In order to process image data including a plurality of pixels, a plurality of pixel groups, each of which includes a plurality of pixels, are extracted from the image data sequentially. Next, it is judged whether each of the pixel groups includes only at least one of a white pixel and a black pixel. At least one first pixel group in the pixel groups is binarized in accordance with an arrangement of the at least one of the white pixel and the black pixel therein, in a case where it is judged that the first pixel group includes only at least one of the white pixel and the black pixel, thereby generating at least one first data item. A first resolution of at least one second pixel group in the pixel groups is reduced to a second resolution, in a case where it is judged that the second pixel group includes at least one pixel other than the white pixel and the black pixel, thereby generating at least one second data item.