Overprint + Blending mode (Isolate Blending or Knockout Group option): from AI to PDF

[sPretzel]

Hi,

This is for CS4. I have an object #1 with a fill (say a rectangle). Below that is object #2 with a stroke (say a straight line). #1 and #2 are grouped. Below all objects is object #3 which has a fill (say another rectangle) and that I am using as background. The group's Opacity is set to Normal 100% (default) but I enable the Knockout Group so #1 and #2 don't interact with each other. I then set the group's stroke and fill to overprint!

Enabling Overprint Preview, #1 and #2 don't show through each other but the group overprints. This is expected. When I Save As Adobe PDF and view the PDF in Acrobat Output Preview with Simulate Overprint, the group is shown to overprint (as expected) but it appears that Knockout Group is discarded, so #1 and #2 show through each other.

I encounter a similar problem with Isolate Blending.

1- Does Saving to Adobe PDF preserve Knockout Group and Isolate Blending when Overprint is enabled?

Any help?

2- In Acrobat, Preflight, where can I see the settings that correspond to Knockout Group and Isolate Blending? Presumably, that would be in Graphic Properties for an object, under Transparency, but I don't see any field that corresponds.

3- In this context where the Opacity is set to Normal 100%, is enabling Knockout Group or Isolate Blending for this object processed as Transparency?

There is a post, somewhat related here. But my problem is not a viewing problem (which happened to show correctly in Acrobat for this particular post). https://community.adobe.com/t5/Illustrator/Knockout-group-blending-modes-not-exporting-as-PDF-correc...

[meganchi]

Are you saving your PDF out as PDF X-4? Depending on which PDF version you save out, it will affect the outcome of the transparency effects in the file.

I'm not sure I undestand why you are knocking something out, yet applying an overprint stroke and fill? What desired result are you looking for? Without a visual, it is hard to answer.

[sPretzel]

Hi maganchi.

No, I am not saving as PDF X-4. However, I am setting Overprint to Preserve in the Overprints and Transparency Flattener Options (PDF 1.3).

Basically, I want object #1 to "punch a hole" in object #2 and both objects #1 and #2 to overprint on the background, which is object #3. Effectively, for object #1, I would like object #2 to act as if it wasn't there, so that object #1 would virtually be sitting directly on the background (object #3).

[Monika Gause]

Please show a screenshot or upload a file. 

[sPretzel]

Monika, meganchi. I have attached a picture with some explanation of the scenario I described in the first post. If you can, please also answer the three questions. I can see a workaround by expanding everything in the group and creating a compound shape but I would prefer something that preserves editing capabilities. Illustrator does what I want, it's the conversion to PDF that doesn't.

Thanks.

In the second and third examples, I forgot to mention that Objects 1 and 2 are set to overprint both stroke and fill (as applicable: Object 1 has only fills and Object 2 has only a stroke).

[Ton Frederiks]

Do you need to save as pdf 1.3?

What happens when you save as 1.4?

[sPretzel]

I will have to double check if I must save in PDF 1.3. I need to flatten transparency.

I just tried PDF 1.4 and it produces the desired output (as shown in the second example). Looking at Preflight for the yellow fill, I don't see any difference in the properties between PDF 1.3 and PDF 1.4.

I don't understand why Knockout Group, in this case, is (or is it?) treated as transparency. Granted, Knockout Group is part of Opacity but here, I use it to avoid transparency!

[Ton Frederiks]

If you really need to flatten transparency, skip the knockout group and try to add 1% black to the yellow color so it will not overprint on the black line.

[sPretzel]

Hi Ton. I appreciate that trick but I am not keen on such schemes because they change the design and then you have to keep track of these things and if there is something else in the way (like a red line), then you have to use another trick for that too and it gets out of hand. I am curious to identify the difference in Preflight for the this object between PDF 1.3 and PDF 1.4 because even though the result is different, I don't see a difference in Preflight.

[Ton Frederiks]

It is not a trick, just a way to avoid transparency.

[Ton Frederiks]

If you really need to flatten the artwork and want to keep the appearance of Overprint, uncheck the Preserve Overprint and Spot Colors in the Flattener options. This will discard the overprint, but keep the appearance.