Data Hiding Based on Connectivity Modification of 3D Mesh

Day by day, the amount of digital data has been rapidly increasing on the Internet. The size of 3D objects is very large and these objects need fast transmissions. Moreover, 3D data security becomes increasingly important for many applications, e.g., confidential transmission, video surveillance, military and medical applications. In this paper we present two new approaches of 3D object data hiding without changing the position of vertices in the 3D space. The main idea of the two proposed methods is to find and to synchronize particular areas of the 3D objects used to embed the message. The embedding is done by changing the connectivity of edges in the selected areas composed of quadrangles. The first proposed approach of data hiding in 3D objects is based on minimum spanning tree (MST) while the second approach is based on the projection on a secret axis of the quadrangle centers. These methods are lossless in the sense that the positions of the vertices are unchanged. Moreover they are blind and do not depend of the order of the data in the files. These two approaches are very interesting when the 3D objects have been digitalized with high precision.De nos jours, des visualisations ainsi que des transferts d’objets 3D sont couramment effectués pour de nombreuses applications allant du jeu vidéo à l’imagerie médicale en passant par l’industrie manufacturière. Dans cet article nous proposons deux nouvelles méthodes permettant de dissimuler des données dans des objets 3D sans modifier la position des sommets. L’idée principale des deux méthodes présentées est de trouver et de synchroniser des zones particulières dans l’objet 3D pouvant être utilisées pour insérer le message. L’insertion de données s’appuie sur la modification de la connexité des arêtes dans les zones sélectionnées composées de quadrangles. La différence entre les deux méthodes présentées est la manière de sélectionner et de synchroniser ces zones d’insertion. Alors que la première méthode s’appuie sur un arbre couvrant minimum (ACM), la seconde méthode utilise un axe sur lequel sont projetés les centres des zones d’insertion. Ces deux méthodes aveugles, protégées par utilisation de clefs secrètes, résistent à des transformations géométriques tels que les rotations, translations ou changement d’échelle et ne sont pas perturbées par des modifications directes de l’ordre des données dans les fichiers originaux. Ces approches trouvent un intérêt certain pour des objets 3D dont les sommets ont été acquis avec une grande précision et dont la modification n’est pas acceptable

High power femtosecond chirped pulse amplification in large mode area photonic bandgap Bragg fibers

International audienceWe report on high power amplification of femtosecond pulses in 40-μm core diameter Yb-doped photonic bandgap Bragg fibers. The robustness to bending and transverse spatial behavior of these fibers is analyzed through simulations. The fibers are used in both stages of a moderately stretched (150 ps) femtosecond chirped pulsed amplification (CPA) system. A compressed average power of 6.3W is obtained using a low-index polymer-coated Bragg fiber with excellent beam quality and high efficiency, in agreement with numerical simulations. The use of an air-clad Bragg fiber allows us to scale the output power to 47 W at a repetition rate of 35MHz. This experiment demonstrates the great potential of Bragg fibers to increase the mode area and the power of practical bending-tolerant femtosecond fiber systems

Picosecond laser source at 1 MHz with continuous tunability in the visible red band

We report the first demonstration to our knowledge of a continuously tunable picosecond laser operating around 1 MHz. The emission can be tuned from 640 to 685 nm and the repetition rate from 200 kHz to 1 MHz with a pulse duration of less than 200 ps. The system is based on a Nd:YVO4 passively Q-switched microchip laser providing a few tens of nJ per pulse. Two cascaded stages of amplification are then used to increase the pulse energy to several microJ . The frequency doubled radiation is then used to pump a periodically-poled-niobate-lithium (PPLN)-based optical parametric generator in an all-solid-state architecture. 20 nJ of tunable signal radiation are obtained. We also demonstrated 300-ps pulses generation in the UV (355 nm) at 1 MHz

Authentification du réseau de craquelures

National audienceExtraction du reseau de craquelures de la joconde sur des clichés pris à différentes époques, et notamment avant et après qu'elle soit volée. Le chapitre décrit les méthodes de traitement d'image utilisées afin d'extraire ces craquelures et de les comparer d'une photo à l'autr

Virtual Sculpture: A Model of Virtual Clay

October 15-17International audienc

Physics Based Models for Viscoplastic Bodies applied to Free Form Modelling with Virtual Clay

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Human Centered System for Computer Aided Replication of Sculptures

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Criterion Independent Hierarchical Segmentation for Unstructured 3D Datasets - Application to Range Images

International audienceWe present a method for the segmentation of unstructured and unfiltered 3D data. The core of this approach is based on the construction of a local neighborhood structure and its recursive subdivision. 3D points will be organized into groups according to their spatial proximity, but also to their similarity in the attribute space. Thanks to this hierarchical approach, this method provides high flexibility to the final level of segmentation. We assume that the 3D image is composed of regions homogeneous according to some criterion (color, curvature, etc.), but no assumption about noise, nor spatial repartition/shape of the regions or points is made. Thus, this approach can be applied to a wide variety of segmentation problems, unlike most existing specialized methods. We demonstrate the performance of our algorithm with experimental results on real range images

Human-Performed Assembly Task Evaluation through a Virtual Operator

International audienceThe study presented in this paper aims at achieving optimal paths for a human-performed assembly task. Optimality, from an operator's point of view, means that minimal fatigue occurs. Trajectories for assembly parts, generated by potential fields, are optimized in terms of the work the operator has to do. Optimization is carried out by genetic algorithm. The trajectories have to satisfy the constraints imposed by physical human limitations. We therefore introduce a virtual human operator in the working environment, and determine by means of inverse kinematics if the trajectories are feasible. Our method is tested on the assembly of a mechanical part in 3D space

Pairwise region-based scan alignment

International audienceIn this paper, we present a new algorithm for the alignment of two 3D scans. The approach uses a region-based matching technique. We make no assumptions about the initial positions of the scans. Regions are described by a probability density function (pdf) computed from low dimensional surface descriptors (curvature or normal cone). The algorithm allows registering directly raw noisy data, possibly with the presence of outliers, without any pre-processing, such as filtering, denoising, or reconstruction. Region correspondence is found using similarity function based on the comparison of regions pdf and under geometry constraints. Results on raw scan data sets are presented to illustrate and evaluate the algorithm