High speed compression of imagery data

Abstract

A system for processing a bit map of pixel data signals representative of a multi-dimensional array of imagery data (e g. alpha-numeric text) for transmission over a facsimile communication channel are compressed by providing a plurality of data compression units, a respective one of which is capable of compressing data supplied to it at a compression rate that is only a fraction of the data rate. The bit map is subsampled by demultiplexing the bit map into sub-arrays of data. The sub-array data is coupled to respective sets of compression units, which executes parallel, two-dimensional compression of the demultiplexed sub-array data. Even though the data subsamples associated with successive rows of the bit map are non-consecutive, and therefore may contribute to a reduction in compression performance in the horizontal direction, because the data is text, successive data samples within each column of a sub-array are inherently more highly correlated with one another than data values that are encountered within respective rows of the original bit map. As a consequence, the two-dimensional data compression operator executed by each unit suffers no loss in output signal quality.