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

Éditorial

Ce troisième numéro spécial de la revue eJRIEPS est consacré aux actes de la 11ème Biennale de l’Association pour la recherche sur l’intervention en sport qui s’est tenue à Lille du 19-21 juin 2018. Le colloque intitulé « L'intervention dans les pratiques physiques, sportives et artistiques : Responsabilités et Stratégies des acteurs » s’est centré sur l’analyse de l’intervention en sport et en éducation physique. Les activités physiques, sportives, et artistiques apparaissent souvent comme u..

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

Optimal Smoothing for Guaranteed Service

We consider a scenario where multimedia data is sent over a network offering a guaranteed service such as ATM VBR or the guaranteed service of the IETF. A smoothing device writes the stream into a networking device for transmission, possibly with some pre-fetching; at the destination, the decoder waits for an initial playback delay and reads the stream from the receive buffer. We consider the problem of whether there exists a smoothing which minimizes the playback delay and the receive buffer size over all possible strategies, given that we know a service curve property for the flow in the network. We show that there does exist such an optimal smoothing. It can be expressed using the deconvolution operator of min-plus algebra. We obtain the smallest playback delay which can be achieved by smoothing, provided that the information about the network is reduced to its service curve . We also give a constructive expression for the deconvolution operator, using a time inversion transform, introduced in the paper. We illustrate on some examples the difference with optimal shaping, a smoothing strategy which aims at minimizing buffer and delay on the sender side but does not allow pre-fetching. We apply the theory to the determination of the minimum T-SPEC required to support a given flow with admissible playback delay or decoding buffer size constraints

Fast keyword detection with sparse time-frequency models

We address the problem of keyword spotting in continuous speech streams when training and testing conditions can be different. We propose a keyword spotting algorithm based on sparse representation of speech signals in a time-frequency feature space. The training speech elements are jointly represented in a common subspace built on simple basis functions. The subspace is trained in order to capture the common time-frequency structures from different occurrences of the keywords to be spotted. The keyword spotting algorithm then employs a sliding window mechanism on speech streams. It computes the contribution of successive speech segments in the subspace of interest and evaluates the similarity with the training data. Experimental results on the TIMIT database show the effectiveness and the noise resilience of the low complexity spotting algorithm

Reliable Transmission of MPEG-2 VBR Video Streams over New Network Adaptation and ATM Adaptation Layers

This paper adresses the transmission of VBR MPEG-2 video streams on top of both Network Adaptation (NAL) and ATM Adaptation Layers (AAL) for real-time multimedia applications. The NAL, specific to MPEG-2, provides a selective data protection mechanism based on syntactic criteria. The AAL provides a reliable transmission by applying per-cell sequence numbering combined with a selective Forward Error Correction (FEC) mechanism based on Burst Erasure codes. Studies carried out with Constant Bit Rate (CBR) video streams showed improvements in terms of network performance evaluated by the cell loss ratio (CLR) as well as in terms of user perceived quality compared to the performance obtained with AAL5 under the same network conditions. This paper proposes improvements at the NAL and presents the results obtained for the transmission of Variable Bit Rate (VBR) video streams. To evalute the impact of cell losses at the application level, we apply a perceptual quality measure to the decoded MPEG-2 sequences which allows us to evaluate performance at the user level

Identification of major factors influencing ELISpot-based monitoring of cellular responses to antigens from mycobacterium tuberculosis

A number of different interferon-c ELISpot protocols are in use in laboratories studying antigen-specific immune responses. It is therefore unclear how results from different assays compare, and what factors most significantly influence assay outcome. One such difference is that some laboratories use a short in vitro stimulation period of cells before they are transferred to the ELISpot plate; this is commonly done in the case of frozen cells, in order to enhance assay sensitivity. Other differences that may be significant include antibody coating of plates, the use of media with or without serum, the serum source and the number of cells added to the wells. The aim of this paper was to identify which components of the different ELISpot protocols influenced assay sensitivity and inter-laboratory variation. Four laboratories provided protocols for quantifying numbers of interferon-c spot forming cells in human peripheral blood mononuclear cells stimulated with Mycobacterium tuberculosis derived antigens. The differences in the protocols were compared directly. We found that several sources of variation in assay protocols can be eliminated, for example by avoiding serum supplementation and using AIM-V serum free medium. In addition, the number of cells added to ELISpot wells should also be standardised. Importantly, delays in peripheral blood mononuclear cell processing before stimulation had a marked effect on the number of detectable spot forming cells; processing delay thus should be minimised as well as standardised. Finally, a pre-stimulation culture period improved the sensitivity of the assay, however this effect may be both antigen and donor dependent. In conclusion, small differences in ELISpot protocols in routine use can affect the results obtained and care should be given to conditions selected for use in a given study. A pre-stimulation step may improve the sensitivity of the assay, particularly when cells have been previously frozen