System for detecting difference between image on primary sheet and image on secondary sheet

摘要

There is disclosed a system for detecting a difference between an image on a primary sheet and an image on a secondary sheet. A microprocessor unit determines whether corresponding ones of first and second image elements representative respectively of the images on the primary and secondary films differ in optical density from each other below a predetermined level. The two corresponding first and second image elements different above the predetermined level are emphasized in optical density difference and alternately displayed on a display screen at a short time interval, so that the dot of the display screen which alternately display these image elements is caused to flicker.