Acrobat preflight check "black object set to knockout" flagging 4-color blacks

Participant ,
Sep 07, 2021 Sep 07, 2021

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I'm having an issue with the Preflight custom check "Black object is set to knock out." It's flagging the things it's supposed to, but it's also flagging 4-color black objects, which should not be overprinting.


Before going on, I know how to create my own custom preflight checks. I can create a new check, or modify this one to exclude anything that includes 4-color fill along with greater than 96% black.


My question is, is there a better way to check for knockout black objects without tripping the flag with 4-color objects?


My goal was to stick as closely as possible to the default, built-in preflight checks that come with Acrobat. Over the past decade or so, through multiple revisions of our preflight checks, we've ended up with multiple copies of checks across multiple profiles, some customized in some way different from the others. We've obviously wanted to clean that up. So we began with just the default install and built the preflight from there.


The stock check under Color: "Black object is set to knock out" is currently "object uses black with a percentage: greater than — 96" plus other checks including "overprint enabled is: not true." The problem we're running into is objects with 4-color black fill, with the black being at or near 100% also satisfying that check, tripping the error. But of course, a 4-color object would not be set to overprint.


Is there a better (stock, default) check I should be using? Or is this just one of those things that I really need to customize to get to work properly?


For example, the stock check for "Effective ink coverage is above [x]%" has a default radius of I believe 15mm. Unfortunately, that is not 15mm total area, but contiguous. You could have multiple 14mm areas across the page, and as long as each is separated by at least 1 pixel all around, you won't get a warning for ink density. This is clearly a problem (that you could check, visually, with the Output Preview panel) but it would "pass" unless that check was modified.

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