An image processing device, which can be incorporated in an image forming apparatus and perform an image processing method, includes a first image sensor unit including multiple image sensor chips arranged in a line to read an image of a document by converting light incident from the document into electrical signals, a chroma calculation unit to calculate chroma data from an image signal constituted by the electrical signals of the image read by the first image sensor unit, and a chroma adjustment unit to adjust the chroma by using the chroma data calculated by the chroma calculation unit to perform, only on a low-chroma image signal, a conversion process for reducing the chroma to suppress color irregularities occurring at intervals corresponding to widths of the multiple image sensor chips of the first image sensor unit.