An image forming device performs functions including: dividing the image into a plurality of band images each including at least one sub-region; creating region data used to identify each sub-region included in the band image; updating the region data such that the region data identifies both first and second uniform sub-regions as a single uniform region of the image when the first uniform sub-region abuts the second uniform sub-region, the first and second uniform sub-regions being included in the first and second band image and classified as the uniform sub-region, respectively; and updating the region data such that the region data identifies both first and second nonuniform sub-regions as a single nonuniform region of the image when the first nonuniform sub-region abuts the second nonuniform sub-region, the first and second nonuniform sub-regions being included in the first and second band image and classified as the nonuniform sub-region, respectively.