Provided is an image processing device used for image processing in an image forming device that executes linear image forming in a first direction repeatedly in a second direction orthogonal to the first direction and executes two-dimensional image forming on a recording medium, the image processing device including: a processor configured to: acquire a phase of a member that contributes to image forming by rotating or circulating in the second direction and calculate, for each of different phases, an input/output gradation characteristic indicating a correspondence relationship in density in the same pixels in pre-output image data and post-output image data acquired by scanning of an image formed on the recording medium; calculates correction data to solve a difference between the input/output gradation characteristic in each of the phases and a reference input/output gradation characteristic; and correct the pre-output image data with the correction data of each of the phases.
