An image processing apparatus, comprising: a decompression-rotation processing module, a rotation-compression processing module one or more image processing modules (13-1,..., 13-N), wherein the first image processing module reads from a first work memory, wherein the last image processing module (13-N) writes into a second work memory; wherein the decompression-rotation processing module is configured to identify a portrait or landscape orientation of an image of the image data, wherein, if a length of the image in a primary scanning or longitudinal direction is larger than a length of the image in a secondary scanning direction, the decompression-rotation processing module is further configured to read out and decompress plural pieces of compressed sub-band data corresponding to plural sub-bands in plural bands, the plural sub-bands located at an identical position in a primary scanning direction; wherein a sub-band corresponds to a subdivision of a band in primary scanning or longitudinal direction, and wherein each band includes a predetermined number of lines; to rotate the respective pieces of sub-band data in a first case by + 90 degrees or in a second case by - 90 degrees, and write the pieces of rotated sub-band data in the first work memory; the rotation-compression processing module is further configured to read out the plural pieces of sub-band data which the one or more image processing modules (13-1,..., 13-N) performed image processing for and stored in the second work memory and to rotate the respective pieces of sub-band data in the first case by - 90 degrees or in the second case by + 90 degrees, and compress the respective pieces of rotated sub-band data; wherein, if the length of the image in a primary scanning direction is either equal to or less than the length of the image in a secondary scanning direction; the decompression-rotation processing module is further configured to read out and decompress plural pieces of compressed sub-band data corresponding to plural sub-bands in plural bands, the plural sub-bands located at an identical position in a primary scanning direction; wherein each band includes a predetermined number of lines; to write the pieces of sub-band data in the first work memory; the rotation-compression processing module is further configured to read out the plural pieces of sub-band data which the one or more image processing modules (13-1,..., 13-N) performed image processing for and stored in the second work memory and to compress the respective pieces of sub-band data. a decompression-rotation processing module, a rotation-compression processing module one or more image processing modules (13-1,..., 13-N), wherein the first image processing module reads from a first work memory, wherein the last image processing module (13-N) writes into a second work memory; wherein the decompression-rotation processing module is configured to identify a portrait or landscape orientation of an image of the image data, wherein, if a length of the image in a primary scanning or longitudinal direction is larger than a length of the image in a secondary scanning direction, the decompression-rotation processing module is further configured to read out and decompress plural pieces of compressed sub-band data corresponding to plural sub-bands in plural bands, the plural sub-bands located at an identical position in a primary scanning direction; wherein a sub-band corresponds to a subdivision of a band in primary scanning or longitudinal direction, and wherein each band includes a predetermined number of lines; to rotate the respective pieces of sub-band data in a first case by + 90 degrees or in a second case by - 90 degrees, and write the pieces of rotated sub-band data in the first work memory; the rotation-compression processing module is further configured to read out the plural pieces of sub-band data which the one or more image processing modules (13-1,..., 13-N) performed image processing for and stored in the second work memory and to rotate the respective pieces of sub-band data in the first case by - 90 degrees or in the second case by + 90 degrees, and compress the respective pieces of rotated sub-band data; wherein, if the length of the image in a primary scanning direction is either equal to or less than the length of the image in a secondary scanning direction; the decompression-rotation processing module is further configured to read out and decompress plural pieces of compressed sub-band data corresponding to plural sub-bands in plural bands, the plural sub-bands located at an identical position in a primary scanning direction; wherein each band includes a predetermined number of lines; to write the pieces of sub-band data in the first work memory; the rotation-compression processing module is further configured to read out the plural pieces of sub-band data which the one or more image processing modules (13-1,..., 13-N) performed image processing for and stored in the second work memory and to compress the respective pieces of sub-band data.