When you prepare artwork for printing, a number of marks are needed for the printer device to register the artwork elements precisely and verify correct color. You can add the following kinds of printer’s marks to your artwork:
Fine (hairline) horizontal and vertical rules that define where the page should be trimmed. Trim marks can also help register (align) one color separation to another.
Small targets outside the page area for aligning the different separations in a color document.
Small squares of color representing the CMYK inks and tints of gray (in 10% increments). Your service provider uses these marks to adjust ink density on the printing press.
Labels the film with the name of the artboard number, the time and date of printout, the line screen used, the screen angle for the separation, and the color of each particular plate. These labels appear at the tops of the images.
A. Star target (not optional) B. Registration mark C. Page information D. Trim marks E. Color bar F. Tint bar
Bleed is the amount of artwork that falls outside of the printing bounding box, or outside the crop area and trim marks. You can include bleed in your artwork as a margin of error—to ensure that the ink is still printed to the edge of the page after the page is trimmed or that an image can be stripped into a keyline in a document. Once you create the artwork that extends into the bleed, you can use Illustrator to specify the extent of the bleed. Increasing the bleed makes Illustrator print more of the artwork that is located beyond the trim marks. The trim marks still define the same size printing bounding box, however.
The size of the bleed you use depends on its purpose. A press bleed (that is, an image that bleeds off the edge of the printed sheet) should be at least 18 points. If the bleed is to ensure that an image fits a keyline, it needs to be no more than 2 or 3 points. Your print shop can advise you on the size of the bleed necessary for your particular job.