Image forming devices, hard imaging methods, and methods of determining a transfer function are described. According to one embodiment, an image forming device includes an image engine configured to provide a marking agent upon media, processing circuitry configured to control the image engine to form a test image upon the media having a specified coverage of the marking agent and to access measurement data indicative of a measured coverage of the marking agent of the test image, storage circuitry configured to store data comprising associations of a plurality of specified coverage values of the marking agent and a plurality of resultant coverage amounts of the marking agent formed upon the media by the image engine corresponding to respective ones of the specified coverage values, and wherein the processing circuitry is further configured to access image data of an image to be formed to identify one of the specified coverage values of the marking agent to be formed upon the media to form the image, to modify the one specified coverage value using the stored data and the measurement data to provide an imaging coverage value, and to control the image engine using the imaging coverage value to form the hard image.