A determining unit determines for each of pages which one of a color output or a monochrome output to perform, based on a color intensity of determination image data containing generated color pixel data and monochrome pixel data on each of pixels generated by a determination image data generating unit based on print job data. An image generating unit generates color image data by extracting the color pixel data on each of the pixels for each of color components upon determination that the color output is to be performed, and generates monochrome image data by extracting the monochrome pixel data on each of the pixels upon determination that the monochrome output is to be performed.