Registration of retinal images from Public Health by minimising an error between vessels using an affine model with radial distortions

In order to estimate a registration model of eye fundus images made of an affinity and two radial distortions, we introduce an estimation criterion based on an error between the vessels. In [1], we estimated this model by minimising the error between characteristics points. In this paper, the detected vessels are selected using the circle and ellipse equations of the overlap area boundaries deduced from our model. Our method successfully registers 96 % of the 271 pairs in a Public Health dataset acquired mostly with different cameras. This is better than our previous method [1] and better than three other state-of-the-art methods. On a publicly available dataset, ours still better register the images than the reference method

Logarithmic mathematical morphology: a new framework adaptive to illumination changes

A new set of mathematical morphology (MM) operators adaptive to illumination changes caused by variation of exposure time or light intensity is defined thanks to the Logarithmic Image Processing (LIP) model. This model based on the physics of acquisition is consistent with human vision. The fundamental operators, the logarithmic-dilation and the logarithmic-erosion, are defined with the LIP-addition of a structuring function. The combination of these two adjunct operators gives morphological filters, namely the logarithmic-opening and closing, useful for pattern recognition. The mathematical relation existing between ``classical'' dilation and erosion and their logarithmic-versions is established facilitating their implementation. Results on simulated and real images show that logarithmic-MM is more efficient on low-contrasted information than ``classical'' MM

Superimposition of eye fundus images for longitudinal analysis from large public health databases

In this paper, a method is presented for superimposition (i.e. registration) of eye fundus images from persons with diabetes screened over many years for diabetic retinopathy. The method is fully automatic and robust to camera changes and colour variations across the images both in space and time. All the stages of the process are designed for longitudinal analysis of cohort public health databases where retinal examinations are made at approximately yearly intervals. The method relies on a model correcting two radial distortions and an affine transformation between pairs of images which is robustly fitted on salient points. Each stage involves linear estimators followed by non-linear optimisation. The model of image warping is also invertible for fast computation. The method has been validated (1) on a simulated montage and (2) on public health databases with 69 patients with high quality images (271 pairs acquired mostly with different types of camera and 268 pairs acquired mostly with the same type of camera) with success rates of 92% and 98%, and five patients (20 pairs) with low quality images with a success rate of 100%. Compared to two state-of-the-art methods, ours gives better results.Comment: This is an author-created, un-copyedited version of an article published in Biomedical Physics \& Engineering Express. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/2057-1976/aa7d1

Technique de mesure des faibles conductibilités électriques sous haute pression

We give solutions of important problems appearing in the study of electrical properties of low conductivity materials with an apparatus for measurements under hydrostatic pressure : preparation of electrical leads with a good insulation, choice of the fluid transmitting the pressure, cell for measurements on liquids.On propose des solutions à des problèmes importants qui se posent dans l'étude des propriétés électriques de corps très peu conducteurs avec un appareillage de mesure sous pression hydrostatique : réalisation de sorties électriques bien isolées, choix du fluide transmetteur de pression, cellule de mesures pour liquides

Longitudinal magneto-optical study of Brown relaxation in ferrofluids : dynamic and transient methods. Application

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Traitement de l'absorption et de la dispersion diélectriques dans le domaine des très basses fréquences par une méthode d'échantillonnage

A spectrometer using a sampling data process and a digital calculator is designed for the study of the dielectric properties of insulating materials in the very low frequency range ( f < 10-1 Hz). This device, built from conventional and versatile digital apparatus, performs better measurements than the classical analog systems (improvement ratios of five and ten are obtained, respectively, on accuracy and sensitivity for loss factor determinations).L'utilisation, aux régimes de très basse fréquence ( < 10-1 Hz), d'une technique d'échantillonnage et d'un calculateur numérique, permet de constituer un spectromètre digital adapté à l'étude des propriétés diélectriques des matériaux isolants dans cette partie du spectre. Ce dispositif, réalisé avec des appareils digitaux assez courants et polyvalents, a des performances nettement supérieures à celles de la méthode analogique classique (gains de 5 et 10 sur la précision et la sensibilité de la mesure du facteur de pertes)

Impédancemètre automatique 100 Ω−1\mathsf{\Omega{-}1} TΩ\mathsf{\Omega}

This work presents a wholly automated high impedance system working in the frequency range 1 mHz–10 kHz and conceived to measure complex impedances ($R_{\rm p}$//$C_{\rm p}$) UP to $10^{12}\Omega$. Therefore we have built, surrounding a gain phase analyser, a high impedance programmable electrometer working on shunt mode. This apparatus using high resistances and low leakage capacitors, resorts to the high impedance electronics, the components are selected by the way of very high insulating Reed switches drived by a VXI bus.Dans ce travail nous présentons un système haute impédance totalement automatique fonctionnant dans la gamme de fréquence 1 mHz–10 kHz et conçu pour la mesure des impédances complexes ($R_{\rm p}$//$C_{\rm p}$) jusqu'à 10$^{12}\Omega$. Pour cela nous avons construit, autour d'un analyseur vectoriel, un électromètre haute impédance programmable fonctionnant en mode shunt. Ce dispositif utilisant des résistances de hautes valeurs et des condensateurs à faibles fuites, fait appel à l'électronique haute impédance ; les composants sont sélectionnés au moyen de relais Reed de très haute isolation commandés par un bus VXI

Influence of particle size distribution on the initial susceptibility of magnetic fluids in the Brown relaxation range

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X-band characterization of anisotropic magnetic materials: application to ferrofluids

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