To reduce the process time and the process cost for a gradation number recovery process and half-tone image enlarging process and prevent the image quality from deteriorating in these processes.

The image processor comprises a window 202 for inputting a dither image of a value N (≥2), a gradation number recovering/enlarging unit 203 for applying a gradation number recovery process and a half-tone image enlarging process to the dither image in the window 202 to recover and enlarge a half-tone image of a value M (>N) and a memory 205 for saving the enlarged half-tone image.