A plurality of gray-scale values is extracted from image signals corresponding to a dimming area to calculate a mean value of the gray-scale values, and at least one of a variance, a standard deviation, a kurtosis, a skewness, a central moment, and an image moment is calculated using the mean value. Then, a representative gray-scale value corresponding to the dimming area is determined using the calculated values, and a dimming function for the light sources included in the dimming area is determined based on the representative gray-scale value. Then, the light sources included in the dimming area are driven based on the dimming function.