1. An image processing device for creating image data used to form an image on a medium, the image processing device comprising: a multi-layer data acquiring part configured to acquire multi-layer data having a required-formation-amount-related value representing a value relating to a formation amount required to form an image in at least one unit region; an expanding part configured to expand, based on a correspondence relationship for expansion, the acquired multi-layer data into a plurality of sets of single-layer data; and a storing part configured to store the correspondence relationship for expansion, the correspondence relationship for expansion having a correspondence relationship between the required-formation-amount-related value in each of the sets of single-layer data and the required-formation-amount-related value in the multi-layer data, the required-formation-amount-related value in the multi-layer data being image data that exceeds a maximum-formation-amount-related value representing a value relating to a maximum formation amount of a color value of the single-layer data with which an image can be printed in the at least one unit region in a single printing process, and the required-formation-amount-related value in the single-layer data being image data that is equal to or less than the maximum-formation-amount-related value.