A signal processing device and method of manufacturing the same include a converting unit converting first, second, and third image data into first sub first image data, first sub second image data, and first sub third image data having gray levels higher than the gray levels of first, second, and third image data, respectively, and second sub first image data, second sub second image data, and second sub third image data having gray levels lower than the gray levels of the first, second, and third image data, respectively, a first correcting unit which compares the first sub image data, corrects the first sub second image data according to the comparison result, and outputs corrected first sub second image data, and a second correcting unit which compares the second sub image data, corrects the second sub second image data according to the comparison result, and outputs corrected second sub second image data.