The image processing performance of a present day or existing page printer, e.g., electrophotographic printer, is improved and accelerated with the use of a detachable intelligent cartridge which contains a CPU and necessary memory to process print data into image dated for the electronic control unit of the printer to which the cartridge is attached. Depending upon the page description language (PDL) to be employed, a cartridge can be selected for use with the printer and accelerate its PDL conversion and printing output. The intelligent cartridge CPU, which is different from the printer CPU, receives print data from the printer and, since the data bus connecting the intelligent cartridge and the electronic control unit of the printer has only a read only capability from the electronic control unit, data transfer to the cartridge is made possible by utilizing the print data as an index for the read address accomplished by the printer CPU. The bit image data is accomplished by the cartridge CPU from print data received via the printer CPU and after data development, the bit image data is transferred to the printer for hardcopy printout.