1. An image forming apparatus comprising: a storage unit configured to store a rendering image having a plurality of tones; a communication interface unit configured to receive print data; a rendering unit configured to render the received print data to a bitmap image; a mergence unit configured to merge the bitmap image and the rendering image into a single mergence image prior to generating binary data corresponding to either of the bitmap image and the rendering image; a binary coding unit configured to perform halftoning on the generated mergence image and to generate binary data corresponding to the mergence image, the binary data corresponding to the mergence image having fewer tones than either of the rendering image and the bitmap image; and a print engine unit configured to form an image on a paper by using the generated binary data.