A controller includes a bit shifter and a stain compensator. The bit shifter may determine a bit shift value corresponding to a stain compensation value according to an area of a display panel. The bit shift value represents a quantity of integer bits and a quantity of decimal bits. At least one of the quantity of integer bits and the quantity of decimal bits corresponds to a quantity of stain compensation steps. The stain compensator may compensate a grayscale value of input image data using the stain compensation value and the bit shift value to generate compensated image data.