COMPARISON METHOD OF COMPRESSED IMAGE DATA AND ITS DEVICE

摘要

PROBLEM TO BE SOLVED: To detect a different part between two images compressed by a variable length encoding system at high speed. SOLUTION: A border of encoding data is detected by successively taking a predetermined bits of the encoding data from the head of the encoding data of a processed image and judging whether the encoding data coincides with a code word in an encoding table used in a compressing process. First, the border of the encoding data of a reference image is detected, DC coefficients of respective blocks are decoded and starting and ending addresses of an AC coefficient are also calculated (S1). Similarly, the starting and ending addresses of the DC coefficient values and the AC coefficient values of respective blocks of compared image are calculated (S2). The different part between respective blocks is detected by comparing the DC coefficient values corresponding to both images and also comparing the encoding data of the AC coefficients (S3 to S10).