PURPOSE: To operate a correction concerned with a surrounding illuminance without using a picture memory, at the time of searching a picture element corresponding to an object to be inspected based on the concentration of the picture element.
CONSTITUTION: A picture signal outputted from an image pickup device 1, and divided into three colors by a video signal processing part 2, is inputted to a comparator circuit 4 The comparator circuit 4 compares only the picture element in an area designated by an inspection area designating part 5 with the threshold value of a concentration range stored in a threshold memory 6. An illuminance detecting part 12 searches the movement average value of the concentration of the picture element in a reference area picked-up by the image pickup device 1. A correction arithmetic part 13 searches the correction value of the concentration based on a reference value stored in a reference concentration memory 14 and the moving average value when a correction timing signal is inputted. The correction value is stored in the threshold memory 6, so that the corrected threshold value can be obtained concerning the surrounding illuminance.
HASHIYA IKUO
OHASHI HIROSHI
