Short Run Commercial Digital Printing Quality

Question

I got back a short run print job from a commercial digital printer recently. The background was designed as a block color, not a gradient or patter or anything, just all the one color; but when printed there were strange lines in it. The lines are very subtle but are definitely present, and quite obvious when you look at the result.

I took a scan in case it helps. The lines are not 100% horizontal they sort of wave a bit and it seems there are vertical lines also.

I'm asking here because the printers said it was a side effect of digital printing and there was nothing which could be done about it for short runs ( 200 ). He said on photos it would be masked by the photo but on solid block colours it would show. Can someone confirm my suspensions that this is not the case? I am surprised because I don't get any lines on my home printer.

I played with the contrast and curves a bit to bring out those lines a bit - there are several if you look carefully but the most obvious 2 are about 2/3 way down particularly on the left.

Answer 1

I don't actually see a well-formed question here, but "Yes" digital printing is not good quality compared to offset press. The lines you describe are hallmarks of the process in my experience and are usually present in high coverage areas.

These high-volume digital printers are typically laser printers. The basic process involves a drum which becomes electrically charged by laser application, which picks up toner particles (plastic) which is placed in contact with the paper while heat is applied. Previous toner deposition and inconsistencies in the paper finish can both conspire to interfere with perfect toner adhesion.

Additionally, these printers do not use the same rotated screen system that offset uses, but tend to use more regular grid or banded patterns.

Digital printing is popular because it is hard to argue with the cost difference and for many applications, nobody cares or notices the quality difference.

If this is an inkjet, then you have a different set of patterns, which will be more "stochastic" in nature, and the paper will have saturation/absorption issues instead of toner adhesion issues in high-fill areas.

Both of these types of printers exhibit the problems you describe to a much greater degree on consumer models. The professional high-volume models are just these consumer models scaled up.

One more point: most digital printers do not handle "custom inks" unless you are specifically paying for and requesting it. There is no such thing as a "solid color" in any printing process with no custom ink specified, unless the solid color is one of the process inks or one of the specific set of inks/toner installed in the machine, and it may be (practically) impossible to specify e.g "pure photo cyan" for an inkjet or laserjet. Since all colors are built up of juxtaposed dots, there is always a pattern.

Answer 2

A properly calibrated, cleaned and maintained commercial digital press like an HP Indigo can produce totally smooth color blocks and washes. I see it done constantly. It does require that the operator keeps the machine maintained and the print heads clean, but it's not actually much of a challenge. With laser (toner) systems it's more of a challenge, but the high end Xerox machines can do it.

Office-caliber machines (including what you'll find in the printing departments of FedEx or Office Depot) and machines that are not properly maintained will give exactly the kind of gruesome result you see, but it's a long time since this was an inherent drawback of the technology.