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Talence, France

Liu Y.,University of Sichuan | Liu Y.,French Institute for Research in Computer Science and Automation | Granier X.,French Institute for Research in Computer Science and Automation | Granier X.,LaBRI Inc
IEEE Transactions on Visualization and Computer Graphics | Year: 2012

In augmented reality, one of key tasks to achieve a convincing visual appearance consistency between virtual objects and video scenes is to have a coherent illumination along the whole sequence. As outdoor illumination is largely dependent on the weather, the lighting condition may change from frame to frame. In this paper, we propose a full imagebased approach for online tracking of outdoor illumination variations from videos captured with moving cameras. Our key idea is to estimate the relative intensities of sunlight and skylight via a sparse set of planar featurepoints extracted from each frame. To address the inevitable feature misalignments, a set of constraints are introduced to select the most reliable ones. Exploiting the spatial and temporal coherence of illumination, the relative intensities of sunlight and skylight are finally estimated by using an optimization process. We validate our technique on a set of reallife videos and show that the results with our estimations are visually coherent along the video sequences. © 2011 IEEE. Source


Bellatreche L.,University of Poitiers | Bouchakri R.,National School in Computer Science | Cuzzocrea A.,CNR Institute for High Performance Computing and Networking | Maabout S.,LaBRI Inc
Proceedings of the ACM Symposium on Applied Computing | Year: 2013

With the explosion of the size of data warehousing applications, the horizontal data partitioning is well adapted to reduce the cost of complex OLAP queries and the warehouse manageability. It is considered as a non redundant optimization technique. Selecting a fragmentation schema for a given data warehouse is NP-hard problem. Several studies exist and propose heuristics to select near optimal solutions. Most of these heuristics are static, since they assume the existence of a priori known set of queries. Note that in real life applications, queries may change dynamically and fragmentation heuristics need to integrate these changes. In this paper, we propose an incremental selection of fragmentation schemes using on genetic algorithms. Intensive experiments are conducted to validate our proposal. Copyright 2013 ACM. Source


Oria V.,New Jersey Institute of Technology | Quang T.T.P.,LaBRI Inc | Saglio J.-M.,Ecole Nationale Superieure des Telecommunications
International Journal of Web Based Communities | Year: 2011

We believe that the most important architectural features for the next generation web publishing systems will certainly be a semantic classification and a selective access to information. As the web is becoming the leading publication channel, the publishing systems should allow publishers to more effectively control the access to the information to be presented to the readers. The current 'share with all or share with friends only' model is limited, even when the access is restricted with a password, and is far from the way people share information in real life: What is said in private is not always what is said in public and what is referred to as public can further be categorised. The webograph prototype presented in the paper explores a restrictive publishing model, called the 'iceberg visibility model', based on dynamic views defined on RSS feed classes and reader groups. Copyright © 2011 Inderscience Enterprises Ltd. Source


Benoit A.,LIP | Benoit A.,Institut Universitaire de France | Canon L.-C.,University of Lorraine | Canon L.-C.,French Institute for Research in Computer Science and Automation | And 4 more authors.
Journal of Scheduling | Year: 2012

This paper deals with the reliability of task graph schedules with transient and fail-stop failures. While computing the reliability of a given schedule is easy in the absence of task replication, the problem becomes much more difficult when task replication is used. We fill a complexity gap of the scheduling literature: our main result is that this reliability problem is #P' -Complete (hence at least as hard as NP-Complete problems), both for transient and for failstop processor failures.We also study the evaluation of a restricted class of schedules, where a task cannot be scheduled before all replicas of all its predecessors have completed their execution. Although the complexity in this case with fail-stop failures remains open, we provide an algorithm to estimate the reliability while limiting evaluation costs, and we validate this approach through simulations. © Springer Science+Business Media, LLC 2011. Source


Broquedis F.,University of Bordeaux 1 | Clet-Ortega J.,University of Bordeaux 1 | Moreaud S.,French Institute for Research in Computer Science and Automation | Furmento N.,French National Center for Scientific Research | And 4 more authors.
Proceedings of the 18th Euromicro Conference on Parallel, Distributed and Network-Based Processing, PDP 2010 | Year: 2010

The increasing numbers of cores, shared caches and memory nodes within machines introduces a complex hardware topology. High-performance computing applications now have to carefully adapt their placement and behavior according to the underlying hierarchy of hardware resources and their software affinities. We introduce the Hardware Locality (hwloc) software which gathers hardware information about processors, caches, memory nodes and more, and exposes it to applications and runtime systems in a abstracted and portable hierarchical manner. hwloc may significantly help performance by having runtime systems place their tasks or adapt their communication strategies depending on hardware affinities. We show that hwloc can already be used by popular highperformance OPENMP or MPI software. Indeed, scheduling OPENMP threads according to their affinities or placing MPI processes according to their communication patterns shows interesting performance improvement thanks to hwloc. An optimized MPI communication strategy may also be dynamically chosen according to the location of the communicating processes in the machine and its hardware characteristics. © 2010 IEEE. Source

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