PURPOSE: To reduce the memory capacity for conversion processing, by rotating seal impression data at a differential angle when seal impression data is subjected to the angle conversion processing in the discriminating system of seal impressions or the like.
CONSTITUTION: A seal impression 3 on a form 2 is read and digitized and is written as seal impression data L. The approximate value of an optimum angle is generated from a controlling part 5 for the purpose of comparing this data L with registered data F of a file 11 to discriminate data L. If pertinent rotated coordinate data do not exist, the first rotated coordinate data X1 and Y1 from respective coordinate data groups AWD in a table T are used to rotate seal impression data L on a memory M1, and the second rotated coordinate data X2 and Y2 are used to rotated seal impression data L on a memory M2 at a differential angle, thus obtaining rotated coordinate data for a required angle.
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