| 摘要 |
PROBLEM TO BE SOLVED: To determine whether it is a sunny area or a shadow area irrespective of whether the image is a color image or a monochrome image even when the image has either one of a sunny area and a shadow area.SOLUTION: An image in which a road where a vehicle passes is captured is acquired (70), and it is determined whether a vehicle is imaged or not (72, 74). When the vehicle is not imaged, a luminance is normalized (76), and it is determined whether an area is a sunny area or a shadow area by comparing distribution of the luminance with a threshold for each partial area obtained by dividing a background area (78 to 88). According to the distribution of the sunny area and the shadow area, a target luminance (exposure control parameter) is set. When the vehicle appears in an imaging range, recognition processing for recognizing characters displayed on the license plate (100) is performed, and exposure conditions of an imaging section are controlled so that an average luminance value in the area of the vehicle can be matched with the target luminance (102). |
