In the present invention, image data from an image input device, including differences of tone levels of picture elements constituting these image data from surrounding picture elements, are figured out and the distribution of these differences of tone levels is prepared. Then, integrated processing, based on this distribution, makes it possible to determine whether each picture element is an edge picture element, a moire picture element or an intermediate picture element. According to the determination, a sharpening filter is applied if the picture elements are edge picture elements, a smoothing filter is applied if they are moire picture elements, or the tones of the original image are held if they are intermediate picture elements. This way of image data retouching makes it possible to carry out the whole execution from determination to retouching in a serial process.