Titus Zaharia

This paper presents a novel method for retrieving different instances of a region or object of interest in a video database. We propose three dynamic region construction and matching algorithms aiming at obtaining the most similar instance of the query model from each candidate image. The first two involve a greedy, dynamic region construction method. The third is based on simulated annealing, and aims at determining a global optimum. An interactive selection mechanism allows the user to select an object directly from the video and to start a query using as input this information in order to access visually similar content. Experimental results show promising performances, with object detection rates of up to 81%.

This paper proposes a novel approach for mono‐resolution 3D mesh compression, called TFAN (Triangle Fan‐based compression). TFAN treats in a unified manner meshes of arbitrary topologies, i.e., manifold or not, oriented or not, while offering a linear computational complexity (with respect to the number of mesh vertices) for both encoding and decoding algorithms. In addition, the TFAN compressed representation is optimized for real‐time decoding applications. In order to validate the proposed approach, two databases have been considered for experimentations. The first is the MPEG‐4 test set, which includes over 3500 general purpose manifold meshes. The second, related to the French national project SEMANTIC‐3D, includes over 4000 computer assisted design (CAD) meshes of highly irregular, non‐manifold topologies. In both cases, the TFAN approach outperforms existing techniques such as MPEG‐4/3DMC (3D Mesh Coding) or Touma and Gotsman, with decoding times lower by an order of magnitude at equivalent or even better levels of compression efficiency (±10% in bitrate). In addition, when applied to non‐manifold 3D data, the compression performances are significantly enhanced (6–30% gain in bitrate). Due to its high compression performances the TFAN approach has been recently retained for ISO standardization, within the framework of the MPEG‐4/AFX standard. Copyright © 2009 John Wiley & Sons, Ltd.

Within the framework of collaborative interactions with 3D numerical copies of real objects inserted in virtual environments, this paper tackles the issue of 3D object reconstruction from multiple calibrated cameras. After examining the various constraints related to collaborative systems, we propose comprehensive, state of the art 3D reconstruction techniques. The main families of approaches are here identified, described, and discussed in detail. An analysis of the literature shows that there is a lack of methods that are able to respond to the needs of the collaborative interaction applications, and that perform adequately in terms of computation time and reconstruction accuracy. Accordingly, we propose a new multiresolution volumetric approach that is able to obtain numerical copies of real objects at multiple resolutions. Experimental results demonstrate that the proposed approach provides accurate reconstructions at reasonable, interactive computation times. The use of the proposed approach for progressive insertion of reconstructed objects in the prototype interfaces MOWGLI and Spin-3D developed by FranceTelecom R&D is also illustrated.