Daniel Cohen-Or (Tel Aviv University, Israel)
Differential Coordinates and Least-Squares Meshes

Representing surfaces in local, rather than global, coordinate systems proves to be useful for various geometry processing applications. In particular, we have been investigating surface representations based on differential coordinates, constructed using the Laplacian operator. Unlike global Cartesian coordinates, that only represent the spatial locations of points on the surface, differential coordinates capture the local surface details which greatly affect the shading of the surface and thus its visual appearance. On polygonal meshes, differential coordinates and the discrete mesh Laplacian operator provide an efficient linear surface reconstruction framework suitable for various mesh processing tasks. In my talk I will discuss the important properties of differential coordinates and show their applications for surface reconstruction. In particular, I will discuss the Least-squares meshes and show some results of details-transfer and surface completion.

Very short bio:

Daniel Cohen-Or is an Associate Professor at the School of Computer Science at Tel-Aviv University. He received a B.Sc. in both Mathematics and Computer Science (1985), an M.Sc. in Computer Science (1986) from Ben-Gurion University, and a Ph.D.~from the Department of Computer Science (1991) at State University of New York at Stony Brook. His current research interest includes, shape modeling, visibility, and image synthesis.

James Greenleaf (Mayo Clinic College of Medicine, USA)
Vibro-acoustography and Vibrometry for Imaging and Measurement of Biological Tissues
Vibro-acoustography is a method of imaging and measurement that uses ultrasound to produce radiation force to vibrate objects. The radiation force is concentrated laterally by focusing the ultrasound beam. The radiation force is limited in depth by intersecting two beams at different frequencies, producing interference between the beams at the difference frequency only at their intersection. This results in a radiation stress of limited spatial extent on or within the object of interest. The resulting harmonic displacement of the object is detected by acoustic emission, ultrasound Doppler, or laser interferometery. The displacement is a complicated function of the object material parameters. However, significant images (Vibro-acoustography) and regional measurements (Vibrometry) can be made with this arrangement. Vibro-acoustography can produce high-resolution, speckle free images of biologically relevant objects such as breast micro-calcification and lesions, vessel calcifications, heart valves, and normal and calcified arteries. Vibrometry can also make spot measurements such as detection of micro bubble contrast agent concentration in vessels. Several examples of these results will be described. Very short bio: Prof. Greenleaf is currently Professor of Biophysics and Associate Professor of Medicine, Mayo Medical School, and Consultant in the Departments of Physiology, Biophysics, and Cardiovascular Disease and Medicine, Mayo Foundation. He has served on the IEEE Technical Committee for the Ultrasonics Symposium for ten years. He is chair of the IEEE UFFCS Subcommittee on Ultrasonics in Medicine/IEEE Measurement Guide Editors, and on the IEEE Medical Ultrasound Committee. Dr. Greenleaf has six patents and is recipient of the 1986 J. Holmes Pioneer award and the William Frye award from the American Institute of Ultrasound in Medicine and is a Fellow of IEEE and AIUM and ASA. Dr. Greenleaf was the Distinguished Lecturer for IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society (1990/1991). His special field of interest is in ultrasonic biomedical imaging science and has published more than 234 articles and edited five books in the field.

Rick Parent (The Ohio-State University, USA)
MARKERLESS MOTION CAPTURE

Motion capture is a popular tool for computer animation, especially for animating the human figure. Motion capture, or mocap as it is more popularly called, requires that the person whose motion is being captured is outfitted with some type of active sensors or passive markers in order for the system to record movement. The positions of these sensors or markers are used to compute the positions of the joints. The joint positions are then used to reconstruct the joint angles over time. These joint angles can then be used with an appropriately configured skeleton to animate a synthetic figure. The problem with conventional motion capture is that it requires expensive equipment, requires extensive set-up and initialization, needs a conditioned environment and is restrictive of the motion being captured. An active area of research is concerned with developing techniques for capturing the motion of a human figure without the instrumentation required by traditional mocap systems. Various approaches have been tried with limited but interesting results. The approaches differ in a number of ways, among them: reconstruction of motion in two dimensions versus three dimensions, use of a single camera versus multiple cameras, use of extracted silhouettes versus use of color and texture, use of limiting assumptions about the motion being tracked, use of knowledge of anatomy and physics, robustness, and responsiveness. I will survey some of these approaches, presenting some results and discussing trade-offs. Our own work, which is a single-camera, extraced silhouette, model-based, 3D approach will be presented. This area of research represents an interesting blend of vision and computer graphics.

Very short bio:

Rick Parent is an Associate Professor in the Computer Science and Engineering Department of Ohio State University (OSU). As a graduate student, Rick worked at the Computer Graphics Research Group (CGRG) at OSU under the direction of Charles Csuri. In 1977, he received his Ph.D. from the Computer and Information Science (CIS) Department, majoring in Artificial Intelligence. For the next three years, he worked at CGRG first as a Research Associate, and then as Associate Director. In 1980 he co-founded and was President of The Computer Animation Company. In 1985, he joined the faculty of the CIS Department (now the Department of Computer Science and Engineering) at Ohio State. Rick's research interests include various aspects of computer animation with special focus on animation of the human figure. He is the author of Computer Animation: Algorithms and Techniques, published by Morgan Kaufmann in 2001. Currently, he is working on facial animation and on using model-based techniques to track human figures in video.

Antonio Oliveira (UFRJ,Brazil)
Enhancing the topology control of snakes and T-Surfaces

Consider a set of simple polygonal curves, disjoint to each other, evolving in the plane by discrete steps. If necessary, after each step, simplicity is recovered by means of splits and disjunction by a merge, when two of them collide.

Implementing the evolution of such curves in an efficient way, requires embedding them into a framework which partitions the plane into cells and redefining the curves so that they do not have an unbounded number of vertices in a same cell.

Topologically Adaptable Snakes (T-snakes), which have been created to segment images with multiple objects, evolve like the curves of the system above. The standard form of enabling these snakes to make topological changes is to consider the union of their contours as a level set of a step dependent function. An alternative approach reduces the time lag, so that, at each step, a snake reaches a single new cell vertex.

In the Loop-snakes model, the snakes move in a way that each region which has not been visited by them is delimited by a loop contained in regularized approximations of the contours where the snakes are [UTF-8?]positioned after a motion step. These loops ÿÿ which are taken as the snakes of the next step - must be distinguished from those defining doubly visited regions. This can be done in constant time at the very moment the loop is created. The whole process can be implemented by examining only the contours, without the need of considering their surroundings. In addition, the curves of a step need to be traversed only once. Moreover, as the processing essentially requires only data produced at the current step, it is easier to refine the cells mesh during the process, revert the evolution direction of a snake and incorporate the structure used to control the topology into the representation of the curves.All these desirable properties have a price. Topological changes get more complicated. However, as the number of these changes is usually irrelevant, compared to that of snaxels, this fact affects slightly the performance of the process.

Bubble T-surfaces are the 3D version of Loop-snakes. The case of a single contracting T-surface, has been studied with more details. If the faces of the moving surfaces are updated in breadth first order it is easier to obtain their bubble structure. That structure corresponds in the 3D case to the loop tree of a planar curve. Different regularization approaches have been tried and new questions like preventing the
unnecessary creation of genus are treated.

Very short bio:

Antonio Alberto Fernandes de Oliveira has graduated in Electronic Engineering(1973) and got his M. Sc and D.Sc. degrees in Mathematics(1974) and Optimization(1979). Since 1975 he has been a professor of the department of Systems Engineering and Computer Sciences of COPPE- Federal University of Rio de Janeiro and was a Visiting Scholar in University of Berkeley from 1988 to1990. Among others, he helped to introduce the areas now covered by SIBGRAPI into the Brazilian University. He took part in the creation of the Computer Graphics group of his department in 1983 and started the research activities/ offered the first regular courses on Computational Geometry (1985) and Computer Vision (1990). He is also the author of three books and his present areas of interest are Procedural Recognition, Reconstruction from Projections and Range-Maps and Segmentation of 2 and 3D-images with
multiple objects.