A obtenção e a reconstrução da geometria tridimensional (3D) de objetos e ambientes têm importância crescente em áreas como visão computacional e computação gráfica. As formas atuais de obtenção e reconstrução 3D necessitam de equipamentos e montagens sofisticadas que, por conseqüência, têm custos elevados e aplicação limitada. Este trabalho apresenta criticamente os principais algoritmos para a reconstrução 3D a partir de par de imagens estéreo e identifica os mais viáveis para utilização com equipamentos convencionais. Por meio da implementação de alguns destes algoritmos, da comparação dos resultados obtidos em sua execução e também pela comparação com os resultados encontrados na literatura, são identificadas as principais deficiências. São propostas adequações aos algoritmos existentes, em particular, é apresentada a proposta da técnica das faixas que proporciona a redução drástica no consumo de memória para o processamento da geometria 3D e que possui desempenho computacional melhor em relação às técnicas tradicionais. Foi implementado um protótipo de sistema de reconstrução 3D que permite a reconstrução pelas diferentes técnicas estudadas e propostas, bem como permite visualizar o cenário reconstruído sob diferentes pontos de vista de forma interativa. / The acquisition and reconstruction of three-dimensional (3D) geometry of objects and environments have their importance growing in areas such as Computer Vision and Computer Graphics. The current methods to acquire and reconstruct three-dimensional data need sophisticated equipments and assemblies, which have expensive costs and limited applications. This work presents the main algorithms for 3D reconstruction using a pair of stereo images and identifies which are viable to use with conventional equipments. Through the implementation of some of these algorithms, by comparing the results obtained and comparing with the results presented in the literature, the main limitations were identified. This work proposes adjustments in the existing algorithms, in particular it proposes the stripping technique, which provides a huge memory usage reduction for 3D geometry processing and better computing performance if compared with traditional approaches. A prototype system for 3D reconstruction was implemented, which allows the reconstruction using the different researched and proposed techniques and allows interactive visualization of the reconstructed scene in different angles.

In den letzten Jahren kommen immer mehr nicht perspektivische Kamerasysteme beim maschinellen Sehen zur Anwendung, die vor allem ein deutlich erweitertes Blickfeld bieten. Das klassische perspektivische Abbildungsmodell lässt sich hier häufig nicht mehr erfolgreich anwenden. In dieser Arbeit wird ein generisches Abbildungsmodell vorgestellt, welches übliche Kamerasysteme akkurat modellieren kann. Solche Kamerasysteme schließen insbesondere klassische perspektivische Systeme, aber auch Fischaugen- und Spiegellinsen-Kamerasysteme ein. Die Nutzung eines einheitlichen Abbildungsmodells ermöglicht schließlich eine einfache Verwendung und Kalibrierung von heterogenen Stereokamerasystemen, also einer Kombination von unterschiedlichen Kameratypen, die vorteilhafte Eigenschaften gegenüber klassischen Stereosystemen bieten. Nicht zuletzt trägt die in dieser Arbeit vorgestellte einheitliche Modellierung und Kalibrierung von Mono- und Stereokamerasystemen dazu bei, Fehler durch falschen Umgang oder falsche Wahl von Methoden der Modellierung oder Kalibrierung zu vermeiden und den Kamerakalibrierprozess insgesamt zu vereinfachen. In dieser Arbeit wurden verschiedene Ansätze der Modellierung untersucht und evaluiert. Es wurde eine generische Modellierung vorgeschlagen, die die untersuchten spezifischen Abbildungsmodelle vollständig ersetzen kann. Für die Kalibrierung nicht linearer Abbildungsmodelle wurde eine einheitliche Methode zur Startwertbestimmung vorgeschlagen und evaluiert. Die Genauigkeit der Kalibrierung mittels einheitlicher Methoden wurde anhand diverser realer Kamerasysteme untersucht und bewertet. Es konnte gezeigt werden, dass die dabei auftretenden Fehler deutlich im Subpixelbereich liegen. Durch Erweiterung des klassischen Konzepts der Epipolargeometrie um die generische Abbildungsmodellierung konnten schließlich heterogene Stereokamerasysteme kalibriert und genaue Stereomodelle abgeleitet werden. / The application of perspective camera systems in photogrammetry and computer vision is state of the art. In recent years non-perspective and especially omnidirectional camera systems have increasingly been used in close-range photogrammetry tasks. In general, the perspective camera model, i.e. pinhole model, cannot be applied when using non-perspective camera systems. However, several camera models for different omnidirectional camera systems are proposed in literature. Using different types of cameras in a heterogeneous camera system may lead to an advantageous combination. The advantages of different camera systems, e.g. field of view and resolution, result in a new enhanced camera system. If these different kinds of cameras can be modeled, using a unified camera model, the total calibration process can be simplified. Sometimes it is not possible to give the specific camera model in advance. In these cases a generic approach is helpful too. Furthermore, a simple stereo reconstruction becomes possible when using a fisheye and a perspective camera for example. In this work camera models for perspective, wide-angle and omnidirectional camera systems were evaluated. A generic camera model were introduced that fully substitutes specific camera models. The crucial initialization of the model''s parameters is conducted using a new generic method that is independent of the particular camera system. The accuracy of this generic camera calibration approach is validated by the calibration of a dozen of real camera systems up to subpixel accuracy. Finally, it has been shown that a unified method of modeling, parameter approximation and calibration of interior and exterior orientation can be applied to a generic stereo system to derive precise 3D object data.

A obtenção e a reconstrução da geometria tridimensional (3D) de objetos e ambientes têm importância crescente em áreas como visão computacional e computação gráfica. As formas atuais de obtenção e reconstrução 3D necessitam de equipamentos e montagens sofisticadas que, por conseqüência, têm custos elevados e aplicação limitada. Este trabalho apresenta criticamente os principais algoritmos para a reconstrução 3D a partir de par de imagens estéreo e identifica os mais viáveis para utilização com equipamentos convencionais. Por meio da implementação de alguns destes algoritmos, da comparação dos resultados obtidos em sua execução e também pela comparação com os resultados encontrados na literatura, são identificadas as principais deficiências. São propostas adequações aos algoritmos existentes, em particular, é apresentada a proposta da técnica das faixas que proporciona a redução drástica no consumo de memória para o processamento da geometria 3D e que possui desempenho computacional melhor em relação às técnicas tradicionais. Foi implementado um protótipo de sistema de reconstrução 3D que permite a reconstrução pelas diferentes técnicas estudadas e propostas, bem como permite visualizar o cenário reconstruído sob diferentes pontos de vista de forma interativa. / The acquisition and reconstruction of three-dimensional (3D) geometry of objects and environments have their importance growing in areas such as Computer Vision and Computer Graphics. The current methods to acquire and reconstruct three-dimensional data need sophisticated equipments and assemblies, which have expensive costs and limited applications. This work presents the main algorithms for 3D reconstruction using a pair of stereo images and identifies which are viable to use with conventional equipments. Through the implementation of some of these algorithms, by comparing the results obtained and comparing with the results presented in the literature, the main limitations were identified. This work proposes adjustments in the existing algorithms, in particular it proposes the stripping technique, which provides a huge memory usage reduction for 3D geometry processing and better computing performance if compared with traditional approaches. A prototype system for 3D reconstruction was implemented, which allows the reconstruction using the different researched and proposed techniques and allows interactive visualization of the reconstructed scene in different angles.

Navegação autônoma é um tópico abrangente cuja atenção por parte da comunidade de robôs móveis vemaumentando ao longo dos anos. O problema consiste em guiar um robô de forma inteligente por um determinado percurso sem ajuda humana. Esta dissertação apresenta um sistema de navegação para ambientes abertos baseado em visão estéreo. Uma câmera estéreo é utilizada na captação de imagens do ambiente e, utilizando o mapa de disparidades gerado por um método estéreo semi-global, dois métodos de detecção de obstáculos são utilizando para segmentar as imagens em regiões navegáveis e não navegáveis. Posteriormente esta classificação é utilizada em conjunto com um método de desvio de obstáculos, resultando em um sistema completo de navegação autônoma. Os resultados obtidos por está dissertação incluem a avaliação de dois métodos estéreo, esta sendo favorável ao método estéreo empregado (semi-global). Foram feitos testes visando avaliar a qualidade e custo computacional de dois métodos para detecção de obstáculos, um baseado em plano e outro baseado em cone. Tais testes deixaram claras as limitações de ambos os métodos e levaram a uma implementação paralela do método baseado em cone. Utilizando uma unidade de processamento gráfico, a versão paralelizada do método baseado em cone atingiu um ganho no tempo computacional de aproximadamente dez vezes. Por fim, os resultados demonstrarão o sistema completo em funcionamento, onde a plataforma robótica utilizada, um veículo elétrico, foi capaz de desviar de pessoas e cones alcançando seu objetivo seguramente / Autonomous navigation is a broad topic that has received increasing attention from the community of mobile robots over the years. The problem is to guide a robot in a smart way for a certain route without human help. This dissertation presents a navigation system for open environments based on stereo vision. A stereo camera is used to capture images of the environment and based on the disparity map generated by a semi-global stereo method, two obstacle detection methods are used to segment the images into navigable and non-navigable regions. Subsequently, this classification is employed in conjunction with a obstacle avoidance method, resulting in a complete autonomous navigation system. The results include an evaluation two stereo methods, this being favorable to the employed stereo method (semi-global). Tests were performed to evaluate the quality and computational cost of two methods for obstacle detection, a plane based one and a cone based. Such tests have left clear the limitations of both methods and led to a parallel implementation of the cone based method. Using a graphics processing unit, a parallel version of the cone based method reached a gain in computational time of approximately ten times. Finally, the results demonstrate the complete system in operation, where the robotic platform used, an electric vehicle, was able to dodge people and cones reaching its goal safely

L’expérience Double Chooz a pour but la mesure précise de l’angle de mélange θ₁₃. Son évaluation repose sur l’étude de la disparition des antineutrinos produits par les réacteurs de la centrale de Chooz, disparition due au phénomène d’oscillation des neutrinos. Deux détecteurs identiques composés de liquide scintillant permettent d’effectuer une mesure relative, diminuant ainsi les incertitudes systématiques. Le détecteur proche, qui fournit la normalisation du flux de neutrinos émis, est en cours d’installation, son achèvement est prévu pour le printemps 2014. Le détecteur lointain, sensible à l’effet de θ₁₃, est situé à un kilomètre environ et prend des données depuis 2011. Dans cette première phase de l’expérience, les données acquises par le détecteur lointain sont comparées à une prédiction du flux de neutrinos émis par les réacteurs pour estimer le paramètre θ₁₃. Au sein de cette thèse, l’expérience Double Chooz et son analyse sont présentées. Une attention particulière est portée à l’étude des bruits de fond et au rejet de signaux parasites constitués de flashs lumineux émis par les photo-multiplicateurs. Les flux de neutrons aux interfaces entre les différents volumes du détecteur affectent la définition du volume d’interaction et partant l’efficacité de détection. L’étude détaillée de ces effets de bord est présentée. Dans le cadre de l’expérience Double Chooz, des études ont été menées afin d’améliorer la prédiction des flux de neutrinos émis par les réacteurs. Ces travaux ont mis à jour un déficit des taux de neutrinos observés dans les expériences passées à courtes distances des réacteurs. Ce déficit pourrait s’expliquer par une oscillation vers une saveur stérile. Le projet Stereo a pour but d’observer la distorsion — caractéristique de l’oscillation — du spectre des neutrinos en énergie et en distance de propagation. Cette thèse s’attache à présenter le concept du détecteur, les simulations réalisées, ainsi que les études de sensibilité. Les différents bruits de fond et les blindages envisagés pour s’en prémunir sont enfin discutés. / The Double Chooz experiment aims to measure the θ₁₃ mixing angle through the disappearance—induced by the oscillation phenomenon—of anti-neutrinos produced by the Chooz nuclear reactors. In order to reduce systematic uncertainties, the experiment relies on the relative comparison of detected signals in two identical liquid scintillator detectors. The near one, giving the normalization of the emitted flux, is currently being built and will be delivered in spring 2014. The far detector, sensitive to θ₁₃, is located at about one kilometer and is taking data since 2011. In this first phase of the experiment, the far detector data are compared to a prediction of the emitted neutrino flux to estimate θ₁₃. In this thesis, the Double Chooz experiment and its analysis are presented, especially the background studies and the rejection of parasitic signals due to light emitted by photo-multipliers. Neutron fluxes between the different detector volumes impact the definition of the fiducial volume of neutrino interactions and the efficiency of detection. Detailed studies of these effects are presented. As part of the Double Chooz experiment, studies were performed to improve the prediction of neutrino flux emitted by reactors. This work revealed a deficit of observed neutrino rates in the short baseline experiments of last decades. This deficit could be explained by an oscillation to a sterile state. The Stereo project aims to observe a typical signature of oscillations: the distortion of neutrino spectra both in energy and baseline. This thesis presents the detector concept and simulations as well as sensitivity studies. Background sources and the foreseen shielding are also discussed.

Interagissant très peu avec leur environnement, les neutrinos peuvent aujourd'hui être clairement détectés à l'aide d'une technologie largement éprouvée reposant sur l'utilisation de liquide scintillant et de photo-multiplicateurs. Les progrès réalisés ces dernières années permettent de réduire la taille et la complexité des détecteurs et laissent ainsi entrevoir les premières applications à ces particules. Première expérience placée à 7,2 m d'un coeur de réacteur nucléaire, le détecteur Nucifer démontre la possibilité de compter les antineutrinos venant du combustible à cette faible distance induisant un environnement très défavorable en terme de bruits de fond. Dans cette thèse, nous présentons l'analyse ayant permis de rejeter les différents bruits de fond venant du réacteur et de son circuit de désactivation mais aussi des muons atmosphériques. Une prédiction du taux d'antineutrinos avec différentes simulations Monte-Carlo a également été réalisée et se trouve en accord avec le taux mesuré dans la limite des incertitudes statistiques et systématiques. Sur près d'un an de prise de données, nous avons pu suivre l'évolution en puissance du réacteur Osiris. Une étude de sensibilité a montré que la présence de plutonium dans le coeur d'Osiris était détectable à 95 % CL dès que cet isotope contribue à hauteur de 10 % de la masse fissile (1,5 kg dans Osiris). En outre, le détecteur a montré une grande stabilité tout au long de la prise de données prouvant que le contrôle à distance des réacteurs nucléaires est possible. Cette expérience ouvre donc la voie à de nouveaux modes de contrôle des réacteurs nucléaires pour les autorités de sûreté. Dans le cadre des travaux sur les spectres d'antineutrinos émis par les réacteurs nucléaires, un déficit a récemment été mis en évidence dans le taux des antineutrinos mesurés pour les expériences à courte distance des réacteurs. Ce déficit, appelé anomalie réacteur, pourrait trouver son origine dans une nouvelle oscillation à travers un état stérile du neutrino à l'électronvolt. L'expérience Stéréo a pour but de trancher sur l'existence ou non de cette oscillation en se plaçant à 10 m du réacteur nucléaire de l'ILL. En observant une distorsion à la fois en énergie et en distance, le détecteur permettra en effet d'apporter une conclusion solide sur ce phénomène. Nous revenons ici sur le développement du projet et sur les différents choix technologiques réalisés pour améliorer la sensibilité de l'expérience. Une attention particulière est portée sur l'estimation des bruits de fond provenant du réacteur nucléaire ainsi que des expériences voisines utilisant des faisceaux de neutrons. Des mesures expérimentales alliées à des simulations ont permis de quantifier les flux de rayons gammas et de neutrons ainsi que leur direction afin de prévoir les blindages nécessaires. Enfin, nous présentons les performances du prototype correspondant à une cellule du détecteur final. / In spite of a faint interaction with their environment, neutrinos can be now clearly detected thanks to a proven technology based on liquid scintillators and photomultiplier tubes. The advances made these last years allow to reduce the size and the complexity of the detectors and therefore naturally lead to the first applications with these particles. As the first experiment to be placed at 7.2 m of a nuclear core, the Nucifer detector demonstrates the possibility of counting antineutrinos coming from the nuclear fuel at such a short baseline despite the very unfavourable environment in term of the background noises. In this thesis, we present an analysis which rejects the various background noises coming from the reactor and its deactivation circuit but also from the atmospheric muons. A prediction of the antineutrino rate with several Monte-Carlo simulations was also performed and is in good agreement with the measured rate, within statistical and systematic uncertainties. After nearly one year of data taking, we were able to follow the power evolution of the reactor Osiris. A sensibility study showed that the presence of plutonium in the Osiris core was detectable at 95 % CL as soon as this isotope contributes at the level of 10 % of the fissile mass (1,5 kg in Osiris). Besides, the detector was very stable throughout the data taking proving that the remote control of nuclear reactor with a neutrino detector is possible. Thus, this experiment opens the way to new control modes of nuclear reactors by the nuclear safety authorities. As part of the work on the antineutrino spectra emitted by nuclear reactors, a deficit was recently highlighted in the observed antineutrino rate for the experiments at short baseline. This deficit, called the reactor anomaly, could be explain by a new oscillation into a sterile state of the neutrino at the electronvolt scale. The Stereo experiment aims to test the existence of this oscillation by performing measurements 10 m away from the ILL nuclear reactor. By observing a distortion pattern of the energy and distance dependence of the neutrino spectrum, the detector will be able to provide a solid proof of this phenomenon. We present here the project development and the various technological choices that we have done to improve the experiment sensibility. The estimation of the background noise coming from the nuclear reactor as well as the nearby experiments using neutron beams has been performed with on-site measurements and simulations to design the shielding of the detector. Eventually we present the performances of the prototype which corresponds to one cell of the final detector.

A novel and efficient methodology is presented for the conversion of stereo to multi-view video in order to address the 3D content requirements for the next generation 3D-TVs and auto-stereoscopic multi-view displays. There are two main algorithmic blocks in such a conversion system / stereo matching and virtual view rendering that enable extraction of 3D information from stereo video and synthesis of inexistent virtual views, respectively. In the intermediate steps of these functional blocks, a novel edge-preserving filter is proposed that recursively constructs connected support regions for each pixel among color-wise similar neighboring pixels. The proposed recursive update structure eliminates pre-defined window dependency of the conventional approaches, providing complete content adaptibility with quite low computational complexity. Based on extensive tests, it is observed that the proposed filtering technique yields better or competitive results against some leading techniques in the literature. The proposed filter is mainly applied for stereo matching to aggregate cost functions and also handles occlusions that enable high quality disparity maps for the stereo pairs. Similar to box filter paradigm, this novel technique yields matching of arbitrary-shaped regions in constant time. Based on Middlebury benchmarking, the proposed technique is currently the best local matching technique in the literature in terms of both precision and complexity. Next, virtual view synthesis is conducted through depth image based rendering, in which reference color views of left and right pairs are warped to the desired virtual view using the estimated disparity maps. A feedback mechanism based on disparity error is introduced at this step to remove salient distortions for the sake of visual quality. Furthermore, the proposed edge-aware filter is re-utilized to assign proper texture for holes and occluded regions during view synthesis. Efficiency of the proposed scheme is validated by the real-time implementation on a special graphics card that enables parallel computing. Based on extensive experiments on stereo matching and virtual view rendering, proposed method yields fast execution, low memory requirement and high quality outputs with superior performance compared to most of the state-of-the-art techniques.

No description available.

The polarization of light was introduced last ten years ago in the field of imaging system is a physical phenomenon that can be controlled for the purposes of the vision system. As that found in the human eyes, in general the imaging sensors are not under construction which is sensitive to the polarization of light. These properties can be measured by adding optical components on a conventional camera. The purpose of this thesis is to develop an imaging system that is sensitive both to the stereoscopic and to the state of polarization. As well as the visual system on a various of insects in nature such as bees, that are have capability to move in space by extracted relevant information from the polarization. The developed prototype should be possible to reconstruct threedimensional of points of interest with the issues associated with a set of parameters of the state of polarization. The proposed system consists of two cameras, each camera equipped with liquid crystal components to obtain two images with different directions of polarization. For each acquisition, four images are acquired: two for each camera. Raised by the key of main capability to return polarization information from two different cameras. After an initial calibration step; geometric and photometric, the mapping of points of interest process is made difficult because of the optical components placed in front of different lenses. A detailed study of different methods of mapping was used to select sensitivity to the polarization effects. Once points are mapped, the polarization parameters of each point are calculated from the four values from four images acquired. The results on real scenes show the feasibility and desirability of this imaging system for robotic applications.

Abstract This work addresses the problems related to three-dimensional modeling of scenes and objects and model evaluation. The work is divided into four main parts. At first, the work concentrates on purely image-based reconstruction while the second part presents a modeling pipeline based on an active depth sensor. Then, the work introduces methods for producing surface meshes from point clouds, and finally, a novel approach for model evaluation is presented. In the first part, this work proposes a multi-view stereo (MVS) reconstruction method that takes a set of images as an input and outputs a model represented as a point cloud. The method is based on match propagation, where a set of initial corresponding points between images is expanded iteratively into larger regions by searching new correspondences in the spatial neighborhood of the existing ones. The expansion is implemented using a best-first strategy, where the most reliable match is always expanded first. The method produces comparable results with the state-of-the-art but significantly faster. In the second part, this work presents a method that merges a sequence of depth maps into a single non-redundant point cloud. In the areas, where the depth maps overlap, the method fuses points together by giving more weight to points which seem to be more reliable. The method overcomes its predecessor both in accuracy and robustness. In addition, this part introduces a method for depth camera calibration. The method develops on an existing calibration approach which was originally designed for the first generation Microsoft Kinect device. The third part of the thesis addresses the problem of converting the point clouds to surface meshes. The work briefly reviews two well-known approaches and compares their ability to produce sparse mesh models without sacrificing accuracy. Finally, the fourth part of this work describes the development of a novel approach for performance evaluation of reconstruction algorithms. In addition to the accuracy and completeness, which are the metrics commonly used in existing evaluation benchmarks, the method also takes the compactness of the models into account. The metric enables the evaluation of the accuracy-compactness trade-off of the models. / Tiivistelmä Tässä työssä käsitellään näkymän tai esineen kolmiulotteista mallintamista ja tulosten laadun arviointia. Työ on jaettu neljään osaan. Ensiksi keskitytään pelkästään valokuvia hyödyntävään mallinnukseen ja sitten esitellään menetelmä syvyyskamerapohjaiseen mallinnukseen. Kolmas osa kuvaa menetelmiä verkkomallien luomiseen pistepilvestä ja lopuksi esitellään menetelmä mallien laadun arviointiin. Ensimmäisessä osassa esitellään usean kuvan stereoon perustuva mallinnusmenetelmä, joka saa syötteenä joukon valokuvia ja tuottaa kuvissa näkyvästä kohteesta pistepilvimallin. Menetelmä perustuu vastinpisteiden laajennukseen, jossa kuvien välisiä pistevastaavuuksia laajennetaan iteratiivisesti suuremmiksi vastinalueiksi hakemalla uusia vastinpistepareja jo löydettyjen läheisyydestä. Laajennus käyttää paras ensin -menetelmää, jossa luotettavin pistevastaavuus laajennetaan aina ensin. Menetelmä tuottaa vertailukelpoisia tuloksia johtaviin menetelmiin verrattuna, mutta merkittävästi nopeammin. Toisessa osassa esitellään menetelmä, joka yhdistää joukon syvyyskameralla kaapattuja syvyyskarttoja yhdeksi pistepilveksi. Alueilla, jotka sisältävät syvyysmittauksia useasta syvyyskartasta, päällekkäiset mittaukset yhdistetään painottamalla luotettavammalta vaikuttavaa mittausta. Menetelmä on tarkempi kuin edeltäjänsä ja toimii paremmin kohinaisemmalla datalla. Lisäksi tässä osassa esitellään menetelmä syvyyskameran kalibrointiin. Menetelmä kehittää jo olemassa olevaa kalibrointityökalua, joka alun perin kehitettiin ensimmäisen sukupolven Microsoft Kinect laitteelle. Väitöskirjan kolmas osa käsittelee pintamallin luomista pistepilvestä. Työ esittelee kaksi hyvin tunnettua menetelmää ja vertailee niiden kykyä luoda harvoja, mutta edelleen tarkkoja malleja. Lopuksi esitellään uudenlainen menetelmä mallinnusmenetelmien arviointiin. Tarkkuuden ja kattavuuden lisäksi, jotka ovat yleisimmät arvioinnissa käytetyt metriikat, menetelmä ottaa huomioon myös mallin pistetiheyden. Metriikan avulla on mahdollista arvioida kompromissia mallin tarkkuuden ja tiheyden välillä.