IMAGE SIGNAL PROCESSING APPARATUS WITH NOISE SUPERIMPOSITION

Noise that is hard for human vision to perceive and corresponds to the kind of an original document is superimposed on an input image signal by an amount corresponding to the kind of the original document. More specifically, a noise selection circuit selects a spatial frequency characteristic and an amplification value table that conform to the kind of an original document. Based on the selected characteristic and table, a noise amount calculation circuit calculates a noise amount corresponding to the image signal. A noise superimposing circuit superimposes the noise thus generated on the image signal.