A printer control section arranged to control a printhead, is operable to cause the printhead to: perform a plurality of passes over a swath of a print medium, the plurality of passes including first and second treatment passes; apply treatment to the print medium in each of the treatment passes, the treatment in each treatment pass being applied according to a respective treatment mask, wherein each treatment mask indicates a corresponding set of pixels to which the treatment may be applied in a pass to which the treatment mask is applied, the treatment mask having a weight indicative of the proportion of pixels in the corresponding set of pixels, and the treatment masks of the first and second passes are such that a weight of the first treatment mask is different from a weight of the second treatment mask.