Variational segmentation of vector-valued images with gradient vector flow

International audienceIn this paper, we extend the gradient vector flow field for robust variational segmentation of vector-valued images. Rather than using scalar edge information, we define a vectorial edge map derived from a weighted local structure tensor of the image that enables the diffusion of the gradient vectors in accurate directions through the 4DGVF equation. To reduce the contribution of noise in the structure tensor, image channels are weighted according to a blind estimator of contrast. The method is applied to biological volume delineation in dynamic PET imaging, and validated on realistic Monte Carlo simulations of numerical phantoms as well as on real images

Layered And Feature Based Image Segmentation Using Vector Filtering

A Sensor is a device that reads the attribute and changes it into a signal that can be simply examined by an observer or instrument. Sensors are worked in daily objects like touch-sensitive elevator buttons, road traffic monitoring system and so on. Each sensor would carry distinctive capabilities to utilize. The objects obtained in the sensor are tracked by many techniques which have been presented earlier. The techniques which make use of the information from diverse sensors normally termed as data fusion. The previous work defined the object tracking using Multi-Phase Joint Segmentation-Registration (MP JSR) technique for layered images. The downside of the previous work is that the MP JSR technique cannot be applied to the natural objects and the segmentation of the object is also being an inefficient one. To overcome the issues, here we are going to present an efficient joint motion segmentation and registration framework with integrated layer-based and feature-based motion estimation for precise data fusion in real image sequences and tracking of interested objects. Interested points are segmented with vector filtering using random samples of motion frames to derive candidate regions. The experimental evaluation is conducted with real image sequences samples to evaluate the effectiveness of data fusion using integrated layer and feature based image segmentation and registration of motion frames in terms of inter frame prediction, image layers, image clarity

Neural Implicit Representations for Physical Parameter Inference from a Single Video

Neural networks have recently been used to analyze diverse physical systems and to identify the underlying dynamics. While existing methods achieve impressive results, they are limited by their strong demand for training data and their weak generalization abilities to out-of-distribution data. To overcome these limitations, in this work we propose to combine neural implicit representations for appearance modeling with neural ordinary differential equations (ODEs) for modelling physical phenomena to obtain a dynamic scene representation that can be identified directly from visual observations. Our proposed model combines several unique advantages: (i) Contrary to existing approaches that require large training datasets, we are able to identify physical parameters from only a single video. (ii) The use of neural implicit representations enables the processing of high-resolution videos and the synthesis of photo-realistic images. (iii) The embedded neural ODE has a known parametric form that allows for the identification of interpretable physical parameters, and (iv) long-term prediction in state space. (v) Furthermore, the photo-realistic rendering of novel scenes with modified physical parameters becomes possible.Comment: Published in IEEE/CVF Winter Conference on Applications of Computer Vision (WACV) 202

Two and three dimensional segmentation of multimodal imagery

The role of segmentation in the realms of image understanding/analysis, computer vision, pattern recognition, remote sensing and medical imaging in recent years has been significantly augmented due to accelerated scientific advances made in the acquisition of image data. This low-level analysis protocol is critical to numerous applications, with the primary goal of expediting and improving the effectiveness of subsequent high-level operations by providing a condensed and pertinent representation of image information. In this research, we propose a novel unsupervised segmentation framework for facilitating meaningful segregation of 2-D/3-D image data across multiple modalities (color, remote-sensing and biomedical imaging) into non-overlapping partitions using several spatial-spectral attributes. Initially, our framework exploits the information obtained from detecting edges inherent in the data. To this effect, by using a vector gradient detection technique, pixels without edges are grouped and individually labeled to partition some initial portion of the input image content. Pixels that contain higher gradient densities are included by the dynamic generation of segments as the algorithm progresses to generate an initial region map. Subsequently, texture modeling is performed and the obtained gradient, texture and intensity information along with the aforementioned initial partition map are used to perform a multivariate refinement procedure, to fuse groups with similar characteristics yielding the final output segmentation. Experimental results obtained in comparison to published/state-of the-art segmentation techniques for color as well as multi/hyperspectral imagery, demonstrate the advantages of the proposed method. Furthermore, for the purpose of achieving improved computational efficiency we propose an extension of the aforestated methodology in a multi-resolution framework, demonstrated on color images. Finally, this research also encompasses a 3-D extension of the aforementioned algorithm demonstrated on medical (Magnetic Resonance Imaging / Computed Tomography) volumes

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

Vortex Extraction Of Vector Fields

Spinning, turbulent structures swirling around its centers within various flow media are known as vortices. The capability of locating and extracting vortical structures in flow data is crucial for understanding the flow. Vortices also have a strong impact on flow control and transport processes. Real-time vortex extraction methods are presented, offering immediate notion of the shape and location of the vortex structures. Using a real-time fluid simulation based on Navier-Stokes equations presented in \cite{Stam:1999:SF}, several vortex extraction methods are interactively performed in real-time. Following vortex extraction methods are implemented using the GPU: vorticity threshold, Q criterion, $\lambda_2$ criterion, the eigenvector method via parallel vectors operator (PVO) and the eigenvector method via coplanar vectors operator (CVO). Diffusional methods outputting flow fields with preserved/enhanced vortical structures are also presented. Such methods are useful for obtaining an alternative insight into vortices within a flow field and can also be used within the real-time simulation. Using a number of human performed gestures for human-computer interaction, special ensemble flow fields are produced. Detecting vortices from these gesture ensemble range flows is introduced as aid for gesture classification. Gesture range data is recorded using the Microsoft Kinect device. Range or scene flow is a 3D vector field describing movement within a scene. Range data consists of images (color channels) and corresponding depth images (depth channels) in which the distance of objects is recorded as a grayscale image. Ensemble range flow is estimated from gesture videos. Ensemble flow describes the overall flow within the scene and is obtained by averaging the structure tensor throughout the scene. Vortices are extracted from an ensemble range flow of the gestures. Their number and location is offering an additional parameter for gesture classification. Collection of methods for detecting vortices and obtaining vector fields with emphasized vortices are introduced in this thesis. Real-time execution of vortex extraction methods offers an instant notion of the nature of the flow. Diffusional methods can serve as a processing step within the real-time vortex extraction. As an additional application, gesture ensemble flow is presented. By detecting its vortices, a parameter for gesture classification is introduced

Deformable Medical Image Registration: A Survey

Deformable image registration is a fundamental task in medical image processing. Among its most important applications, one may cite: i) multi-modality fusion, where information acquired by different imaging devices or protocols is fused to facilitate diagnosis and treatment planning; ii) longitudinal studies, where temporal structural or anatomical changes are investigated; and iii) population modeling and statistical atlases used to study normal anatomical variability. In this technical report, we attempt to give an overview of deformable registration methods, putting emphasis on the most recent advances in the domain. Additional emphasis has been given to techniques applied to medical images. In order to study image registration methods in depth, their main components are identified and studied independently. The most recent techniques are presented in a systematic fashion. The contribution of this technical report is to provide an extensive account of registration techniques in a systematic manner.Le recalage déformable d'images est une des tâches les plus fondamentales dans l'imagerie médicale. Parmi ses applications les plus importantes, on compte: i) la fusion d' information provenant des différents types de modalités a n de faciliter le diagnostic et la planification du traitement; ii) les études longitudinales, oú des changements structurels ou anatomiques sont étudiées en fonction du temps; et iii) la modélisation de la variabilité anatomique normale d'une population et les atlas statistiques. Dans ce rapport de recherche, nous essayons de donner un aperçu des différentes méthodes du recalage déformables, en mettant l'accent sur les avancées les plus récentes du domaine. Nous avons particulièrement insisté sur les techniques appliquées aux images médicales. A n d'étudier les méthodes du recalage d'images, leurs composants principales sont d'abord identifiés puis étudiées de manière indépendante, les techniques les plus récentes étant classifiées en suivant un schéma logique déterminé. La contribution de ce rapport de recherche est de fournir un compte rendu détaillé des techniques de recalage d'une manière systématique

Innovative mathematical and numerical models for studying the deformation of shells during industrial forming processes with the Finite Element Method

The doctoral thesis "Innovative mathematical and numerical models for studying the deformation of shells during industrial forming processes with the Finite Element Method" aims to contribute to the development of finite element methods for the analysis of stamping processes, a problematic area with a clear industrial application. To achieve the proposed objectives, the first part of this thesis covers the solid-shell elements. This type of element is attractive for the simulation of forming processes, since any type of three-dimensional constitutive law can be formulated without the need to consider any additional conjecture. Additionally, the contact of both sides can be easily treated. This work first presents the development of a triangular prismatic solid-sheet element, for the analysis of thick and thin sheets with capacity for large deformations. This element is in total Lagrangian formulation, and uses neighboring elements to compute a field of quadratic displacements. In the original formulation, a modified right Cauchy tensor was obtained; however, in this work, the formulation is extended obtaining a modified strain gradient, which allows the concepts of push-forward and pull-back to be used. These concepts provide a mathematically consistent method for the definition of temporary derivatives of tensors and, therefore, can be used, for example, to work with elasto-plasticity. This work continues with the development of the contact formulation used, a methodology found in the bibliography on computational contact mechanics for implicit simulations. This formulation consists of an exact integration of the contact interface using mortar methods, which allows obtaining the most consistent integration possible between the integration domains, as well as the most exact possible solution. The most notable contribution of this work is the consideration of dual augmented Lagrange multipliers as an optimization method. To solve the system of equations, a semi-smooth Newton method is considered, which consists of an active set strategy, also extensible in the case of friction problems. The formulation is functional for both frictionless and friction problems, which is essential for simulating stamping processes. This frictional formulation is framed in traditional friction models, such as Coulomb friction, but the development presented can be extended to any type of friction model. The remaining necessary component for the simulation of industrial processes are the constitutive models. In this work, this is materialized in the formulation of plasticity considered. These constitutive models will be considered plasticity models for large deformations, with an arbitrary combination of creep surfaces and plastic potentials: the so-called non-associative models. To calculate the tangent tensor corresponding to these general laws, numerical implementations based on perturbation methods have been considered. Another fundamental contribution of this work is the development of techniques for adaptive remeshing, of which different approaches will be presented. On the one hand, metric-based techniques, including the level-set and Hessian approaches. These techniques are general-purpose and can be considered in both structural problems and fluid mechanics problems. On the other hand, the SPR error estimation method, more conventional than the previous ones, is presented. In this area, the contribution of this work consists in the estimation of error using the Hessian and SPR techniques for the application to numerical contact problems.La tesis doctoral "Modelos matemáticos y numéricos innovadores para el estudio de la deformación de láminas durante los procesos de conformado industrial por el Método de los Elementos Finitos" pretende contribuir al desarrollo de métodos de elementos finitos para el análisis de procesos de estampado, un área problemática con una clara aplicación industrial. De hecho, este tipo de problemas multidisciplinares requieren el conocimiento de múltiples disciplinas, como la mecánica de medios continuos, la plasticidad, la termodinámica y los problemas de contacto, entre otros. Para alcanzar los objetivos propuestos, la primera parte de esta tesis abarca los elementos de sólido lámina. Este tipo de elemento resulta atractivo para la simulación de procesos de conformado, dado que cualquier tipo de ley constitutiva tridimensional puede ser formulada sin necesidad de considerar ninguna conjetura adicional. Además, este tipo de elementos permite realizar una descripción tridimensional del cuerpo deformable, por tanto, el contacto de ambas caras puede ser tratado fácilmente. Este trabajo presenta en primer lugar el desarrollo de un elemento de sólido-lámina prismático triangular, para el análisis de láminas gruesas y delgadas con capacidad para grandes deformaciones. Este elemento figura en formulación Lagrangiana total, y emplea los elementos vecinos para poder computar un campo de desplazamientos cuadráticos. En la formulación original, se obtenía un tensor de Cauchy derecho modificado (¯C); sin embargo, en este trabajo, la formulación se extiende obteniendo un gradiente de deformación modificado (¯F), que permite emplear los conceptos de push-forward y pull-back. Dichos conceptos proveen de un método matemáticamente consistente para la definición de derivadas temporales de tensores y, por tanto, puede ser usado, por ejemplo, para trabajar con elasto-plasticidad. El elemento se basa en tres modificaciones: (a) una aproximación clásica de deformaciones transversales de corte mixtas impuestas; (b) una aproximación de deformaciones impuestas para las Componentes en el plano tangente de la lámina; y (c) una aproximación de deformaciones impuestas mejoradas en la dirección normal a través del espesor, mediante la consideración de un grado de libertad adicional. Los objetivos son poder utilizar el elemento para la simulación de láminas sin bloquear por cortante, mejorar el comportamiento membranal del elemento en el plano tangente, eliminar el bloqueo por efecto Poisson y poder tratar materiales elasto-plásticos con un flujo plástico incompresible, así como materiales elásticos cuasi-incompresibles o materiales con flujo plástico isocórico. El elemento considera un único punto de Gauss en el plano, mientras que permite considerar un número cualquiera de puntos de integración en su eje, con el objetivo de poder considerar problemas con una significativa no linealidad en cuanto a plasticidad. Este trabajo continúa con el desarrollo de la formulación de contacto empleada, una metodología que se encuentra en la bibliografía sobre la mecánica de contacto computacional para simulaciones implícitas. Dicha formulación consiste en una integración exacta de la interfaz de contacto mediante métodos de mortero, lo que permite obtener la integración más consistente posible entre los dominios de integración, así como la solución más exacta posible. La implementación también considera varios algoritmos de optimización, como la optimización mediante penalización. La contribución más notable de este trabajo es la consideración de multiplicadores de Lagrange aumentados duales como método de optimización. Estos permiten condensar estáticamente el sistema de ecuaciones, lo que permite eliminar los multiplicadores de Lagrange de la resolución y, por lo tanto, permite la consideración de solvers iterativos. Además, la formulación ha sido adecuadamente linealizada, asegurando la convergencia cuadrática del problema. Para resolver el sistema de ecuaciones, se considera un método de Newton semi-smooth, que consiste en una estrategia de set activo, extensible también en el caso de problemas friccionales. La formulación es funcional tanto para problemas sin fricción como para problemas friccionales, lo que es esencial para la simulación de procesos de estampado. Esta formulación friccional se enmarca en los modelos de fricción tradicionales, como la fricción de Coulomb, pero el desarrollo presentado puede extenderse a cualquier tipo de modelo de fricción. Esta formulación de contacto es totalmente compatible con el elemento sólido-lámina introducido en este trabajo. El componente necesario restante para la simulación de procesos industriales son los modelos constitutivos. En este trabajo, esto se ve materializado en la formulación de plasticidad considerada. Estos modelos constitutivos se considerarán modelos de plasticidad para grandes deformaciones, con una combinación arbitraria de superficies de fluencia y potenciales plásticos: los llamados modelos no asociados. Para calcular el tensor tangente correspondiente a estas leyes generales, se han considerado implementaciones numéricas basadas en métodos de perturbación. Otra contribución fundamental de este trabajo es el desarrollo de técnicas para el remallado adaptativo, de las que se presentarán distintos enfoques. Por un lado, las técnicas basadas en métricas, incluyendo los enfoques level-set y Hessiano. Estas técnicas son de propósito general y pueden considerarse tanto en la aplicación de problemas estructurales como en problemas de mecánica de fluidos. Por otro lado, se presenta el método de estimación de errores SPR, más convencional que los anteriores. En este ámbito, la contribución de este trabajo consiste en la estimación de error mediante las técnicas de Hessiano y SPR para la aplicación a problemas de contacto numérico. Con los desarrollos previamente introducidos, estaremos en disposición de introducir los casos de aplicación centrados en el contexto de procesos de estampado. Es relevante destacar que estos ejemplos son comparados con las soluciones de referencia disponibles en la bibliografía como forma de validar los desarrollos presentados hasta este punto. El presente documento está organizado de la siguiente manera. El primer capítulo establece los objetivos y revisa la bibliografía acerca de los temas clave de este trabajo. El segundo capítulo hace una introducción de la mecánica de medios continuos y los conceptos relativos al Método de los Elementos Finitos (MEF), necesarios en los desarrollos que se presentarán en los capítulos siguientes. El tercer capítulo aborda la formulación del elemento sólido-lámina, así como del elemento de lámina sin grados de libertad de rotación que inspira el sólido-lámina desarrollado. Esta parte muestra varios ejemplos académicos que son comúnmente empleados en la bibliografía como problemas de referencia de láminas. El cuarto capítulo presenta la formulación desarrollada para la resolución de problemas de contacto numérico, consistente en una formulación implícita de integración exacta mediante métodos mortero y multiplicadores de Lagrange aumentados duales. Este capítulo incluye, asimismo, varios ejemplos comúnmente encontrados en la bibliografía, que generalmente son considerados para su validación. El quinto capítulo presenta la formulación de plasticidad empleada, incluyendo algunos detalles técnicos desde el punto de vista de la implementación, así como varios ejemplos de validación. El sexto capítulo muestra los algoritmos de remallado adaptativo desarrollados en el contexto de este trabajo, y presenta varios ejemplos, que incluyen no solo casos estructurales, sino también de mecánica de fluidos. El séptimo capítulo encapsula algunos casos de validación y aplicación para procesos de estampado. El capítulo final comprende las conclusiones, así como los trabajos que podrían continuar el presente estudio.Postprint (published version