Occlusion-Aware Multi-View Reconstruction of Articulated Objects for Manipulation

The goal of this research is to develop algorithms using multiple views to automatically recover complete 3D models of articulated objects in unstructured environments and thereby enable a robotic system to facilitate further manipulation of those objects. First, an algorithm called Procrustes-Lo-RANSAC (PLR) is presented. Structure-from-motion techniques are used to capture 3D point cloud models of an articulated object in two different configurations. Procrustes analysis, combined with a locally optimized RANSAC sampling strategy, facilitates a straightforward geometric approach to recovering the joint axes, as well as classifying them automatically as either revolute or prismatic. The algorithm does not require prior knowledge of the object, nor does it make any assumptions about the planarity of the object or scene. Second, with such a resulting articulated model, a robotic system is then able to manipulate the object either along its joint axes at a specified grasp point in order to exercise its degrees of freedom or move its end effector to a particular position even if the point is not visible in the current view. This is one of the main advantages of the occlusion-aware approach, because the models capture all sides of the object meaning that the robot has knowledge of parts of the object that are not visible in the current view. Experiments with a PUMA 500 robotic arm demonstrate the effectiveness of the approach on a variety of real-world objects containing both revolute and prismatic joints. Third, we improve the proposed approach by using a RGBD sensor (Microsoft Kinect) that yield a depth value for each pixel immediately by the sensor itself rather than requiring correspondence to establish depth. KinectFusion algorithm is applied to produce a single high-quality, geometrically accurate 3D model from which rigid links of the object are segmented and aligned, allowing the joint axes to be estimated using the geometric approach. The improved algorithm does not require artificial markers attached to objects, yields much denser 3D models and reduces the computation time

Reconstruction interactive de modèles hiérarchiques par sculpture d'espace

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

Analysis of 3D human gait reconstructed with a depth camera and mirrors

L'évaluation de la démarche humaine est l'une des composantes essentielles dans les soins de santé. Les systèmes à base de marqueurs avec plusieurs caméras sont largement utilisés pour faire cette analyse. Cependant, ces systèmes nécessitent généralement des équipements spécifiques à prix élevé et/ou des moyens de calcul intensif. Afin de réduire le coût de ces dispositifs, nous nous concentrons sur un système d'analyse de la marche qui utilise une seule caméra de profondeur. Le principe de notre travail est similaire aux systèmes multi-caméras, mais l'ensemble de caméras est remplacé par un seul capteur de profondeur et des miroirs. Chaque miroir dans notre configuration joue le rôle d'une caméra qui capture la scène sous un point de vue différent. Puisque nous n'utilisons qu'une seule caméra, il est ainsi possible d'éviter l'étape de synchronisation et également de réduire le coût de l'appareillage. Notre thèse peut être divisée en deux sections: reconstruction 3D et analyse de la marche. Le résultat de la première section est utilisé comme entrée de la seconde. Notre système pour la reconstruction 3D est constitué d'une caméra de profondeur et deux miroirs. Deux types de capteurs de profondeur, qui se distinguent sur la base du mécanisme d'estimation de profondeur, ont été utilisés dans nos travaux. Avec la technique de lumière structurée (SL) intégrée dans le capteur Kinect 1, nous effectuons la reconstruction 3D à partir des principes de l'optique géométrique. Pour augmenter le niveau des détails du modèle reconstruit en 3D, la Kinect 2 qui estime la profondeur par temps de vol (ToF), est ensuite utilisée pour l'acquisition d'images. Cependant, en raison de réflections multiples sur les miroirs, il se produit une distorsion de la profondeur dans notre système. Nous proposons donc une approche simple pour réduire cette distorsion avant d'appliquer les techniques d'optique géométrique pour reconstruire un nuage de points de l'objet 3D. Pour l'analyse de la démarche, nous proposons diverses alternatives centrées sur la normalité de la marche et la mesure de sa symétrie. Cela devrait être utile lors de traitements cliniques pour évaluer, par exemple, la récupération du patient après une intervention chirurgicale. Ces méthodes se composent d'approches avec ou sans modèle qui ont des inconvénients et avantages différents. Dans cette thèse, nous présentons 3 méthodes qui traitent directement les nuages de points reconstruits dans la section précédente. La première utilise la corrélation croisée des demi-corps gauche et droit pour évaluer la symétrie de la démarche, tandis que les deux autres methodes utilisent des autoencodeurs issus de l'apprentissage profond pour mesurer la normalité de la démarche.The problem of assessing human gaits has received a great attention in the literature since gait analysis is one of key components in healthcare. Marker-based and multi-camera systems are widely employed to deal with this problem. However, such systems usually require specific equipments with high price and/or high computational cost. In order to reduce the cost of devices, we focus on a system of gait analysis which employs only one depth sensor. The principle of our work is similar to multi-camera systems, but the collection of cameras is replaced by one depth sensor and mirrors. Each mirror in our setup plays the role of a camera which captures the scene at a different viewpoint. Since we use only one camera, the step of synchronization can thus be avoided and the cost of devices is also reduced. Our studies can be separated into two categories: 3D reconstruction and gait analysis. The result of the former category is used as the input of the latter one. Our system for 3D reconstruction is built with a depth camera and two mirrors. Two types of depth sensor, which are distinguished based on the scheme of depth estimation, have been employed in our works. With the structured light (SL) technique integrated into the Kinect 1, we perform the 3D reconstruction based on geometrical optics. In order to increase the level of details of the 3D reconstructed model, the Kinect 2 with time-of-flight (ToF) depth measurement is used for image acquisition instead of the previous generation. However, due to multiple reflections on the mirrors, depth distortion occurs in our setup. We thus propose a simple approach for reducing such distortion before applying geometrical optics to reconstruct a point cloud of the 3D object. For the task of gait analysis, we propose various alternative approaches focusing on the problem of gait normality/symmetry measurement. They are expected to be useful for clinical treatments such as monitoring patient's recovery after surgery. These methods consist of model-free and model-based approaches that have different cons and pros. In this dissertation, we present 3 methods that directly process point clouds reconstructed from the previous work. The first one uses cross-correlation of left and right half-bodies to assess gait symmetry while the other ones employ deep auto-encoders to measure gait normality

Material Recognition Meets 3D Reconstruction : Novel Tools for Efficient, Automatic Acquisition Systems

For decades, the accurate acquisition of geometry and reflectance properties has represented one of the major objectives in computer vision and computer graphics with many applications in industry, entertainment and cultural heritage. Reproducing even the finest details of surface geometry and surface reflectance has become a ubiquitous prerequisite in visual prototyping, advertisement or digital preservation of objects. However, today's acquisition methods are typically designed for only a rather small range of material types. Furthermore, there is still a lack of accurate reconstruction methods for objects with a more complex surface reflectance behavior beyond diffuse reflectance. In addition to accurate acquisition techniques, the demand for creating large quantities of digital contents also pushes the focus towards fully automatic and highly efficient solutions that allow for masses of objects to be acquired as fast as possible. This thesis is dedicated to the investigation of basic components that allow an efficient, automatic acquisition process. We argue that such an efficient, automatic acquisition can be realized when material recognition "meets" 3D reconstruction and we will demonstrate that reliably recognizing the materials of the considered object allows a more efficient geometry acquisition. Therefore, the main objectives of this thesis are given by the development of novel, robust geometry acquisition techniques for surface materials beyond diffuse surface reflectance, and the development of novel, robust techniques for material recognition. In the context of 3D geometry acquisition, we introduce an improvement of structured light systems, which are capable of robustly acquiring objects ranging from diffuse surface reflectance to even specular surface reflectance with a sufficient diffuse component. We demonstrate that the resolution of the reconstruction can be increased significantly for multi-camera, multi-projector structured light systems by using overlappings of patterns that have been projected under different projector poses. As the reconstructions obtained by applying such triangulation-based techniques still contain high-frequency noise due to inaccurately localized correspondences established for images acquired under different viewpoints, we furthermore introduce a novel geometry acquisition technique that complements the structured light system with additional photometric normals and results in significantly more accurate reconstructions. In addition, we also present a novel method to acquire the 3D shape of mirroring objects with complex surface geometry. The aforementioned investigations on 3D reconstruction are accompanied by the development of novel tools for reliable material recognition which can be used in an initial step to recognize the present surface materials and, hence, to efficiently select the subsequently applied appropriate acquisition techniques based on these classified materials. In the scope of this thesis, we therefore focus on material recognition for scenarios with controlled illumination as given in lab environments as well as scenarios with natural illumination that are given in photographs of typical daily life scenes. Finally, based on the techniques developed in this thesis, we provide novel concepts towards efficient, automatic acquisition systems

GPU data structures for graphics and vision

Graphics hardware has in recent years become increasingly programmable, and its programming APIs use the stream processor model to expose massive parallelization to the programmer. Unfortunately, the inherent restrictions of the stream processor model, used by the GPU in order to maintain high performance, often pose a problem in porting CPU algorithms for both video and volume processing to graphics hardware. Serial data dependencies which accelerate CPU processing are counterproductive for the data-parallel GPU. This thesis demonstrates new ways for tackling well-known problems of large scale video/volume analysis. In some instances, we enable processing on the restricted hardware model by re-introducing algorithms from early computer graphics research. On other occasions, we use newly discovered, hierarchical data structures to circumvent the random-access read/fixed write restriction that had previously kept sophisticated analysis algorithms from running solely on graphics hardware. For 3D processing, we apply known game graphics concepts such as mip-maps, projective texturing, and dependent texture lookups to show how video/volume processing can benefit algorithmically from being implemented in a graphics API. The novel GPU data structures provide drastically increased processing speed, and lift processing heavy operations to real-time performance levels, paving the way for new and interactive vision/graphics applications.Graphikhardware wurde in den letzen Jahren immer weiter programmierbar. Ihre APIs verwenden das Streamprozessor-Modell, um die massive Parallelisierung auch für den Programmierer verfügbar zu machen. Leider folgen aus dem strikten Streamprozessor-Modell, welches die GPU für ihre hohe Rechenleistung benötigt, auch Hindernisse in der Portierung von CPU-Algorithmen zur Video- und Volumenverarbeitung auf die GPU. Serielle Datenabhängigkeiten beschleunigen zwar CPU-Verarbeitung, sind aber für die daten-parallele GPU kontraproduktiv . Diese Arbeit präsentiert neue Herangehensweisen für bekannte Probleme der Video- und Volumensverarbeitung. Teilweise wird die Verarbeitung mit Hilfe von modifizierten Algorithmen aus der frühen Computergraphik-Forschung an das beschränkte Hardwaremodell angepasst. Anderswo helfen neu entdeckte, hierarchische Datenstrukturen beim Umgang mit den Schreibzugriff-Restriktionen die lange die Portierung von komplexeren Bildanalyseverfahren verhindert hatten. In der 3D-Verarbeitung nutzen wir bekannte Konzepte aus der Computerspielegraphik wie Mipmaps, projektive Texturierung, oder verkettete Texturzugriffe, und zeigen auf welche Vorteile die Video- und Volumenverarbeitung aus hardwarebeschleunigter Graphik-API-Implementation ziehen kann. Die präsentierten GPU-Datenstrukturen bieten drastisch schnellere Verarbeitung und heben rechenintensive Operationen auf Echtzeit-Niveau. Damit werden neue, interaktive Bildverarbeitungs- und Graphik-Anwendungen möglich

Utilisation de miroirs dans un système de reconstruction interactif

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

Rééclairage par génération de cartes de normales en composition vidéo numérique

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

Towards 3D Scanning from Digital Images by Novice Users

The uptake of hobbyist 3D printers is being held back, in part, due to the barriers associated with creating a computer model to be printed. One way of creating such a computer model is to take a 3D scan of a pre-existing object using multiple digital images of the object showing the object from different points of view. This document details one way of doing this, with particular emphasis on camera calibration: the process of estimating camera parameters for the camera that took an image. In common calibration scenarios, multiple images are used where it is assumed that the internal parameters, such as zoom and focus settings, are fixed between images and the relative placement of the camera between images needs to be estimated. This is not ideal for a novice doing 3D scanning with a “point and shoot” camera where these internal parameters may not have been held fixed between images. A common coordinate system between images with a known relationship to real-world measurements is also desirable. Additionally, in some 3D scanning scenarios that use digital images, where it is expected that a trained individual will be doing the photography and internal settings can be held constant throughout the process, the images used for doing the calibration are different from those that are used to do the object capture. A technique has been developed to overcome these shortcomings. It uses a known printed sheet of paper, called the calibration sheet, that the object to be scanned sits on so that object acquisition and camera calibration can be done from the same image. Each image is processed independently with reference to the known size of the calibration sheet so the output is automatically to scale and minor camera calibration errors with one image do not propagate and affect estimates of camera calibration parameters for other images. The calibration process developed is also one that will work where large parts of the calibration sheet are obscured

Interactive mixed reality rendering in a distributed ray tracing framework

The recent availability of interactive ray tracing opened the way for new applications and for improving existing ones in terms of quality. Since today CPUs are still too slow for this purpose, the necessary computing power is obtained by connecting a number of machines and using distributed algorithms. Mixed reality rendering - the realm of convincingly combining real and virtual parts to a new composite scene - needs a powerful rendering method to obtain a photorealistic result. The ray tracing algorithm thus provides an excellent basis for photorealistic rendering and also advantages over other methods. It is worth to explore its abilities for interactive mixed reality rendering. This thesis shows the applicability of interactive ray tracing for mixed (MR) and augmented reality (AR) applications on the basis of the OpenRT framework. Two extensions to the OpenRT system are introduced and serve as basic building blocks: streaming video textures and in-shader AR view compositing. Streaming video textures allow for inclusion of the real world into interactive applications in terms of imagery. The AR view compositing mechanism is needed to fully exploit the advantages of modular shading in a ray tracer. A number of example applications from the entire spectrum of the Milgram Reality-Virtuality continuum illustrate the practical implications. An implementation of a classic AR scenario, inserting a virtual object into live video, shows how a differential rendering method can be used in combination with a custom build real-time lightprobe device to capture the incident light and include it into the rendering process to achieve convincing shading and shadows. Another field of mixed reality rendering is the insertion of real actors into a virtual scene in real-time. Two methods - video billboards and a live 3D visual hull reconstruction - are discussed. The implementation of live mixed reality systems is based on a number of technologies beside rendering and a comprehensive understanding of related methods and hardware is necessary. Large parts of this thesis hence deal with the discussion of technical implementations and design alternatives. A final summary discusses the benefits and drawbacks of interactive ray tracing for mixed reality rendering.Die Verfügbarkeit von interaktivem Ray-Tracing ebnet den Weg für neue Anwendungen, aber auch für die Verbesserung der Qualität bestehener Methoden. Da die heute verfügbaren CPUs noch zu langsam sind, ist es notwendig, mehrere Maschinen zu verbinden und verteilte Algorithmen zu verwenden. Mixed Reality Rendering - die Technik der überzeugenden Kombination von realen und synthetischen Teilen zu einer neuen Szene - braucht eine leistungsfähige Rendering-Methode um photorealistische Ergebnisse zu erzielen. Der Ray-Tracing-Algorithmus bietet hierfür eine exzellente Basis, aber auch Vorteile gegenüber anderen Methoden. Es ist naheliegend, die Möglichkeiten von Ray-Tracing für Mixed-Reality-Anwendungen zu erforschen. Diese Arbeit zeigt die Anwendbarkeit von interaktivem Ray-Tracing für Mixed-Reality (MR) und Augmented-Reality (AR) Anwendungen anhand des OpenRT-Systems. Zwei Erweiterungen dienen als Grundbausteine: Videotexturen und In-Shader AR View Compositing. Videotexturen erlauben die reale Welt in Form von Bildern in den Rendering-Prozess mit einzubeziehen. Der View-Compositing-Mechanismus is notwendig um die Modularität einen Ray-Tracers voll auszunutzen. Eine Reihe von Beispielanwendungen von beiden Enden des Milgramschen Reality-Virtuality-Kontinuums verdeutlichen die praktischen Aspekte. Eine Implementierung des klassischen AR-Szenarios, das Einfügen eines virtuellen Objektes in eine Live-Übertragung zeigt, wie mittels einer Differential Rendering Methode und einem selbstgebauten Gerät zur Erfassung des einfallenden Lichts realistische Beleuchtung und Schatten erzielt werden können. Ein anderer Anwendungsbereich ist das Einfügen einer realen Person in eine künstliche Szene. Hierzu werden zwei Methoden besprochen: Video-Billboards und eine interaktive 3D Rekonstruktion. Da die Implementierung von Mixed-Reality-Anwendungen Kentnisse und Verständnis einer ganzen Reihe von Technologien nebem dem eigentlichen Rendering voraus setzt, ist eine Diskussion der technischen Grundlagen ein wesentlicher Bestandteil dieser Arbeit. Dies ist notwenig, um die Entscheidungen für bestimmte Designalternativen zu verstehen. Den Abschluss bildet eine Diskussion der Vor- und Nachteile von interaktivem Ray-Tracing für Mixed Reality Anwendungen

Interactive mixed reality rendering in a distributed ray tracing framework

The recent availability of interactive ray tracing opened the way for new applications and for improving existing ones in terms of quality. Since today CPUs are still too slow for this purpose, the necessary computing power is obtained by connecting a number of machines and using distributed algorithms. Mixed reality rendering - the realm of convincingly combining real and virtual parts to a new composite scene - needs a powerful rendering method to obtain a photorealistic result. The ray tracing algorithm thus provides an excellent basis for photorealistic rendering and also advantages over other methods. It is worth to explore its abilities for interactive mixed reality rendering. This thesis shows the applicability of interactive ray tracing for mixed (MR) and augmented reality (AR) applications on the basis of the OpenRT framework. Two extensions to the OpenRT system are introduced and serve as basic building blocks: streaming video textures and in-shader AR view compositing. Streaming video textures allow for inclusion of the real world into interactive applications in terms of imagery. The AR view compositing mechanism is needed to fully exploit the advantages of modular shading in a ray tracer. A number of example applications from the entire spectrum of the Milgram Reality-Virtuality continuum illustrate the practical implications. An implementation of a classic AR scenario, inserting a virtual object into live video, shows how a differential rendering method can be used in combination with a custom build real-time lightprobe device to capture the incident light and include it into the rendering process to achieve convincing shading and shadows. Another field of mixed reality rendering is the insertion of real actors into a virtual scene in real-time. Two methods - video billboards and a live 3D visual hull reconstruction - are discussed. The implementation of live mixed reality systems is based on a number of technologies beside rendering and a comprehensive understanding of related methods and hardware is necessary. Large parts of this thesis hence deal with the discussion of technical implementations and design alternatives. A final summary discusses the benefits and drawbacks of interactive ray tracing for mixed reality rendering.Die Verfügbarkeit von interaktivem Ray-Tracing ebnet den Weg für neue Anwendungen, aber auch für die Verbesserung der Qualität bestehener Methoden. Da die heute verfügbaren CPUs noch zu langsam sind, ist es notwendig, mehrere Maschinen zu verbinden und verteilte Algorithmen zu verwenden. Mixed Reality Rendering - die Technik der überzeugenden Kombination von realen und synthetischen Teilen zu einer neuen Szene - braucht eine leistungsfähige Rendering-Methode um photorealistische Ergebnisse zu erzielen. Der Ray-Tracing-Algorithmus bietet hierfür eine exzellente Basis, aber auch Vorteile gegenüber anderen Methoden. Es ist naheliegend, die Möglichkeiten von Ray-Tracing für Mixed-Reality-Anwendungen zu erforschen. Diese Arbeit zeigt die Anwendbarkeit von interaktivem Ray-Tracing für Mixed-Reality (MR) und Augmented-Reality (AR) Anwendungen anhand des OpenRT-Systems. Zwei Erweiterungen dienen als Grundbausteine: Videotexturen und In-Shader AR View Compositing. Videotexturen erlauben die reale Welt in Form von Bildern in den Rendering-Prozess mit einzubeziehen. Der View-Compositing-Mechanismus is notwendig um die Modularität einen Ray-Tracers voll auszunutzen. Eine Reihe von Beispielanwendungen von beiden Enden des Milgramschen Reality-Virtuality-Kontinuums verdeutlichen die praktischen Aspekte. Eine Implementierung des klassischen AR-Szenarios, das Einfügen eines virtuellen Objektes in eine Live-Übertragung zeigt, wie mittels einer Differential Rendering Methode und einem selbstgebauten Gerät zur Erfassung des einfallenden Lichts realistische Beleuchtung und Schatten erzielt werden können. Ein anderer Anwendungsbereich ist das Einfügen einer realen Person in eine künstliche Szene. Hierzu werden zwei Methoden besprochen: Video-Billboards und eine interaktive 3D Rekonstruktion. Da die Implementierung von Mixed-Reality-Anwendungen Kentnisse und Verständnis einer ganzen Reihe von Technologien nebem dem eigentlichen Rendering voraus setzt, ist eine Diskussion der technischen Grundlagen ein wesentlicher Bestandteil dieser Arbeit. Dies ist notwenig, um die Entscheidungen für bestimmte Designalternativen zu verstehen. Den Abschluss bildet eine Diskussion der Vor- und Nachteile von interaktivem Ray-Tracing für Mixed Reality Anwendungen