Transform coding of images using interleaved blocks

Abstract

A method of coding images based on interleaved blocks is proposed. These block have irregular outlines with both holes and islands. It is shown that if they are designed by the application of ‘n-cycles’ to a rectangular array, the resulting block shapes interleave perfectly without overlap. Used in transform coding, they substantially reduce the visiblity of block structure at low data rates. Experimental investigations are reported which identified desirable properties of interleaved blocks, in terms of their degree of overlap and interior distribution of pels. The pre-and post-transformations associated with the use of such blocks are easily accomplished by a simple modification of pel addressing routines, this being the only processing overhead incurred. Limited experiments on another form of overlapping block, which merged rather than interleaved with its neighbours, are also reported. These were computationally more involved and tended to magnify interblock contrasts.