An image processing apparatus is provided for realizing a higher speed print-out of a scan image. It is determined whether an input data type stored in metadata of document data is PDL or not (S1609). If the input data type is “full-page image”, page data is divided into blocks and a thread is allotted to each of the blocks (S1608). If the input data type is not “full-page image”, the process goes to S1603. Subsequently, DL data is generated from vector data in the document, the DL data is added to the document, and the DL data is rendered into a bit map (S1603 to S1605). If the threads are processed by a plurality of processors, respectively, it becomes possible to carry out the processing in parallel and thereby to realize higher speed processing, when the input data type is “full page image”.