Françoise Groliere

An efficient error concealment implementation for MPEG-4 video streams

This paper presents an efficient error concealment implementation for damaged MPEG-4 video bitstreams. The chosen spatial and temporal concealment algorithms are designed to fit in real-time decoders and are advantageously combined in a hybrid spatial/temporal approach to provide visually more plausible pictures than basic concealment techniques. In addition, the encoder impact on the visual quality of the reconstruction in presence of channel errors is highlighted.

From Spin Transition to Display and Memory Devices

Abstract After a presentation of a user-friendly and reliable optical technique to characterize the spin transition phenomenon in iron II derivatives, this paper describes the first realization of a thermally addressed display. This new technology, still at the beginning of its development, is promising for further recording or display applications.

A DCT-domain filtering algorithm for MPEG-4 encoding

One of the well-known weaknesses of block-based video compression schemes such as MPEG-4, at low bit-rates, is blocking artifacts. They can be well removed by post-processing solutions offering an efficient deblocking filter, unfortunately at the cost of a significant increase of the decoding process complexity. In this paper, we propose a new method to reduce blocking artifacts (thus increasing the visual quality of sequences or the compression rate) at the encoding stage to get rid of, or to help, the post-processing step. We consider a filtering operation in the DCT domain, applied on blocks before quantization to leave the decoding process unmodified. The solution is adaptive and focuses on regions which would be a priori blocky regarding some texture features and encoding parameters. It is based on the mix of quantization step reduction at the frame level, with DCT coefficients low-pass filtering at the block level, on top of any bit-rate regulation module. Tests showed the efficiency of the method: the sequences encoded with our DCT filter are cleaner, with less ringing and, above all, fewer blocking artifacts than the ones without any processing. Visual quality is therefore better for a constant bit consumption. Depending on cases, post-processing is either useless or improved by our process.