1. A defogging system comprising at least one processor configured to implement: an illuminance sensor detecting a surrounding illuminance; a level determiner determining a defogging level of an input image based on the detected surrounding illuminance; and a defogger determining a fog state of the input image based on a histogram of the input image, and adaptively defog the input image according to the determined fog state and defogging level, wherein the defogger comprises: a histogram generator configured to generate the histogram of the input image; a fog detector configured to detect a first minimum brightness value and a first maximum brightness value from the histogram, the first minimum brightness value and the first maximum brightness value corresponding to a pre-set cumulative probability; and a scaling unit configured to scale the input image by respectively resetting the first minimum brightness value and the first maximum brightness value to a second minimum brightness value and a second maximum brightness value according to the defogging level determined based on the detected surrounding illuminance.