Literatura académica sobre el tema "Smooth texture"

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 109-112).<br>The work in this thesis focuses on two main computer vision research topic: image segmentation and texture modeling. Information theoretic measures have been applied to image segmentation algorithms for the past decade. In previous work, common measures such as mutual information or J divergence have been used. Algorithms typically differ by the measure they use and the features they use to segment an image. When both the information measure and the features change, it is difficult to compare which algorithm actually performs better and for what reason. Though we do not provide a solution to this problem, we do compare and contrast three distances under two different measures. This thesis considers two forms of information theoretic based image segmentation algorithms that have previously been considered. We denote them here as the label method and the conditional method. Gradient ascent velocities are derived for a general Ali-Silvey distance for both methods, and a unique bijective mapping is shown to exist between the two methods when the Ali-Silvey distance takes on a specific form. While the conditional method is more commonly considered, it is implicitly limited by a two-region segmentation by construction. Using the derived mapping, one can easily extend a binary segmentation algorithm based on the conditional method to a multiregion segmentation algorithm based on the label method. The importance of initializations and local extrema is also considered, and a method of multiple random initializations is shown to produce better results.<br>(cont.) Additionally, segmentation results and methods for comparing the utility of the different measures are presented. This thesis also considers a novel texture model for representing textured regions with smooth variations in orientation and scale. By utilizing the steerable pyramid of Simoncelli and Freeman, the textured regions of natural images are decomposed into explicit local attributes of contrast, bias, scale, and orientation. Once found, smoothness in these attributes are imposed via estimation of Markov random fields. This combination allows for demonstrable improvements in common scene analysis applications including segmentation, reflectance and shading estimation, and estimation of the radiometric response function from a single grayscale image.<br>by Jason Chang.<br>S.M.

La reconstruction 3D monoculaire déformable est le problème général d'estimation de forme 3D d'un objet déformable à partir d'images 2D. Plusieurs scénarios ont émergé : le Shape-from-Template (SfT) et le Non-Rigid Structure-from-Motion (NRSfM) sont deux approches qui ont été grandement étudiées pour leur applicabilité. La première utilise une seule image qui montre un objet se déformant et un patron (une forme 3D texturée de l'objet dans une pose de référence). La seconde n'utilise pas de patron, mais utilise plusieurs images et estime la forme 3D dans chaque image. Les deux approches s'appuient sur le mouvement de points de correspondances entre les images et sur des a priori de déformations, restreignant ainsi leur utilisation à des surfaces texturées qui se déforment de manière lisse. Cette thèse fait avancer l'état de l'art du SfT et du NRSfM dans deux directions. La première est l'étude du SfT dans le cas de patrons 1D (c’est-à-dire des courbes comme des cordes et des câbles). La seconde direction est le développement d'algorithmes de SfT et de NRSfM qui exploitent plusieurs indices visuels et qui résolvent des cas réels et complexes non-résolus précédemment. Nous considérons des déformations isométriques et reconstruisons la partie extérieure de l'objet. Les contributions techniques et scientifiques de cette thèse sont divisées en quatre parties.La première partie de cette thèse étudie le SfT curvilinéaire, qui est le cas du patron curvilinéaire plongé dans un espace 2D ou 3D. Nous proposons une analyse théorique approfondie et des solutions pratiques pour le SfT curvilinéaire. Malgré son apparente simplicité, le SfT curvilinéaire s'est avéré être un problème complexe : il ne peut pas être résolu à l'aide de solutions locales non-holonomes d'une équation différentielle ordinaire et ne possède pas de solution unique, mais un nombre fini de solutions ambiguës. Une contribution technique majeure est un algorithme basé sur notre théorie, qui génère toutes les solutions ambiguës. La deuxième partie de cette thèse traite d'une limitation des méthodes de SfT : la reconstruction de plis. Cette limitation vient de la parcimonie de la contrainte de mouvement et de la régularisation. Nous proposons deux contributions qui s'appuient sur un cadre de minimisation d'énergie non-convexe. Tout d'abord, nous complétons la contrainte de mouvement avec une contrainte robuste de bord. Ensuite, nous modélisons implicitement les plis à l'aide d'une représentation dense de la surface basée maillage et d'une contrainte robuste de lissage qui désactive automatiquement le lissage de la courbure sans connaître a priori la position des plis.La troisième partie de cette thèse est dédiée à une autre limitation du SfT : la reconstruction de surfaces peu texturées. Cette limitation vient de la difficulté d'obtenir des correspondances (parcimonieuses ou denses) sur des surfaces peu texturées. Comme l'ombrage révèle les détails sur des surfaces peu texturées, nous proposons de combiner l'ombrage avec le SfT. Nous présentons deux contributions. La première est une initialisation en cascade qui estime séquentiellement la déformation de la surface, l'illumination de la scène, la réponse de la caméra et enfin les albédos de la surface à partir d'images monoculaires où la surface se déforme. La seconde est l'intégration de l'ombrage à notre précédent cadre de minimisation d'énergie afin de raffiner simultanément les paramètres photométriques et de déformation.La dernière partie de cette thèse relâche la connaissance du patron et aborde deux limitations du NRSfM : la reconstruction de surfaces peu texturées avec des plis. Une contribution majeure est l'extension du second cadre d'optimisation pour la reconstruction conjointe de la forme 3D de la surface sur toutes les images d'entrée et des albédos de la surface sans en connaître un patron<br>Monocular deformable 3D reconstruction is the general problem of recovering the 3D shape of a deformable object from monocular 2D images. Several scenarios have emerged: the Shape-from-Template (SfT) and the Non-Rigid Structure-from-Motion (NRSfM) are two approaches intensively studied for their practicability. The former uses a single image depicting the deforming object and a template (a textured 3D shape of this object in a reference pose). The latter does not use a template, but uses several images and recovers the 3D shape in each image. Both approaches rely on the motion of correspondences between the images and deformation priors, which restrict their use to well-textured surfaces which deform smoothly. This thesis advances the state-of-the-art in SfT and NRSfM in two main directions. The first direction is to study SfT for the case of 1D templates (i.e. curved, thin structures such as ropes and cables). The second direction is to develop algorithms in SfT and NRSfM that exploit multiple visual cues and can solve complex, real-world cases which were previously unsolved. We focus on isometric deformations and reconstruct the outer part of the object. The technical and scientific contributions of this thesis are divided into four parts. The first part of this thesis studies the case of a curvilinear template embedded in 2D or 3D space, referred to Curve SfT. We propose a thorough theoretical analysis and practical solutions for Curve SfT. Despite its apparent simplicity, Curve SfT appears to be a complex problem: it cannot be solved locally using exact non-holonomic partial differential equation and is only solvable up to a finite number of ambiguous solutions. A major technical contribution is a computational solution based on our theory, which generates all the ambiguous solutions.The second part of this thesis deals with a limitation of SfT methods: reconstructing creases. This is due to the sparsity of the motion constraint and regularization. We propose two contributions which rely on a non-convex energy minimization framework. First, we complement the motion constraint with a robust boundary contour constraint. Second, we implicitly model creases with a dense mesh-based surface representation and an associated robust smoothing constraint, which deactivates curvature smoothing automatically where needed, without knowing a priori the crease location. The third part of this thesis is dedicated to another limitation of SfT: reconstructing poorly-textured surfaces. This is due to correspondences which cannot be obtained so easily on poorly-textured surfaces (either sparse or dense). As shading reveals details on poorly-textured surfaces, we propose to combine shading and SfT. We have two contributions. The first is a cascaded initialization which estimates sequentially the surface's deformation, the scene illumination, the camera response and then the surface albedos from deformed monocular images. The second is to integrate shading to our previous energy minimization framework for simultaneously refining deformation and photometric parameters.The last part of this thesis relaxes the knowledge of the template and addresses two limitations of NRSfM: reconstructing poorly-textured surfaces with creases. Our major contribution is an extension of the second framework to recover jointly the 3D shapes of all input images and the surface albedos without any template

Solid surfaces featuring a spatial variation of surface wettability along particular directions on their surface, referred to as wettability gradient surfaces, are becoming increasingly important in practical applications such as enhancement of boiling and condensation heat transfer and separation of immiscible liquids in smart micro-fluidic devices. With the aid of an external energy input, such as mechanical vibration or impact kinetic energy, a liquid drop on such surfaces gets propelled towards more wettable region on the surface. A fundamental study of impact dynamics of liquid drops on such solid surfaces is relevant in understanding their effectiveness. The present thesis reports a combined experimental and theoretical study on the impact dynamics of liquid drops on solid surfaces comprising a smooth portion and a groove-textured portion separated by a junction line (dual-textured surfaces). Three different dual-textured surfaces – two made of intrinsically hydrophilic stainless steel and one of intrinsically hydrophobic poly-di-methyl-siloxane (PDMS) – are considered. Liquid drops, with Weber number (We) in the range 1–100, are impacted on the junction of the dual-textured surfaces and the entire impact dynamics across the junction is captured using a high speed video camera. Experiments of drop impact on the homogeneous surface portions of dual-textured surfaces (far away from the junction) are also conducted. The temporal variation of drop contact radius measured from the junction line on smooth and groove-textured portions of the dual-textured surfaces exhibits four distinct stages – primary spreading, primary receding, secondary spreading on more wettable surface portion, and final equilibrium – with the final outcome being the bulk movement and deposition of liquid drop away from the junction towards the more hydrophilic surface portion. Secondary parameters characterizing each of these different stages are extracted from these measurements and a one-to-one comparison between dual-textured and homogenous surfaces is presented. A significant effect of dual-texture nature is seen on the receding process of impacting drops. On the dual-textured surfaces, the receding velocity of impacting drop on the groove-textured portion is always greater than that on the smooth portion. The asymmetry in drop receding results in a drop drift velocity towards the more wettable surface portion leading to an enhanced secondary drop spreading on the more wettable smooth portion. The drop drift velocity shows a decrease with We at low We and remains almost constant at higher We after a particular value of We. Correspondingly, the ratio of the maximum drop spread factor achieved during the secondary spreading (βm2) to that during the primary spreading (βm) is seen to decrease with We at low We and remains constant at higher We. Owing to the differences in the static equilibrium wetting difference, βm2/βm is more on the stainless steel dual-textured surfaces than on the PDMS dual-textured surface. The presence of dual-texture results in a higher final spread on more wettable smooth portion and smaller final spread on less wettable textured portion of the dual-textured surfaces and this difference decreases with We. The difference in final spread factors between the smooth and textured portions is more on the stainless steel dual-textured surfaces than the PDMS dual-textured surface. The bulk drop movement (ξ), characterized in terms of distance measured from the junction to the final drop center, decreases with We at low We and remains constant at higher We on the stainless steel dual-textured surfaces whereas it remains constant at low We and decreases at higher We on the PDMS dual-textured surface. ξ on the PDMS dual-textured surface is always less than that on the stainless dual-textured surface due to the lower wetting difference across the junction of the former. Comparison of the trends of secondary parameters with the predictions from theoretical models reported in literature showed a lack of agreement. This is due to various physical processes encountered by impacting drop on the groove-textured surface, identified through experiments of drop impact on homogeneous groove-textured surfaces, such as (i) convex shape of liquid-vapor interface near contact line at maximum spreading, (ii) impregnation of drop liquid into the grooves during impact, and (iii) contact line pinning of spreading drop at the asperity edges of surface texture, as well as the wetting difference in dual-textured surfaces. The inclusion of these physical processes under conventional energy conservation approach is seen to predict the experimentally observed trends of maximum drop spread factor on the groove-textured portions. A force balance model, applied to the liquid drop configuration at the beginning of drop receding on the dual-textured surfaces, predicts the qualitative trend of ξ with We on all surfaces. Drop liquid impregnation into the grooves of textured portion at We > Wecr (critical We corresponding to transition from Cassie to impaled state) is proposed as a possible physical mechanism to account for the explanation of the specific trends of ξ with We. A theoretical model formulated using force balance at the three phase contact line beneath impacting drop on groove-textured surface is presented for the prediction of Wecr.

Mechanically Stabilized Earth (MSE) walls retain soil on steep, unstable slopes with crest loads. Over the last decade, they are becoming quite popular due to their low cost-to-benefit ratio, design flexibility, and ease of construction. Like any civil infrastructure, MSE walls need to be continuously monitored according to transportation asset management criteria during and after the construction stage to ensure that their expected serviceability measures are met and to detect design and/or construction issues, which could lead to structural failure. Current approaches for monitoring MSE walls are mostly qualitative (e.g., visual inspection or examination). Besides being time consuming, visual inspection might have inconsistencies due to human subjectivity. Other monitoring approaches are based on using total station, geotechnical field instrumentations, and/or Static Terrestrial Laser Scanning (TLS). These instruments are capable of providing highly accurate, reliable performance measures. However, the underlying data acquisition and processing strategies are time-consuming and are not scalable. This research focuses on a comprehensive strategy using a Mobile LiDAR Mapping System (MLS) for the acquisition and processing of point clouds covering the MSE wall. The strategy produces standard serviceability measures, as defined by the American Association of State Highway and Transportation Officials (AASHTO) – e.g., longitudinal and transversal angular distortions. It also delivers a set of recently developed measures (e.g., out-of-plane offsets and 3D position/orientation deviations for individual panels constituting the MSE wall). Moreover, it is also capable of handling MSE walls with smooth or textured panels with the latter being the focus of this research due to its more challenging nature. For this study, an ultra-high-accuracy wheel-based MLS has been developed to efficiently acquire reliable data conducive to the development of the standard and new serviceability measures. To illustrate the feasibility of the proposed acquisition/processing strategy, two case studies in this research have been conducted with the first one focusing on the comparative performance of static and mobile LiDAR in terms of the agreement of the derived serviceability measures. The second case study aims at illustrating the feasibility of the proposed strategy in handling large textured MSE walls. Results from both case studies confirm the potential of using MLS for efficient, economic, and reliable monitoring of MSE walls.