Alain Ayache

Robust B-spline snakes for ultrasound image segmentation

Snake-based methods are commonly used to segment ultrasound images. However, their performance is generally limited because of the specific properties of this kind of images. This paper addresses the sensitivity of parametric active contours to speckle within ultrasound images. We propose a new B-spline snake model, founded on two original external energies specifically tailored for the segmentation of biomedical speckled images. First, the curve is attracted from a wide capture range with an expansion energy that facilitates the snake initialization. Then, it is accurately fitted on the region boundaries with an energy that allows precise positioning of the curve along edges in ultrasound images. A mutual inhibition function is designed to control the two energies. Results on real ultrasound images are presented and quantitatively compared to the boundaries manually outlined by experts. Our method improves the precision of heart cavities segmentation.

A robust speckle reducing anisotropic diffusion

This paper deals with anisotropic diffusion in images affected by speckle. Two existing methods are reviewed. The first is a robust diffusion technique, non adapted to speckle, based on the Tukey function. The second applies an isotropic diffusion to speckle but lacks robustness. The contribution of this paper is to create a robust anisotropic diffusion filter adapted to speckle. The proposed approach is based on the two reviewed methods and introduces an original diffusion tensor Experimentation results are presented and the performance of the three methods compared. The proposed algorithm shows significant enhancement.

Quasi-automatic initialization for parametric active contours

Active contour is a well-known image segmentation technique, commonly used to find object boundaries in images. Its main benefit is its ability to retrieve an ordered collection of points. However, fitting precisely a deformable contour to actual boundaries depends strongly on its initialization and requires adjusting various parameters. This paper presents an original method to initialize quasi-automatically explicit deformable models when segmenting regions that require no change of topology. The proposed method relies on a careful study of the gradient vector flow. Two original concepts are introduced, namely strong and weak divergence centers. The analysis of the properties of these centers leads to establishing a quasi-automatic method to setup an initial curve that will reach all the boundaries of a target region. Results using synthetic and real images are presented, showing the validity of our approach.

A general quasi-automatic initialization for snakes: application to ultrasound images

Segmentation with active contours is heavily dependent on the initialization. In this paper we propose a novel method for a quasi-automatic initialization of deformable models. Our method relies on the use of an additional energy based on the gradient vector flow. We define the centers of strong and weak divergence and use them to set up the initial curve. As our goal is the segmentation of the heart cavities, we also propose a new gradient vector field for ultrasound images based on the coefficient of variation. Results on real ultra-sound images are presented and compared to the boundaries manually outlined by an expert. They confirm the potential of the method.

NETPRO: an innovative approach to network project based learning

The development of information and communication technology has lead to the reorganisation of work methods and processes. More and more tasks are accomplished in a collaborative way by geographically distributed teams. These new working methods require proper training and appropriate skills, especially the ability to work in virtual environments. NETPRO (Network Based Project Learning in Engineering Education) is a European pilot project that addresses these issues. Its objective is to elaborate an innovative network based project learning model for engineering education and to develop web-based tools for implementing and supporting this pedagogy. This paper discusses some features of project-based pedagogy and proposes a model of a project-based learning management system.

A framework for adapting instruction to cognitive learning styles

We present the main components of an adaptive tutoring system based on cognitive learning styles. A Bayesian network is used to model the student learning style. An original domain model based on Bloom taxonomy is adopted. An instruction adaptation module matches the student style to the domain model based on pedagogical rules that can be modified.

Axial stereovision: modelization and comparison between two calibration methods

In passive binocular stereovision, there are generally two approaches: the lateral stereovision and the axial stereovision. The authors present a study relating more particularly to axial stereovision. Most of the works on axial stereovision have been theoretical. These studies have not been followed by real experiments because their authors could not produce a practical description of an axial stereovision system. The present authors propose a method to get a real axial stereovision system by calibration then by rectification. They also compare their axial stereovision system calibration method to the only one serious calibration process they found in the existing papers.<<ETX>>

Multisensor High-Performance Terminal for Indoor Infrared Cellular Network

This communication describes the High-Performance Terminal of the ESPRIT II Factory Customer Premise Network project. In the first section, a brief description of the network architecture is given, showing the function of this terminal. It is shown that it is expected to integrate Audio-Signal Processing up to the level of the automatic recognition of acoustic signatures, and Image processing up to feature extraction and image compression. The second section is devoted to the description of the signal processing algorithms, together with some relevant results of the recognition procedure. The third section gives an insight of the image processing algorithms, with a special attention paid to their 3-D capability.

Comparison between two axial stereovision systems

In this paper, general characteristics of <1x ia l stcreovision systems arc presented. The advantages and disadvantages of these systems arc examined. The experimental results with video-camera displacement and a video-camera with a 1.00111 system arc present ed and we conclude that it is more interesting to vary video-camera fornl length than to increase he displacement of t he video-camera w it h a fixed focal length.

A Color-Based System For Fruit Sorting

Image analysis is a powerful means to solve automatically many problems in industrial applications. In that purpose, the realization of an efficient prototype for color based sorting of fruits, has been undertaken in the laboratory. The prototype has to sort apples, as well as different kinds of red apples than different kinds of green apples. The device is able to sort simultaneously apples on several conveyor-belts. i Versus most of existing devices, which merely average the radiometries of a part of the fruit, by analogical means, our system analyses the whole surface. By taking each pixel information into account after digitization of the image, we can avoid the drawback to do not care about color non-homogeneity.