Design for Print - Registration marks & ink trapping

Registration Marks

Registration marks are usaually added by the imagesetter when it prints out your film. You can easily create your own vector registration mark in illustrator and save it as a small four colour eps file. The registration marks are made up of all four process colours at a 100%.

The greatest difficulty arising from the use of rich black is in trapping with other elements. for an example a brochure that has a solid black cover with a line of white type running across it. If a rich black is used. there will be a regitration problem around the edge of the white type. It will probably have a thin cyan line visible along one edge and perhaps a magenta line on the other edge.

The following method works well to over come this problem, send the printer 2 copies of the final file. File 1, tell the printer to only run the black film. The second version is an exact copy of the first with one exception, a white outline has been added to the type, thereby forcing all four colours away from it.

Ink trapping

When an offset printed document uses more than one ink on the same page, each ink must be printed in register (perfectly aligned) with any other inks that it abuts, so that there is no gap where the different inks meet. However, it’s impossible to ensure exact registration for every object on every sheet of paper running through a printing press, so misregistration of inks can occur. Misregistration causes an unintended gap between inks.

You can compensate for misregistration by slightly expanding one object so that it overlaps an object of a different color—a process known as trapping. By default, placing one ink over another knocks out, or removes, any inks underneath to prevent unwanted color mixing; but trapping requires that inks overprint, or print on top of each other, so that at least a partial overlap is achieved.