Reconstrução 3D a partir de imagens stereo

A reconstrução 3D é uma das várias áreas que estão inseridas no campo da Visão Computacional. A reconstrução 3D com recurso a imagens stereo consiste numa técnica ótica. Esta técnica usa como input duas ou mais imagens de uma cena ou de um objeto e permite obter um modelo 3D desta cena ou objeto. Nesta dissertação é apresentada uma metodologia de reconstrução 3D que usa como input um par de imagens stereo, obtidas com recurso a duas webcams. As câmaras usadas para captar estas imagens são calibradas antes de ser iniciada a reconstrução 3D. Com recurso a algoritmos especializados são detetadas as linhas presentes nas imagens captadas. Assim, nesta dissertação apresenta-se também um algoritmo de deteção de linhas baseado na Transformada de Hough. Quando o processo de deteção de linhas termina, são identificadas correspondências entre estas linhas. Os algoritmos criados para este efeito são também apresentados nesta dissertação. Finalmente, é reconstruído o modelo 3D do objeto presente no par de imagens stereo; Abstract: 3D Reconstruction From Stereo Images 3D reconstruction is one of several areas that are included in the Computer Vision field. 3D reconstruction from stereo images is an optical technique. This technique uses two or more images of a scene or object as input and outputs a 3D model of this scece or object. This dissertation introduces a methodology that allows for 3D reconstruction with a pair of stereo images, obtained with two webcams. These cameras are calibrated before the 3D reconstruction starts. The lines present in the pair of stereo images are detected with specialized algorithms. Thus, in this dissertation it is also presented a line detection algorithm based on the Hough Transform. Once the line detection process is completed, the correspondences between the lines detected in the stereo pair are found. The algorithms created to identify these correspondences are also presented in this dissertation. Finally, the 3D model of the object shown in the stereo images is produced

Digital Restoration of Damaged Historical Parchment

In this thesis we describe the development of a pipeline for digitally restoring damaged historical parchment. The work was carried out in collaboration with London Metropolitan Archives (LMA), who are in possession of an extremely valuable 17th century document called The Great Parchment Book. This book served as the focus of our project and throughout this thesis we demonstrate our methods on its folios. Our aim was to expose the content of the book in a legible form so that it can be properly catalogued and studied. Our approach begins by acquiring an accurate digitisation of the pages. We have developed our own 3D reconstruction pipeline detailed in Chapter 5 in which each parchment is imaged using a hand-held digital-SLR camera, and the resulting image set is used to generate a high-resolution textured 3D reconstruction of each parchment. Investigation into methods for flatting the parchments demonstrated an analogy with surface parametrization. Flattening the entire parchment globally with various existing parametrization algorithms is problematic, as discussed in Chapters 4, 6, and 7, since this approach is blind to the distortion undergone by the parchment. We propose two complementary approaches to deal with this issue. Firstly, exploiting the fact that a reader will only ever inspect a small area of the folio at a given time, we proposed a method for performing local undistortion of the parchments inside an interactive viewer application. The application, described in Chapter 6, allows a user to browse a parchment folio as the application un-distorts in real-time the area of the parchment currently under inspection. It also allows the user to refer back to the original image set of the parchment to help with resolving ambiguities in the reconstruction and to deal with issues of provenance. Secondly, we proposed a method for estimating the actual deformation undergone by each parchment when it was damaged by using cues in the text. Since the text was originally written in straight lines and in a roughly uniform script size, we can detect the the variation in text orientation and size and use this information to estimate the deformation. in Chapter 7 we then show how this deformation can be inverted by posing the problem as a Poisson mesh deformation, and solving it in a way that guarantees local injectivity, to generate a globally flattened and undistorted image of each folio. We also show how these images can optionally be colour corrected to remove the shading cues baked into the reconstruction texture, and the discolourations in the parchment itself, to further improve legibility and give a more complete impression that the parchment has been restored. The methods we have developed have been very well received by London Metropolitan Archives, as well the the larger archival community. We have used the methods to digitise the entire Great Parchment Book, and have demonstrated our global flattening method on eight folios. As of the time of writing of this thesis, our methods are being used to virtually restore all of the remaining folios of the Great Parchment Book. Staff at LMA are also investigating potential future directions by experimenting with other interesting documents in their collections, and are exploring the possibility of setting up a service which would give access to our methods to other archival institutions with similarly damaged documents