Image compression method and apparatus

Systems and methods for controlling compression of image data by a quality controller include obtaining a desired target number of bits to be generated from compression of a current image area using a predetermined compression protocol, determining a calculated quantisation level based on the desired number of bits using a predetermined relationship between the number of bits and quantisation level, selecting a discrete quantisation level from a plurality of predetermined discrete quantisation levels based on the calculated quantisation level, determining a predicted number of bits that would result from compression of the current image area at the selected discrete quantisation level using the predetermined relationship, determining whether the predicted number of bits exceeds the desired number of bits and, if not, providing to an encoder information to enable the encoder to determine a set of compression parameters associated with the selected discrete quantisation level.