AN IMAGE COMPRESSION SYSTEM AND METHOD OF DETERMINING QUANTISATION PARAMETERS THEREFOR

摘要

An image compression system (1) having a wavelet transform module (3) for decomposing an input image subdivided into blocks using a wavelet transformation utilises a statistics generator (7) to determine average statistics over several blocks to provide an indication of the activity of a current image block. This activity value is passed to a quantisation control module (8) which determines quantisation parameters for a quantisation module (4) which quantises the transform coefficients output from the wavelet transform module (3). The quantised transform coefficients are coded for onward transmission or storage by coder (5). The quantisation control module (8) also receives bit rate information for the current image block from a rate monitoring module, which determines the bit rate for the current block from a desired bit rate and information on the number of bits used for the previous image block.