1. An image forming apparatus which discharges ink onto a recording medium to form an image on a surface of the recording medium, comprising: a preprocessing unit that applies preprocess liquid on the surface of the recording medium before the image is formed, an application quantity of the preprocess liquid being determined based at least on a kind of the ink; and a postprocessing unit that applies postprocess liquid, which is different from the preprocess liquid, onto the recording medium after the image is formed, an application quantity of the postprocess liquid being determined based at least on the kind of the ink.