An interpolation processor interpolates reference correction data stored in a ROM according to the level (gray scale) to generate correction data DHr which correspond to gray scales available for image data, for each of a plurality of reference coordinates. The correction data DHr are stored in a correction table. From the correction data DHr stored in the correction table, an address generator specifies storage locations at which correction data DHr1 to DHr4 are stored, which correspond to four reference coordinates surrounding the coordinates, based on X-coordinate data, Y-coordinate data, and the image data. An arithmetic unit interpolates the correction data DHr1 to DHr4, which are read from the correction table, according to the coordinates and generates correction data Dh. An adder adds the correction data Dh to the image data to generate corrected image data. It is thus possible to remove nonuniformity of luminance and nonuniformity of color in a display screen.