Denis Hamad

Four wheel steering control by fuzzy approach

This study introduces a fuzzy four-wheel steering control design method for automotive vehicles. After the analysis of some stability aspects of the vehicle lateral motion, including front steering angle variations, the representation of vehicle nonlinear model by Takagi-Sugeno (T-S) fuzzy model is presented. Next, based on the fuzzy model, a fuzzy controller is developed to improve the stability of the vehicle. Sufficient conditions for stability and stabilization of the T-S fuzzy model using fuzzy feedback controllers is given. To demonstrate the effectiveness of the proposed fuzzy controller, simulation results are given showing the performance improvements of the vehicle in terms of the stability and the maneuverability in critical situations.

Constraint scores for semi-supervised feature selection: A comparative study

Recent feature selection scores using pairwise constraints (must-link and cannot-link) have shown better performances than the unsupervised methods and comparable to the supervised ones. However, these scores use only the pairwise constraints and ignore the available information brought by the unlabeled data. Moreover, these constraint scores strongly depend on the given must-link and cannot-link subsets built by the user. In this paper, we address these problems and propose a new semi-supervised constraint score that uses both pairwise constraints and local properties of the unlabeled data. Experiments using Kendalls coefficient and accuracy rates, show that this new score is less sensitive to the given constraints than the previous scores while providing similar performances.

LBP histogram selection for supervised color texture classification

In this paper, we propose a Local Binary Pattern (LBP) histogram selection approach. It consists in assigning to each histogram a score which measures its efficiency to characterize the similarity of the textures within the different classes. The histograms are then ranked according to the proposed score and the most discriminant ones are selected. Experiments, which have been carried out on benchmark color texture image databases, show that the proposed histogram selection approach is able to improve the classification performances.

Bounded Influence Support Vector Regression for Robust Single-Model Estimation

Support vector regression (SVR) is now a well-established method for estimating real-valued functions. However, the standard SVR is not effective to deal with severe outlier contamination of both response and predictor variables commonly encountered in numerous real applications. In this paper, we present a bounded influence SVR, which downweights the influence of outliers in all the regression variables. The proposed approach adopts an adaptive weighting strategy, which is based on both a robust adaptive scale estimator for large regression residuals and the statistic of a ldquokernelizedrdquo hat matrix for leverage point removal. Thus, our algorithm has the ability to accurately extract the dominant subset in corrupted data sets. Simulated linear and nonlinear data sets show the robustness of our algorithm against outliers. Last, chemical and astronomical data sets that exhibit severe outlier contamination are used to demonstrate the performance of the proposed approach in real situations.

Introduction to spectral clustering

Spectral clustering methods are based on graph and matrix theories. Their principle is simple: given some data inputs, build similarity matrix, analyse the spectrum of its Laplacian matrix, and often get a perfect clustering from the eigenvectors analysis. This paper presents an introduction to spectral clustering methods and some applications in signal and image segmentation.

A new benchmark image test suite for evaluating colour texture classification schemes

Several image test suites are available in the literature to evaluate the performance of classification schemes. In the framework of colour texture classification, OuTex-TC-00013 (OuTex) and Contrib-TC-00006 (VisTex) are often used. These colour texture image sets have allowed the accuracies reached by many classification schemes to be compared. However, by analysing the classification results obtained with these two sets of colour texture images, we have noticed that the use of colour histogram yields a higher rate of well-classified images compared to colour texture features. It does not take into account any texture information in the image, this incoherence leads us to question the relevance of these two benchmark colour texture sets for measuring the performances of colour texture classification algorithms. Indeed, the partitioning used to build these two sets consists of extracting training and validating sub-images of an original image. We show that such partitioning leads to biased classification results when it is combined with a classifier such as the nearest neighbour. In this paper a new relevant image test suite is proposed for evaluating colour texture classification schemes. The training and the validating sub-images come from different original images in order to ensure that the correlation of the colour texture images is minimized.

K-means Clustering Algorithm in Projected Spaces

Clustering has been known as a popular technique for pattern recognition, image processing, and data mining. Unfortunately, all known clustering algorithms tend to break down in high dimensional spaces; this is due to the inherent sparsity of the points. We investigate, in this paper, the use of linear and nonlinear principal manifolds for learning low-dimensional representations for clustering. Several leading methods: PCA, KPCA, Sammon, and CCA are examined and tested in clustering experiments using synthetic and real datasets from the UCI databases. We compare the clustering performance of the K-means algorithm on data projected by these projection methods. The experimental results show that K-means clustering on data projected by KPCA outperforms those projected by the three other methods

Image noise detection in global illumination methods based on FRVM

Global illumination methods based on stochastic techniques provide photo-realistic images. However, they are prone to stochastic perceptual noise that can be reduced by increasing the number of paths as proved by Monte Carlo theory. The problem of finding the required number of paths in order to ensure that human observers cannot perceive any noise is still open. Until now, we do not know precisely which features are considered by the human visual system (HVS) for the evaluation of the image quality. This paper proposes a relevant model to predict which image highlights perceptual noise by using fast relevance vector machine (FRVM). This model can then be used in any progressive stochastic global illumination method in order to find the visual convergence threshold of different parts of any image. A comparative study of this model with experimental psycho-visual scores demonstrates the good consistency between these scores and the model quality measures. The proposed model has also been compared with SVM model and gives competitive performances.

Robust Regression and Outlier Detection with SVR: Application to Optic Flow Estimation.

The robust regression is an important tool for the analysis of data contamined by outliers. In computer vision, the optic flow computation is considered as belonging to this kind of problem. In this paper, we discuss a robust optic flow computation based on a modified support vector regression (SVR) technique. We experimentally show that the proposed method significantly improves the robustness against outliers compared to traditional SVR. Next, we illustrate the performances of the method for the optic flow computation problem from noised image sequences.

Control of a robot manipulator and pendubot system using artificial neural networks

The paper introduces artificial neural networks for the conventional control of robotic systems for better tracking performance. Different advanced dynamic control techniques are explained and a new second order recursive algorithm has been developed to tune the weights of the neural network. The problem of real-time control of a Pendubot system in difficult situations has been addressed. Examples, such as positioning and balancing structures, are presented and performances are compared to a conventional PD controller.