Patent ID: 6724817
Filing Date: 2004-04-20
Classification: H04N

Abstract:
An image compression apparatus for compressing an image data signal comprising one or more image data blocks, the apparatus comprising a transform module arranged to transform the or each image data block into an array of frequency coefficients; a quantization module arranged to quantize each of said frequency coefficients according to a respective quantization coefficient; a compression control module arranged to eliminate each frequency coefficient having a magnitude less than a threshold value; an entropy encoding module arranged to generate a coded data element for each non-zero and non-eliminated frequency coefficient to produce a compressed data signal, wherein the image data signal is processed in image segments, each image segment comprising at least one image data block, and a respective target volume is set for each image segment, the apparatus being arranged to measure the volume of the compressed data signal produced for each image segment, to calculate the difference between the respective target volume and respective measured volume for each image segment, and to sum the calculated differences, the compression control module being arranged to adapt the level of compression applied by the apparatus depending on the value of said summed calculated differences.