Some properties of the spinor fourier transform

In this paper, the theory of the spinor Fourier transform introduced in [Batard T, Berthier M, Saint-Jean C, Clifford-Fourier Transform for Color Image Processing, Geometric Algebra Computing for Engineering and Computer Science (E. Bayro-Corrochano and G. Scheuermann Eds.), Springer, London, 2010, pp. 135–161] is further developed. While in the original paper, the transform was determined for vector-valued functions only, it now will be extended to functions taking values in the entire Clifford algebra. Next, two bases are determined under which this Fourier transform is diagonalizable. A main stumbling block for further applications, in particular concerning filter design in the Fourier domain, is the lack of a proper convolution theorem. This problem will be tackled in the final section of this paper

Hyperparameter-free losses for model-based monocular reconstruction

This work proposes novel hyperparameter-free losses for single view 3D reconstruction with morphable models (3DMM). We dispense with the hyperparameters used in other works by exploiting geometry, so that the shape of the object and the camera pose are jointly optimized in a sole term expression. This simplification reduces the optimization time and its complexity. Moreover, we propose a novel implicit regularization technique based on random virtual projections that does not require additional 2D or 3D annotations. Our experiments suggest that minimizing a shape reprojection error together with the proposed implicit regularization is especially suitable for applications that require precise alignment between geometry and image spaces, such as augmented reality. We evaluate our losses on a large scale dataset with 3D ground truth and publish our implementations to facilitate reproducibility and public benchmarking in this field.Peer ReviewedPostprint (author's final draft

Spinor Fourier Transform for Image Processing

We propose in this paper to introduce a new spinor Fourier transform for both grey-level and color image processing. Our approach relies on the three following considerations: mathematically speaking, defining a Fourier transform requires to deal with group actions; vectors of the acquisition space can be considered as generalized numbers when embedded in a Clifford algebra; the tangent space of the image surface appears to be a natural parameter of the transform we define by means of so-called spin characters. The resulting spinor Fourier transform may be used to perform frequency filtering that takes into account the Riemannian geometry of the image. We give examples of low-pass filtering interpreted as diffusion process. When applied to color images, the entire color information is involved in a really non marginal process

Implementation of a NEP in Java

TheNetworks of Evolutionary Processors (NEPs) are computing mechanisms directly inspired from the behavior of cell populations more specifically the point mutations in DNA strands.These mechanisms are been used for solving NP-complete problems by means of a parallel computation postulation.This paper describes an implementation of the basic model of NEP and includes the possibility of designing some of the most common variants of it by means of a graphic user interface which eases the configuration of a given problem. It is a system designed to be used in a multicore processor in order to benefit from the multi thread use

Variational models for color image correction inspired by visual perception and neuroscience

Reproducing the perception of a real-world scene on a display device is a very challenging task which requires the understanding of the camera processing pipeline, the display process, and the way the human visual system processes the light it captures. Mathematical models based on psychophysical and physiological laws on color vision, named Retinex, provide efficient tools to handle degradations produced during the camera processing pipeline like the reduction of the contrast. In particular, Batard and Bertalmío [J Math. Imag. Vis. 60(6), 849-881 (2018)] described some psy-chophysical laws on brightness perception as covariant derivatives, included them into a variational model, and observed that the quality of the color image correction is correlated with the accuracy of the vision model it includes. Based on this observation, we postulate that this model can be improved by including more accurate data on vision with a special attention on visual neuro-science here. Then, inspired by the presence of neurons responding to different visual attributes in the area V1 of the visual cortex as orientation, color or movement, to name a few, and horizontal connections modeling the interactions between those neurons, we construct two variational models to process both local (edges, textures) and global (contrast) features. This is an improvement with respect to the model of Batard and Bertalmío as the latter can not process local and global features independently and simultaneously. Finally, we conduct experiments on color images which corroborate the improvement provided by the new models

MODELISATION DES SYSTÈMES DE CONVERSION DE L'ÉNERGIE ÉLECTRIQUE DANS UN CONTEXTE PLURIDISCIPLINAIRE

Ce mémoire retrace mes activités d’Enseignant-Chercheur depuis ma nomination à l’IUT de Nantesen 1993. Ce document témoigne de l’évolution de mes travaux de recherche effectués au cours deces 20 dernières années au gré des rapprochements des différents laboratoires de la région Nantaise.La modélisation de la chaîne de conversion de l’énergie électrique est la ligne directrice de monactivité.Mes premiers travaux sont liés aux thématiques développées au sein du GE44 puis de l’IREENA.Ils concernent tout d’abord la modélisation des convertisseurs de puissance et des dispositifsd’alimentation électrique pour l’optimisation de la régulation des convertisseurs et la maitrise de lapollution des réseaux.Un paramètre essentiel dans le dimensionnement des convertisseurs de puissance est la températuredes semiconducteurs. Les compétences acquises durant ces premières années ont été mises à profitpour élaborer un simulateur électrothermique rendant compte de l’évolution de la température dejonction des semiconducteurs en fonction des différentes conditions de fonctionnement. Desmodèles thermiques compacts ont été développés pour optimiser la simulation numérique desconvertisseurs statiques.Depuis une dizaine d’années, mes activités de recherche se sont recentrées autour d’uneproblématique liée au transport de données sur les réseaux d’énergie. Ce domaine fut l’occasion dedévelopper des activités pluridisciplinaires au sein du laboratoire. Cette activité se situe à lafrontière de l’électronique de puissance et des communications numériques. Les premiers travauxcorrespondent à la transmission de données sur un réseau modulé en largeur d’impulsion (MLI) ausein d’une association convertisseur-machine à des fins de commande et de monitoring. Lesseconds travaux abordent la gestion des batteries Li-ion dans une application d’éclairage autonome.Le point commun aux deux dernières activités est la transmission de données par une technologiedu type courant porteur en ligne (CPL). Depuis 2012, cette problématique est incluse dans l’équipeSystèmes de Communications Numériques (SCN) du laboratoire IETR

Les arts de faire bureaucratique(s) de Nollywood

This article uses ethnography to explore the heterogeneous arts of practicing bureaucratization of relatively autonomous West-African movie producers who have successfully emancipated from public television in the context of structural adjustment. Through the uses of guilds and associations, a fragile self-proclaimed elite of Nigerian cinema unfolds forms of creative adaptation dealing with the processes of bureaucratization of society. As these practitioners have to invent ways of “making do” bureaucratization, they reappropriate it and even circumvent some of its forms. At the same time, they “play bureaucratic”, that is to say they showcase themselves as willing to practice norms that come from the models of both liberal democracy and global capitalism. The bureaucratization of Nollywood actually turns out as the regulation of this allegedly informal space as a market working for the nation-state.Cet article explore, par l’ethnographie, l’hétérogénéité des arts de faire bureaucratique(s) de producteurs audiovisuels ouest-africains relativement autonomes, qui se sont émancipés avec succès de la télévision publique nigériane au moment de l’ajustement structurel. Au travers d’associations professionnelles, une fragile élite autoproclamée du cinéma nigérian déploie des formes d’adaptation créative devant « faire avec » les processus de bureaucratisation de la société. Ces praticiens se réapproprient, voire contournent, des formes de bureaucratisation, tout en « faisant bureaucratique », c’est-à-dire en se (re)présentant tout disposés à mettre en œuvre des normes issues des modèles de la démocratie libérale et du capitalisme global. Finalement, la bureaucratisation de Nollywood se caractérise par la régulation de cet espace réputé informel saisi comme marché au service de l’État-nation