1. A defog system comprising: an illuminance sensor configured to detect ambient illuminance; and at least one processor to implement: a level determiner configured to determine a defog level of an input image based on the ambient illuminance; and a defogger configured to determine whether to defog the input image based on skewness and kurtosis of a histogram of the input image, and, in response to the defogger determining to defog the input image, determine a fog condition of the input image based on a cumulative probability of the histogram, and defog the input image based on the defog level.