There is disclosed an image processor including a display screen, a color image storage, a monochrome image storage, an image presenter, an image-area designator, a color-data replacer, and an outputter. The color image storage stores color image data constituted by a plurality of pieces of color data. The monochrome image storage stores monochrome image data obtained by converting the color image data and constituted by a plurality of pieces of color data. The image presenter can operate to present on the display screen a color image on the basis of the color image data stored in the color image storage, and a monochrome image on the basis of the monochrome image data stored in the monochrome image storage. The image-area designator can designate at least a part of at least one of the color image and the monochrome image that are presented on the display screen by the image presenter. The color-data replacer replaces one of the pieces of color data constituting the monochrome image data and corresponding to the part designated by the image-area designator, with another piece of color data. The outputter outputs the monochrome image data including the substituted piece of color data by the color-data replacer.