| 摘要 |
PROBLEM TO BE SOLVED: To output an alarm on sudden dirt by detecting that a part of a mobile object is hidden and judging the dirt of a light receiving part. SOLUTION: When a vehicle is to pass under an image pickup device where partial dirt occurs, the vehicle is viewed on a background image (P1). When the passing vehicle passes the part of dirt, the vehicle is viewed under a part (it is actually dirt) recognized to be the background image (P2). A part coming out higher than the vehicle is recognized to be dirt although luminance is lower than the vehicle. Since luminance is dropped in the part of dirt by it itself, the area of a part whose luminance is lower than prescribed one is made to correspond to the number of memories in a frame buffer after the vehicle passes and that the number of the memories becomes larger than a threshold which is previously set is detected (P3). A picture recognition device outputs the alarm of the occurrence of dirt to an output line and imparts it to a maintenance part.
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