Catálogo de publicaciones - libros

Multicast and Broadcast Service (MBS) is a novel application supported by the currently released IEEE 802.16e. This service can increase the efficiency of WiMAX networks. The key management and distribution is crucial to evolve MBS efficiently and safely. In this paper, we present a group-based key distribution algorithm GKDA to provide a more scalable solution to reduce the key updating overhead, therefore a base station (BS) can support and maintain more MBS users. Theoretical analyses and simulation results have proven the performance and advantage of our algorithm. In addition, GKDA can strengthen the network security.

In this paper, we propose a watermarking algorithm working directly on JPEG bit-stream. The algorithm embeds watermark bits by modifying de-quantized DC coefficients. By improving an existing embedding method for watermark bit, the quality of the watermarked image can be improved greatly while keeping the same robustness of the original method. Further more, we analyze the performance of the watermarking algorithm against re-quantization and recompression. We give the relationship among the watermarking strength, the quality factor of JPEG compression and the BER (Bit Error Rate) of the watermark. Experiment results support the analysis. Compared with several JPEG-based algorithms in literature, the robustness to JPEG recompression of the proposed algorithm is better than most of them when recompression quality factor is above 30.

Although no scalability is explicitly defined in the H.264/ AVC specification, some forms of scalability can be achieved by using the available coding tools in a creative way. In this paper we will explain how to use the data partitioning tool to perform a coarse form of SNR scalability. The impact of various parameters, including the presence of IDR frames and the number of intra-coded macroblocks per frame, on bit rate and bit rate savings and on quality and quality loss will be discussed. Furthermore we will introduce and elaborate a possible use case for the technique proposed in this paper.

Scalable bitstreams are used today to contribute to the Universal Multimedia Access (UMA) philosophy, i.e., accessing multimedia anywhere, at anytime, and on any device. Bitstream structure description languages provide means to adapt scalable bitstreams in order to extract a lower quality version. This paper introduces a real-time XML-based framework for content adaptation by relying on BFlavor, a combination of two existing bitstream structure description languages (i.e., the MPEG-21 Bitstream Syntax Description Language (BSDL) and the Formal Language for Audio-Visual Representation extended with XML features (XFlavor)). In order to use BFlavor with state-of-the-art media formats, we have added support for transparent retrieval of context information and support for emulation prevention bytes. These extensions are validated by building a BFlavor code for bitstreams compliant with the scalable extension of the H.264/AVC specification. Performance measurements show that such a bitstream (containing a bitrate of 17 MBit/s) can be adapted in real-time by a BFlavor-based adaptation framework (with a speed of 27 MBit/s).

The ever increasing diversity of multimedia technology presents a growing challenge to interoperability in as new content formats are developed. The Bitstream Binding Language (BBL) addresses this problem by providing a format-independent language to describe how multimedia content is to be delivered. This paper proposes extensions to BBL that enable a generic, scalable streaming server architecture. In this architecture, new content formats are supported by providing a simple file with instructions as to how the software may be streamed. This approach removes any need to modify existing software to provide such support.

Apart from the computer vision community, an always increasing number of scientific domains show a great interest for image analysis techniques. This interest is often guided by practical needs. As examples, we can cite all the medical imagery systems, the satellites images treatment and botanical databases. A common point of these applications is the large image collections that are generated and therefore require some automatic tools to help the scientists. These tools should allow clear structuration of the visual information and provide fast and accurate retrieval process. In the framework of the plant genes expression study we designed a content-based image retrieval (CBIR) system to assist botanists in their work. We propose a new contour-based shape descriptor that satisfies the constraints of this application (accuracy and real-time search). It is called Directional Fragment Histogram (DFH). This new descriptor has been evaluated and compared to several shape descriptors.

To improve coding efficiency, the H.264/AVC video coding standard uses new coding tools, such as variable block size, quarter-pixel-accuracy motion estimation, multiple reference frames, intra prediction and a loop filter. Using these coding tools, H.264/AVC achieves significant improvement in coding efficiency compared with existing standards. However, the encoder complexity also increases tremendously. Among the tools, macroblock mode decision and motion estimation contribute most to total encoder complexity. This paper focuses on complexity reduction in macroblock mode decision. Of the macroblock modes which can be selected, inter8×8 and intra4×4 have the highest complexity. We propose three methods for complexity reduction, one for intra4×4 in intra-frames, one for inter8×8 in inter-frames, and one for intra4×4 in inter-frames. Simulation results show that the proposed methods save about 56.5% of total encoding time compared with the H.264/AVC reference implementation.

Multiview video coding (MVC) plays an important role in three-dimensional audio-video (3DAV) systems. Multiview video display systems are built to provide interactive video services and quality of services (QoS) provided by the system is currently under consideration. MVC encoder uses advanced coding schemes and group of GOP (GoGOP) structure to pursue high compressibility. There is a conflict between compressibility and access ability, i.e., QoS of interaction. In this paper, several evaluation functions are proposed to measure the load and access ability of multiview video system. A nonlinear multipurpose mathematical model based on these functions is provided for interaction analysis. On considering the model, the access ability is a factor to be taken into account for encoder when high compressibility is the primary, and so is the compressibility when trying to achieve high access ability.

3D video, which is composed of a sequence of mesh models and can provide the user with interactivity, is attracting increasing attention in many research groups. However, it is time-consuming and expensive to generate 3D video sequences. In this paper, a motion composition method is proposed to edit 3D video based on the user’s requirements so that 3D video can be re-used. By analyzing the feature vectors, the hierarchical motion structure is parsed and then a motion database is set up by selecting the representative motions. A motion graph is constructed to organize the motion database by finding the possible motion transitions. Then, the best path is searched based on a proposed cost function by a modified Dijkstra algorithm after the user selects the desired motions in the motion database, which are called key motions in this paper. Our experimental results show the edited 3D video sequence looks natural and realistic.

This paper presents a new approach for audio clip retrieval based on Earth Mover’s Distance (EMD). Instead of using frame-based or salient-based features in most existing methods, our approach propose a segment-based representation, and allows many-to-many matching among audio segments for the clip similarity measure, which is capable of tolerating errors due to audio segmentation and various audio effects. We formulate audio clip retrieval as a graph matching problem in two stages. In the first stage, segment-based feature is employed to represent the audio clips, which can not only capture the change property of audio clip, but also keep and present the change relation and temporal order of audio features. In the second stage, based on the result of the segment similarity measure, a weighted graph is constructed to model the similarity between two clips. EMD is proposed to compute the minimum cost of the weighted graph as the similarity value between two audio clips. Experimental results show that the proposed approach is better than some existing methods in terms of retrieval and ranking capabilities.