Method of fast processing image data for improving reproducibility of image

A method of processing image data to generate output image data for driving a display panel is provided. In the method, a new resolution for input image data is set according to a resolution of the display panel. A first virtual screen is divided into a plurality of pixel areas according to the new resolution set for the input image data. A second virtual screen having a sub-pixel array structure of the display panel is superimposed on the first virtual screen. A mask wider than a sub-pixel area on the superimposed second virtual screen is laid on each sub-pixel area. An area ratio of the area of each pixel portion on the first virtual screen included in each mask to the area of the mask is obtained and set. The new resolution and the area ratios are applied to a driving device of the display panel. The input image data having an original resolution is transformed into image data having the new resolution. The sum of the results of multiplying an area ratio of the area of each pixel portion on the first virtual screen included in each mask by the transformed image data of the pixel areas, respectively, is generated as output image data of a sub-pixel corresponding to the mask.