Although stereoscopic depth perception has been a common subject of research since 1838, it is only recently that a fundamental division between two types of stereoscopic processing -- first-order and second-order -- has been identified. The precise functioning of the neural mechanisms that underlie these processing streams, however, is not yet understood. It was first confirmed that first-order stereopsis mechanisms are best investigated with vertically oriented stimuli at small disparities , whereas second-order stereopsis mechanisms prefer stimuli at large disparities. It has been postulated that the second-order stereopsis mechanisms are insensitive to stimulus spatial frequency content, but this was found not to be the case. Four different explanations were investigated to account for this result: nonlinearities of the early visual system and screen, absolute and relative orientation of the stimuli, and the possibility of the second-order mechanism being multiple. The last of these possibilities was found to be the most plausible, based on the data collected. It has long been thought that vergence may play an important role in stereopsis because both systems use disparity cues. This relationship was investigated using briefly presented "second-order" stimuli and both experienced and naive subjects. A disparity sign judgement (front/back) to disparate stimuli was made while vergence eye movements were recorded. Stimuli were presented over a range of orientations, presentation times, disparities and contrasts. The vergence responses were found to be uncorrelated with the disparity sign judgements and it was concluded that vergence does not influence stereopsis under these conditions. Finally, the role that first- and second-order stereopsis mechanisms play within tilt percepts induced by orientation disparities were investigated. Subjects were presented with two different types of stimuli with either carrier, envelope, or both carrier and envelope orientation disparities. The stimulus with no "first-order reference" could not be perceived in depth with the envelope orientation disparity alone. When this stimulus had both carrier and envelope orientation disparities, depth tilt was still perceived. It was concluded that the perception of stereoscopic tilt is a first-order process.

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When seen through a stereoscope, a Gabor pattern (a Gaussian enveloped sinusoid) that is masked by visual noise is more readily detectable when it appears in front of or behind the noise than when it is embedded in the noise itself. The enhanced visibility brought about by stereo cues is referred to as binocular unmasking. In this work, we investigated whether binocular unmasking may also occur with visual objects more complex than simple Gabor patterns, and with tasks more demanding than detection. Specifically, we examined the effects of binocular unmasking in the detection, categorization, and identification of noise masked images of natural objects. We observed the occurrence of binocular unmasking in all three tasks. However, the size of this effect was greater for detection performance than for categorization or identification performance; the latter two benefited to the same extent by the availability of stereoscopic cues. We argue that these results suggest that low level stereoscopic depth cues may play a helpful role, not only in simple detection tasks with psychophysical stimuli, but also in the perception of complex stimuli depicting natural objects.

When seen through a stereoscope, a Gabor pattern (a Gaussian enveloped sinusoid) that is masked by visual noise is more readily detectable when it appears in front of or behind the noise than when it is embedded in the noise itself. The enhanced visibility brought about by stereo cues is referred to as binocular unmasking. In this work, we investigated whether binocular unmasking may also occur with visual objects more complex than simple Gabor patterns, and with tasks more demanding than detection. Specifically, we examined the effects of binocular unmasking in the detection, categorization, and identification of noise masked images of natural objects. We observed the occurrence of binocular unmasking in all three tasks. However, the size of this effect was greater for detection performance than for categorization or identification performance; the latter two benefited to the same extent by the availability of stereoscopic cues. We argue that these results suggest that low level stereoscopic depth cues may play a helpful role, not only in simple detection tasks with psychophysical stimuli, but also in the perception of complex stimuli depicting natural objects.

Ce mémoire de thèse traite de la mise en correspondance d'images pour des applications de vision stéréoscopique ou de stabilisation d'images de caméras vidéo. les méthodes de mise en correspondance reposent généralement sur l'utilisation de points d'intérêts dans les images, c'est-à-dire de points qui présentent de fortes discontinuités d'intensité lumineuse. Nous présentons tout d'abord un nouveau descripteur de points d'intérêt, obtenu au moyen d'un filtre anisotropique rotatif qui délivre en chaque point d'intérêt une signature mono-dimensionnelle basée sur un gradient d'intensité. Invariant à la rotationpar construction, ce descripteur possède de trés bonnes propriétés de robustesse et de discrimination. Nous proposons ensuite une nouvelle méthode d'appariement invariante aux transformations euclidiennes et affines. Cette méthode exploite la corrélation des signatures sous l'hypothèse de faibles déformations, et définit une mesure de distance nécessaire à l'appariement de points. Les résultats obtenus sur des images difficiles laissent envisager des prolongements prometteurs de cette méthode. / This thesis adresses the issue of image matching for stereoscopic vison applications and image stabilization of video cameras. Methods of mapping are generally based on the use of interest points in the images, i.e. of points which have strong discontinuities in light intensity. We first present a new descriptor of points of interest, obtained by means of an anisotropic rotary filter which delivers at each point of interest a one-dimensional signature based on an intensity gradient. Invariant to rotation by construction, thisdescriptor has very good properties of robustness and discrimination. We then propose a new matching method invariant to Euclidean and affine transformations. This method exploits the correlation of the signatures subject to moderate warping, and defines a distance measure, necesssary for the matching of points. the results obtained on difficult images augur promising extentions to this method.

Αντικείμενο της παρούσας εργασίας είναι η υψομετρική ανίχνευση θέσης κινούμενου ρομπότ. Για τον υπολογισμό της θέσης του ρομπότ χρησιμοποιήθηκε ένα στερεοσκοπικό σύστημα δύο ίδιων παράλληλων καμερών. Οι εσωτερικές παράμετροι των δύο καμερών και το μήκος της βασικής γραμμής είναι γνωστά. Θεωρείται για ευκολία ότι όλος ο όγκος του ρομπότ αναπαριστάται απο ένα σημείο P με συντεταγμένες (X,Y,Z) ώς προς σύστημα συντεταγμένων με αρχή το κέντρο προβολής της αριστερής κάμερας. Για τον εντοπισμό του ρομπότ αποκτήθηκαν δύο ακολουθίες βίντεο, μια για κάθε κάμερα, στις οποίες έγινε κατάτμηση κίνησης με την μέθοδο διαφοράς διαδοχικών καρέ. Στη συνέχεια ακολούθησε επεξεργασία εικόνας στα καρέ και των δύο ακολουθιών για την εξαγωγή των περιοχών που απεικονίζουν το αντικείμενο στο επίπεδο της εικόνας. Κατόπιν, υπολογίστηκαν οι θέσεις των κέντρων βάρους των περιοχών για τις δύο ακολουθίες , Pl(xl,yl) και Pr(xr,yr) αντίστοιχα. Τα σημεία αυτά αναπαριστούν το σημείο P στην αριστερή και στη δεξιά ακολουθία εικόνων. Ακολούθησε αντιστοίχιση σημείων μεταξύ των δύο ακολουθιών με βάση την επιπολική γεωμετρία. Τα σημεία στα οποία βρέθηκε αντιστοιχία χρησιμοποιήθηκαν για τον υπολογισμό της θέσης του σημείου P με την μέθοδο της τριγωνοποίησης. / The object of this thesis is the position detection of a moving robot. To calculate the position of the robot a stereoscopic system of two identical parallel cameras was used. The intrinsic parameters of the cameras and the length of the baseline are given. To simplify the problem it is assumed that the entire robot can be represented by a point P with (X,Y,Z) coordinates with respect to the coordinate system of the left camera center of projection. To detect the robot two video image sequences were acquired, one for each camera, to which motion segmentation was applied with the frame differencing method. After that, image proseccing was implemented to the frame sequences in order to find the region that represents the robot in the image plane. The centroids of the regions were calculated in the two sequences,Pl(xl,yl) and Pr(xr,yr) respectively. Those points represent the point P in the image planes of the left and right camera. Finally the restriction of epipole geometry was used to find matches between those points. Using those matches the coordinates of P were calculated with the triangulation method.

Made available in DSpace on 2016-06-02T19:06:22Z (GMT). No. of bitstreams: 1 6596.pdf: 13694392 bytes, checksum: e1c7e2c6a28770665631b8b56c490c57 (MD5) Previous issue date: 2014-12-16 / Aid to navigation systems can be used to help the visually impaired to perform daily tasks, such as their mobility and orientation. The objective of this project is to develop a prototype of an aid to navigation system for visually impaired people in indoors environments. The system has video sensors that detect obstacles ahead and markers containing points of interest that may be useful to the user, as doors and stairs. The methodology of this work involves selecting tools, computer vision techniques and digital image processing that may be useful to implement a prototype to validate the proposed work. As a result, a prototype was created that detects obstacles in real-time as well as points of interest. / Os sistemas de auxílio à navegação podem ser utilizados para auxiliar deficientes visuais a realizar tarefas do cotidiano, como por exemplo sua locomoção e orientação. O objetivo deste projeto é desenvolver um protótipo de um sistema de auxílio à navegação para deficientes visuais em ambientes internos. O sistema possui sensores de vídeo que detectam obstáculos à frente, e marcadores contendo pontos de interesse que possam ser de utilidade ao usuário como portas e escadas. A metodologia deste trabalho implica em selecionar ferramentas e técnicas de visão computacional e processamento digital de imagens que possam ser de utilidade à implementação de um protótipo que valide o trabalho proposto. Como resultado, foi criado um protótipo que detecta obstáculos em tempo real, assim como pontos de interesse.

La fabrication de pièces manufacturées génère un nombre très important de données de différents types définissant les géométries de fabrication ainsi que la qualité de production. Ce travail de thèse s’inscrit dans le cadre de la réalisation d’un système de vision cognitif dédié à l’évaluation d’objets 3D manufacturés incluant éventuellement des surfaces gauches, en tenant compte des tolérances géométriques et des incertitudes. Ce système permet un contrôle exhaustif de pièces manufacturées et offre la possibilité d’une inspection tridimensionnelle automatique de la pièce. La mise en place d’un système de mesures multi-capteurs (passifs et actifs) a permis d’améliorer significativement la qualité d’évaluation par le biais d’une reconstruction tridimensionnelle enrichie de l’objet à évaluer. En particulier, nous avons employé simultanément un système stéréoscopique de vision et un système à projection de lumière structurée afin de reconstruire les contours et les surfaces de différents objets 3D. / Producing industrially manufactured parts generates a very large number of data of various types defining the manufacturing geometries as well as the quality of production. This PhD work has been carried out within the framework of the realization of a cognitive vision system dedicated to the 3D evaluation of manufactured objects including possibly free form surfaces, taking into account the geometric tolerances and uncertainties. This system allows the comprehensive control of manufactured parts, and provides the means for their automated 3D dimensional inspection. The implementation of a multi-sensor (passive and active) measuring system enabled to improve significantly the assessment quality through an enriched three-dimensional reconstruction of the object to be evaluated. Specifically, we made use simultaneously of a stereoscopic vision system and of a structured light based system in order to reconstruct the edges and surfaces of various 3D objects.

Les travaux présentés dans cette thèse concernent le thème des fonctionnalités visuelles qu'il convient d'embarquer sur un robot mobile, afin qu'il puisse se déplacer dans son environnement. Plus précisément, ils ont trait aux méthodes de perception par vision stéréoscopique dense, de modélisation de l'environnement par grille d'occupation, et de suivi visuel d'objets, pour la navigation autonome d'un robot mobile dans un environnement d'intérieur. Il nous semble important que les méthodes de perception visuelle soient à la fois robustes et rapide. Alors que dans les travaux réalisés, on trouve les méthodes globales de mise en correspondance qui sont connues pour leur robustesse mais moins pour être employées dans les applications temps réel et les méthodes locales qui sont les plus adaptées au temps réel tout en manquant de précision. Pour cela, ce travail essaye de trouver un compromis entre robustesse et temps réel en présentant une méthode semi-locale, qui repose sur la définition des distributions de possibilités basées sur une formalisation floue des contraintes stéréoscopiques.Il nous semble aussi important qu'un robot puisse modéliser au mieux son environnement. Une modélisation fidèle à la réalité doit prendre en compte l'imprécision et l'incertitude. Ce travail présente une modélisation de l'environnement par grille d'occupation qui repose sur l'imprécision du capteur stéréoscopique. La mise à jour du modèle est basée aussi sur la définition de valeurs de crédibilité pour les mesures prises.Enfin, la perception et la modélisation de l'environnement ne sont pas des buts en soi mais des outils pour le robot pour assurer des tâches de haut niveau. Ce travail traite du suivi visuel d'un objet mobile comme tâche de haut niveau. / This work concerns visual functionalities to be embedded in a mobile robot for navigation purposes. More specifically, it relates to methods of dense stereoscopic vision based perception, grid occupancy based environment modeling and object tracking for autonomous navigation of mobile robots in indoor environments.We consider that is important for visual perception methods to be robust and fast. While in previous works, there are global stereo matching methods which are known for their robustness, but less likely to be employed in real-time applications. There are also local methods which are more suitable for real time but imprecise. To this aim, this work tries to find a compromise between robustness and real-time by proposing a semi-local method based on the definition of possibility distributions built around a fuzzy formalization of stereoscopic constraints.We consider also important for a mobile robot to better model its environment. To better fit a model to the reality we have to take uncertainty and inaccuracy into account. This work presents an occupancy grid environment modeling based on stereoscopic sensor inaccuracy.. Model updating relies on the definition of credibility values for the measures taken.Finally, perception and environment modeling are not goals but tools to provide robot high-level tasks. This work deals with visual tracking of a moving object such as high-level task.

In this thesis the main objectives were to improve the liquid crystal shutters and to develop a stereoscopic vision application called 3D Dual View. The vision quality of a 3D system based on active glasses is direct related to the performance of the liquid crystal shutters. There are a lot of parameters that plays an important role in the quality of 3D glasses. Thus, efforts were concentrated in the organization of the liquid crystal molecules between the substrates and in the liquid crystal itself. We studied different configurations of shutters using nematic liquid crystal and ferroelectric liquid crystal (smectic), with and without polymer. Furthermore, the ferroelectric samples were analyzed using a full optical snapshot matrix Mueller polarimenter made by UBO (Université de Bretagne Occidentale) in partnership with Télécom-Bretagne. The second part was the development of 3D Dual View System. It is a stereoscopic vision system based on a mixture of active and passive 3D solution which displays a 3D image that can be viewed simultaneously by two spectators, but from different perspectives. To allow two different points-of-view of a scene or object in three dimensions, the system has to multiplex four images, one pair to form the 3D image for one viewer in one perspective and the other pair for the second viewer in other perspective. We describe different techniques to multiplex and demultiplex the video streams taking into account the physiological aspects, market, image quality and the crosstalk. The crosstalk between the images leads to an effect called ghosting, which the viewer sees a low intensity image that belongs to the other viewer. Then, we also characterized the ghosting effect (crosstalk) and proposed an algorithm of ghostbusting to compensate it.