1. An article of manufacture comprising a non-transitory machine-readable medium including data that, when accessed by a machine, cause the machine to: generate an inverse transfer function for each of a plurality of gray levels based on a target response and a measured response; receive one or more un-calibrated halftones; transform un-calibrated threshold values in the one or more un-calibrated halftones via the inverse transfer function to generate calibrated halftone threshold values; generate one or more calibrated halftones based on the calibrated halftone threshold values; process image data using the one or more calibrated halftones; and print the image data.