Partial match retrieval of multidimensional data

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Tatouage d'images cryptées pour l'aide au télédiagnostic

Le développement d'interfaces de visualisation à distance pour des images médicales rencontre des problèmes de sécurité de données. Dans ce papier, nous présentons une combinaison des techniques de cryptage et de tatouage d'images. Nous proposons un système permettant de transférer des images médicales de manière sécurisée en générant une clef pour crypter l'image, puis en tatouant l'image avec la clef de cryptage et les données concernant le patient

A General Two-Pass Method Integrating Specular and Diffuse Reflection

International audienceWe analyse some recent approaches to the global illumination problem by introducing the corresponding reflection operators, and we demonstrate the advantages of a two-pass method. A generalization of the system introduced by Wallace et al. at Siggraph '87 to integrate diffuse as well as specular effects is presented. It is based on the calculation of extended form-factors, which allows arbitrary geometries to be used in the scene description, as well as refraction effects. We also present a new sampling method for the calculation of form-factors, which is an Mternative to the hemi-cube technique introduced by Cohen and Greenberg for radiosity calculations. This method is particularly well suited to the extended form-factors calculation. The problem of interactive display of the picture being created is also addressed by using hardware-assisted projections and image composition to recreate a complete specular view of the scene

Average cost of orthogonal range queries in multiattribute trees

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The analysis of simple list structures

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The Visibility Skeleton: A Powerful and Multi-Purpose Global Visibility Tool

International audienceMany problems in computer graphics and computer vision require accurate global visibility information. Previous approaches have typically been complicated to implement and numerically unstable, and often too expensive in storage or computation. The Visibility Skeleton is a new powerful utility which can efficiently and accurately answer visibility queries for the entire scene. The Visibility Skeleton is a multi-purpose tool, which can solve numerous different problems. A simple construction algorithm is presented which only requires the use of well known computer graphics algorithmic components such as ray-casting and line/plane intersections. We provide an exhaustive catalogue of visual events which completely encode all possible visibility changes of a polygonal scene into a graph structure. The nodes of the graph are extremal stabbing lines, and the arcs are critical line swaths. Our implementation demonstrates the construction of the Visibility Skeleton for scenes of over a thousand polygons. We also show its use to compute exact visible boundaries of a vertex with respect to any polygon in the scene, the computation of global or on-the-fly discontinuity meshes by considering any scene polygon as a source, as well as the extraction of the exact blocker list between any polygon pair. The algorithm is shown to be manageable for the scenes tested, both in storage and in computation time. To address the potential complexity problems for large scenes, on-demand or lazy contruction is presented, its implementation showing encouraging first results

Average Efficiency of Data Structures for Binary Image Processing

International audienceThis letter adresses the problem of computing the average values associated to geometric decompositions of binary quadtrees, under a faisly general branching process probabilistic model adapted to these types of trees

Conservative Visibility Preprocessing Using Extended Projections

International audienceVisualisation of very complex environments can be significantly accelerated using occlusion culling. In this paper we present a visibility preprocessing method which efficiently computes potentially visible geometry for volumetric viewing cells. We introduce novel extended projection operators, which permits efficient occlusion culling with respect to all viewpoints within a cell, and takes into account the combined occlusion effect of multiple occluders. We use extended projection of occluders onto a set of projection planes to create extended occlusion maps; we show how to efficiently test occludees against these occlusion maps to determine occlusion with respect to the entire cell. We also present an improved projection operator for certain specific but important configurations. An important advantage of our approach is that we can re-project extended projections onto a series of projection planes (via an occlusion sweep), and thus accumulate occlusion information from multiple blockers. This new approach allows the creation of effective occlusion maps for previously hard-to-treat scenes such as leaves of trees in a forest. Graphics hardware is used to accelerate both the extended projection and reprojection operations. We present a complete implementation of our preprocessing algorithm demonstrating significant speedup with respect to view-frustum culling only, without the computational overhead of on-line occlusion culling