Hexagonal structure for intelligent vision

Using hexagonal grids to represent digital images have been studied for more than 40 years. Increased processing capabilities of graphic devices and recent improvements in CCD technology have made hexagonal sampling attractive for practical applications and brought new interests on this topic. The hexagonal structure is considered to be preferable to the rectangular structure due to its higher sampling efficiency, consistent connectivity and higher angular resolution and is even proved to be superior to square structure in many applications. Since there is no mature hardware for hexagonal-based image capture and display, square to hexagonal image conversion has to be done before hexagonal-based image processing. Although hexagonal image representation and storage has not yet come to a standard, experiments based on existing hexagonal coordinate systems have never ceased. In this paper, we firstly introduced general reasons that hexagonally sampled images are chosen for research. Then, typical hexagonal coordinates and addressing schemes, as well as hexagonal based image processing and applications, are fully reviewed. © 2005 IEEE

Error analysis and planning accuracy for dimensional measurement in active vision inspection

This paper discusses the effect of spatial quantization errors and displacement errors on the precision dimensional measurements for an edge segment. Probabilistic analysis in terms of the resolution of the image is developed for 2D quantization errors. Expressions for the mean and variance of these errors are developed. The probability density function of the quantization error is derived. The position and orientation errors of the active head are assumed to be normally distributed. A probabilistic analysis in terms of these errors is developed for the displacement errors. Through integrating the spatial quantization errors and the displacement errors, we can compute the total error in the active vision inspection system. Based on the developed analysis, we investigate whether a given set of sensor setting parameters in an active system is suitable to obtain a desired accuracy for specific dimensional measurements, and one can determine sensor positions and view directions which meet the necessary tolerance and accuracy of inspection.published_or_final_versio

UMA PROPOSTA PARA ADAPTAÇÃO DE UMA CÂMERA CCD NO ORTO-PROJETOR WILD AVIOPLAN OR 1 PARA DIGITALIZAR DIAPOSITIVOS

O objetivo deste trabalho é desenvolver e testar uma técnica para aproveitar o Ortoprojetor Wild Avioplan OR 1, adaptando nele uma câmera CCD para digitalizar diapositivos de fotografias aéreas 230 mm x 230mm.A câmera CCD é adaptada sobre o porta-placa do OR 1 e uma iluminação por baixo dessa placa se faz necessária. Os quadros capturados, justapostos, são posteriormente juntados para se obter a imagem da área total varrida pelo aparelho. Para tanto, desenvolveu-se: um suporte para a conexão da câmera CCD; um procedimento para orientação do sistema; um software para controlar o OR1; e um software para a captura automatizada e junção das imagens. Testes foram realizados e os resultados apresentados indicam a viabilidade do processo. Abstract This work aims at developing and testing a technique in which the Wild Avioplan OR 1 Orthoprojector is used, adapting a CCD camara to it, in order to digitalize slides of 230mm by 230mm air photographs. The CCD camara is adapted on the board-rack of the OR 1 and ilumination is made necessary under this board. The frames that werw captured and justaposed, are then gathered so that there can be na image of the total area run by the device. For that, we developed a support for the connection of the CCD camara; a procedure for the orientation of the system; a software to control the OR 1; and a software for the automatized capturing and gathering the images. Test were made and the results indicate the viability of this process

Corrélation de mesures sonar avec un modèle numérique de terrain

Ce papier présente une méthode de localisation d'engins sous-marins par mise en correspondance d'un banc de mesures bathymétriques délivrées par un sonar multifaisceau avec un modèle numérique de terrain (MNT). Cette mise en correspondance est réalisée par l'utilisation d'une extension des formules classiques de corrélation prenant en compte le fait que les données sonar ne sont pas échantillonnées de façon régulière dans l'espace de représentation du MNT. Le couplage de cet algorithme avec un estimateur de mouvement permet de réduire la dimension de l'espace de recherche. Les résultats obtenus avec un modèle réel de relief sous-marin illustrent les performances des algorithmes présentés

Three Dimensional Shape Reconstruction with Dual-camera Measurement Fusion

Recently, three-dimensional (3D) shape measurement technologies have been extensively researched in the fields such as computer science and medical engineering. They have been applied in various industries and commercial uses, including robot navigation, reverser engineering and face and gesture recognition. Optical 3D shape measurement is one of the most popular methods, which can be divided into two categories: passive 3D shape reconstruction and active 3D shape imaging. Passive 3D shape measurement techniques use cameras to capture the object with only ambient light. Stereo vision (SV) is one of the typical methods in passive 3D measurement approaches. This method uses two cameras to take photos of the scene from different viewpoints and extract the 3D information by establishing the correspondence between the photos captured. To translate the correspondence to the depth map, epipolar geometry is applied to determine the depth of each pixel. Active 3D shape imaging methods add diverse active light sources to project on the object and use the camera to capture the scene with pre-defined patterns on the object’s surface. The fringe projection profilometry (FPP) is a representative technique among active 3D reconstruction methods. It replaces one of the cameras in stereo vision with a projector, and projects the fringe patterns onto the object before the camera captures it. The depth map can be built via triangulations by analysing the phase difference between patterns distorted by the object’s surface and the original one. Those two mainstream techniques work alone in different scenarios and have various advantages and disadvantages. Active stereo vision (ASV) has excellent dynamic performance, yet its accuracy and spatial resolution are limited. On the other hand, 3D shape measurement methods like FPP have higher accuracy and speed; however, their dynamic performance varies depending on the codification schemes chosen. This thesis presents the research on developing a fusion method that contains both passive and active 3D shape reconstruction algorithms in one system to combine their advantages and reduce the budget of building a high-precision 3D shape measurement system with good dynamic performance. Specifically, in the thesis, we propose a fusion method that combines the epipolar geometry in ASV and triangulations in the FPP system by a specially designed cost function. This way, the information obtained from each system alone is combined, leading to better accuracy. Furthermore, the correlation of object surface is exploited with the autoregressive model to improve the precision of the fusion system. In addition, the expectation maximization framework is employed to address the issue of estimating variables with unknown parameters introduced by AR. Moreover, the fusion cost function derived before is embedded into the EM framework. Next, the message passing algorithm is applied to implement the EM efficiently on large image sizes. A factor graph is derived from fitting the EM approach. To implement belief propagation to solve the problem, it is divided into two sub-graphs: the E-Step factor graph and the M-Step factor graph. Based on two factor graphs, belief propagation is implemented on each of them to estimate the unknown parameters and EM messages. In the last iteration, the height of the object surface can be obtained with the forward and backward messages. Due to the consideration of the object’s surface correlation, the fusion system’s precision is further improved. Simulation and experimental results are presented at last to examine the performance of the proposed system. It is found that the accuracy of the depth map of the fusion method is improved compared to fringe projection profilometry or stereo vision system alone. The limitations of the current study are discussed, and potential future work is presented

Novel Approaches in Structured Light Illumination

Among the various approaches to 3-D imaging, structured light illumination (SLI) is widely spread. SLI employs a pair of digital projector and digital camera such that the correspondences can be found based upon the projecting and capturing of a group of designed light patterns. As an active sensing method, SLI is known for its robustness and high accuracy. In this dissertation, I study the phase shifting method (PSM), which is one of the most employed strategy in SLI. And, three novel approaches in PSM have been proposed in this dissertation. First, by regarding the design of patterns as placing points in an N-dimensional space, I take the phase measuring profilometry (PMP) as an example and propose the edge-pattern strategy which achieves maximum signal to noise ratio (SNR) for the projected patterns. Second, I develop a novel period information embedded pattern strategy for fast, reliable 3-D data acquisition and reconstruction. The proposed period coded phase shifting strategy removes the depth ambiguity associated with traditional phase shifting patterns without reducing phase accuracy or increasing the number of projected patterns. Thus, it can be employed for high accuracy realtime 3-D system. Then, I propose a hybrid approach for high quality 3-D reconstructions with only a small number of illumination patterns by maximizing the use of correspondence information from the phase, texture, and modulation data derived from multi-view, PMP-based, SLI images, without rigorously synchronizing the cameras and projectors and calibrating the device gammas. Experimental results demonstrate the advantages of the proposed novel strategies for 3-D SLI systems

Enhanced Reality Visualization in a Surgical Environment

Enhanced reality visualization is the process of enhancing an image by adding to it information which is not present in the original image. A wide variety of information can be added to an image ranging from hidden lines or surfaces to textual or iconic data about a particular part of the image. Enhanced reality visualization is particularly well suited to neurosurgery. By rendering brain structures which are not visible, at the correct location in an image of a patient's head, the surgeon is essentially provided with X-ray vision. He can visualize the spatial relationship between brain structures before he performs a craniotomy and during the surgery he can see what's under the next layer before he cuts through. Given a video image of the patient and a three dimensional model of the patient's brain the problem enhanced reality visualization faces is to render the model from the correct viewpoint and overlay it on the original image. The relationship between the coordinate frames of the patient, the patient's internal anatomy scans and the image plane of the camera observing the patient must be established. This problem is closely related to the camera calibration problem. This report presents a new approach to finding this relationship and develops a system for performing enhanced reality visualization in a surgical environment. Immediately prior to surgery a few circular fiducials are placed near the surgical site. An initial registration of video and internal data is performed using a laser scanner. Following this, our method is fully automatic, runs in nearly real-time, is accurate to within a pixel, allows both patient and camera motion, automatically corrects for changes to the internal camera parameters (focal length, focus, aperture, etc.) and requires only a single image

Calibração e aplicação de camaras digitais

Orientador: Quintino DalmolinCo-orientador: João Bosco LugnaniDissertação (mestrado) - Universidade Federal do ParanaResumo: Com o desenvolvimento tecnológico que caracteriza algumas áreas do conhecimento, como por exemplo a visão de máquina e a fotogrametria digital, a utilização de imagens adquiridas por câmaras digitais vem crescendo consideravelmente em função do seu potencial de aplicação. Em consequência disto, grandes esforços são feitos no sentido de melhorar a qualidade das informações métricas, o que só é possível quando as fontes de erros, inerentes ao processo de aquisição da imagem por uma câmara digital, são conhecidas. E neste contexto que são abordados, neste trabalho, os problemas que ocorrem durante o processo de aquisição destas imagens, bem como algumas técnicas de calibração de câmaras digitais, além de procedimentos de parametrização. Foram implementados programas que possibilitaram calibrar a câmara digital HR-600 da Universidade Federal do Paraná, e das técnicas utilizadas, aquela que forneceu os melhores resultados foi a auto-calibração por feixes de raios, onde foram parametrizados os elementos f, x0 , y0 , K1, A e B. Finalmente, para ilustrar um possível campo de aplicação de tais câmaras, apresenta-se uma concepção para o desenvolvimento de um Sistema de Controle de Qualidade, por fotogrametria digital.Abstract: Due to the wide range of applications of the digital camera, its use has been increasing considerably with the development of new technologies, as in the areas of machine vision and digital phothogrammetry. As a result, it is necessary to improve the accuracy of the geometric measurements taken by the digital cameras. This is possible only if the source of erros that impairs the quality of the image acquired by digital cameras is known. This work approaches some problems that occur during the acquisition process of the images as well in some calibration techniques. Some computational programs were developed and implanted and they have made it possible to calibrate the HR-600 digital camera, at the UFPR. Better results were obtained with the self-calibration by bundle adjustment with additional parameters f, x0 , y0 ,k1 , A and B. At last, this study shows the principles for the development of a quality-control system using digital photogrammetry, so as to ilustrate potential applications

Error analysis and system improvements in phase-stepping methods for photoelasticity.

In the past automated photoelasticity has been demonstrated to be one of the most efficient technique for determining the complete state of stress in a 3-D component. However, the measurement accuracy, which depends on many aspects of both the theoretical foundations and experimental procedures, has not been studied properly. The objective of this thesis is to reveal the intrinsic properties of the errors, provide methods for reducing them and finally improve the system accuracy. A general formulation for a polariscope with all the optical elements in an arbitrary orientation was deduced using the method of Mueller Matrices. The deduction of this formulation indicates an inherent connectivity among the optical elements and gives a knowledge of the errors. In addition, this formulation also shows a common foundation among the photoelastic techniques, consequently, these techniques share many common error sources. The phase-stepping system proposed by Patterson and Wang was used as an examplar to analyse the errors and provide the proposed improvements. This system can be divided into four parts according to their function, namely the optical system, light source, image acquisition equipment and image analysis software. All the possible error sources were investigated separately and the methods for reducing the influence of the errors and improving the system accuracy are presented. To identify the contribution of each possible error to the final system output, a model was used to simulate the errors and analyse their consequences. Therefore the contribution to the results from different error sources can be estimated quantitatively and finally the accuracy of the systems can be improved. For a conventional polariscope, the system accuracy can be as high as 99.23% for the fringe order and the error less than 5 degrees for the isoclinic angle. The PSIOS system is limited to the low fringe orders. For a fringe order of less than l.5, the accuracy is 94.60% for fringe orders and the error about 6 degrees for the isoclinic angle if the undefined zones are ignored