Gwenaelle Marquant

Extended spatial scalability for non dyadic video formats: from SDTV to HDTV

High Definition Television is currently a hot topic that generates research and commercial interests in video industry. This paper relates to video coding devices and methods for easy and fast conversion of video formats for digital TV. The proposed algorithm provides a generic framework that allows any video format conversions in a scalable way. We focused particularly on solutions to extract Standard Definition video signals from High Definition ones. Practically, we address spatial scalability solutions between video formats that are not linked up by dyadic decomposition and/or istropic decomposition. The challenge is to generate a single scalable bitstream in a compliant way that permits any spatial resolution decodings while saving bandwidth compared to classical simulcast approaches. Practically, our scalable coder is based on a multi-layer approach and on frame scales and borders introduction. Moreover, to encode/decode the macroblocks of the high resolution pictures, usual video coding approaches exploit the inheritance knowing the macroblocks of the decoded low resolution pictures. Approaches for inter-layer prediction of motion data have already been proposed for dyadic decompositions but do not work in case of non dyadic inter-layer resolutions. Consequently we propose a different managing of the inter layer prediction. All these techniques have been successfully implemented in the MPEG-SVC reference software. Obtained results achieve good coding efficiency and are comparable to the simulcast state of the art while providing features induced by scalability.

Mesh-based scalable video coding with rate-distortion optimization

Recent development in video coding research deals with the use of hierarchical and/or adaptative mesh for video representation. Concurrently, transmitted bit rates have to be reduced to adapt to the network available bandwidth. Some previous works deal with adaptative node sampling according to image content. However, adaptative hierarchical proposed approaches do not optimize a compromise between distortion and bitrate: the representation coding cost is often stated but not taken into account as a constraint. Compared to these methods, this paper proposes for considering an adaptative hierarchical mesh based representation whose splitting criterion optimizes both the coding cost and the image rendering. Jointly, node value optimization, adaptative quantization, cheap coding tree and a wavelet approach are presented. To illustrate our different proposed methods, experimental results are shown and compared to the JPEG picture coding format.