1. A method of modifying an optical scanner and engraver for optically scanning copy and engraving a printing plate such that a plurality of sets of copy, at least one of which requires one gradation curve transfer function and at least another one of which requires another gradation curve transfer function, can be simultaneously scanned and a printing plate engraved, the optical scanner and engraver having a carrier for a plurality of sets of copy, a plurality of optical scanners, one for each set of copy, each scanner producing an electrical signal output representing the scanned copy, a plurality of engravers, one for each of the scanners, each responsive to an input signal to engrave the printing plate to reproduce one set of scanned copy, a storage device for storing a plurality of gradation curve transfer functions and, a signal processing unit coupled to the optical scanners, the engravers and the storage device and having a random access memory first location for storing a first gradation curve transfer function received from the storage device wherein the signal processing unit converts each scanner electrical signal output to a corresponding engraver input signal in accordance with the first gradation curve transfer function, the method comprising: providing means for storing in a random access memory second location a second gradation curve transfer function received from the storage device, providing a first switch for selectively directing the gradation curve transfer function received from the storage device for storage alternatively either in the first or the second random access memory locations, providing a plurality of switches, one for each set of scanners and engravers, for directing the signal processing unit to individually convert each scanner electrical signal output to its corresponding engraver signal input in accordance selectively with either the first or the second gradation curve transfer function.