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Overprint effect with Postscript output - an issue

Posted by Ken Dowling 
We discovered that overprint effect with postcript output to EPS appears to be subject to RBG (or maybe CMYK outout) colour selection for purple.

Checking the first digital print for the live run for Champs maps, the mapper noticed that overprint was not working. Yet it had been OK in test runs. After some bewilderment, two of us came to the same conclusion from different thought processes. One clue was that we had changed the purple composition for this run. So we changed it back and got the correct overprint effect.

I notice the Help does say this process isn't perfect for Postscript output so hopefully this might make it a bit mnore perfect if not previously known. As I cannot tell whether the culprit is the one of the set RGB components or one of the components of CMYK output her is a setting that worked and another that didn't. g and y seem good initial targets but I'll leave it to Finn to suss out.

This worked: r179 g26 b255 which I believe equates to c30 m90 y0 k0.
This didn't: r179 g0 b217 which I believe equates to c30 m100 y15 k0.

We also noticed that if the EPS was distilled to EPS, an valid overprint effect appeared to disappear. If this occurs, go to Adobe Reader or Acrobat Preferences | Page Display and turn on Use Overprint Preview. Haven't had time to find out whether that also ensures it prints correctly.
I erred in my last para of previous post. I said "EPS was distilled to EPS" whereas I meant "EPS distilled to PDF".

btw Finn, how am I supposed to enter a spam code with a backward 'E'? :-)

Finn Arildsen
Re: Overprint effect with Postscript output - an issue
September 17, 2009 10:04PM

You're right about the overprint effect seemingly "disappearing" when exporting s EPS or distilling to PDF. Not all PostScript "devices" support overprint effect, notably most PostScript printers do not support overprint effect. One of the exceptions is Adobe Illustrator. As you mention, if you use "Overprint Preview" in Illustrator, you'll see the effect, and you can print from Illustrator and get the effect on the printer.

I'm not sure I follow you with regard to the colour composition of the purple colour having any influence on overprint effect working or not.

To analyse this further, I think I need to know if you have "Simulate overprint effect on PostScript printers" on or off in File / Standard settings for this PC ?

Best regards,

PS: My guess is that a backward 'E' is the number 3... I agree that the spam prevention code can be somewhat difficult, but I tell you if it weren't there, there would be tons of spam messages advertising this and that in the forum.
Hi Finn

1. I don't have Illustrator - Adobe Acrobat Professional comes with Acrobat Distiller which reads EPS files and converts to PDF. All professional print centres will have this product although many or most will also have Illustrator but the latter is more time consuming.

So there are now 2 ways to get overprint effect via EPS export.

2. We had overprint effect on in both Standard settings and Course Layout in printing a total of 96 courses for a multi day event. The only variable in whether overprint effect worked or didn't appeared to be the composition of the colour purple.

3. I'll send the actual examples once the events are over and the organisers are OK with a map being released.

Yes you were right - it was a 3 in the Spam code. I OK with spam codes but that one puzzled me for some reason.

Regards, Ken
Hi Finn

Any progress on this issue? Last time we conversed you had narrowed down the colour composition that gives rise to the issue but hadn't got a fix on why that would happen.

Regards, Ken
Finn Arildsen
Re: Overprint effect with Postscript output - an issue
October 27, 2009 09:15AM
Hi Ken,

I'm sorry that I haven't gotten round to updating the forum on the outcome of our off-line discussion. I'll provide details here as soon as I get a chance.

The bottom of the issue is that PostScript overprint effect as implemented by Adobe has some side effects, so that for certain color combinations overprint effect is not effectuated by the Adobe tools.

It would be interesting to understand the inner workings of Adobe Reader/Illustrator. This is probably a longer term item.

Best regards,

Edited 1 time(s). Last edit at 10/27/2009 09:30AM by finn.

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