26 research outputs found

    OmniSCV: An omnidirectional synthetic image generator for computer vision

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    Omnidirectional and 360º images are becoming widespread in industry and in consumer society, causing omnidirectional computer vision to gain attention. Their wide field of view allows the gathering of a great amount of information about the environment from only an image. However, the distortion of these images requires the development of specific algorithms for their treatment and interpretation. Moreover, a high number of images is essential for the correct training of computer vision algorithms based on learning. In this paper, we present a tool for generating datasets of omnidirectional images with semantic and depth information. These images are synthesized from a set of captures that are acquired in a realistic virtual environment for Unreal Engine 4 through an interface plugin. We gather a variety of well-known projection models such as equirectangular and cylindrical panoramas, different fish-eye lenses, catadioptric systems, and empiric models. Furthermore, we include in our tool photorealistic non-central-projection systems as non-central panoramas and non-central catadioptric systems. As far as we know, this is the first reported tool for generating photorealistic non-central images in the literature. Moreover, since the omnidirectional images are made virtually, we provide pixel-wise information about semantics and depth as well as perfect knowledge of the calibration parameters of the cameras. This allows the creation of ground-truth information with pixel precision for training learning algorithms and testing 3D vision approaches. To validate the proposed tool, different computer vision algorithms are tested as line extractions from dioptric and catadioptric central images, 3D Layout recovery and SLAM using equirectangular panoramas, and 3D reconstruction from non-central panoramas

    Enhancing 3D Visual Odometry with Single-Camera Stereo Omnidirectional Systems

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    We explore low-cost solutions for efficiently improving the 3D pose estimation problem of a single camera moving in an unfamiliar environment. The visual odometry (VO) task -- as it is called when using computer vision to estimate egomotion -- is of particular interest to mobile robots as well as humans with visual impairments. The payload capacity of small robots like micro-aerial vehicles (drones) requires the use of portable perception equipment, which is constrained by size, weight, energy consumption, and processing power. Using a single camera as the passive sensor for the VO task satisfies these requirements, and it motivates the proposed solutions presented in this thesis. To deliver the portability goal with a single off-the-shelf camera, we have taken two approaches: The first one, and the most extensively studied here, revolves around an unorthodox camera-mirrors configuration (catadioptrics) achieving a stereo omnidirectional system (SOS). The second approach relies on expanding the visual features from the scene into higher dimensionalities to track the pose of a conventional camera in a photogrammetric fashion. The first goal has many interdependent challenges, which we address as part of this thesis: SOS design, projection model, adequate calibration procedure, and application to VO. We show several practical advantages for the single-camera SOS due to its complete 360-degree stereo views, that other conventional 3D sensors lack due to their limited field of view. Since our omnidirectional stereo (omnistereo) views are captured by a single camera, a truly instantaneous pair of panoramic images is possible for 3D perception tasks. Finally, we address the VO problem as a direct multichannel tracking approach, which increases the pose estimation accuracy of the baseline method (i.e., using only grayscale or color information) under the photometric error minimization as the heart of the “direct” tracking algorithm. Currently, this solution has been tested on standard monocular cameras, but it could also be applied to an SOS. We believe the challenges that we attempted to solve have not been considered previously with the level of detail needed for successfully performing VO with a single camera as the ultimate goal in both real-life and simulated scenes

    Combining omnidirectional vision with polarization vision for robot navigation

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    La polarisation est le phénomène qui décrit les orientations des oscillations des ondes lumineuses qui sont limitées en direction. La lumière polarisée est largement utilisée dans le règne animal,à partir de la recherche de nourriture, la défense et la communication et la navigation. Le chapitre (1) aborde brièvement certains aspects importants de la polarisation et explique notre problématique de recherche. Nous visons à utiliser un capteur polarimétrique-catadioptrique car il existe de nombreuses applications qui peuvent bénéficier d'une telle combinaison en vision par ordinateur et en robotique, en particulier pour l'estimation d'attitude et les applications de navigation. Le chapitre (2) couvre essentiellement l'état de l'art de l'estimation d'attitude basée sur la vision.Quand la lumière non-polarisée du soleil pénètre dans l'atmosphère, l'air entraine une diffusion de Rayleigh, et la lumière devient partiellement linéairement polarisée. Le chapitre (3) présente les motifs de polarisation de la lumière naturelle et couvre l'état de l'art des méthodes d'acquisition des motifs de polarisation de la lumière naturelle utilisant des capteurs omnidirectionnels (par exemple fisheye et capteurs catadioptriques). Nous expliquons également les caractéristiques de polarisation de la lumière naturelle et donnons une nouvelle dérivation théorique de son angle de polarisation.Notre objectif est d'obtenir une vue omnidirectionnelle à 360 associée aux caractéristiques de polarisation. Pour ce faire, ce travail est basé sur des capteurs catadioptriques qui sont composées de surfaces réfléchissantes et de lentilles. Généralement, la surface réfléchissante est métallique et donc l'état de polarisation de la lumière incidente, qui est le plus souvent partiellement linéairement polarisée, est modifiée pour être polarisée elliptiquement après réflexion. A partir de la mesure de l'état de polarisation de la lumière réfléchie, nous voulons obtenir l'état de polarisation incident. Le chapitre (4) propose une nouvelle méthode pour mesurer les paramètres de polarisation de la lumière en utilisant un capteur catadioptrique. La possibilité de mesurer le vecteur de Stokes du rayon incident est démontré à partir de trois composants du vecteur de Stokes du rayon réfléchi sur les quatre existants.Lorsque les motifs de polarisation incidents sont disponibles, les angles zénithal et azimutal du soleil peuvent être directement estimés à l'aide de ces modèles. Le chapitre (5) traite de l'orientation et de la navigation de robot basées sur la polarisation et différents algorithmes sont proposés pour estimer ces angles dans ce chapitre. A notre connaissance, l'angle zénithal du soleil est pour la première fois estimé dans ce travail à partir des schémas de polarisation incidents. Nous proposons également d'estimer l'orientation d'un véhicule à partir de ces motifs de polarisation.Enfin, le travail est conclu et les possibles perspectives de recherche sont discutées dans le chapitre (6). D'autres exemples de schémas de polarisation de la lumière naturelle, leur calibrage et des applications sont proposées en annexe (B).Notre travail pourrait ouvrir un accès au monde de la vision polarimétrique omnidirectionnelle en plus des approches conventionnelles. Cela inclut l'orientation bio-inspirée des robots, des applications de navigation, ou bien la localisation en plein air pour laquelle les motifs de polarisation de la lumière naturelle associés à l'orientation du soleil à une heure précise peuvent aboutir à la localisation géographique d'un véhiculePolarization is the phenomenon that describes the oscillations orientations of the light waves which are restricted in direction. Polarized light has multiple uses in the animal kingdom ranging from foraging, defense and communication to orientation and navigation. Chapter (1) briefly covers some important aspects of polarization and explains our research problem. We are aiming to use a polarimetric-catadioptric sensor since there are many applications which can benefit from such combination in computer vision and robotics specially robot orientation (attitude estimation) and navigation applications. Chapter (2) mainly covers the state of art of visual based attitude estimation.As the unpolarized sunlight enters the Earth s atmosphere, it is Rayleigh-scattered by air, and it becomes partially linearly polarized. This skylight polarization provides a signi cant clue to understanding the environment. Its state conveys the information for obtaining the sun orientation. Robot navigation, sensor planning, and many other applications may bene t from using this navigation clue. Chapter (3) covers the state of art in capturing the skylight polarization patterns using omnidirectional sensors (e.g fisheye and catadioptric sensors). It also explains the skylight polarization characteristics and gives a new theoretical derivation of the skylight angle of polarization pattern. Our aim is to obtain an omnidirectional 360 view combined with polarization characteristics. Hence, this work is based on catadioptric sensors which are composed of reflective surfaces and lenses. Usually the reflective surface is metallic and hence the incident skylight polarization state, which is mostly partially linearly polarized, is changed to be elliptically polarized after reflection. Given the measured reflected polarization state, we want to obtain the incident polarization state. Chapter (4) proposes a method to measure the light polarization parameters using a catadioptric sensor. The possibility to measure the incident Stokes is proved given three Stokes out of the four reflected Stokes. Once the incident polarization patterns are available, the solar angles can be directly estimated using these patterns. Chapter (5) discusses polarization based robot orientation and navigation and proposes new algorithms to estimate these solar angles where, to the best of our knowledge, the sun zenith angle is firstly estimated in this work given these incident polarization patterns. We also propose to estimate any vehicle orientation given these polarization patterns. Finally the work is concluded and possible future research directions are discussed in chapter (6). More examples of skylight polarization patterns, their calibration, and the proposed applications are given in appendix (B). Our work may pave the way to move from the conventional polarization vision world to the omnidirectional one. It enables bio-inspired robot orientation and navigation applications and possible outdoor localization based on the skylight polarization patterns where given the solar angles at a certain date and instant of time may infer the current vehicle geographical location.DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

    Noncentral catadioptric systems with quadric mirrors : geometry and calibration

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    Tese de doutoramento em Engenharia Electrotécnica (Informática) apresentada à Faculdade de Ciências e Tecnologia da Universidade de CoimbraNesta dissertação de doutoramento estudamos e analisamos a geometria dos sistema catadióptricos não-centrais compostos por uma câmara pinhole ou ortográfica e um espelho curvo, cuja forma é uma quádrica não degenerada, incluindo elipsóides, que podem ser esferas, hiperbolóides e parabolóides. A geometria destes sistemas de visão é parameterizada, analisando o fenómeno de formação da imagem, e é composta pelos parâmetros intrínsecos da câmara, os parâmetros da superfície do espelho e a posição e orientação da câmara em relação ao espelho e ao sistema de referência do mundo. A formação da imagem é estudada numa perspectiva puramente geométrica, focando principalmente o modelo de projecção e a calibração do sistema de visão. As principais contribuições deste trabalho incluem a demonstração de que num sistema catadióptrico não-central com um câmara em perspectiva e uma quádrica não degenerada, o ponto de reflexão na superfície do espelho (projectando na imagem qualquer ponto 3D do mundo) pertence a uma curva quártica que é dada pela intersecção de duas superfícies quádricas. O correspondente modelo de projecção é também desenvolvido e é expresso através de uma equação não linear implícita, dependente de um único parâmetro. Relativamente `a calibração destes sistemas de visão, foi desenvolvido um método de calibração, assumindo o conhecimento dos parâmetros intrínsecos da câmara em perspectiva e de um conjunto de pontos 3D expressos em coordenadas locais (estrutura 3D do mundo). Informação acerca do contorno aparente do espelho é também usada para melhorar a precisão da estimação. Um outro método de calibração é proposto, assumindo uma calibração prévia do sistema no sentido de um modelo geral de câmara (correspondências entre pontos na imagem e raios incidentes no espaço). Adicionalmente, a posição e orientação (pose) da câmara em relação ao espelho e ao sistema de referência do mundo são estimadas usando métricas algébricas e equações lineares (escritas para um método de calibração que também é apresentado). Considera-se a câmara como pré-calibrada. São desenvolvidas e apresentadas experiências com simulações extensivas e também com imagens reais de forma a testar a robustez e precisão dos métodos apresentados. As principais conclusões apontam para o facto de estes sistemas de visão serem altamente não lineares e a sua calibração ser possível com boa precisão, embora difícil de alcançar com precisão muito elevada, especialmente se o sistema de visão tem como objectivo aplicações direccionadas para a precisão. Apesar disso, pode observar-se que a informação da estrutura do mundo pode ser complementada com informação adicional, tal como o contorno aparente da quádrica, de forma a melhorar a qualidade dos resultados de calibração. Na verdade, o uso do contorno aparente do espelho pode, por si, melhorar drasticamente a precisão da estimação.In this PhD thesis we study and analyze the geometry of noncentral catadioptric systems composed by a pinhole or orthographic camera and a non-ruled quadric shaped mirror, that is to say an ellipsoid, which can be a sphere, a hyperboloid or a paraboloid surface. The geometry of these vision systems is parameterized by analyzing the image formation and is composed by the intrinsic parameters of the camera, the parameters of the mirror surface and the poses of the camera in relation to the mirror and to the world reference frames. Image formation is studied in a purely geometrical way, focusing mainly on the projection model and on the calibration of the vision system. The main contributions include the proof that in a noncentral catadioptric system with a perspective camera and a non degenerate quadric the reflection point on the surface (projecting any given 3D world point to the image) is on the quartic curve that is the intersection of two quadrics. The projection model related to the previous definition of the reflection point is also derived and is expressed as an implicit non linear function on a single unknown. In what concerns the calibration of these vision systems, we developed a calibration method assuming the knowledge of the intrinsic parameters of the perspective camera and of some 3D points in a local reference frame (structure) . Information about the apparent contour is also used to enhance the accuracy of the estimation. Another calibration method is proposed, assuming a previous calibration of the system in the sense of a general camera model (correspondences between image points and incident lines in space). Additionally, the camera-mirror and camera-world poses are estimated using algebraic metrics and linear equations (derived for a calibration method that is also presented). The camera is considered to be pre-calibrated. Experiments with extensive simulations and also using real images are performed to test the robustness and accuracy of the methods presented. The main conclusions are that these vision systems are highly non linear and that their calibration is possible with good accuracy but difficult to achieve with very high accuracy, specially if the vision system is aimed at being used for accuracy-driven applications. Nevertheless it is observed that structure of the world can be complemented with some additional information as the quadric apparent contour in order to improve the quality of the calibration results. Actually, the use of the apparent contour can dramatically improve the accuracy of the estimation

    Omnidirectional Light Field Analysis and Reconstruction

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    Digital photography exists since 1975, when Steven Sasson attempted to build the first digital camera. Since then the concept of digital camera did not evolve much: an optical lens concentrates light rays onto a focal plane where a planar photosensitive array transforms the light intensity into an electric signal. During the last decade a new way of conceiving digital photography emerged: a photography is the acquisition of the entire light ray field in a confined region of space. The main implication of this new concept is that a digital camera does not acquire a 2-D signal anymore, but a 5-D signal in general. Acquiring an image becomes more demanding in terms of memory and processing power; at the same time, it offers the users a new set of possibilities, like choosing dynamically the focal plane and the depth of field of the final digital photo. In this thesis we develop a complete mathematical framework to acquire and then reconstruct the omnidirectional light field around an observer. We also propose the design of a digital light field camera system, which is composed by several pinhole cameras distributed around a sphere. The choice is not casual, as we take inspiration from something already seen in nature: the compound eyes of common terrestrial and flying insects like the house fly. In the first part of the thesis we analyze the optimal sampling conditions that permit an efficient discrete representation of the continuous light field. In other words, we will give an answer to the question: how many cameras and what resolution are needed to have a good representation of the 4-D light field? Since we are dealing with an omnidirectional light field we use a spherical parametrization. The results of our analysis is that we need an irregular (i.e., not rectangular) sampling scheme to represent efficiently the light field. Then, to store the samples we use a graph structure, where each node represents a light ray and the edges encode the topology of the light field. When compared to other existing approaches our scheme has the favorable property of having a number of samples that scales smoothly for a given output resolution. The next step after the acquisition of the light field is to reconstruct a digital picture, which can be seen as a 2-D slice of the 4-D acquired light field. We interpret the reconstruction as a regularized inverse problem defined on the light field graph and obtain a solution based on a diffusion process. The proposed scheme has three main advantages when compared to the classic linear interpolation: it is robust to noise, it is computationally efficient and can be implemented in a distributed fashion. In the second part of the thesis we investigate the problem of extracting geometric information about the scene in the form of a depth map. We show that the depth information is encoded inside the light field derivatives and set up a TV-regularized inverse problem, which efficiently calculates a dense depth map of the scene while respecting the discontinuities at the boundaries of objects. The extracted depth map is used to remove visual and geometrical artifacts from the reconstruction when the light field is under-sampled. In other words, it can be used to help the reconstruction process in challenging situations. Furthermore, when the light field camera is moving temporally, we show how the depth map can be used to estimate the motion parameters between two consecutive acquisitions with a simple and effective algorithm, which does not require the computation nor the matching of features and performs only simple arithmetic operations directly in the pixel space. In the last part of the thesis, we introduce a novel omnidirectional light field camera that we call Panoptic. We obtain it by layering miniature CMOS imagers onto an hemispherical surface, which are then connected to a network of FPGAs. We show that the proposed mathematical framework is well suited to be embedded in hardware by demonstrating a real time reconstruction of an omnidirectional video stream at 25 frames per second

    Global Shipping Container Monitoring Using Machine Learning with Multi-Sensor Hubs and Catadioptric Imaging

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    We describe a framework for global shipping container monitoring using machine learning with multi-sensor hubs and infrared catadioptric imaging. A wireless mesh radio satellite tag architecture provides connectivity anywhere in the world which is a significant improvement to legacy methods. We discuss the design and testing of a low-cost long-wave infrared catadioptric imaging device and multi-sensor hub combination as an intelligent edge computing system that, when equipped with physics-based machine learning algorithms, can interpret the scene inside a shipping container to make efficient use of expensive communications bandwidth. The histogram of oriented gradients and T-channel (HOG+) feature as introduced for human detection on low-resolution infrared catadioptric images is shown to be effective for various mirror shapes designed to give wide volume coverage with controlled distortion. Initial results for through-metal communication with ultrasonic guided waves show promise using the Dynamic Wavelet Fingerprint Technique (DWFT) to identify Lamb waves in a complicated ultrasonic signal

    Vision Sensors and Edge Detection

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    Vision Sensors and Edge Detection book reflects a selection of recent developments within the area of vision sensors and edge detection. There are two sections in this book. The first section presents vision sensors with applications to panoramic vision sensors, wireless vision sensors, and automated vision sensor inspection, and the second one shows image processing techniques, such as, image measurements, image transformations, filtering, and parallel computing

    Kaleidoscopic imaging

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    Kaleidoscopes have a great potential in computational photography as a tool for redistributing light rays. In time-of-flight imaging the concept of the kaleidoscope is also useful when dealing with the reconstruction of the geometry that causes multiple reflections. This work is a step towards opening new possibilities for the use of mirror systems as well as towards making their use more practical. The focus of this work is the analysis of planar kaleidoscope systems to enable their practical applicability in 3D imaging tasks. We analyse important practical properties of mirror systems and develop a theoretical toolbox for dealing with planar kaleidoscopes. Based on this theoretical toolbox we explore the use of planar kaleidoscopes for multi-view imaging and for the acquisition of 3D objects. The knowledge of the mirrors positions is crucial for these multi-view applications. On the other hand, the reconstruction of the geometry of a mirror room from time-of-flight measurements is also an important problem. We therefore employ the developed tools for solving this problem using multiple observations of a single scene point.Kaleidoskope haben in der rechnergestützten Fotografie ein großes Anwendungspotenzial, da sie flexibel zur Umverteilung von Lichtstrahlen genutzt werden können. Diese Arbeit ist ein Schritt auf dem Weg zu neuen Einsatzmöglichkeiten von Spiegelsystemen und zu ihrer praktischen Anwendung. Das Hauptaugenmerk der Arbeit liegt dabei auf der Analyse planarer Spiegelsysteme mit dem Ziel, sie für Aufgaben in der 3D-Bilderzeugung praktisch nutzbar zu machen. Auch für die Time-of-flight-Technologie ist das Konzept des Kaleidoskops, wie in der Arbeit gezeigt wird, bei der Rekonstruktion von Mehrfachreflektionen erzeugender Geometrie von Nutzen. In der Arbeit wird ein theoretischer Ansatz entwickelt der die Analyse planarer Kaleidoskope stark vereinfacht. Mithilfe dieses Ansatzes wird der Einsatz planarer Spiegelsysteme im Multiview Imaging und bei der Erfassung von 3-D-Objekten untersucht. Das Wissen um die Spiegelpositionen innerhalb des Systems ist für diese Anwendungen entscheidend und erfordert die Entwicklung geeigneter Methoden zur Kalibrierung dieser Positionen. Ein ähnliches Problem tritt in Time-of-Flight Anwendungen bei der, oft unerwünschten, Aufnahme von Mehrfachreflektionen auf. Beide Problemstellungen lassen sich auf die Rekonstruktion der Geometrie eines Spiegelraums zurückführen, das mit Hilfe des entwickelten Ansatzes in allgemeinererWeise als bisher gelöst werden kann

    A novel approach to programmable imaging using MOEMS

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    New advancements in science are frequently sparked by the invention of new instruments. Possibly the most important scientific instrument of the past fifty years is the digital computer. Among the computers many uses and impacts, digital imaging has revolutionized images and photography, merging computer processing and optical images. In this thesis, we merge an additional reconfigurable micro-mechanical domain into the digital imaging system, introducing a novel imaging method called Programmable Imaging. With our imaging method, we selectively sample the object plane, by utilizing state-of-the-art Micro-Optical-Electrical-Mechanical Systems (MOEMS) of mirror arrays. The main concept is to use an array of tiny mirrors that have the ability to tilt in different directions. Each mirror acts as an “eye” which images a scene. The individual images from each mirror are then reassembled, such that all of the information is placed into a single image. By exact control of the mirrors, the object plane can be sampled in a desired fashion, such that post-processing effects, such as image distortion and digital zoom, that are currently performed in software can now be performed in real time in hardware as the image gets captured. It is important to note that even for different sampling or imaging functions, no hardware components or settings are changed in the system.In this work, we present our programmable imaging system prototype. The MOEMS chipset used in our prototype is the Lucent LambdaRouter mirror array. This device contains 256 individually-controlled micro-mirrors, which can be tilted on both the x and y axes ±8o. We describe the theoretical model of our system, including a system model, capacity model, and diffraction results. We experimentally prototype our programmable imaging system using both a single mirror, followed by multiple mirrors. With the single mirror imaging, we explore examples related to single projection systems and give details of our required mirror calibration. Using this technique, we show mosaic images, as well as images in which a single pixel was extracted for every mirror tilt. Using this single pixel approach, the greatest capabilities of our programmable imaging are realized. When using multiple mirrors to image an object, new features of our system are demonstrated. In this case, the object plane can be viewed from different perspectives. From these multi-perspective images, virtual 3-D images can be created. In addition, stereo depth estimation can be performed to calculate the distance between the object and the image plane. This depth measurement is significant, as the depth information is taken with only one image from only one camera.Ph.D., Electrical Engineering -- Drexel University, 200
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