A method is for processing image data for recording by an image forming apparatus that discharges ink droplets from a plurality of nozzles. The method includes reading out image data corresponding to one line constituted by a series of dots aligning in a main scanning direction. The method further includes calculating a faulty discharge error, which occurs at a non-discharge position on a line at which no ink droplet is discharged from a defective one of the plurality of nozzles. The method further includes controlling distribution of the faulty discharge error to a line that is downstream relative to a line on which the non-discharge position occurs according to a limit setting that limits distribution of the faulty discharge error.