A Big Sur solution to overprint errors

Blognosticator Head

As I was winding south from Big Sur last Friday, where I had spent the day making a GigaPan image of the Julia Pfeiffer Burns State Beach, my phone rang (I had been in a No Service area for over six hours!). I pulled over to take the call, of course.

It was my wife (a graphic designer) calling to ask about a problem she was having with a logo that had been drawn by a local ad agency in Adobe Illustrator. It was strange, she said. The logo appeared in the ad on her screen, and it appeared in the PDF file she created of a page with the ad placed in it.

Acrobat screen

But, the lettering of the logo disappeared when she proofed it on our laser printer. It was driving her crazy.

Acrobat Output Preview

As I passed Piedras Blancas Lighthouse, I tried to get back into my prepress frame of mind. I scoured my memory banks for similar problems. I had a vague notion that I had encountered an Illustrator file once that had a disappearing element in it. What on earth caused it?

With the surf hitting the rocks to my right, and with 45 miles still to go before I could be there to dissect the problem, I thumbed through my brain-index, looking for a reference, but I came up blank.

I was listening to Beethoven’s Emperor Concerto on my car stereo, and was enjoying the second movement with its quiet pizzicato cello part when it hit me. It was probably something having to do with overprint. I accelerated, and made my way south through Cayucos and Morro Bay, excited by the idea of being the knock-out knight in shining armor who saves the day for my damsel-in-distress.

(You have to forgive a guy his fantasies.)

If, when drawing something white (0,0,0,0 CMYK) in Illustrator, you set that object to overprint, Illustrator will interrupt you with a warning saying that this won’t work, unless it’s part of a transparency effect. Most of us treat these warnings as so much “blah, blah, blah” and click on through. But, this is one to which you should pay attention.

Overprint warning

Overprinting colors works fine – when there are colors to overprint – for example, overprinting yellow on top of cyan will create a solid green in the final printing. But overprinting white creates nothing – zilch.

Overprinting white under or over a color will cause that color to overprint it, and you will see only the other color. It’s a strange concept, but it’s valid. White overprinting doesn’t work (unless you’re printing white ink on top of something).

What the agency wanted, of course, was a white knock-out from the color or image under the logo. And, with any color other than white, the overprint would have worked.

Illustrator overprint menu

The best approach to this is to select Overprint Preview in Illustrator (above) to see the effect of your overprints. If something disappears from the screen when you choose it, you’ve got a problem. If colors change, then you have overprint.

It’s easy to fix. Just select the erroneously assigned white overprint, and uncheck the Overprint checkbox in the Attributes menu (below). The overprint will go away, and knock-out will be done instead.

Overprint checkbox


About Brian Lawler

Brian Lawler is an Emeritus Professor of Graphic Communication at California Polytechnic State University, San Luis Obispo and was a Guest Professor at Hochschule München from September, 2021 to September, 2022. He writes about graphic arts processes and technologies for various industry publications, and on his blog, The Blognosticator.
This entry was posted in Mistakes you can avoid, Printing and Printing Processes, Software and tagged , , , . Bookmark the permalink.

2 Responses to A Big Sur solution to overprint errors

  1. The big issue is that many PDF readers, including Mac OS X Preview, do not know the concept of ‘overprinting’, therefor showing it ‘wrong’. Showing it ‘wrong’ means that in this case the white text is visible. But a decent PDF RIP, which knows about overprinting, will show it correctly, being: not showing the white text.

    A few years ago we at VIGC did a study on PDF viewers. At that moment only Adobe Acrobat and Adobe Reader (on Mac and Win, NOT on iOS, Android, Windows Phone!) show overprinting correctly. We also created a small ‘PDF viewer check’, which you can download for free: http://www.vigc.org/vigc-pdf-viewer-check/

    And it is not only PDF viewers that have that problem: also a number of LFP RIPs have that problem… So everybody with a LFP device should check if his RIP correctly outputs PDFs. The Ghent Output Suite is a great tool to do that: http://www.gwg.org/download/test-suites/ghent-output-suite/ And it is also for free

    • Brian Lawler says:

      Thank you, Eddy, for the input.

      I also tested the file with prepress tools in Adobe Acrobat, and the Output Preview tool in Acrobat will cause the overprint white to disappear (correct). It shows as white in Acrobat until I invoke the Output Preview, then the white disappears (correct). Overprint preview in Illustrator shows it correctly, as does the Overprint Preview function in Adobe InDesign.

      It’s important that all of us use the tools available to preview jobs so that errors like this one don’t end up in print.


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