US 6,724,817 B1 · Adaptive image data compression

Abstract

The invention relates to a method and apparatus for compressing an image data signal. The apparatus includes a compression control module arranged to eliminate frequency components produced from the image data signal which have a magnitude less than a threshold value. The apparatus compares the volume of the compressed image data signal with a target volume and selects to increase or decrease the applied compression level depending on the outcome of the comparison. The compression level is increased by increasing the threshold value and deacreased by decreasing the threshold value. The compression level, or ratio, is thus adaptable in real-time in order to meet a target volume for the compressed image. This is particularly advantageous in applications where, for example, the compressed image signal is to be transmitted over a fixed bandwidth link. The method and apparatus of the invention are particularly suitable for use in the implementation of the JPEG basline image compression standard.

Claims16

Dependent claims

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.

In 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;
and an entropy encoding module arranged to generate a coded data element for each non-zero 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, a method of adapting the level of compression applied by the apparatus, the method comprising:
measuring the volume of the compressed data signal produced for each image segment;
calculating the difference between the respective target volume and respective measured volume for each image segment;
summing the calculated differences;
and adapting the level of compression applied by the apparatus depending on the value of said summed calculated differences.

4 more elements

Dependencies are inferred from the claim text.

Adaptive image data compression

Life of this patent

Adaptive image data compression

Life of this patent

Abstract

Claims16