Image compression featuring selective re-use of prior compression data

Abstract

This disclosure provides a compression system for edited images which have previously been compressed. The preferred system uses software to track and determine the nature of edits made to each image frame. Each image frame is divided into spatial regions, and codes defining the nature of changes are then stored in a set of tables called the “registry of edits.” When it is time to compress images for output, re-compression software interrogates the registry to determine whether spatial regions in the frame has been altered in a manner that undermines the integrity of the original compression data. For example, if a compressed image signal is modified in the spatial domain to add the logo of a local television station, most of each image frame will remain unchanged and the original motion vectors and residuals (or other compressed representation) from an input signal may be re-used, thereby saving substantial processing time and minimizing introduction of additional quantization errors. The preferred embodiment may be used with most any digital editor or computer to substantially reduce the processing time and resources required to provide a compressed output signal.