A pixel in a photograph region image to be subjected to blacking is subjected to a brightness modulation processing so that the pixel is modulated to any of “a pixel having the brightness to be subject to blacking” and “a pixel having the brightness not to be subject to blacking”. Specifically, the modulation by noise addition converts some pixels for which original pixel values are to be subjected to blacking to a pixel having the brightness not subjected to blacking. Thereby, “a pixel having the brightness not to be subject to blacking” thus converted has no change in brightness in the blacking processing. Consequently, a pixel at which the blacking processing is not generated can be caused to exist in the photograph image. As a result, even when the blacking processing set for character/line region is similarly set for the photograph region, the effect of the blacking can be reduced.