53 research outputs found

    Calibration of smartphone’s rear dual camera system

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    This paper aims to calibrate smartphone’s rear dual camera system which is composed of two lenses, namely; wide-angle lens and telephoto lens. The proposed approach handles large sized images. Calibration was done by capturing 13 photos for a chessboard pattern from different exposure positions. First, photos were captured in dual camera mode. Then, for both wide-angle and telephoto lenses, image coordinates for node points of the chessboard were extracted. Afterwards, intrinsic, extrinsic, and lens distortion parameters for each lens were calculated. In order to enhance the accuracy of the calibration model, a constrained least-squares solution was applied. The applied constraint was that the relative extrinsic parameters of both wide-angle and telephoto lenses were set as constant regardless of the exposure position. Moreover, photos were rectified in order to eliminate the effect of lens distortion. For results evaluation, two oriented photos were chosen to perform a stereo-pair intersection. Then, the node points of the chessboard pattern were used as check points

    IMAGE DISTORTION CORRECTION FOR BIPRISM-BASED SINGLE-LENS STEREOVISION SYSTEM

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    Ph.DDOCTOR OF PHILOSOPH

    Locating regions of interest prior to X-ray imaging using stereo-photogrammetry

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    The research project aims at locating regions of interest (ROIs) on human subjects prior to X-ray imaging on the Lodox Statscan whole body imaging system

    Digital Multispectral Map Reconstruction Using Aerial Imagery

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    Advances made in the computer vision field allowed for the establishment of faster and more accurate photogrammetry techniques. Structure from Motion(SfM) is a photogrammetric technique focused on the digital spatial reconstruction of objects based on a sequence of images. The benefit of Unmanned Aerial Vehicle (UAV) platforms allowed the ability to acquire high fidelity imagery intended for environmental mapping. This way, UAV platforms became a heavily adopted method of survey. The combination of SfM and the recent improvements of Unmanned Aerial Vehicle (UAV) platforms granted greater flexibility and applicability, opening a new path for a new remote sensing technique aimed to replace more traditional and laborious approaches often associated with high monetary costs. The continued development of digital reconstruction software and advances in the field of computer processing allowed for a more affordable and higher resolution solution when compared to the traditional methods. The present work proposed a digital reconstruction algorithm based on images taken by a UAV platform inspired by the work made available by the open-source project OpenDroneMap. The aerial images are inserted in the computer vision program and several operations are applied to them, including detection and matching of features, point cloud reconstruction, meshing, and texturing, which results in a final product that represents the surveyed site. Additionally, from the study, it was concluded that an implementation which addresses the processing of thermal images was not integrated in the works of OpenDroneMap. By this point, their work was altered to allow for the reconstruction of thermal maps without sacrificing the resolution of the final model. Standard methods to process thermal images required a larger image footprint (or area of ground capture in a frame), the reason for this is that these types of images lack the presence of invariable features and by increasing the image’s footprint, the number of features present in each frame also rises. However, this method of image capture results in a lower resolution of the final product. The algorithm was developed using open-source libraries. In order to validate the obtained results, this model was compared to data obtained from commercial products, like Pix4D. Furthermore, due to circumstances brought about by the current pandemic, it was not possible to conduct a field study for the comparison and assessment of our results, as such the validation of the models was performed by verifying if the geographic location of the model was performed correctly and by visually assessing the generated maps.Avanços no campo da visão computacional permitiu o desenvolvimento de algoritmos mais eficientes de fotogrametria. Structure from Motion (SfM) é uma técnica de fotogrametria que tem como objetivo a reconstrução digital de objectos no espaço derivados de uma sequência de imagens. A característica importante que os Veículos Aérios não-tripulados (UAV) conseguem fornecer, a nível de mapeamento, é a sua capacidade de obter um conjunto de imagens de alta resolução. Devido a isto, UAV tornaram-se num dos métodos adotados no estudo de topografia. A combinação entre SfM e recentes avanços nos UAV permitiram uma melhor flexibilidade e aplicabilidade, permitindo deste modo desenvolver um novo método de Remote Sensing. Este método pretende substituir técnicas tradicionais, as quais estão associadas a mão-de-obra intensiva e a custos monetários elevados. Avanços contínuos feitos em softwares de reconstrução digital e no poder de processamento resultou em modelos de maior resolução e menos dispendiosos comparando a métodos tradicionais. O presente estudo propõe um algoritmo de reconstrução digital baseado em imagens obtidas através de UAV inspiradas no estudo disponibilizado pela OpenDroneMap. Estas imagens são inseridas no programa de visão computacional, onde várias operações são realizadas, incluindo: deteção e correspondência de caracteristicas, geração da point cloud, meshing e texturação dos quais resulta o produto final que representa o local em estudo. De forma complementar, concluiu-se que o trabalho da OpenDroneMap não incluia um processo de tratamento de imagens térmicas. Desta forma, alterações foram efetuadas que permitissem a criação de mapas térmicos sem sacrificar resolução do produto final, pois métodos típicos para processamento de imagens térmicas requerem uma área de captura maior, devido à falta de características invariantes neste tipo de imagens, o que leva a uma redução de resolução. Desta forma, o programa proposto foi desenvolvido através de bibliotecas open-source e os resultados foram comparados com modelos gerados através de software comerciais. Além do mais, devido à situação pandémica atual, não foi possível efetuar um estudo de campo para validar os modelos obtidos, como tal esta verificação foi feita através da correta localização geográfica do modelo, bem como avaliação visual dos modelos criados

    How to build a 2d and 3d aerial multispectral map?—all steps deeply explained

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    UIDB/04111/2020 PCIF/SSI/0102/2017 IF/00325/2015 UIDB/00066/2020The increased development of camera resolution, processing power, and aerial platforms helped to create more cost-efficient approaches to capture and generate point clouds to assist in scientific fields. The continuous development of methods to produce three-dimensional models based on two-dimensional images such as Structure from Motion (SfM) and Multi-View Stereopsis (MVS) allowed to improve the resolution of the produced models by a significant amount. By taking inspiration from the free and accessible workflow made available by OpenDroneMap, a detailed analysis of the processes is displayed in this paper. As of the writing of this paper, no literature was found that described in detail the necessary steps and processes that would allow the creation of digital models in two or three dimensions based on aerial images. With this, and based on the workflow of OpenDroneMap, a detailed study was performed. The digital model reconstruction process takes the initial aerial images obtained from the field survey and passes them through a series of stages. From each stage, a product is acquired and used for the following stage, for example, at the end of the initial stage a sparse reconstruction is produced, obtained by extracting features of the images and matching them, which is used in the following step, to increase its resolution. Additionally, from the analysis of the workflow, adaptations were made to the standard workflow in order to increase the compatibility of the developed system to different types of image sets. Particularly, adaptations focused on thermal imagery were made. Due to the low presence of strong features and therefore difficulty to match features across thermal images, a modification was implemented, so thermal models could be produced alongside the already implemented processes for multispectral and RGB image sets.publishersversionpublishe

    Stereo vision for facet type cameras

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    Ausgehend von den Facettenaugen der Insekten haben Wissenschaftler seit 10 Jahren viele künstliche Facettenaugensysteme erstellt, die auf der Multi-Apertur-Optik basieren. Im Vergleich zu den auf Single-Apertur-Optik basierenden Systemen sind diese Systeme kleiner und leichter. Außerdem haben solche Systeme ein großes Sichtfeld und eine hohe Empfindlichkeit. Das eCley (Electronic cluster eye) ist ein neues künstliches Facettenaugensystem, das Bilder mit Super-Pixel-Auflösung erstellen kann, welches vom Sehsystem der parasitären Wespe „Xenos Peckii“ inspiriert ist. Wegen seiner ausgezeichneten Fähigkeiten sind eCley-Systeme in den Bereichen ärztliche Untersuchung, Identitätsauthentifizierung, Roboternavigation und Flugkörperlenkung angewendet worden. Aber solche Anwendungen basieren nur auf der Datenverarbeitung im 2D-Bereich. Wenn jedoch mit einem eCley-System räumliche 3D-Daten erzeugt werden können, kann man nur mit eCley 3D-Rekonstruktion, Lokalisierung und Entfernungsmessung erledigen, die man vorher mit anderen Geräten durchführen musste. Zwar können je zwei horizontal benachbarte Mikrokameras im eCley als ein Stereo-Sehsystem genutzt werden, aber es ist nicht leicht, die räumlichen Informationen durch so kleine Kameras zu erhalten. Die von der Mikrokamera gemachten Fotos haben nur eine ziemlich niedrige Auflösung. Außerdem ist die Tiefenveränderung der Szene kleiner als 1 Pixel, wenn die Entfernung größer als 86mm ist, d.h. dass viele verbreitete Algorithmen zum Stereosehen mit eCley nicht gut funktionieren können. Um die verbreiteten Stereosehalgorithmen mit dem eCley besser anwenden zu können, wurde eine neue Methode dafür im Bereich des Subpixel-Stereosehen erstellt. Diese Methode basiert auf der positiven Eigenschaft des eCleys, dass die Kanten des Ziels im eCley sehr gut behalten werden können. Im Übergang zwischen Bilder benachbarter Mikrokameras gibt es zahlreiche Tiefeninformationen. Mit diesen Tiefeninformationen kann der entsprechende Subpixelabstand ausgerechnet werden. Danach kann die Entfernung des Ziels mit dem Subpixelabstand berechnet werden. Aufgrund der Struktur des eCleys haben wir in dieser Doktorarbeit ein mathematisches Modell des Stereosehens für eCley abgeleitet. Dazu werden die optische Ausrichtung und die geometrische Korrektur, die die Voraussetzungen zur präzisen Messung sind, diskutiert. Zum Schluss haben wir die Subpixel-Baseline-Methode, die auf der Helligkeit und den Gradienten basiert, und die Echtzeit-Messung für den Subpixelabstand, die auf der Eigenschaft der Kanten basiert, entwickelt. Um unsere Methode zu überprüfen, haben wir viele künstliche und reale Szenenbilder angewendet. Das Ergebnis zeigt, dass unsere Methode die Messung zum Subpixelabstand für Stereopixelpaare ausgezeichnet realisiert hat. Außerdem funktioniert diese Methode in vielen komplexen Umgebungen robust. Das bedeutet, dass die Methode die Fähigkeit des eCleys verbessert hat, die 3D-Umgebung zu erkennen. Das eCley kann daher in verschiedenen 3D-Anwendungsbereichen eingesetzt werden.In the last decade, scientists have put forth many artificial compound eye systems, inspired by the compound eyes of all kinds of insects. These systems, employing multi-aperture optical systems instead of single-aperture optical systems, provide many specific characteristics, such as small volume, light weight, large view, and high sensitivity. Electronic cluster eye (eCley) is a state-of-the-art artificial superposition compound eye with super resolution, which is inspired by a wasp parasite called the Xenos Peckii. Thanks to the inherent characteristics of eCley, it has successfully been applied to aspects of medical inspection, personal identification, bank safety, robot navigation, and missile guidance. However, all these applications only involve a two-dimensional image space, i.e., no three-dimensional (3D) information is provided. Conceiving of the ability of detecting 3D space information using eCley, the performances of 3D reconstruction, object position, and distance measurement will be obtained easily from the single eCley rather than requiring extra depth information devices. In practice, there is a big challenge to implementing 3D space information detection in the minimized eCley, although structures similar to stereo vision exist in each pair of adjacent channels. In the case of an imaging channel with short focal length and low resolution, the determination of the depth information not only is an ill-posed problem but also varies in the range of one pixel from quite near distance (≥86 mm), which restricts the applicability of popular stereo matching algorithms to eCley. Taking aim at this limitation, and with the goal of satisfying the real demands of applications in eCley, this thesis mainly studies a novel method of subpixel stereo vision for eCley. This method utilizes the significant property of object edges still retained in eCley, i.e., the transitional areas of edges contain rich information including the depths or distances of objects, to determine subpixel distances of the corresponding pixel pairs in the adjacent channels, to further obtain the objects' depth information by employing the triangle relationship. In the whole thesis, I mainly deduce the mathematical model of stereo vision in eCley theoretically based on its special structure, discuss the optical correction and geometric calibration that are essential to high precision measurement, study the implementation of methods of the subpixel baselines for each pixel pair based on intensity information and gradient information in transitional areas, and eventually implement real-time subpixel distance measurement for objects through these edge features. To verify the various methods adopted, and to analyze the precision of these methods, I employ an artificial synthetical stereo channel image and a large number of real images captured in diverse scenes in my experiments. The results from either a process or the whole method prove that the proposed methods efficiently implement stereo vision in eCley and the measurement of the subpixel distance of stereo pixel pairs. Through a sensitivity analysis with respect to illumination, object distances, and pixel positions, I verify that the proposed method also performs robustly in many scenes. This stereo vision method extends the ability of perceiving 3D information in eCley, and makes it applicable to more comprehensive fields such as 3D object position, distance measurement, and 3D reconstruction

    Towards a Unified Theory of Sensor Pattern Noise: An analysis of dark current, lens effects, and temperature bias in CMOS image sensors

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    Matching images to a discrete camera is of significance in forensic investigation. In the case of digital images, forensic matching is possible through the use of sensor noise present within every image. There exist misconceptions, however, around how this noise reacts under variables such as temperature and the use of different lens systems. This study aims to formulate a revised model of the additive noise for an image sensor to determine if a new method for matching images to sensors could be created which uses fewer resources than the existing methods, and takes into account a wider range of environmental conditions. Specifically, a revised noise model was needed to determine the effects of different lens systems and the impact of temperature on sensor noise. To determine the revised model, an updated literature search was conducted on the background theory relating to CMOS sensors, as the existing work focuses on CCD imaging sensors. This theory was then applied using six off the shelf CMOS imaging sensors with integrated lens systems. An image sensor was examined under scanning electron microscopy and through the use of Energydispersive x-ray spectroscopy the non-uniform structure of individual pixels was visually observed within the sensor. The lens systems were removed and made interchangeable through the use of a 3D printed camera housing. Lens effects were assessed by swapping lens systems between the cameras and using a pinhole lens to remove all optical effects. The temperature was controlled using an Arduino controlled Peltier plate device, and dark current images were obtained at different temperatures using a blackout lens. It was observed that dark current could be used to identify the temperature of the image sensor at the time of acquisition, contrary to the statements in existing literature that sensor pattern noise is temperature invariant. It was shown that the lens system contributes approximately a quarter of the signal power xii used for pattern matching between the image and sensor. Moreover, through the use of targeted signal processing methods and simple ”Goldilocks” filters processing times could be reduced by more than half by sacrificing precision without losing accuracy. This work indicates that sensor pattern noise, while already viable for forensic identification of images to a specific camera, can also be used for identification of an image to a specific lens system and an image sensors temperature. It has also shown that a tool using sensor pattern noise may have a viable future as a forensic method of triage when confronted with large image data sets. Such additional information could prove effective for forensic investigators, intelligence agencies and police when faced with any form of crime involving imaging technology such as fraud, child exploitation or terrorism.Thesis (Ph.D.) -- University of Adelaide, School of Electrical & Electronic Engineering, 201

    Pattern Recognition

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    A wealth of advanced pattern recognition algorithms are emerging from the interdiscipline between technologies of effective visual features and the human-brain cognition process. Effective visual features are made possible through the rapid developments in appropriate sensor equipments, novel filter designs, and viable information processing architectures. While the understanding of human-brain cognition process broadens the way in which the computer can perform pattern recognition tasks. The present book is intended to collect representative researches around the globe focusing on low-level vision, filter design, features and image descriptors, data mining and analysis, and biologically inspired algorithms. The 27 chapters coved in this book disclose recent advances and new ideas in promoting the techniques, technology and applications of pattern recognition
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