1. An image scanning apparatus, comprising: a scanning unit configured to scan an original document and generate a scanned image; a storage unit configured to store the generated scanned image; an image processor including a plurality of image processing modules, the plurality of image processing modules separately including a plurality of buffers configured to store the scanned image of block units, and configured to read the generated scanned image in preset block units and perform image processing on the scanned image read in block units sequentially using the plurality of image processing modules; and a controller configured to store the image-processed scanned image in the storage unit.