Perceptual Quality Metric as a Performance Tool for ATM Adaptation of MPEG-2 Based Multimedia Applications

In this paper we study the perceptual impact of data loss on MPEG-2 video coded streams transmitted over an ATM network. This impact is measured using a perceptual quality metric based on a spatio-temporal model of the human visual system. Video streams have been transmitted on top of both new network and ATM adaptation layers which provide a robust transmission by applying per-cell sequence numbering combined with a selective Forward Error Correction (FEC) mechanism. We compare their performance against a transmission over AAL5. Results show that the proposed AAL behaves better in terms of both network performance and perceived quality of the MPEG-2 decoded sequenc

Enseigner avec des classes hétérogènes en EPS

National audienceLes hétérogénéités en éducation physique relèvent de deux types de variables prépondérantes : les niveaux d'habiletés, les orientations de genre . Pour ces dernières les sociologues expliquent les formes de scolarisation différentielle des filles et des garçons en mettant en avant deux explications majeures : les effets du curriculum caché qui ne prendrait pas en considération les rapports sexués aux savoirs, et l'inégalité des interactions professeurs - élèves selon les sexes. Les garçons sont décrits comme dominant l'espace de la classe ce qui expliquerait qu'ils bénéficient de davantage d'attention de leur professeur. L'approche didactique, en s'intéressant aux apprentissages différentiels des élèves en EPS (plus particulièrement dans ce chapitre ceux liés au genre) prolonge et nuance ces analyses. Elle met en évidence des phénomènes ténus et complexes à l'origine de certaines inégalités de traitement. En même temps, elle souligne combien professeurs et élèves dans leur diversité réussissent à créer des conditions d'étude permettant la réussite de beaucoup. Dans la dynamique interactive la manière dont les élèves s'engagent dans l'étude est en partie le résultat de phénomènes différentiels impliquant conjointement le professeur, les élèves et les savoirs en jeu dans les tâches proposées. Les hétérogénéités qui en résultent relèvent de l'effet combiné de multiples facteurs : le niveau d'habileté (sur un continuum forts - faibles), le genre (sur un continuum féminin vs masculin), la nature des attentes professorales en lien avec le type de tâche proposée et le type de savoir valorisé. Le contrat didactique différentiel est un outil théorique permettant d'expliquer les modes de construction des hétérogénéités scolaires in situ. Les phénomènes différenciateurs sont inéluctables. Ils peuvent avoir pour conséquences certaines cristallisations à l'origine des difficultés ou échecs de certaines filles et certains élèves faibles. Ainsi, le professeur au fil des interactions doit être attentif à maintenir la double valence des tâches permettant aux élèves, selon leur orientation de genre ou leur niveau d'habiletés de tirer parti des milieux didactiques qui leur sont proposés

Perceptual Quality Measure using a Spatio-Temporal Model of the Human Visual System

This paper addresses the problem of quality estimation of digitally coded video sequences. The topic is of great interest since many products in digital video are about to be released and it is thus important to have robust methodologies for testing and performance evaluation of such devices. The inherent problem is that human vision has to be taken into account in order to assess the quality of a sequence with a good correlation with human judgment. It is well known that the commonly used metric, the signal-to-noise ratio is not correlated with human vision. A metric for the assessment of video coding quality is presented. It is based on a multi- channel model of human spatio-temporal vision that has been parameterized for video coding applications by psychophysical experiments. The visual mechanisms of vision are simulated by a spatio-temporal filter bank. The decomposition is then used to account for phenomena as contrast sensitivity and masking. Once the amount of distortions actually perceived is known, quality estimation can be assessed at various levels. The described metric is able to rate the overall quality of the decoded video sequence as well as the rendition of important features of the sequence such as contours or textures

A new flexible and modular QoS mapping framework based on psychophysics

Accounting for the perceiving conditions that make up the delivery environment of an application helps improve the efficiency of QoS provisioning systems. It is useless to transmit information whose absence cannot be noticed by the end-user under the actual perceiving conditions. Until now, QoS architectures mostly focused on the transport system and did not integrate the studies achieved in the psychophysics area. In this paper, we propose a QoS framework that accounts for the perceiving conditions. Moreover, our framework is both flexible - i.e., customizable at will by the manager - and modular, with a clear and fine-grained layering. New mechanisms and their supporting characteristics, such as experimental curves, may be very easily introduced and managed in the proposed architecture. A case study is carried out, which shows the applicability of the framework for a video-on-demand provisioning system

Joint Inversion of Fracture Model Properties for CO2 Storage Monitoring or Oil Recovery History Matching

International audienceFor oil recovery or CO2 storage, "reservoirs" are commonly used to designate geological structures where oil can be found or CO2 can be stored. All reservoirs present a heterogeneity in terms of rock type and properties (such as porosity and permeability). In addition, some of these reservoirs present fractures and faults. Fractured reservoirs are an important part of the oil reserves in the world (Middle East, Gulf of Mexico, etc.) and some of them are important reservoirs in terms of oil volume and productivity in spite of the fractures. In addition, studies of reservoirs for geologic storage of CO2 have shown the existence of diffuse fractures and faults and their strong impacts on flow. A key point in fractured reservoirs is to understand the geometry and hydraulic conductivity of the network formed by the fractures. This requires the construction of a reservoir model that integrates all available conceptual knowledge and quantitative data. The topic of the present paper deals with a new methodology able to perform the history matching of a fractured reservoir model by adapting the sub-seismic fault properties and positions. The main difficulty of this work is to generate a sub-seismic fault network whose fault positions can be easily modified while respecting the statistical fault model. The sub-seismic fault model we have chosen allows us to obtain a sub-seismic fault network that is consistent with the seismic fault network and that succeeds in capturing the specific spatial organization of the faults. In a first step, the geometry of the seismic fault network is characterized using fractal methods. Sub-seismic faults are then generated according to a stochastic algorithm. Finally, the geometry of this discrete fracture network is optimized in order to match the hydrodynamic data about the reservoir. The optimization algorithm modifies the sub-seismic fault positions, leading to the history matching of the reservoir model. Fractal properties are preserved during the deformation process. These different steps are demonstrated on a realistic synthetic case

User-Oriented QoS in Packet Video Delivery

We focus on packet video delivery, with an emphasis on the quality of service perceived by the end-user. A video signal passes through several subsystems, such as the source coder, the network and the decoder. Each of these can impair the information, either by data loss or by introducing delay. We describe how each of the subsystems can be tuned to optimize the quality of the delivered signal, for a given available bit rate in the network. The assessment of end-user quality is not trivial. We present recent research results, which rely on a model of the human visual system

Management of multimedia resources: from a generic information model to its application to an MPEG2 video codec

New open service architectures provide a management framework for telecommunications services, telecommunications networks and computing resources. However, the introduction of multimedia applications in these architectures will require the management of the underlying multimedia resources (e.g., codecs, converters, etc). Multimedia resources are the basic components that support multimedia communications. In this paper, we tackle this issue by proposing a generic management information model for multimedia resources and then instantiate it for the management of an MPEG2 video codec. This information model provides a data representation of the multimedia resources in order to manage them efficiently