Image data compression-a time to take stock

The technique of image coding (image `compression´), resided in the research laboratory for several decades before the massive upsurge of interest in its application over the past ten years or so which now seems destined to leave the lives of few individuals in the developed world untouched. The development of the processing algorithms is discussed, together with the international determination to produce a set of standards. On the one hand, then, there were research workers around the world coding still images and video sequences at lower and lower rates, and on the other (once the discipline had matured sufficiently) increasing pressure to use the results gained in the laboratories as a practical way of overcoming the basic problem of the huge bandwidth or capacity needed to transmit or store an image of reasonable resolution in its uncoded form. The paper examines both of these activities, and their relationship, before seeing whether, indeed, there is now a logical way forward. The basic traditional techniques-prediction, transformation, motion compensation and variable wordlength coding form the basis of all activities presently proposed with the possible exception of MPEG-IV