In an image processing apparatus, a color/monochrome determination section determines whether color image data is image data indicative of a color document or image data indicative of a monochrome document, regardless of which color setting is selected to output image data, and a control section stores a determination result and the color image data in a storage device so that they are correlated with each other. Upon receiving a change instruction to change the color setting, the control section generates output image data, following a color setting that is changed according to the change instruction, on the basis of the determination result and the color image data each stored in the storage device. As a result, even if the color setting is desired to be changed, it is possible to carry out output processing without reading the document from an image reading apparatus again.