1. An image processing apparatus, having a color conversion section for converting image data into monochrome image data, which supplies the monochrome image data to a printing apparatus for executing image printing and supplies the monochrome image data to an image display device for displaying a preview, the image processing apparatus comprising: a color matching section for performing, on the monochrome image data to be supplied to the image display device, a color matching process of reducing differences in color between an image to be outputted by the image display device and an image to be outputted by the printing apparatus; and a color correction section for performing color correction on three or more colors of image data that are supplied to the printing apparatus, the image display device displaying RGB image data, and the color correction section and the color matching section being realized by a common circuit, and the image processing apparatus including no preview processing circuit for generating a preview image, and in a case where the preview is displayed, the color conversion section converting RGB image data into CMY monochrome image data, and the color matching section converting the CMY monochrome image data into RGB monochrome image data in accordance with characteristics of the printing apparatus and characteristics of the image display device, in a case where the image printing is executed, the color conversion section converting the RGB image data into the CMY monochrome image data, and the color correction section performing no processing on the CMY monochrome image data.