PURPOSE: To decide the abnormality (defect) of a mark accurately and easily by comparing a sample image subjected to correction of inclination angle with an operated sample image.
CONSTITUTION: An image picked up by a first device in a device group printed with an identical character and an identical mark is subjected to A/D conversion 2 and stored in a multilevel memory 3. On the other hand, a CPU 10 determines the inclination angle of the image and operates the position of character region. The CPU 10 also operates an optimal threshold value for binarization based on the results of lightness histogram and binarizes the data stored in the memory 3 and then stores the binarized data in a memory 8 for sample image. The image of device in second and subsequent groups is then processed similarly and the inclination angle of a sample image thus operated is corrected 13 by the difference from the inclination angle of a sample image and stored in a sample image memory 6. A difference detector 14 compares the contents of the memories 6, 8 and if any difference is detected, the longitudinal, lateral, and oblique dimensions thereat are detected 15-18. If the detected distance exceeds a predetermined distance, a decision is made that the mark is abnormal and an alarm 19 is delivered.
SATO HAJIME
KIMURA YORIAKI
YOSHIDA KOSAKU
