According to examples, a method comprises receiving, at a processor, print job data relating to a print job to be performed by a print apparatus, the print job data defining order in which a plurality of colour separation images are to be transferred onto an imaging surface of the print apparatus. The method may comprise determining, based on the print job data, a number of null segments to be inserted into the print job and a location at which each null segment is to be inserted amongst the plurality of colour separation images. A print apparatus and a machine-readable machine are also disclosed.