La numérisation est un procédé qui consiste à enregistrer un objet dans un ordinateur pour pouvoir ensuite le manipuler à l'aide d'outils informatiques. Nous nous intéressons dans ce manuscrit à la numérisation d'objets tridimensionnels. Il s'agit tout d'abord d'enregistrer leur forme. De nombreuses méthodes ont été développées pour répondre à ce problème, et nous nous concentrerons sur les objets représentés par des maillages. Sur ces objets, il est alors utile de pouvoir représenter des attributs tels que la couleur, la température ou la charge électrique, selon l'application. Nous proposons deux approches complémentaires pour aborder ce problème. La première est fondée sur le placage de textures. Cette technique consiste à déplier (paramétrer) le maillage à plat sur une image dans laquelle l'attribut est stocké. Une valeur récupérée dans l'image est ainsi associée à chaque point de l'objet. Nous proposerons une méthode permettant de masquer l'artéfact des coutures qui est inhérent à cette technique. Déplier le maillage nécessite qu'il soit de bonne qualité, ce qui n'est pas toujours le cas. Nous décrivons donc également dans un second temps une approche de l'échantillonnage d'une surface via un diagramme de Voronoï restreint. Nous expliquons en particulier comment calculer efficacement un tel objet et comment l'optimiser par rapport à un critère de qualité. Ces résultats sont ensuite appliqués au problème de l'ajustement de surfaces / Digitalisation is an operation which consists in storing an object in a computer for further manipulation using data processing tools. In this document, we are interested in the digitalisation of three-dimensional objects. It is first a matter of recording the shape of the object. Many methods have been developed to address this problem, and we will focus on objects described as meshes. On such objects the storage of attributes like colour, temperature or electrical charge is often useful, depending on the application. We will describe two complementary approaches to deal with this issue. The first one relies on texture mapping. This technique consists in unfolding ? parametrising ? the mesh on a flat image in which the attribute is stored. A value recovered from the image can therefore be associated with each point of the object. We will describe a method which hides the seam artifact, commonly encountered using this technique. Unfolding the mesh demands that its quality be good, which is not always the case. We thus secondly describe a surface sampling method based on a restricted Voronoï diagram. We especially detail how to efficiently compute such an object and how to optimise it with respect to some quality measure. These results are then applied to the surface fitting problem

<p>This thesis covers topics relevant to model-based coding. Model-based coding is a promising very low bit rate video coding technique. The idea behind this technique is to parameterize a talking head and to extract and transmit the parameters describing facial movements. At the receiver, the parameters are used to reconstruct the talking head. Since only high-level animation parameters are transmitted, very high compression can be achieved with this coding scheme. This thesis covers the following three key problems.</p><p>Although it is a fundamental problem, the initialization problem, has been neglected some extent in the literature. In this thesis, we pay particular attention to the study of this problem. We propose a pseudo-automatic initialization scheme: an Analysis-by-Synthesis scheme based on Simulated Annealing. It has been proved to be an efficient scheme.</p><p>Owing to technical advance today and the newly emerged MPEG-4 standard, new schemes of performing texture mapping and motion estimation are suggested which use sample based direct texture mapping; the feasibility of using active motion estimation is explored which proves to be able to give more than 10 times tracking resolution. Based on the matured face detection technique, Dynamic Programming is introduced to face detection module and work for face tracking.</p><p>Another important problem addressed in this thesis is how to evaluate the face tracking techniques. We studied the evaluation problems by examining the commonly used method, which employs a physical magnetic sensor to provide "ground truth". In this thesis we point out that it is quite misleading to use such a method.</p>

This thesis covers topics relevant to model-based coding. Model-based coding is a promising very low bit rate video coding technique. The idea behind this technique is to parameterize a talking head and to extract and transmit the parameters describing facial movements. At the receiver, the parameters are used to reconstruct the talking head. Since only high-level animation parameters are transmitted, very high compression can be achieved with this coding scheme. This thesis covers the following three key problems. Although it is a fundamental problem, the initialization problem, has been neglected some extent in the literature. In this thesis, we pay particular attention to the study of this problem. We propose a pseudo-automatic initialization scheme: an Analysis-by-Synthesis scheme based on Simulated Annealing. It has been proved to be an efficient scheme. Owing to technical advance today and the newly emerged MPEG-4 standard, new schemes of performing texture mapping and motion estimation are suggested which use sample based direct texture mapping; the feasibility of using active motion estimation is explored which proves to be able to give more than 10 times tracking resolution. Based on the matured face detection technique, Dynamic Programming is introduced to face detection module and work for face tracking. Another important problem addressed in this thesis is how to evaluate the face tracking techniques. We studied the evaluation problems by examining the commonly used method, which employs a physical magnetic sensor to provide "ground truth". In this thesis we point out that it is quite misleading to use such a method.

Topology-related issues are becoming increasingly important in Computer Graphics. This research examines the use of topological analysis for solving two important problems in 3D Graphics: surface parameterization, and vector field design on surfaces. Many applications, such as high-quality and interactive image synthesis, benefit from the solutions to these problems. Surface parameterization refers to segmenting a 3D surface into a number of patches and unfolding them onto a plane. A surface parameterization allows surface properties to be sampled and stored in a texture map for high-quality and interactive display. One of the most important quality measurements for surface parameterization is stretch, which causes an uneven sampling rate across the surface and needs to be avoided whenever possible. In this thesis, I present an automatic parameterization technique that segments the surface according to the handles and large protrusions in the surface. This results in a small number of large patches that can be unfolded with relatively little stretch. To locate the handles and large protrusions, I make use of topological analysis of a distance-based function on the surface. Vector field design refers to creating continuous vector fields on 3D surfaces with control over vector field topology, such as the number and location of the singularities. Many graphics applications make use of an input vector field. The singularities in the input vector field often cause visual artifacts for these applications, such as texture synthesis and non-photorealistic rendering. In this thesis, I describe a vector field design system for both planar domains and 3D mesh surfaces. The system provides topological editing operations that allow the user to control the number and location of the singularities in the vector field. For the system to work for 3D meshes surface, I present a novel piecewise interpolating scheme that produces a continuous vector field based on the vector values defined at the vertices of the mesh. I demonstrate the effectiveness of the system through several graphics applications: painterly rendering of still images, pencil-sketches of surfaces, and texture synthesis.

In this study, an appearance reconstruction method based on extraction of material re&amp / #64258 / ectance properties of a three-dimensional (3D) object from its twodimensional (2D) images is explained. One of the main advantages of this system is that the reconstructed object can be rendered in real-time with photorealistic quality in varying illumination conditions. Bidirectional Re&amp / #64258 / ectance Distribution Functions (BRDFs) are used in representing the re&amp / #64258 / ectance of the object. The re&amp / #64258 / ectance of the object is decomposed into di&amp / #64256 / use and specular components and each component is estimated seperately. While estimating the di&amp / #64256 / use components, illumination-invariant images of the object are computed from the input images, and a global texture of the object is extracted from these images by using surface particles. The specular re&amp / #64258 / ectance data are collected from the residual images obtained by taking di&amp / #64256 / erence between the input images and corresponding illumination-invariant images, and a Lafortune BRDF model is &amp / #64257 / tted to these data. At the rendering phase, the di&amp / #64256 / use and specular components are blended into each other to achieve a photorealistic appearance of the reconstructed object.

Volume rendering is one of the branches of scientific visualization. Its popularity has grown in the recent years, and due to the increase in the computation speed of the graphics hardware of the desktop systems, became more and more accessible. Visualizing volumetric datasets using volume rendering technique requires a large amount of trilinear interpolation operations that are computationally expensive. This situation used to restrict volume rendering methods to be used only in high-end graphics workstations or with special-purpose hardware. In this thesis, an application tool has been developed using hardware accelerated volume rendering techniques on commercial graphics processing devices. This implementation has been developed with a 3D texture based approach using bump mapping for building an illumination model with OpenGL API. The aim of this work is to propose visualization methods and tools for rendering medical image datasets at interactive rates. The methods and tool are validated and compared with a commercially available software.

This research focuses on the development of polymer microfabrication technologies for the realization of two major components of a pneumatic tactile display: a microactuator array and a complementary microvalve (control) array. The concept, fabrication, and characterization of a kinematically-stabilized polymeric microbubble actuator (¡°endoskeletal microbubble actuator¡±) were presented. A systematic design and modeling procedure was carried out to generate an optimized geometry of the corrugated diaphragm to satisfy membrane deflection, force, and stability requirements set forth by the tactile display goals. A refreshable Braille cell as a tactile display prototype has been developed based on a 2x3 endoskeletal microbubble array and an array of commercial valves. The prototype can provide both a static display (which meets the displacement and force requirement of a Braille display) and vibratory tactile sensations. Along with the above capabilities, the device was designed to meet the criteria of lightness and compactness to permit portable operation. The design is scalable with respect to the number of tactile actuators while still being simple to fabricate. In order to further reduce the size and cost of the tactile display, a microvalve array can be integrated into the tactile display system to control the pneumatic fluid that actuates the microbubble actuator. A piezoelectrically-driven and hydraulically-amplified polymer microvalve has been designed, fabricated, and tested. An incompressible elastomer was used as a solid hydraulic medium to convert the small axial displacement of a piezoelectric actuator into a large valve head stroke while maintaining a large blocking force. The function of the microvalve as an on-off switch for a pneumatic microbubble tactile actuator was demonstrated. To further reduce the cost of the microvalve, a laterally-stacked multilayer PZT actuator has been fabricated using diced PZT multilayer, high aspect ratio SU-8 photolithography, and molding of electrically conductive polymer composite electrodes.

Ces dernières années ont vu l'émergence de la capture des modèles spatio-temporels (modélisation 4D) à partir d'images réelles, avec de nombreuses applications dans les domaines de post-production pour le cinéma, la science des sports, les études sociales, le divertissement, l'industrie de la publicité. A partir de plusieurs séquences vidéos, enregistrées à partir de points de vue variés, la modélisation 4D à partir de vidéos utilise des modèles spatio-temporels pour extraire des informations sur la géométrie et l'apparence de scènes réelles, permettant de les enregistrer et de les reproduire. Cette thèse traite du problème de la modélisation d'apparence.La disponibilité des donnée d'images offre de grands potentiels pour les reconstructions haute fidélité, mais nécessite des méthodes plus élaborées. En outre, les applications du monde réel nécessitent des rendus rapides et des flux réduits de données. Mais l'obtention de représentations d'apparence compactes, indépendantes du point de vue, et à grande résolution est toujours un problème ouvert.Pour obtenir ces caractéristiques, nous exprimons l'information visuelle de l'objet capturé dans un espace de texture commun. Les observations multi-caméra sont considérées comme des réalisations de l'apparence commune et un modèle linéaire est introduit pour matérialiser cette relation. Le modèle linéaire d'apparence proposé permet une première étude du problème de l'estimation d'apparence dans le cas multi-vue et expose les sources variées de bruit et les limitations intrinsèques du modèle.Basé sur ces observations, et afin d'exploiter l'information visuelle de la manière la plus efficace, nous améliorons la méthode en y intégrant un modèle de super-résolution 2D. Le modèle simule le procédé de capture d'image avec une concaténation d'opérations linéaires, générant les observation d'image des différents points de vue et permettant d'exploiter la redondance. Le problème de super-résolution multi-vue résultant est résolu par inférence bayésienne et une représentation haute-résolution d'apparence est fournie permettant de reproduire la texture de l'objet capturé avec grand détail.La composante temporelle est intégrée par la suite au modèle pour permettre d'y recouper l'information visuelle commune sous-jacente. En considérant des petits intervalles de temps ou l'apparence de l'objet ne change pas drastiquement, une représentation super-résolue cohérente temporellement est introduite. Elle explique l'ensemble des images de l'objet capturé dans cet intervalle. Grâce à l'inférence statistique Bayésienne, l'apparence construite permet des rendus avec une grande précision à partir de point de vue nouveau et à des instants différent dans l'intervalle de temps prédéfini.Pour améliorer l'estimation d'apparence d'avantage, l'inter-dépendance de la géométrie et de la photométrie est étudiée et exploitée. Les modélisations de la géométrie et de l'apparence sont unifiées dans le framework de super-résolution permettant une amélioration géométrique globale, ce qui donne à son tour une amélioration importante de l'apparence.Finalement pour encoder la variabilité de l'apparence dynamique des objets subissant plusieurs mouvements, une représentation indépendante du point de vue s'appuyant sur l'analyse en composantes principales est introduite. Cette représentation décompose la variabilité sous-jacente d'apparence en texture propres et déformations propres. La méthode proposée permet de reproduire les apparences de manière précise avec des représentation compactes. Il permet également l'interpolation et la complétion des apparences.Cette étude montre que la représentation compacte, indépendante du point de vue, et super-résolue proposée permet de confronter les nouvelles réalités du problème de modélisation d'apparence. Elle représente un contribution vers des représentations d'apparence 4D haute-qualité et ouvre de nouvelles directions de recherche dans ce domaine. / Capturing spatio-temporal models (4D modelling) from real world imagery has received a growing interest during the last years urged by the increasing demands of real-world applications and the tremendous amount of easily accessible image data. The general objective is to produce realistic representations of the world from captured video sequences. Although geometric modelling has already reached a high level of maturity, the appearance aspect has not been fully explored. The current thesis addresses the problem of appearance modelling for realistic spatio-temporal representations. We propose a view-independent, high resolution appearance representation that successfully encodes the high visual variability of objects under various movements.First, we introduce a common appearance space to express all the available visual information from the captured images. In this space we define the representation of the global appearance of the subject. We then introduce a linear image formation model to simulate the capturing process and to express the multi-camera observations as different realizations of the common appearance. Identifying that the principle of Super-Resolution technique governs also our multi-view scenario, we extend the image generative model to accommodate it. In our work, we use Bayesian inference to solve for the super-resolved common appearance.Second, we propose a temporally coherent appearance representation. We extend the image formation model to generateimages of the subject captured in a small time interval. Our starting point is the observation thatthe appearance of the subject does not change dramatically in a predefined small time interval and the visual information from each view and each frame corresponds to the same appearance representation.We use Bayesian inference to exploit the visual redundant as well as the hidden non-redundant information across time, in order to obtain an appearance representation with fine details.Third, we leverage the interdependency of geometry and photometry and use it toestimate appearance and geometry in a joint manner. We show that by jointly estimating both, we are able to enhance the geometry globally that in turn leads to a significant appearance improvement.Finally, to further encode the dynamic appearance variability of objects that undergo several movements, we cast the appearance modelling as a dimensionality reduction problem. We propose a view-independent representation which builds on PCA and decomposesthe underlying appearance variability into Eigen textures and Eigen warps. The proposed framework is shown to accurately reproduce appearances with compact representations and to resolve appearance interpolation and completion tasks.

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Theoretical part of this project is focused on rendering of volumetric data. It compares and appraise individual methods and thus readers get a good basic knowledge of commonnest causes of problems. Texture Mapped Volume Rendering and Volume Ray-casting methods are described in detail and the latter method is used in implementation of graphic system designed in this thesis. Secondary goals of this work are usage of less powerful hardware for volume-rendering, methods of optimization and dynamic change of output quality.