A driver device for a display panel. Pixel cells are arranged on respective display lines of the display panel. Each N adjacent display lines makes one display line group. N is an integer of two or more. The pixels in each display line group are driven to emit light at different luminance levels based on one of M different dither patterns. One of the M dither patterns is selected sequentially and in predetermined periods, and the selected dither pattern is used. M is less than N. In the dither processing, N different weighting values are allocated to the N display lines in the display line group, respectively.