Color space for CYMK printing

[Gianni Becattini]

When I export a document to a CYMK pdf for the "printer" (not the device, the company that prints the document on paper), must I set the flag "Convert images color space"?

Thanks

[RobWu]

Normally, the print company would send you the exact specs for delivering a PDF for print.
I would contact them for that.

rob

[Gianni Becattini]

Sure, I understand, but what does this flag exactly do?

[NotMyFault]

If active, converts all images (placed files, visible in Ressource Manager) into the color format of the main document (at export).

if inactive, leave them in their color format.

 

https://affinity.help/publisher2/en-US.lproj/pages/Media/resourceManager.html

 

[Gianni Becattini]

Thanks for answering. But to a not-expert like me, it seems that they should always use the same color format.

Am I wrong? 

[NotMyFault]

It totally depends on the use case and capabilities of the printer. No one size fits it all.

converting images to CMYK increases file size. Keeping them in RGB may cause color issues, or produce better color rendition depending on print device / RIP Modul of printer / print driver. Re-encoding images (e.g. by forced color format conversion or resample if DPI is over xyz can increase file size or cause jpg artifacts.

it depends. If in doubt, test which settings works better before ordering an expensive print (large size, huge number of copies). Nobody from the forum can tell you. 

Edited April 10 by NotMyFault
Edited last sentence to improve clarity about context

[Gianni Becattini]

Thanks, very kind

[matisso]

11 minutes ago, NotMyFault said:

Nobody can tell you.

Actually, the print company by all means should tell you. If they have decent colour management knowledge, that is. Ask them about their default colour profile, if it’s specific to their machines they should provide it for you, and if all they say is “we just want CMYK, no profiles” stay away if the job is important colour wise. Because that’s a telltale sign they know jack about colour management. 

There’s a lot more to colour than just CMYK vs RGB.

Basically, when it comes to embedded images, if you leave it unchecked they will remain in whatever colour space they were in your document. Now, if it differs from the output (printer) colour space, either

a) they will be converted to the output colour space, or
b) the company will come back to you and say they have a problem with that, see above.

If you want to convert, you need to know what CMYK profile you should have as a working space. Euroscale? FOGRA? Coated, uncoated, etc.? Depending on the machine, paper stock, these will differ and the company should know this. If not, it’s the question who’s paying if the colours end up not as expected.

[lacerto]

The setting basically affects only placed raster images and converts them into the color mode specified by the Color Space control on the same dialog box. It does not have effect on e.g. placed SVG, Affinity and PDF documents, whether showing in the Resource Manager or not (these are converted if necessary to the color mode determined by the said Color Space control, unless placed to be passed through).

Raster images are often left unconverted when using PDF/X-3 and PDF/X-4 production methods, because in these cases the image ICCs are embedded in the produced CMYK PDF for correct processing. There are some other uses, as well, especially forcing the setting on when producing DeviceCMYK export files (files without any ICCs included) without using PDF/X-methods, since basically all other presets support mixed color mode output [without specific production rules] and accordingly leave the option therefore unchecked. Single color mode DeviceCMYK and ICC-less files however are typically the most problem-free files for press production (assuming that they are properly prepared, using the document color profile appropriate for the task and media).