Patent ID: 7542616

Claim:
An image data compressing apparatus comprising: an image data compressor for compressing image data input thereto at first and second compression rates to produce first and second compressed data, respectively; an approximate-expression table including a plurality of different predetermined sample data sizes and a plurality of predetermined approximate expressions which correspond to said plurality of different predetermined sample data sizes, respectively; an approximate-expression selector for selecting an approximate expression from said plurality of predetermined approximate expressions, said selected approximate expression corresponding to a first sample data size nearest a data size of said first compressed data among said plurality of different predetermined sample data sizes, each of said plurality of predetermined approximate expressions indicating a change of a data size in response to a compression rate; and a compression rate determining unit for determining said second compression rate by (1) changing a compression rate of said selected approximate expression, (2) calculating a second sample data size with the changed compression rate and (3) determining the second compression rate to be the rate corresponding to the calculated second sample data size within a predetermined threshold range of a target data size.