1. A system for auto exposure, the system comprising: an exposure feature value extractor to extract an exposure feature value using a brightness value of an input image; an exposure correction determination unit to determine whether an exposure correction with respect to the input image is necessary by comparing the exposure feature value with an exposure target value; an exposure target value adjusting unit to adjust the exposure target value based on the brightness value of the input image, when the exposure correction is necessary; and an auto exposure unit to calculate an exposure correction value of the exposure feature value based on the adjusted exposure target value, and to perform auto exposure according to the exposure correction value.