1. An image forming apparatus comprising: a storage portion storing image data that is an output target; a preview image generating circuit that generates a preview image from the image data based on an output setting; an output image generating circuit that generates an output image from the image data based on the output setting; a data information obtaining circuit that obtains data information from output image data of the output image, and discards the output image data from which the data information was obtained; and a display circuit that displays the data information together with the preview image.