a method of generating halftone print data for overlapping end portions of a pair of consecutive printhead chips includes the step of generating continuous tone print data for an array of the printhead chips . an initial dither matrix to be applied to the continuous tone print data is generated . overlap data representing an extent of overlap of the end portions is generated . the overlap data is applied to the initial dither matrix with a summation means to generate an output value . the output value is applied to the continuous tone print data .