An image forming apparatus for forming an image corresponding to an image signal on a recording material, comprising: a signal processor which generates an image-formation control signal by subjecting the image signal to a signal processing process including a screening process selectively using one of plural types of different processing screens; an image forming unit which includes an intermediate transfer medium, and which forms the image by forming a toner image on the intermediate transfer medium corresponding to the image-formation control signal and transferring and fixing the toner image to a recording material; and a detector which detects a quantity of the toner carried on the intermediate transfer medium as the toner image, wherein the signal processing process performed by the signal processor includes a tone correction process for compensating for a gamma characteristics of the apparatus based on a detection result given by the detector detecting a toner image formed as a patch image by using the processing screen and a transferring/fixing characteristics, which represents a relation between a quantity of toner constituting a toner image carried on the intermediate transfer medium and a density of an image formed on the recording material as a result of transferring and fixing the toner image to the recording material, previously determined in correspondence to the processing screen.