What does "Use color profile" do?

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1. In the Document setup > Color management, I've told Scribus which color profiles to use. These (Edit: The RGB-profiles) are used if the images in my document don't have any embedded profiles. Correct?

2. When exporting a printer-ready PDF the Save as PDF/Color tab has the option "Use Color Profile" (with hover help box: "Embed a color profile for images"). What does this do?

When not selected, my final PDF increases drastically in size (from 21MB to 33 MB).

(I'm exporting to Acrobat 5/PDF 1.4. Running Scribus 1.4 on Ubuntu 12.04.)

Edit: I've not checked "Do not use embedded color profiles" -- I understand that this is for overriding the profiles which are embedded into the images. I've also checked the documentation (http://documentation.scribus.net/index.php/PDF_Export) but the option I'm wondering about is not mentioned there.




In the Packt publishing book "Scribus 1.3.5", the author writes:

"When activating the Use Color Profile for images, Scribus will use profiles embedded in your photos (in GIMP this can be done with Image | Mode | Apply a color profile or maybe your camera has embedded one into your photos). If your pictures actually have no profiles, or if you're not sure of the profiles embedded, do not use an embedded color profile and add your own."

But I thought this was the default way of working? This should mean that an unchecked "Use color profile" makes Scribus use only the profiles assigned in Document setup > Color management.

Logically, "Use color profile" is checked when selecting PDF X-3.

But what about the hover text, "Embed a color profile for images"? That sounds more like PDF X-3 *only* stuff...

Any isn't it strange that my final printer-ready PDF *increases* in size when "Use color profile" is unchecked (because embedding profiles should increase file size).

I'm confused...


Finally, this is how it works:

If  "Use Color Profile" is NOT CHECKED (and "Output intended for" is set to "Printer" in the "Save as PDF" dialog), every images will be converted to CMYK according to your color management setup. That is why the size increases -- CMYK uses 4 channels (C, M, Y and K) as opposed to RGB (R, G and B).

If it is checked, images are not converted ("CMYKed") but the color profile embedded in the image will be embedded in the PDF too.