An image processing apparatus receives an input image signal and an input value defining a characteristic of an image to be printed in a dimensional system selected from a plurality of dimensional systems, whereupon, the input value is converted to corresponding numerical values in the other dimensional systems and the received input image signal is processed for conversion to a desired image signal in accordance with the converted numbered values. Such desired image signal is then supplied to a printer for printing the respective image. Further, a display monitors the input value defining a characteristic of the image to be printed and also the converted numerical values in the other dimensional systems.