An image processing device includes: a first gradation-process determining unit that determines a type of gradation process for a process-color toner plate in accordance with halftone mode information; a second gradation-process determining unit that determines a type of gradation process for a special toner plate other than a process color in accordance with the type of gradation process determined by the first gradation-process determining unit; and a halftone processing unit that performs halftone processes in accordance with the types of gradation processes that are determined by the first gradation-process determining unit and the second gradation-process determining unit.