Emmanuel Reusens

Joint optimization of representation model and frame segmentation for generic video compression

Abstract This paper describes a new image sequence compression system capable of efficiently representing any type of visual data at very low bit-rate. The coder presents a flexible structure open to evolution. Thanks to a perfect rate and frame quality control, buffer regulation issue is solved. The technique relies on the joint optimization of two degrees of freedom, namely adaptive representation model and adaptive frame support partition. Optimization is performed in a rate-distortion sense and is based on the theory of optimal resources allocation. System performances are evaluated in a particular environment, namely at very low bit-rate in the framework of video-telephony applications. Simulation results demonstrate the efficiency of the system over bit-rates ranging from 4.6 to 32 kbit/s.

Dynamic approach to visual data compression

This paper presents the Swiss Federal Institute of Technology (EPFL) proposal to MPEG-4 video coding standardization activity. The proposed technique is based on a novel approach to audio-visual data compression entitled dynamic coding. The newly born multimedia environment supports a plethora of applications which cannot be covered adequately by a single compression technique. Dynamic coding offers the opportunity to combine several compression techniques and segmentation strategies. Given a particular application, these two degrees of freedom can be constrained and assembled in order to produce a particular profile which meets the set of specifications dictated by the application. The basic principles of this approach are presented together with the data representation system. The major characteristics of dynamic coding are reviewed, along with simulation results showing the performance of such an approach in a very low bit-rate video coding environment.

Overlapped adaptive partitioning for image coding based on the theory of iterated functions systems

Memoryless blockwise partitioning induces blockiness artifacts highly disturbing to the human visual system. This paper presents a new partitioning with overlapped blocks in the context of image coding based on iterated transformations systems. Each block of the partition is extended by n pixels. As usual each cell is expressed as the contractive transformation of another part of the image. During the decoding, values of pixels corresponding to overlapped regions are computed as the weighted sum of the different contributions leading to that pixel. This overlapped partitioning is embedded in a quadtree segmentation of the image support. In order to avoid blurring effects in small blocks while maintaining efficiency in bigger ones, the overlapping width n is a function of the block size. Simulations show a very significant improvement of the visual quality of decoded images with no increase of the bitrate request.<<ETX>>

Sequence Coding based on the Fractal Theory of Iterated Tranformations Systems

A new scheme for sequence coding based on the iterated functions systems theory is presented. The method relies on a 3D approach in which the sequence is adaptively partitioned. Each partition block can be coded either by using the spatial self similarities or by exploiting temporal redundancies. The proposed system shows very good performances when compared to other existing methods.

Dynamic coding of visual information

This paper introduces a novel approach to visual data compression. The approach, named dynamic coding, consists of an effective competition between several representation models used for describing data portions. The image data is represented as the union of several regions each approximated by a representation model locally appropriate. The dynamic coding concept leads to attractive features such as genericness, flexibility, and openness and is therefore particularly suited to a multimedia environment in which many types of applications are involved. Dynamic coding is a general proposal to visual data compression and many variations on the same theme may be designed. They differ by the particular procedure by which the data is segmented into objects and the local representation model selected. As an illustrative example, a video compression scheme based on the principles of dynamic coding is presented. This compression algorithm performs a joint optimization of the segmentation (restricted to a so-called generalized quadtree partition) together with the representation models associated with each data segment. Four representation models are competing namely, fractal, motion compensation, text and graphics, and background modes. Optimality is defined with respect to a rate-distortion tradeoff and the optimization procedure leads to a multicriterion segmentation.

Dynamic video coding-an overview

In this paper, we present an overview of the dynamic coding approach, together with recent developments carried out in this framework. Dynamic coding is a general approach to the problem of visual data representation in the context of multimedia. This approach consists of a dynamic combination of multiple representation models and segmentation strategies. Given an application, these two degrees of freedom are assembled so as to yield a specific profile which meets the specifications dictated by the application. The data is represented as the union of data segments, each described within a locally appropriate representation model. In order to illustrate this approach, a video compression system, based on the principles of dynamic coding, is proposed in the context of video-telephone/conference applications. This algorithm has been submitted to the MPEG-4 committee as a proposal for the first round of tests in November 1995. Recent developments have been added: in particular, a procedure enabling the generation of an object-oriented scalable bitstream is presented here. In order to reduce the blocking artifacts which are noticeable at high compression ratios, a post-processing technique is proposed.

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.

New techniques for subband/wavelet transform coefficient coding applied to still image compression

New techniques for redundancy removal of quantized coefficients of a wavelet transform are discussed. Several strategies are developed to improve the redundancy reduction stage in subband/wavelet based image compression. The influence of the scanning path in coding the coefficients of the subbands after transformation are pointed out and solutions are proposed for exploiting the correlation between the coefficients in a more efficient way. New methods are also proposed to encode the address of non zero coefficients using blocks in both the lossy and lossless approach. Simulations show a better performance of the proposed techniques when compared to classical methods, while maintaining an efficient implementation complexity.

New trends in very low bit rate video coding—an overview

Publisher Summary This chapter provides an overview of existing approaches that target very low bit rates. It gives a review of high-compression image-coding techniques and provides overviews of video coding techniques aimed at very low bit rates. These have been classified into four classes: waveform, object-based, model-based, and fractal-based coding techniques. Then, pre- and postprocessing of the visual information is overviewed in this chapter. Existing products in the market are described and finally, conclusions are drawn in the last section. It is clear that the techniques developed for still pictures can be either extended to 3D signals or a hybrid approach can be defined based on motion compensation. Waveform-based techniques can prove efficient when proper low-bit-rate-oriented features are added. However, other techniques specifically designed for very low bit-rate applications show significant promise, namely object-oriented, model-based, and fractal-based techniques.

Visual data compression using the fractal theory and dynamic coding

These Ecole polytechnique federale de Lausanne EPFL, n° 1590 (1996)Section de systemes de communicationInstitut de genie electrique et electroniqueLaboratoire de traitement des signaux 1 Reference doi:10.5075/epfl-thesis-1590Print copy in library catalog Record created on 2005-03-16, modified on 2016-08-08