PURPOSE: To provide a method to correctly detect the stains and the dust of an image sensor before they affect the images to be read.
CONSTITUTION: An optical reader converts the light reflected on a slip into electric signals by an image sensor 1 and performs the amplification, A/D conversion and binarization of the output of the sensor 1 through an amplifier 2, an A/D converter 3 and a binarizing circuit 4 respectively. A detecting means 7 is added to the optical reader to detect the presence or absence of the vertical component of the black picture element included in a clear area of the slip and the position information on the vertical component out of a video memory 6 which stores image of the slip, together with a storing means 8 which stores the information on the presence/absence and the position of the vertical component of the black picture element detected by the means 7, and a means 9 which decides the presence of stains or dust of the sensor 1 and outputs an alarm when the vertical components are detected at the same position based on the information on the presence/absence of the vertical component and its position that is acquired by the precedent reading of the slip and the information acquired by the present reading of the slip.
KAMIMURA TOSHIRO
CHIBA KIYOUKA
