Picture Coding: The Use of a Viewer Model in Source Encoding

In early work in picture coding, Graham stressed the role of the viewer and Powers and Staras concluded t h a t if large reductions in bit-rate are to be achieved they must come from "nonstatistical" (perceptual) redundancies. 1 - 2 However, there have been few attempts to explicitly incorporate the viewer in the encoder design. Unfortunately, there is no general method for handling complex viewer fidelity criteria, especially when one is concerned with how pleasing a picture appears. f Nevertheless ad hoc techniques have been proposed and evaluated and have achieved a certain measure of success. 3-8 Source encoding, in its most general form, can be diagrammed as shown in Fig. 1. The first stage is an irreversible operation which generates a discrete signal as a result of a quite general multidimensional quantization process. The resulting discrete signal may still be redundant due to the presence of statistical dependencies; these are removed in the second stage of reversible processing in which a digital * Presented, in part, at the 1972 IEEE International Symposium on Information Theory. * See Ref. 9 for a discussion on viewer fidelity criteria. 1271