Re-identifying people in the crowd

Developing an automated surveillance system is of great interest for various reasons including forensic and security applications. In the case of a network of surveillance cameras with non-overlapping fields of view, person detection and tracking alone are insufficient to track a subject of interest across the network. In this case, instances of a person captured in one camera view need to be retrieved among a gallery of different people, in other camera views. This vision problem is commonly known as person re-identification (re-id). Cross-view instances of pedestrians exhibit varied levels of illumination, viewpoint, and pose variations which makes the problem very challenging. Despite recent progress towards improving accuracy, existing systems suffer from low applicability to real-world scenarios. This is mainly caused by the need for large amounts of annotated data from pairwise camera views to be available for training. Given the difficulty of obtaining such data and annotating it, this thesis aims to bring the person re-id problem a step closer to real-world deployment. In the first contribution, the single-shot protocol, where each individual is represented by a pair of images that need to be matched, is considered. Following the extensive annotation of four datasets for six attributes, an evaluation of the most widely used feature extraction schemes is conducted. The results reveal two high-performing descriptors among those evaluated, and show illumination variation to have the most impact on re-id accuracy. Motivated by the wide availability of videos from surveillance cameras and the additional visual and temporal information they provide, video-based person re-id is then investigated, and a su-pervised system is developed. This is achieved by improving and extending the best performing image-based person descriptor into three dimensions and combining it with distance metric learn-ing. The system obtained achieves state-of-the-art results on two widely used datasets. Given the cost and difficulty of obtaining labelled data from pairwise cameras in a network to train the model, an unsupervised video-based person re-id method is also developed. It is based on a set-based distance measure that leverages rank vectors to estimate the similarity scores between person tracklets. The proposed system outperforms other unsupervised methods by a large margin on two datasets while competing with deep learning methods on another large-scale dataset

Revisiting some practical issues in the implementation of model-free control

International audienceThis paper simplifies several aspects of the practical implementation of the newly introduced model-free control and of the corresponding "intelligent" PID controllers (M. Fliess, C. Join, "Model-free control and intelligent PID controllers: towards a possible trivialization of nonlinear control?," 15th IFAC Symp. System Identif, Saint-Malo, 2009. URL: http://hal.inria.fr/inria-00372325/en/). Four examples with their computer simulations permit to test our techniques

Nonlinear control for linear motors with friction - Application to an inverted pendulum system

International audienceA linear motor is used here as an actuator for a cart-pendulum system. The global, upward stabilization of the inverted position is aimed at. In such an under-actuated situation, (i) constraints on the motor motion (limited length) have to be taken into account and (ii) friction effects may have a strong influence (limit cycles). A two-step path planning-plus-tracking strategy allows for dealing with constraint (i). Regarding point (ii), and since friction effects are hardly modeled, a second-order sliding mode algorithm is chosen. The resulting controller is designed without any knowledge of neither the electromagnetic circuits of the linear motor (the model is a simple gain), nor the friction models (only upper bounds for the friction forces acting on both the linear motor and pendulum are required). Experimental results show good performances in tracking and regulation, both for the swing-up and stabilization phases of the inverted pendulum

Stabilisation de systèmes mécaniques sous-actionnés par commande quasi-homogène

National audienceUne commande par modes glissants d'ordre 2 est réalisée pour le contrôle de systèmes mécaniques sous-actionnés opérant en milieu incertain. Afin de stabiliser un système sous-actionné autour de sa position d'équilibre instable, une commande robuste quasi-homogène est construite pour générer un régime glissant d'ordre 2 sur une surface de glissement convenablement choisie. La dynamique équivalente par rapport à cette sortie fictive est alors asymptotiquement stable. Les performances de la loi de commande proposée sont illustrées par une étude expérimentale sur un pendule inversé

Characterization of " low-pass filtering " for some nonlinear ODE's

International audienceThe characterization of low-pass linear filters is nowadays a simple question relying on eigenvalue criteria, Bode diagram, Nyquist or Nichols plots. For nonlinear systems, the problem is more tricky. The present work tempts to develop a methodology for the characterization of " low-pass filtering " for nonlinear systems. Inspired by the DiPerna-Lions theory and relying on the theory of characteristics, the proposed method associates to the nonlinear ODE a linear transport PDE. A characterization of " low-pass filtering " is then deduced from developments on the PDE. Smooth ODE's of the form \dot{x} = F (x) are considered where the vector field F (x) is perturbed by an additive, rapidly oscillating, noise m which may have a big magnitude F (x + m). An intuitive observation is proved in this first contribution: if F has bounded derivatives, then the sensitivity of x to m decreases as the bound gets smaller or as m fluctuates faster

Nanometer-Scale Resolution Achieved with Nonradiative Excitation

International audienceNonradiative Excitation Fluorescence Microscopy (NEFM) is a promising technique allowing the observation of biological samples beyond the diraction limit. By coating a substrate with an homogeneous monolayer of quantum dots (QDs), NEFM is achieved through a nonradiative energy transfer from QDs (donors) to dye molecules located in the sample (acceptors). The excitation depth of the sample is then given by the För-ster radius, which corresponds to few nanometers above the surface. The powerful axial resolution of NEFM is highlighted by observing the adhesion of Giant Unilamellar Vesi-cles (GUVs) on strong interaction with coated surfaces. In this paper, we demonstrate that the QD-quenching level is valuable to calculate and map the distance between the membrane and the surface with a high precision along the optical axis. By tuning the electrostatic interactions between the membrane and the substrate, we have been able to measure a height displacement of ≈ 1 nm of the lipid membrane. The experimental results were discussed according to simulations, which take into account all the common forces appearing between lipid membranes and surfaces

An algebraic method for multi-dimensional derivative estimation

International audienceThis communication revisits the algebra-based results for derivative estimation presented by Fliess and coauthors in 2005. It is proposed, here, to consider multidimensional functions, namely scalar or vector fields of several variables. Such fields are locally represented by a vector Taylor series expansion, and a computation technique is presented so to put successive partial derivatives (for instance, the gradient, the Hessian matrix...) as functions of iterated integrals of the measured quantities

Vers une simplification de la commande non linéaire : l'exemple d'un avion à décollage vertical

International audience``Model-Free Control'' and ``Control with a Restricted Model'', which were recently introduced, yield an elementary and easy to tune control strategy for a ``Planar Vertical Take-off and Landing'' (PVTOL) aircraft, which has been largely studied in the academic literature via various advanced nonlinear control techniques. The efficiency of our approach is demonstrated by several convincing computer simulations

A continuous-time framework for least squares parameter estimation

International audienceThis paper proposes a continuous-time framework for the least-squares parameter estimation method through evolution equations. Nonlinear systems in the standard state space representation that are linear in the unknown, constant parameters are investigated. Two estimators are studied. The first one consists of a linear evolution equation while the second one consists of an impulsive linear evolution equation. The paper discusses some theoretical aspects related to the proposed estimators: uniqueness of a solution and an attractive equilibrium point which solves for the unknown parameters. A deterministic framework for the estimation under noisy measurements is proposed using a Sobolev space with negative index to model the noise. The noise can be of large magnitude. Concrete signals issued from an electronic device are used to discuss numerical aspects

Vers une commande sans modèle d'un palier magnétique

International audienceModel-free control is applied to a magnetic bearing, which is a quite important industrial device. The experimental results are compared to those obtained via other control techniques