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Min Gyu Choi
Assistant Professor |
Short Biosketch I am an assistant professor in the Department of Computer Science at Kwangwoon University. My research is in the area of computer graphics. I am particularly interested in character animation and physically-based modeling and simulation. (I received the BS, MS, and PhD degrees in computer science from Korea Advanced Institute of Science and Technology, Korea, in 1996, 1998, and 2003, respectively.) |
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Last
update: April 16. 2007  |
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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. Supplementary video:
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. Supplementary material:
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. Supplementary video:
for simulating
dynamic movements of complex hairstyles. Assuming that hair consists of
a number of wisps, we propose methods for simulating dynamic wisp
movements and handling wisp–body collisions and wisp–wisp interactions.
For 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, so that it can handle wisp–body collisions efficiently
without the need for backtracking or taking sub–timesteps. In
addition, the simulator handles wisp–wisp collisions based on the
impulse while taking account of 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. Supplementary video:
IEEE Transactions on Visualization and
Computer Graphics 2005. 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 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. Supplementary video:
