16. An image forming method comprising: convening page description language to page description language corresponding to a plurality of areas; generating image data based on the convened page description language; retaining the convened page description language and the generated image data; comparing the retained page description language retained and the convened page description language; and outputting the retained image data in case the converted page description language in response to the comparison and the retained page description language correspond with each other, and outputting the generated image data in case the converted page description language in response to the comparison and the retained page description language do not correspond with each other.
16. An image forming method comprising: convening page description language to page description language corresponding to a plurality of areas; generating image data based on the convened page description language; retaining the convened page description language and the generated image data; comparing the retained page description language retained and the convened page description language; and outputting the retained image data in case the converted page description language in response to the comparison and the retained page description language correspond with each other, and outputting the generated image data in case the converted page description language in response to the comparison and the retained page description language do not correspond with each other. 17. The image forming method according to claim 16 , wherein the area includes an area where one page is divided in two directions.