Potential overprint problems


I have a PDF document with grayscale content in it. I was thinking about converting it to CMYK (to K only, to be more precise) by using the option Promote Gray to CMYK Black and Preserve Black Objects in Adobe Acrobat (Tools > Print Production > Convert Color).

The conversion works fine, but afterwards, the preflight warns me that I have black objects set to knockout. This preflight check is called Potential Overprint Problems. I think that this happens because the objects were previously grey, so they were not set to overprint.

I don't know if this is a big problem, cause visually everything looks fine. Note that Acrobat is set to Overprint Preview while I'm viewing the document (Edit > Preferences > Page Display > Use Overprint Preview).

The black objects where the preflight locates the problem are vectors (fills and strokes). They were exported as PDFs from Illustrator (in grey) and they were placed in Indesign on a white (paper) background.

After the conversion to CMYK, I tried the Pitstop plugin (global change: Change Overprint) to solve the problem and it seems that it works. It automatically sets all the black objects (>97%) to overprint.

But I want to be sure that I'm doing everything right and I don't want to mess up something, so thank you in advance for your opinions.
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You seem unsure of how the next step - a rip - will handle your artwork.
So to be extra sure - generate (save as) a hi-res (300dpi+) jpeg (BITMAP) from Acrobat.
Then zoom in to areas you think may be of concern.
We still make 'dot' (colorized tiff BITMAP) proofs of 300 or 600 dpi to send clients.
These 'grayscale' colorized tiffs also show possible font errors or reflows because you see what you will get.
You shuld then be able to send your original file, vector+bitmap PDF, to your printer for ripping.
If everything looks fine that's a start.

A few things to check.
Is your Acrobat set up correctly to show overprint?
Acrobat Preferences > Page Display > Use Overprint Preview. It should be set to 'Always' Default is "Only for PDF/X files'

If you have PitStop check that the overprint mode that is added is OPM 1, not OPM 0. The Inspector will tell you that.

100% K will overprint objects underneath.
You can see the effect in Acrobat Output Prevew by toggling off the black separation.

When Overprint Preview is open, Acrobat will also simulate the overprint effect.
See attachment below, right 100% overprints 100% Magenta, left 100% does not Overprint.

Hope that helps.


  • Screenshot 2022-12-11 at 17.00.25.png
    Screenshot 2022-12-11 at 17.00.25.png
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I'm sorry, but I don't see the point if we only have one separation/channel. If it’s just Black, you really don’t need to overprint, don’t you?

It is true that as a general rule black text should always be defined with overprint, but in some scenarios we could say that preflight reports may contain "false errors" once interpreted by the end user. An example could be when they report black text is set to knock-out (no overprint), but that text is on top of "paper" and not on top of another color element.


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