1. A method of manipulating an image, comprising the steps of: scanning an image line-by-line to obtain scan data; writing the scan data into a buffer; after the buffer has M lines of scan data which extend to an end of the image, performing the steps of: rotating image data of a block of M lines by N pixels of the scan data and writing the block which has been rotated to a memory; and rotating image data of other blocks of the scan data in the buffer having M lines of the scan data and writing the other blocks which have been rotated into memory.