Split PDF to color separations

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nna
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Split PDF to color separations

Post by nna » Tue Jan 11, 2022 10:54 am

Hi all

I'm trying to figure out a way to split a single page PDF into color separations. Is there a way with PitStop Server? Or do I need to work through Acrobat with a PS printer and script the whole thing? Any input is greatly appreciated.

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magnussandstrom
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Re: Split PDF to color separations

Post by magnussandstrom » Tue Jan 11, 2022 12:36 pm

IMHO, If you want to do this (in a safe and consistent way) with various input PDF:s, containing different objects, color spaces and effects you should use a RIP. Or you could try a combination of GhostScript, ImageMagick and Pitstop. But never the less, you need to create bitmap objects (pixel images) of the PDF if you don't want to end up with overprint- and trapping issues.

If your input PDF:s are simple CMYK+spot files, maybe it could be done with some Pitstop Action list's.
Last edited by magnussandstrom on Tue Jan 11, 2022 10:30 pm, edited 2 times in total.
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freddyp
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Re: Split PDF to color separations

Post by freddyp » Tue Jan 11, 2022 1:52 pm

There is a safe and consistent way of doing this: use the "Remap color" action and remap a Channel to the spot color None (that is a spot color with a special meaning in PDF).

There is of course the limitation that it will not work with RGB objects, only with CMYK objects and spot colors. DeviceGray objects can be treated in the same way as black.

The annoying thing is the automation of this. Let us take the simple case of CMYK. You need 4 action lists, one that removes MYK, one that removes CYK, etc. This is easily manageable: four connections to four instances of PitStop Server each with a different action list. But what if you can also have spot colors, but you do not know how many and the names of the spot colors are not always the same? You could potentially need hundreds of action lists. I smell an app :D. No promises!

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magnussandstrom
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Re: Split PDF to color separations

Post by magnussandstrom » Tue Jan 11, 2022 10:29 pm

Hi Freddy, I did try your suggested approach (remap Channel to spot color None) with the Ghent_PDF-Output-Test-V50_ALL_X4_1.pdf and the result was not without errors. Maybe I did something wrong?
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Re: Split PDF to color separations

Post by abailescollins » Tue Jan 11, 2022 11:59 pm

Hi Magnus
The GWG Test Suite is not a good test for this.
That file is built with special constructions, some of it hand coded.
It's sole purpose is to test PDF/X-4 compatibility for rips and software, and identify any problem PDF constructions.
It's useless for anything else.

regards
abc (GWG Technical Officer)

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magnussandstrom
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Re: Split PDF to color separations

Post by magnussandstrom » Wed Jan 12, 2022 9:20 am

Hi Andrew! The reason I tried the GWG Output Test Suite was because it contains so many different effects and elements, I thought it would be a good benchmark (objects that might be present in a production file). I am also using the GWG Output Test Suite (as one of many files) when evaluating flattening and DeviceLink results etc. But maybe it's not always fit for purpose..

Back to the original topic:
Since the author of the thread doesn't tell us what kind of PDF-files he/she are going to process, and what he/she is going to do with the files after they are separated, it's hard to give a specific answer of the best approach. But if the files are going to be ripped/printed after separation, trapping might still be an issue if not ripping the composite file.
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nna
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Re: Split PDF to color separations

Post by nna » Tue Jan 18, 2022 9:49 am

Thank you for your replies! The files to process are single page PDFs, colors vary. Might be CMYK only, might contain a number of spot colors. I hadn't thought about trapping, you're right... Could the files not be trapped before splitting them into separations?

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Re: Split PDF to color separations

Post by freddyp » Tue Jan 18, 2022 11:13 am

The file being trapped or not does not affect the splitting as such, but the traps will of course be visible in the separated result.

Picture a yellow rectangle touching a smaller black rectangle. When you zoom in on the result you would notice that the yellow rectangle has a bulge in the area where it touches a black rectangle. That bulge is also there in the composite file but there you would not notice it.

Is that a problem?

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Re: Split PDF to color separations

Post by r.zegwaard » Wed Jan 19, 2022 4:25 pm

@FreddyP : Can you tell some more about this SpotColor None?

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Re: Split PDF to color separations

Post by freddyp » Wed Jan 19, 2022 5:26 pm

PDF specifies 2 special colorants in the Separation color space (that is a difficult way of saying there are two spot color names with a special meaning): All and None. I am sure that most of you have already encountered All because this is often used for trim marks, but probably None is not as well-known. The PDF specification says: The special colorant name None shall not produce any visible output. At first sight that does not make it very useful, except in this case where it can be used to replace one colorant that produces a color by another one that produces nothing.

In PitStop you can add this spot color to the PitStop color database. Make sure an object is selected and in the Inspector - Fill - Actions go to the Color picker. You will see a structure just like for preflight profiles, action lists, etc. and likewise you will find a section "Local". Right click - New. This opens a dialog where you can specify a new color. As it has to be a spot color you MUST check "Define as Spot Color alternate values". The CMYK values you define are all 0% and the name MUST be "None". OK.

You have now defined the spot color None and you can use it as a color in every place where PitStop allows you to choose a color (amongst others in Remap channel to take just a random example).

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Re: Split PDF to color separations

Post by r.zegwaard » Thu Jan 27, 2022 10:10 am

@FreddyP: I've tried this approach but it seems that this doesn't respect overprint of CMYK over a spotcolor.

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Re: Split PDF to color separations

Post by freddyp » Thu Jan 27, 2022 3:48 pm

@r.zegwaard: could you share a (simplified) file that illustrates what you mean?

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Re: Split PDF to color separations

Post by r.zegwaard » Wed Feb 02, 2022 9:41 am

Hi Freddy,

Looking at this sample, I would expect the left CMYK bars to knock out on the underlying text.
I'll send you the PDFs and Actionlist with the "Upload to Enfocus" tool.

Original
Image

Result
Image

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