Patent ID: 7881545

Claim:
An image data compression method for generating compressed data of image data, comprising the steps of: dividing the image data into predetermined regions; generating modeled data by extracting a feature of the image data for each of the regions, the modeled data being data whose image reproducibility varies when a part of the modeled data is thinned out step by step; determining a thinning-out threshold value, the thinning-out threshold value being used when the compressed data is generated by thinning out data from the modeled data, and the thinning-out threshold value having a value such that data quantity of the compressed data becomes equal to or less than predetermined target data quantity; and generating the compressed data by thinning out data from the modeled data based on the determined thinning-out threshold value, wherein the image data is pseudo gradation image data that is obtained by a pseudo gradation process performed on multi gradation image data with a dither pattern, and wherein the step of generating the modeled data includes the following steps: generating a representative value of the image data of each of the regions; generating an indicator that indicates whether or not a pseudo gradation image dot pattern that is a dot pattern indicated by the pseudo gradation image data can be reproduced correctly when a dot pattern of the region is reproduced based on the representative value, and comparing a reproduced dot pattern with the pseudo gradation image dot pattern of the region, with said reproduced dot pattern being produced based on a representative value of the region and the dither pattern; if the reproduced dot pattern is equal to the pseudo gradation image dot pattern, the representative value is included in the modeled data; and if the reproduced dot pattern is not equal to the pseudo gradation image dot pattern, the following data will be generated and included in the modeled data: (1) data that indicates a mismatching degree between the reproduced dot pattern and the pseudo gradation image dot pattern; (2) the representative value of the region; and (3) the pseudo gradation image dot pattern.