Quad encoded display

A colour raster display system based on picture encoding is described. Encoding pictures as a means of data compression has a long history and is a technique of interest to anyone working with complex pictures. Its primary value is the lower bandwidths required of transmission channels, but its more frugal use of store is not to be overlooked. A quad tree as a means of encoding area-coherent pictures is used because it retains spatial information in a form which is still amenable to processing. The combination of this with compression makes this a particularly useful form of coding for raster-style colour pictures, and this paper addresses the problems which had to be overcome in order to construct a display directly exploiting the quad tree and related forms. The potential of such a display for rapidly handling very large amounts of pictorial data and for application to picture-archive retrieval is also discussed. The system has been constructed, is fully operational and incorporates roam and zoom operations. Sample pictures are included.