1. An image display method for displaying print preview images corresponding to document data, the method comprising: generating print preview images, wherein each print preview image corresponds to a respective page of the document data and the document data has a plurality of pages; starting to display the print preview images before the print preview images have been generated for all of the plurality of pages of the document data; accepting an instruction of a process regarding at least one of the displayed print preview images before the generation of all of the print preview images is completed; and executing the process before the generation of all of the print preview images is completed.