An image forming apparatus and method in which a controller is capable of executing image processing of its own are disclosed. The controller has an RF unit for processing image information, a halftone image processor, a density corrector and a patch generator. The engine includes a modulator corresponding to the RF unit, a halftone image processor different from that of the controller, a density controller, modulator and patch generator corresponding to the halftone processor of the engine, a sensor for sensing the density of formed patches, and a control unit for controlling the density of an image on the basis of a signal from the sensor. The engine sends the controller a signal relating to density control.