DATA COMPRESSION OF IMAGE DATA SEPERATED INTO FREQUENCY COMPONENT DATA IN A TWO-DIMENSIONAL SPATIAL FREQUENCY DOMAIN

A data compression system decorrelates input data into sets of frequency component data. Different sets of frequency component data are entropy encoded using different coding tables matched to the data values characteristic of the sets of frequency component data they are used to compress. Matching the coding tables to the sets of frequency component data improves compression. The order in which the data values from within each set of frequency component data is fed to the entropy encoder is varied to exploit any intra-set correlation.