1,721,218 research outputs found
Parole a domicilio. Professioni domiciliari di cura all’epoca della pandemia
No full textIl volume intende affrontare il tema delle professioni di cura domiciliare nell'area aretina toscana attraverso un progetto di ricerca azione con l'utilizzo delle storie di vit
Perspective Shape-from-Shading Problem: A Unified Convergence Result for Several Non-Lambertian Models
Full text linkShape-from-Shading represents the problem of computing the three-dimensional shape of a surface given a single gray-value image of it as input. In a recent paper, we showed that the introduction of an attenuation factor in the brightness equations related to various perspective Shape-from-Shading models allows us to ensure the well-posedness of the corresponding differential problems. Here, we propose a unified convergence result of a numerical scheme for several non-Lambertian reflectance models. This result is interesting since it can be easily extended to other non-Lambertian models in a unified and, therefore, powerful framework
On the Segmentation of Astronomical Images via Level-Set Methods
No full textAstronomical images are of crucial importance for astronomers since they contain a lot of information about celestial bodies that can not be directly accessible. Most of the information available for the analysis of these objects starts with sky explorations via telescopes and satellites. Unfortunately, the quality of astronomical images is usually very low with respect to other real images and this is due to technical and physical features related to their acquisition process. This increases the percentage of noise and makes more difficult to use directly standard segmentation methods on the original image. In this work we will describe how to process astronomical images in two steps: in the first step we improve the image quality by a rescaling of light intensity whereas in the second step we apply level-set methods to identify the objects. Several experiments will show the effectiveness of this procedure and the results obtained via various discretization techniques for level-set equations
A scheme for the game p-Laplacian and its application to image inpainting
Full text linkWe propose a new numerical scheme for the game p-Laplacian, based on a semi-Lagrangian
approximation. We focus on the 2D version of the game p-Laplacian, with the aim to apply
the new scheme in the context of image processing. Specifically, we want to solve the so-called
inpainting problem, which consists in reconstructing one or more missing parts of an image using
information taken from the known part. The numerical tests show the reliability of the proposed
method and the advantages of taking a p > 1 in terms of execution time and accurac
Numerical hints for insulation problems
Full text linkIn this work we analyze a problem of thermal insulation from the numerical point of view via finite element method. Physically, we are considering a domain of given temperature, thermally insulated by surrounding it with a constant amount of thermal insulator. From the mathematical point of view, this problem is composed by an elliptic partial differential equation with Robin–Dirichlet boundary conditions. Our question is related to the best (or worst) shape for the external domain, in terms of heat dispersion (of course, under prescribed geometrical constraints)
Analysis and approximation of some shape-from-shading models for non-Lambertian surfaces
Full text linkThe reconstruction of a 3D object or a scene is a classical inverse problem in Computer Vision. In the case of a single image this is called the Shape-from-Shading (SfS) problem and it is known to be ill-posed even in a simplified version like the vertical light source case. A huge number of works deals with the orthographic SfS problem based on the Lambertian reflectance model, the most common and simplest model which leads to an eikonal-type equation when the light source is on the vertical axis. In this paper, we want to study non-Lambertian models since they are more realistic and suitable whenever one has to deal with different kind of surfaces, rough or specular. We will present a unified mathematical formulation of some popular orthographic non-Lambertian models, considering vertical and oblique light directions as well
as different viewer positions. These models lead to more complex stationary non-linear partial differential equations of Hamilton-Jacobi type which can be regarded as the generalization of the classical eikonal equation corresponding to the Lambertian case. However, all the equations corresponding to the models considered here (Oren-Nayar and Phong) have a similar structure so we can look for weak solutions to this class in the viscosity solution framework. Via this unified approach, we are able to develop a semi-Lagrangian approximation scheme for the Oren-Nayar and the Phong model and to prove a general convergence result. Numerical simulations on synthetic and real images will illustrate the effectiveness of this approach and the main features of the scheme, also comparing the results with previous results in the literature
A Convergent Semi-Lagrangian Scheme for the Game ∞-Laplacian
Full text linkWe propose a new semi-Lagrangian scheme for the game infinity-Laplacian. We demonstrate the convergence of the scheme to the viscosity solution of the given problem, showing its consistency, monotonicity, and stability. The proof of this result is established following the Barles-Souganidis analysis. This analysis assumes convergence at the boundary in a strong sense and is applied to our proposed scheme, augmented with an artificial viscosity term
A comparison of non-Lambertian models for the shape-from-shading problem
No full textIn this paper we present in a unified approach Shape-from-Shading models under orthographic projection for non-Lambertian surfaces and compare them with the classical Lambertian model. Those non-Lambertian models have been proposed in the literature by various authors in order to take into account more realistic surfaces such as rough and specular surfaces. The advantage of our unified mathematical model is the possibility to easily modify a single differential model to various situations just changing some control parameters. Moreover, the numerical approximation we propose is valid for that general model and can be easily adapted to the real situation. Finally, we compare the models on some benchmarks including real and synthetic images
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