Method for selecting jpeg quantization tables for low bandwidth

Abstract

A method of compressing color source image data includes forming a quantization table with a 'supra-threshold' term. This method includes a step of selecting a set of target images, where each target image includes one or more image elements such as text. These image elements are then analyzed to identify those that are more important for visual quality. These 'supra-threshold' terms are then selected that gives a larger weight to the quantization table elements that correspond to important image elements and a smaller weight to the table elements that correspond to less important image elements. This process selectively weights the characteristics of each DCT basis vectors. By giving larger weights to the table elements that correspond to the 'up-downness' of the image, i.e., the vertical attributes of the image elements, and the 'left-rightness' of the image, i.e., the horizontal attributes of the image elements, and smaller weights to the table elements corresponding to the 'criss-crossedness' of the image, i.e., the diagonal attributes of the image elements, the visual quality of an image that includes text can be preserved while significantly increasing the compression ratio.