CMYK Blend Space changes to RGB in Acrobat

[Stavre0D4C]

I have a PDF with RGB content that I plan to convert to CMYK in Acrobat later.

I replaced a couple of pages in this PDF in Acrobat (plz note that the new pages have CMYK images on them) and the Output Preview>Object Inspector says that the Blend Space for these images is RGB, not CMYK, which is strange.

Before exporting these pages from Indesign, I doublechecked whether Edit>Blend Space is set to CMYK, and then I checked the exported pages (as standalone files) and they were fine, but when they are inserted into this PDF, it changes to RGB. Why is that and is this a big problem if it goes to a printshop like this?

Thanks.

[JR Boulay]

You should update your skills:

https://creativepro.com/cmyk-vs-rgb/

https://creativepro.com/rgb-workflow-from-photoshop-to-final-pdf/

[Stavre0D4C]

@JR Boulay

I apologize if I'm wrong, but your links are very general, i.e. they don't explain why this unwanted change of the blend space is happening, at least not directly.

It seems that the inserted (CMYK) pages adopt this from the other (RGB) pages in the document. When I check the CMYK pages as standalone files, before inserting them into the main PDF, they're fine. Before exporting from Indesign, I always doublecheck Edit>Blend Space to see whether it is set to CMYK or RGB, so this unwanted change definetly happens in Acrobat.

I know that the way I work now (mixing CMYK and RGB content) may be untidy, but as far as I know, it is possible to convert the RGB content to CMYK in the end (i.e. I can convert a page or a range of pages to CMYK in the end).

[JR Boulay]

OK I didn't quite understand the question.

So I think the answer can be found here in your export settings. What are they ?

[Stavre0D4C]

No, my ID export settings are fine, since the resulting files are fine, i.e. after export, the Output Preview>Object Inspector in Acrobat shows CMYK images with CMYK Transparency Blend space, which is what I want for these pages.

The problem begins when these pages are inserted into an already existing PDF that has RGB content and RGB Transparency Blend Space (when replacing pages in Acrobat).

After insertion of these CMYK pages, it seems that they "adopt" the RGB Transparency Blend Space from the host document. The images on the inserted pages remain CMYK, just the Transparency Blend Space changes to RGB.

I wonder is that normal and whether it can create problems in print. I thought that the inserted pages will somehow remain 'autonomous' and unaffected by the rest, even tho they are inserted into a different enviroment.

[JR Boulay]

That's it, I think I've finally figured it out. 😉
(English is not my native language)

Yes it's normal. It is managed at the document level.

This is one of the new features of the PDF 2.0 format: now this management will be done at the page level.

But this is not yet implemented in Acrobat.