Designing for Digital Printing
Digital presses have improved dramatically over the past several years. When you factor in the press and the paper, as well as the images involved, you almost need a printer’s loupe to tell the difference between digital printing and traditional offset. Colors are vibrant but not garish, and there is an increasing amount of detail in the highlights and shadows with each new digital press brought to market.
Nevertheless, there are still several things you can do to minimize the remaining flaws in the technology while drawing attention to its good points.
First we should distinguish among three separate digital technologies: direct imaging presses (such as the Heidelberg Quickmaster DI), toner- (powder) and liquid-based xerography (also called electrophotography), and ink-jet.
The first, direct-imaging, is (usually) a waterless printing process based on imaging the printing plates while they are on press. Plates are burned by laser within the press itself. The job is printed, and the plates are then rolled up into a waste canister so new plates can be imaged—all while on press.
Unlike xerography and ink-jet, the direct-imaging press, while considered digital, prints one image many times. You can print a superb product with high line screens in the photos, but your job output cannot change from impression to impression (page to page), as is the case with xerography and ink-jet.
You would use this technology for a short-run, small-format job. The maximum sized press sheet is slightly larger than 13”x18”, so this press would be ideal for a brochure or small poster but not for a book made up of signatures.
Since this is a waterless press, in which a silicone coating is removed in image areas of the printing plate, your colors will be vibrant, and higher than usual line screens will allow for crisp, detailed photographs.
You do not need to design your printed piece any differently for the direct-imaging press than you would for a regular offset press.
Xerography comes in several flavors. Whether you choose the NexPress, iGen, Indigo, or Xeikon, you are charging an internal drum with electricity and then discharging the electricity in non-image areas so the image area of the drum will attract toner or ink particles. Then you are fusing these ink or toner particles to paper with heat and pressure. Unlike the direct-imaging press, every sheet that leaves this press can be different from the last. You can change a word, or you can change all the text and images on a page. This is basically a complex, color Xerox machine.
The first thing you should remember in designing for this kind of press is that you must choose paper appropriate for the equipment: paper that will withstand the intense heat and pressure of the process. Digital printing papers now come in coated and uncoated options, and you have an ever-increasing variety to choose from. However, you must choose a paper guaranteed to work on the equipment. That is, traditional offset presses are more forgiving in the area of paper choice. If you choose the wrong paper for a xerographic press, the toner might not adhere well to the substrate and might flake off in areas. Therefore, check a few samples before committing to a particular sheet, and discuss this issue at length with your print provider.
The next thing to keep in mind is that xerographic presses are usually 4-color presses. If you need to print a PMS color, you will usually choose the nearest process color build to this PMS color. Unfortunately, though, some PMS colors don’t have completely accurate process color builds. Some look like mud. So how can you get around this problem if you really need a particular color? The Indigo press provides extra colors beyond the usual 4-color set: i.e., orange and violet in addition to the process colors. These will often allow you to achieve a closer match to a problematic PMS color. Also, separate Pantone-certified colors exist for the Indigo press. You can add these to the mix, but they will increase the cost of your job because they are not standard and therefore require more presswork and clean-up.
Beyond color fidelity is the issue of color evenness. On toner-based xerographic presses, large areas of color often look banded, mottled or uneven. On these presses, maintaining consistency over large areas is problematic. So what can you do to avoid this? Have your printer run samples to gauge the potential extent of the problem. Then add a little patterning (or noise) to the solid color, reduce the amount of color, and/or reduce the size of the color area.
Although still possible on ink-based digital presses (like the Indigo), this problem with banding or blending within larger areas of color is usually less visible.
This is a two-part article. Look for more information on designing for digital presses (including ink-jet presses) in next month’s issue of Quick Tips.
[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]