Bruno Rouchouze

Motion-compensated generic coding of video based on a multiresolution data structure

We present a generic video codec, which is able to compress image sequences efficiently regardless of their input formats. In addition, this codec supports a wide range of bit rates, without significant changes in its main architecture. A multiresolution representation of the data is generated by a Gabor-like wavelet transform. The motion estimation is performed by a locally adaptive multigrid block-matching technique. This codec can handle both interlaced and progressive input sequences, the temporal redundancies being exploited by interframe/interfield coding. A perceptual quantization of the resulting coefficients is then performed, followed by adaptive entropy coding. Simulations using different test sequences demonstrate a reconstructed signal of good quality for a wide range of bit rates. Thereby demonstrating that this codec can perform generic coding with reduced complexity and high efficiency.

Image compression using subband/wavelet transform and adaptive multiple-distribution entropy coding

Image compression methods using subband/wavelet transform and adaptive multiple distribution entropy coding (AMDEC) are presented. The methods are suitable for the coding of still images, as well as, motion compensated prediction error images for video compression. First, the subband/wavelet transform coefficients are uniformly quantized. For still image coding perception based weight quantization is used. Space filling scanning, subband partitioning and classification methods are used in dividing the original source of quantized coefficients into a number of subsources with corresponding distributions. A hierarchical partition priority coding (PPC) approach is followed, that is, given a suitable partitioning of their range, the transform coefficients are ordered based on their magnitude. AMDEC is applied to the output of PPC, which contains magnitude and location information, using adaptive arithmetic coding based on the histograms of the various subsources. Experimental results on standard monochromatic images and video-conference image sequences demonstrate the great performance of the proposed AMDEC methods.

New trends in image data compression

This paper gives an overview of a number of advanced techniques for image compression, which are under investigation in the Signal Processing Laboratory at the Swiss Federal Institute of Technology of Lausanne. Various applications ranging from High definition television (HDTV) to multimedia will be discussed. In particular, systems based on subband decomposition, edge based representation, as well as symmetries will be presented.

Interlaced image sequence coding for digital TV

This paper presents a method for interlaced image sequence coding for digital TV. The interlaced nature of the CCIR 601 format, which is the current standard for digital TV, is a serious drawback in most digital video codecs. In order to obtain a more efficient compression, we propose to process only the fields of one parity instead of processing the frames resulting from interlaced to progressive format change. The fields of the other parity are predicted using spatial interpolation based on the corresponding decoded fields, and the prediction error is also coded and transmitted. In this way, the decoder can reconstruct the odd and even parity fields with a reduced transmission cost. Experimental results, where the proposed interlaced coding method is applied to Gabor-like wavelet transform coding of MPEG2 image sequences, show a very good performance.

Interlaced image sequence coding for digital TV using adaptive quantization

A method for interlaced image sequence coding for digital TV is presented. In order to obtain a more efficient compression, only the fields of one parity are compressed instead of compressing the frames resulting from interlaced to progressive format change. The fields of the other parity are predicted using spatio-temporal interpolation based on the corresponding decoded fields, and the prediction error is coded and transmitted. In this way, the decoder can reconstruct the odd and even parity fields with a reduced transmission cost. Experimental results, where the proposed interlaced coding method is applied to Gabor-like wavelet transform coding of MPEG2 image sequences, show a very good performance of the proposed scheme.

Use of wavelet packets for image sequence coding

A new method for image sequence coding involving a wavelet packets transform is proposed to compact the energy of the transformed signal while preserving acceptable restitution quality. Based on an interframe coding scheme, the sequence is split into groups of frames where a similarity between successive frames exists. The best basis is generated for the first intra-frame, the first inter-predicted frame and the first inter-interpolated frame of each group and conserved for the following corresponding frames to reduce the computational complexity. Two different methods for on-line selection of the best basis are presented. The choice of the proposed technique is validated by experimental results where a codec based on motion compensated wavelet packets transform is presented.