Françoise J. Prêteux

Variability of bronchial measurements obtained by sequential CT using two computer-based methods

This study aimed to evaluate the variability of lumen (LA) and wall area (WA) measurements obtained on two successive MDCT acquisitions using energy-driven contour estimation (EDCE) and full width at half maximum (FWHM) approaches. Both methods were applied to a database of segmental and subsegmental bronchi with LAu2009>u20094xa0mm2 containing 42 bronchial segments of 10 successive slices that best matched on each acquisition. For both methods, the 95% confidence interval between repeated MDCT was between –1.59 and 1.5xa0mm2 for LA, and –3.31 and 2.96xa0mm2 for WA. The values of the coefficient of measurement variation (CV10, i.e., percentage ratio of the standard deviation obtained from the 10 successive slices to their mean value) were strongly correlated between repeated MDCT data acquisitions (ru2009>u20090.72; pu2009<u20090.0001). Compared with FWHM, LA values obtained using EDCE were higher for LAu2009<u200915xa0mm2, whereas WA values were lower for bronchi with WAu2009<u200913xa0mm2; no systematic EDCE underestimation or overestimation was observed for thicker-walled bronchi. In conclusion, variability between CT examinations and assessment techniques may impair measurements. Therefore, new parameters such as CV10 need to be investigated to study bronchial remodeling. Finally, EDCE and FWHM are not interchangeable in longitudinal studies.

MPEG-4 Part 25: A graphics compression framework for XML-based scene graph formats

This paper introduces a new model for applying 3D graphics compression to arbitrary scene graphs, recently adopted by MPEG in Part 25 of the MPEG-4 standard. The goal of the model is twofold: to liberate the powerful MPEG compression techniques from the scene graph representation based on BIFS and to position the compression as a transparent layer in the 3D graphics chain, thus making it easy to integrate in third party authoring tools or end-user applications. In addition, intrinsic features of the compression tools such as progressive decoding or streaming are preserved. Currently implemented on top of COLLAborative Design Activity (COLLADA) and eXtensible 3D (X3D), the proposed model will leverage the deployment of MPEG-4 compression for 3D graphics. The software implementation, publicly available under ISO license, is introduced and reports and analyses of the compression results on large database are outlined in the document.

Statistical motion vector analysis for object tracking in compressed video streams

Compressed video is the digital raw material provided by video-surveillance systems and used for archiving and indexing purposes. Multimedia standards have therefore a direct impact on such systems. If MPEG-2 used to be the coding standard, MPEG-4 (part 2) has now replaced it in most installations, and MPEG-4 AVC/H.264 solutions are now being released. Finely analysing the complex and rich MPEG-4 streams is a challenging issue addressed in that paper. The system we designed is based on five modules: low-resolution decoder, motion estimation generator, object motion filtering, low-resolution object segmentation, and cooperative decision. Our contributions refer to as the statistical analysis of the spatial distribution of the motion vectors, the computation of DCT-based confidence maps, the automatic motion activity detection in the compressed file and a rough indexation by dedicated descriptors. The robustness and accuracy of the system are evaluated on a large corpus (hundreds of hours of in-and outdoor videos with pedestrians and vehicles). The objective benchmarking of the performances is achieved with respect to five metrics allowing to estimate the error part due to each module and for different implementations. This evaluation establishes that our system analyses up to 200 frames (720x288) per second (2.66 GHz CPU).

MPEG-4 AVC domain watermarking transparency

The ever-increasing Internet distribution of video content is echoed in ever-increasing efforts to devise systems balancing copyright protection and user rights. Watermarking is such an example: by persistently and imperceptibly associating some data with the host video, it offers at the same time a reliable and user-friendly solution for copyright infringement tracking. This paper takes a closer look at the apparent contradiction between watermarking (using the visual redundancy of the video to embed the data) and compression (eliminating the visual redundancy in order to speed up distribution and to alleviate storage requirements). In this respect, the viability of compressed domain watermarking is evaluated by analysing the visual effects of the MPEG-4 AVC stream alteration. The corpus consists of 10 video sequences of about 25 minutes each, coded at 256kbps and 64 kbps.

A Triangle-Fan-based approach for low complexity 3D mesh compression

This paper proposes a novel approach for mono-resolution 3D mesh compression, called TFAN (Triangle Fan-based compression). TFAN treats in a unified manner meshes of arbitrary topologies, i.e. manifold or not, oriented or not, while supporting real-time decoding. The proposed approach has been evaluated on both manifold and non-manifold databases, including more than 7000 3D mesh models. Experiments show that the TFAN approach outperforms existing techniques such as MPEG-4 3DMC or Tourna & Gotsman, with decoding times lower by an order of magnitude at equivalent or even better levels of compression efficiency (+/-10% in bitrate). When applied to non-manifold 3D data, the compression performances are significantly enhanced (6% to 30% gain in bitrate). Due to its high compression performances TFAN has been recently retained for ISO MPEG-4 standardization.

When MPEG-4 and COLLADA meet for a complete solution of distributing and rendering 3D graphics assets

In this paper we present an implementation of a 3D graphics player showing for a first time worldwide a successful integration between COLLADA, a standard for representing 3D graphics assets, and MPEG-4, a standard for compression and delivery of the assets.

On-Line Animation System for Learning and Practice Cued Speech

This paper presents a set of technologies developed with the goal to improve the learning and practice of Cued Speech (CS). They are based on 3D graphics and are covering the entire end-to-end content chain: production, transmission and visualization. Starting from the requirements of an online system for CS, the research and development path took into account real-time constraints, personalization, user acceptability and equally important, the easiness and feasibility of the deployment. The original components of the system include 3D graphics and animation encoders, streaming servers and visualization engines and are validated in two applications: a web service for text to animation conversion and a chat service supporting two or more users.

Auto-production 3D Graphics Content for Mobile Communication

In this paper we present a new mobile service that enable auto-production of 3D graphics content for mobile platform. The general benefit of this service is that it enriches the content of the communication, containing a video stream of an animated avatars produced by dedicated servers controlled by the mobile end-user. The approach consists in selecting an avatar, download it on the mobile phone as a 3D object and composing the message by playing with avatar instead of typing text. Message can be enriched more by adding background to the scene and subtitles for animation sub-sequences. The tests performed show the feasibility of the proposed solution in terms of transmission cost.

The watermarking attacks in the MPEG-4 AVC domain

The explosion of VoD and HDTV services opened a new direction in watermarking applications: compressed domain watermarking, promising at least tenfold speed increase. While sound technical approaches to this emerging field are already available in the literature, at our best knowledge the present paper is the first related theoretical study. It considers the ISO/IEC 14496-10:2005 standard (also known as MPEG-4 AVC) and objectively describes with information theory concepts (noisy channel, noise matrices) the effects of the real-life watermarking attacks (like rotations, linear and non-linear filtering, StirMark). All the results are obtained on a heterogeneous corpus of 7 video sequences summing up to about 3 hours.

Probability density function estimation for video in the DCT domain

Regardless the final targeted application (compression, watermarking, texture analysis, indexation, ...), image/video modelling in the DCT domain is generally approached by tests of concordance with some well known pdfs (like Gaussian, generalised Gaussian, Laplace, Rayleigh ...). Instead of forcing the images/videos to stick to such theoretical models, our study aims at estimating the true pdf characterising their behaviour. In this respect, we considered three intensively used ways of applying DCT, namely on whole frames, on 4x4 blocks, and on 8x8 blocks. In each case, we first prove that a law modelling the corresponding coefficients exists. Then, we estimate this law by Gaussian mixtures and finally we identify the generality of such model with respect to the data on which it was computed and to the estimation method it relies on.