Liste des séminaires à venir :
Le 3 october 2019, 14h-15h, salle 314.
Emmanuel Soubies (CNRS, IRIT)
Title: Relationships between necessary optimality conditions for the l2-l0 minimization problem.
Abstract: In this talk, we will discuss the relationships between necessary optimality conditions for the l0-regularized least-squares minimization problem. Such conditions are the roots of the plethora of algorithms that have been designed to cope with this NP-hard problem. Indeed, as global optimality is in general intractable, these algorithms only ensure the convergence to suboptimal points that verify some necessary (not sufficient) optimality conditions. The degree of restrictiveness of these conditions is thus directly related to the performance of the algorithms. Within this context, we will first review the commonly used necessary optimality conditions as well as known relationships between them. Then, we will complete this hierarchy of conditions by proving new inclusion properties between the sets of candidate solutions associated to them. Moreover, we will provide a quantitative analysis of these sets. Finally, we will present numerical experiments that illustrates the fact that the performance of an algorithm is related to the restrictiveness of the optimality condition verified by the point it converges to. Joint work with Laure Blanc-Féraud and Gilles Aubert.
Le 3 october 2019, 15h-16h, salle 314.
Yvain Queau (CNRS, GREYC)
Title: Variational methods for photometric 3D-reconstruction
Abstract: Shape-from-shading (SfS) is a classic inverse problem consisting in reconstructing a 3D-shape from a single photography. Yet, it is an ill-posed problem, and its numerical solving is challenging. This talk will discuss the benefits of variational methods for modeling SfS, and for solving its ambiguities through the introduction of natural Bayesian priors. Efficient splitting-based algorithms will be presented, which yield state-of-the-art results on various real-world applications such as depth super-resolution for RGBD sensors. Possible combinations with deep learning techniques will eventually be briefly discussed.
Le 7 november 2019, 14h-15h, salle 314.
Rémi Bardenet (CNRS, Cristal)
Title:
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Le 7 november 2019, 15h-16h, salle 314.
Loïc Denis (Laboratoire Hubert Curien UMR 5516 CNRS / Université de Saint-Etienne)
Title: Exoplanet detection by direct imaging: a data-processing method based on patch covariances
Abstract: The search for exoplanets is a very active subject in astronomy. Direct observation of exoplanets requires the combination of a large telescope, an extreme adaptive-optics system, a coronagraph, and dedicated data processing methods. This presentation will discuss the importance of a good statistical model of the data and describe an approach to account for the non-stationary spatial correlations in the background signal. Compared to existing approaches, this model more closely describes the data and thus leads to improved sensitivity, more accurate photometric and astrometric characterizations and more reliable results (in particular, a controlled probability of false alarms). Results obtained with the SPHERE instrument operated by the ESO at the Very Large Telescope in Chile confirm the performance of the method. An extension of the model to microscopy will also be presented. This is a joint work with Olivier Flasseur (Laboratoire Hubert Curien, CNRS/Univ St Etienne/IOGS), Eric Thiébaut and Maud Langlois (Centre de Recherche en Astrophysique de Lyon, CNRS/Univ Lyon 1/ENS Lyon).
Le 5 december 2019, 14h-15h, salle 314.
Aurélie Bugeau (LABRI, Univ. Bordeaux)
Title:
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Le 5 december 2019, 15h-16h, salle 314.
Marianne Clausel (IECL, Univ. Lorraine)
Title:
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Pour 2019-2020, les dates sont les suivantes :