In an image processing apparatus, the generating unit generates print data indicating whether a dot having one of a plurality of sizes is formed or not, by performing a halftone process on original image data. The correcting unit generates corrected print data by correcting the print data. The dividing unit divides the edge part data of the print data into a plurality of block data. The index value determining unit determines, for each block data, an index value relating to an amount of ink to be used based on the plurality of dot data included in the each block data. The changing unit changes, for each block data, the size information of at least one dot data among the plurality of dot data included in the each block data based on the index value such that the amount of ink to be used becomes reduced.