A data processing apparatus includes a diagonal detector, a first processor, and a second processor. The diagonal detector may determine whether a red-blue data set includes data for controlling a display device to display any diagonal line, the display device including subpixels arranged in first-type lines and second-type lines that are alternately disposed, the red-blue data set including 9 data values that correspond to 9 subpixels among the subpixels, the 9 subpixels forming a 3-by-3 array that includes a center subpixel, the 9 data values including a center data value that corresponds to the center subpixel. The first/second processor may process the center data value using a first/second coefficient to produce a first/second value that corresponds to the center subpixel if the center subpixel is in the first-type/second-type lines.