An image processor includes an automatic color determining unit that determines whether an input image signal including a plurality of color signals indicates a color image or a monochrome image, an operation panel for accepting selection of a color processing mode for applying color image processing and a monochrome processing mode for applying monochrome image processing, a filtering processor that applies image processing of at least one of the color processing and the monochrome processing, and an output controller. Even when the monochrome processing mode is accepted, the image processor applies monochrome image processing based on a determination result of the automatic color determining unit.