1. A flat panel display, comprising: a look-up table (LUT) storing a dither mask; a dithering unit configured to produce a plurality of dither masks based on the dither mask stored in the LUT, and to apply different ones of the dither masks to image data during each successive frame period to generate dithered data, wherein the number of perceived gray levels of the dithered data is greater than the number of perceived gray levels of the image data; and a sub-frame mapping unit configured to map the dithered data to a plurality of sub-frame data patterns included in one frame and to output the mapped data, wherein the dithering unit comprises: a calculator configured to produce dither masks; and a dither unit configured to generate the dithered data, wherein the calculator produced the dither masks by subtracting a number from all numbers including in the stored dither masks.