Target detection with a liquid crystal-based passive Stokes polarimeter

International audienceWe present an imaging system that measures the polarimetric state of the light coming from each point of a scene. This system, which determines the four components of the Stokes vector at each spatial location, is based on a liquid-crystal polarization modulator, which makes it possible to acquire fourdimensional Stokes parameter images at a standard video rate. We show that using such polarimetric images instead of simple intensity images can improve target detection and segmentation performance

Une methode d'etude de la diffusion photonique par des surfaces rugueuses

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 82260 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Improving segmentation maps using polarization imaging

ABSTRACT Within the frame of polarimetric imagery, segmentation of 4 × 4 Mueller images consists in isolating objects that have different polarizing properties. Such objects are either partial polarizers, rotators or phasors. This means that there are 3 main polarization classes to consider. The difficulty in polarimetric segmentation comes from the fact that the relations between each of the mentioned class and the 4 × 4 elements of a Mueller matrix are not completely identified. Rather than dealing with unidentified quantities, Mueller images are transformed into intensity images so that robust classical segmentation procedures such as Hidden Markov Chain (HMC) can be applied. Such transformation is possible because it is the reversion procedure of the Mueller matrices retrieval procedure. Also, it is worth mentioning that the noise in the intensity images can be inferred so that the approach is mathematically rigorous. When applied to simulated or recorded images, it appears that the method outperforms approaches based on direct segmentation of Mueller images

Mise au point de méthodes polarimétriques pour la stéréovision

Les applications de vision par ordinateur nécessitent de plus en plus des outils efficaces pour le calcul des descriptifs scéniques des objets manufacturés. Dans ce cadre, la stéréoscopie apparaît aujourd'hui comme une modalité maîtrisée de reconstruction d'objets tridimensionnels par imagerie optique. Le principe conventionnel repose sur l'acquisition d'une paire d'images issues d'un capteur dont la position aura été modifiée. L'aspect algorithmique lié au traitement est marqué par une étape délicate appelée \appariement" dont l'objectif est de trouver avec la plus grande précision permise les points communs aux deux images, recherche basée à la fois sur les propriétés géométriques des droites dites épipolaires et sur une procédure de minimisation de l'erreur de positionnement. Lorsqu'un objet est transparent ou lorsqu'il présente des arêtes vives devant le capteur, l'aveuglement de la caméra qui en résulte se traduit par une perte d'information de contour portée par les points invisibles ou saturés dans les images stéréoscopiques. En revanche, en imagerie optique active, la possibilité de modifier la polarisation de l'éclairement et celle des états d'analyse permet de faire apparaître les contours transparents ou d'atténuer l'intensité des arêtes vives grâce notamment à la réponse de Fresnel des interfaces, couplée à la diffusion liées aux inhomogénéités surfaciques ou volumiques. Dans ce travail doctoral, nous avons développé une approche stéréoscopique avec les images de Mueller afin de lever les ambiguïtés rencontrées lors d'acquisitions d'images conventionnelles. Une telle modalité, l'imagerie polarimétriques, représente naturellement une solution aux contraintes physiques auxquelles est soumise la stéréoscopie conventionnelle.Within the frame of industrial object inspection, the stereoscopic reconstruction technique seems to be an achieved method for three-dimensional objects reconstruction by optical imagery. The conventional technique rests on the acquisition of a pair of images resulting from a camera sensor which position has been modi ed. The algorithmic aspect related to the treatment is marked by a delicate stage called \matching" which objective is to nd with the highest possible degree of accuracy the common points to both images, a search based at the same time on the geometrical properties of the lines known as epipolar and on a procedure of minimization of the error of positioning. When an object is transparent or when it has an active contour in front of the camera sensor, the blindness of the camera which results from it causes a loss of information of contours carried by the invisible or saturated points in the stereoscopic images. On the other hand, active optical imagery consists in modifying polarization states that are generated or analyzed by the illumination or the observation systems. This permits to reveal transparent contours or to attenuate the high reflecting intensities thanks in particular to the Fresnel response of the interfaces, coupled with the di®usion related to the surface or volumetric inhomogeneities. In this work, we have developed a stereoscopic approach based on Mueller images which allows to reduce ambiguities confronted with usual imaging techniques. Such a method, the polarimetric imagery, represents naturally a solution to the physical constraints to which is subjected conventional stereoscopy.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Waveguide driven photonic jet : FEM, issues and perspectives

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Boundary Impedance Operator to Study Tipped Parallel Plate Waveguides

International audienceAn integral method is proposed to compute the field at the vicinity of the tip of a full planar waveguide with perfect electric conductor boundaries. It is based on an impedance operator which permits to relate parallel components of the electromagnetic field so that the usual coupled integral equations with hypersingular kernels may be avoided. Comparison with a well-established finite-element-based approach shows good agreement. Because the method is fast, it could be incorporated in optimization procedures such as waveguide driven photonic jets enhancement