An image processor includes a tone converter operable when a pixel of input image data is determined as having a value greater in color saturation than a prescribed saturation value. In this operation, the tone converter changes a threshold for each color in a dither matrix associated with the pixel to make the thresholds different in correspondence to color component values of the pixel. The tone converter generates color component values of the pixel constituting image data to be output, based on comparisons between the respective color component values and the changed thresholds.