skin diseases.

Polychlorinated biphenyls (PCBs) and 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) are major environmental pollutants, and their effects on the human body critically depend on the aryl hydrocarbon receptor (AhR). The aim of this study was to evaluate the significance of the AhR and its ligands in chronic inflammatory skin diseases such as atopic dermatitis (AD) and psoriasis. Expression of AhR‐related mRNA was increased in lesional skin from patients with AD and psoriasis compared to those of normal skin from healthy controls. The AhR and aryl hydrocarbon receptor nuclear translocator were colocalized in the nuclei of keratinocytes at the lower epidermis of psoriatic lesions, which suggested activation of the AhR pathway. After treatment of normal human epidermal keratinocytes with TCDD or PCBs, IL‐6 and IL‐8 production were increased. The results of this study suggest that AhR is highly expressed in the acute lesional skin of patients with AD and psoriasis, and the AhR pathway is activated especially in psoriasis.

Image Dequantization: Restoration of Quantized Colors

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.