Clustering-based Methods for Fast Epitome Generation

International audienceThis paper deals with epitome generation, mainly dedicated here to image coding applications. Existing approaches are known to be memory and time consuming due to exhaustive self-similarities search within the image for each non-overlapping block. We propose here a novel approach for epitome construction that first groups close patches together. In a second time the self-similarities search is performed for each group. By limiting the number of exhaustive searches we limit the memory occupation and the processing time. Results show that interesting complexity reduction can be achieved while keeping a good epitome quality (down to 18.08 % of the original memory occupation and 41.39 % of the original processing time)

Video modeling via implicit motion representations

Video modeling refers to the development of analytical representations for explaining the intensity distribution in video signals. Based on the analytical representation, we can develop algorithms for accomplishing particular video-related tasks. Therefore video modeling provides us a foundation to bridge video data and related-tasks. Although there are many video models proposed in the past decades, the rise of new applications calls for more efficient and accurate video modeling approaches.;Most existing video modeling approaches are based on explicit motion representations, where motion information is explicitly expressed by correspondence-based representations (i.e., motion velocity or displacement). Although it is conceptually simple, the limitations of those representations and the suboptimum of motion estimation techniques can degrade such video modeling approaches, especially for handling complex motion or non-ideal observation video data. In this thesis, we propose to investigate video modeling without explicit motion representation. Motion information is implicitly embedded into the spatio-temporal dependency among pixels or patches instead of being explicitly described by motion vectors.;Firstly, we propose a parametric model based on a spatio-temporal adaptive localized learning (STALL). We formulate video modeling as a linear regression problem, in which motion information is embedded within the regression coefficients. The coefficients are adaptively learned within a local space-time window based on LMMSE criterion. Incorporating a spatio-temporal resampling and a Bayesian fusion scheme, we can enhance the modeling capability of STALL on more general videos. Under the framework of STALL, we can develop video processing algorithms for a variety of applications by adjusting model parameters (i.e., the size and topology of model support and training window). We apply STALL on three video processing problems. The simulation results show that motion information can be efficiently exploited by our implicit motion representation and the resampling and fusion do help to enhance the modeling capability of STALL.;Secondly, we propose a nonparametric video modeling approach, which is not dependent on explicit motion estimation. Assuming the video sequence is composed of many overlapping space-time patches, we propose to embed motion-related information into the relationships among video patches and develop a generic sparsity-based prior for typical video sequences. First, we extend block matching to more general kNN-based patch clustering, which provides an implicit and distributed representation for motion information. We propose to enforce the sparsity constraint on a higher-dimensional data array signal, which is generated by packing the patches in the similar patch set. Then we solve the inference problem by updating the kNN array and the wanted signal iteratively. Finally, we present a Bayesian fusion approach to fuse multiple-hypothesis inferences. Simulation results in video error concealment, denoising, and deartifacting are reported to demonstrate its modeling capability.;Finally, we summarize the proposed two video modeling approaches. We also point out the perspectives of implicit motion representations in applications ranging from low to high level problems

Techniques de codage d'images basées représentations parcimonieuses de scènes et prédiction spatiale multi-patches

In recent years, video compression eld has increased signicantly since the apparitionof H.264/AVC standard and of its successor HEVC. Spatial prediction in these standardsare based on the unidirectional propagation of neighboring pixels. Although very effectiveto extend pattern with the same characteristics, this prediction has limited performances toextrapolate complex textures. This thesis aims at exploring new spatial prediction schemesto improve the current intra prediction techniques, by extending these local schemes toglobal, multidimensional and multi-patches schemes. A hybrid prediction method based ontemplate and block matching is first investigated. This hybrid approach is then extended tomulti-patchs-based prediction of type "Neighbor Embedding" (NE). The other part of thisthesis is dedicated to the study of epitome image within the scope of image compression.The idea is to exploit spatial redundancies in the original image in order to rst extracta summary image containing the texture patches the most representative of the image,and then use this compacted representation to rebuild the original image. The conceptof epitome has been incorporated in two compression schemes, one of these algorithms isin rupture with the traditional techniques since the image blocks are processed, both atencoder and decoder sides, in a spatial order that depends on the image content and this inthe interest of propagating image structures. In this last compression algorithm, extendedH.264 Intra directional prediction modes and advanced multi-patches prediction methodshave been also included. These different solutions have been integrated in a H.264/AVCencoder in order to assess their coding performances with respect to H.264 intra modesand the state of the art relative to these dierent techniques.Au cours de ces dernières années, le domaine de la compression vidéo a connu un essorconsidérable avec le standard H.264/AVC et l'arrivée de son successeur HEVC. La prédictionspatiale de ces standards repose sur la propagation unidirectionnelle de pixels voisins.Bien que très efficace pour étendre des motifs répondants aux mêmes caractéristiques,cette prédiction présente des performances limitées lorsqu'il s'agit de propager des texturescomplexes. Cette thèse vise à explorer de nouveaux schémas de prédiction spatiale afind'améliorer les techniques actuelles de prédiction intra, en étendant ces schémas locaux etmonodimensionnels à des schémas globaux, multidimensionnels et multi-patches. Une première méthode de prédiction hybride intégrant correspondance de bloc et correspondancede gabarit (template) a été investiguée. Cette approche hybride a ensuite été étendue enprédiction multi-patches de type "neighbor embedding" (NE). L'autre partie de la thèseest dédiée à l'étude des épitomes dans un contexte de compression d'images. L'idée estd'exploiter la redondance spatiale de l'image d'origine afin d'extraire une image résumécontenant les patches de texture les plus représentatifs de l'image, puis ensuite utilisercette représentation compacte pour reconstruire l'image de départ. Ce concept d'épitome aété intégré dans deux schémas de compression, l'un de ces algorithmes s'avère vraiment enrupture avec les techniques traditionnelles dans la mesure où les blocs de l'image sont traités, à l'encodeur et au décodeur, dans un ordre spatial qui dépend du contenu et cela dansun souci de propagation des structures de l'image. Dans ce dernier algorithme de compression,des modes de prédiction directionnelle intra H.264 étendus et des méthodes avancéesde prédiction multi-patches y ont été également introduits. Ces différentes solutions ont étéintégrées dans un encodeur de type H.264/AVC afin d'évaluer leurs performances de codagepar rapport aux modes intra H.264 et à l'état de l'art relatif à ces différentes techniques

Direct computation of the packing entropy of granular materials

Granular materials are the second most manipulated material in industry after water and their properties are of great importance for the pharmaceutical, food, mechanosynthesis and semiconductor industries. Up to 60% of the capacity of some industrial plants is used to process them. This thesis describes computer simulations that aim to evaluate the number of distinct packings of a granular material or, more generally, the socalled ‘granular entropy’. Monte Carlo simulations are used to probe the energy landscape of jammed systems of disks interacting via a repulsive, finiterange potential. In these simulations we make use of a soft-sphere model with a hard core that approaches the hard-sphere model as the width of the soft shell is decreased. To compute the packing entropy, we use and develop Monte Carlo techniques to determine the volumes of the basins of attraction of the potential energy minima at different system sizes. Such Monte Carlo simulations require energy minimisation after every trial move to make sure that all accepted moves keep the system within the same basin of attraction. Hence efficient energy minimisation is a point of paramount significance in this work. A first objective was to find a suitable minimisation algorithm. We report a study of the basins of attraction for potential energy minima defined by different minimisation algorithms for an atomic system. The findings indicate that whereas some minimisation algorithms produce compact basins, others produce basins with complex boundaries or basins consisting of disconnected parts. For the remainder of our work, the FIRE algorithm was chosen because it produces compact basins at a reasonable computational cost. Once the minimisation algorithm is chosen a numerical approach is used to compute the number of ways in which N particles can pack into a given volume V . This technique extends the existing methods in such a way that it can be applied to much larger systems than before (over 100 particles instead of 16). Many of the caveats of previous methods are addressed. Using this novel approach, the system size dependence of the number of distinct packings of a system of poly-disperse soft disks is studied. Our simulations enable us to validate a more than 20 years old conjecture due to Edwards. The distribution of jamming densities produced by different protocols has been studied. We found that the distribution of jamming volumes that are generated by starting from different initial densities cannot be characterised by an Edwards’-style compactivity although it is possible to construct an ensemble where compactivity is well defined.Becas Chile, CONICY

Liquid-Solid Transitions with Applications to Self-Assembly.

We study the thermodynamic and kinetic pathways by which liquids transform into solids, and their relation to the metastable states that commonly arise in self-assembly applications. As a case study in the formation of ordered metastable solids, we investigate the atomistic mechanism by which quasicrystals form. We show that the aperiodic growth of quasicrystals is controlled by the ability of the growing quasicrystal "nucleus" to incorporate kinetically trapped atoms into the solid phase with minimal rearrangement. In a related study, we propose a two-part mechanism for forming 3d dodecagonal quasicrystals by self-assembly. Our mechanism involves (1) attaching small mobile particles to the surface of spherical particles to encourage icosahedral packing and (2) allowing a subset of particles to deviate from the ideal spherical shape, to discourage close-packing. In addition to studying metastable ordered solids, we investigate the phenomenology and mechanism of the glass transition. We report measurements of spatially heterogeneous dynamics in a system of air-driven granular beads approaching a jamming transition, and show that the dynamics in our granular system are quantitatively indistinguishable from those for a supercooled liquid approaching a glass transition. In a second study of the glass transition, we use transition path sampling to study the structure, statistics and dynamics of localized excitations for several model glass formers. We show that the excitations are sparse and localized, and their size is temperature-independent. We show that their equilibrium concentration is proportional to exp[-Ja(1/T-1/To)], where "Ja" is the energy scale for irreversible particle displacements of length "a," and "To" is an onset temperature. We show that excitation dynamics is facilitated by the presence of other excitations, causing dynamics to slow in a hierarchical way as temperature is lowered. To supplement our studies of liquid-solid transitions, we introduce a shape matching framework for characterizing structural transitions in systems with complex particle shapes or morphologies. We provide an overview of shape matching methods, explore a particular class of metrics known as "harmonic descriptors," and show that shape matching methods can be applied to a wide range of nanoscale and microscale assembly applications.Ph.D.Chemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78931/1/askeys_1.pd

Heterogeneities in Metallic Glasses: Atomistic Computer Simulations on the Structure and Mechanical Properties of Copper–Zirconium Alloys and Composites

The present thesis deals with molecular dynamics computer simulations of heterogeneities in copper–zirconium metallic glasses, ranging from intrinsic structural fluctuations to crystalline secondary phases. These heterogeneities define, on a microscopic scale, the properties of the glass, and an understanding of their nature and behaviour is required for deriving the proper structure–property relations. In terms of composite systems, we start with the amorphisation of copper nanolayers embedded in a metallic glass matrix. While copper is an fcc metal with a high propensity for crystallisation, amorphisation can in fact occur in such systems for thermodynamic reasons. This is due to interface effects, which are also known from heterogeneous interfaces in crystals or from grain boundary complexions, although in absence of lattice mismatch. In single-phase glasses, intrinsic heterogeneities are often discussed in terms of soft spots or geometrically unfavourable motifs (GUMs), which can be considered to be mechanically weaker, defective regions of the glass. We investigate the relation between these motifs and the boson peak, an anomaly in the vibrational spectrum of all glasses. We demonstrate a relation between the boson peak and soft spots by analysing various amorphous and partially amorphous samples as well as high-entropy alloys. Finally, we treat the plastic deformation of glasses, with and without crystalline secondary phases. We propose an explanation for the experimentally observed variations of propagation direction, composition, and density along a shear band. These variations of propagation direction are small in the case of single-phase glasses. A considerably greater influence on shear band propagation can be exerted by precipitates. We systematically investigate composites ranging from low crystalline volume fraction up to systems which resemble a nanocrystalline metal. In this context, we derive a mechanism map for composite systems and observe the breakdown of these mechanisms with increasing crystalline volume fraction during the transition towards the nanocrystalline state

Epitome-based image compression using translational sub-pel mapping

International audienceThis paper addresses the problem of epitome construction for image compression. An optimized epitome construction method is first described, where the epitome and the associated image reconstruction, are both successively performed at full pel and sub-pel accuracy. The resulting complete still image compression scheme is then discussed with details on some innovative tools. The PSNR-rate performance achieved with this epitome-based compression method is significantly higher than the one obtained with H.264 Intra and with state of the art epitome construction method. A bit-rate saving up to 16% comparatively to H.264 Intra is achieved

Library buildings around the world

"Library Buildings around the World" is a survey based on researches of several years. The objective was to gather library buildings on an international level starting with 1990