PDF export slightly changes CMYK values

[Andy Otto]

I have a document that I'm working in generic CMYK. When I export a PDF (for print) using the document profile, checking the output preview in Adobe, or opening the PDF in Affinity, I notice that the CMYK values have changed by a few points. Any reason for this? There is no conversion from RGB. These are colours of vectors.

[thomaso]

Hi Andy Otto,

Welcome to the Affinity Forums,

Could you please give a bit more details to understand what might have happened?

In which Affinity app have you created that document, and in which OS ?
is the creating app the same as the exporting app?

Are all colors shifted or just in particular objects (colors)?
Are pixel, or are vector objects affected?
Are there linked or embedded resources with possibly different profiles placed in your document?

 

[Andy Otto]

It was in Affinity Designer. It's happening in an embedded .eps logo. When I double click it I make sure the colours are accurate and then export the PDF, but when I re-import the PDF the colours on those vector objects are off slightly. Are you saying that the embedded .eps graphic is in a different profile? How could I change that?

[thomaso]

A container document (= e.g. .afpub) and its content (= placed file, e.g. .afdesign or .eps) can have different profiles (and therefore even different color spaces). For both files you can set its profile in its Document Setting... >  Color. For a placed file you can open it inside the container app with double-click to get access to its Document Color setting in the new opened document window, named e.g. "Embedded".

That means in your sample workflow are four profiles involved:
1. creator .afdesign > 2. exported .eps > 3. container doc for re-imported .eps > 4. exported PDF from containing document.

Since they have also different file formats/types they also can have different capabilities to handle color mixing, for instance if a PDF export is set to flatten transparency (e.g. a layers blend mode on a color underneath). For all of them additionally a monitor profile is involved, too, which makes a final decision (conversion) what color get presented to your eyes on screen. To reduce any color conversion the involved documents can all be set to use only one identical profile, whereas at last at least the monitor profile always converts to RGB.

Furthermore on both, import and export, there is an option to either "Convert Colors" or not – whereas I still don't understand whether or how the import setting does work: it appears to be always set to "Convert" AND when I switch it to "Assign" I could not notice an impact yet AND it is always reset to "Convert" when I re-open this options window, even if immediately after closing it. So, concerning this Convert/Assign option for placed resources I am lost and can't recommend anything because of my lack of understanding how or if it works. Possibly and hopefully someone else can shed some light on this aspect on profile handling with Convert/Assign for placed imports.