1. A controller for controlling respective amounts of ink and water supplied to a printing machine, comprising: (a) an object region setting element for setting a plurality of object regions in a reference image to be printed, said object regions being set based on reference image data representing said reference image; (b) a read element for reading an image of printed matter corresponding to said reference image to obtain print image data; (c) a comparison element for comparing said reference image data and said print image data for each of said object regions to obtain an image comparison result; and (d) a control variable calculation element for calculating control variables for ink and water in said printing machine, said control variables being calculated based on both a regional characteristic and said image comparison result obtained for each of said object regions.