An image processing apparatus is provided that can accurately and rapidly perform color/monochrome judgment for print image data. In the image forming apparatus, a command analyzing unit interprets externally received PDL data, and a first color/monochrome judging unit performs the color/monochrome judgment based on an attribute of an image object. When a data type of the attribute is not raster image data and color information is monochrome, it is immediately judged that the image is monochrome. Only when the first color/monochrome judging unit judges that the image is color, a second color/monochrome judging unit performs the color/monochrome judgment every time a rendering unit generates band data. If at least one pixel of color data exists, it is judged that the image is color. With such a configuration, the color/monochrome judgment can be performed accurately and rapidly.