CMYK to RGB - Does it work?

[Dynamic Office]

Just wanted to confirm something I'm 90% sure I already know the answer to but... Converting images from RGB to CMYK then converting back from CMYK to RGB doesn't work, does it?

Though i know technically you can do it, the question is, should you?

The process of converting an image from RGB to CMYK loses the vibrant colour gamut so converting that back to RGB won't restore what is already lost, this is what I understand anyway.

Of course, I still have my images backed up as RGB, though I'd made some edits to over 200 images while they were CMYK so if it can be done, I'd prefer to convert it back but i don't want to compromise on the quality so if I need to re-edit then I will.

And yes, I understand that I should have just placed RGB images into InDesign and let it do the conversion when exporting as PDF but old habits die hard and it's been drilled into me for 10 years that everything must be imported as CMYK... perhaps a lesson learnt!

Any information would be appreciated, thanks

[Test Screen Name · Accepted solution]

Well, I'd quibble with "doesn't work". It does what you say, which is exactly what it is supposed to do and must do. Vibrant RGBs will be lost. If it somehow tried to restore them, that wouldn't be correct colour management. THEN, it wouldn't be working. But yes, apart from that choice of words, you are spot on.

[Dynamic Office]

As I wrote that, my thought process changed so I wrote "Though I know technically you can do it, the question is, should you?" which I think was me correcting myself!

As Photoshop is constantly updating and adding new features I just wanted to make sure it hadn't updated the above!

Many thanks for confirming!

[D Fosse]

charlesd8830180  wrote

And yes, I understand that I should have just placed RGB images into InDesign and let it do the conversion when exporting as PDF but old habits die hard and it's been drilled into me for 10 years that everything must be imported as CMYK... perhaps a lesson learnt!

Standard procedure today is to work in RGB, place RGB in InDesign, and then convert to final press CMYK when exporting to PDF.

There are good reasons for that. With this workflow, the ID document can easily be repurposed for different press conditions, using different CMYK output. You should never convert from CMYK to CMYK - this will among other things cause 100K blacks to convert to 4 color (rich) blacks.

If your RGB colors are out of gamut in the CMYK destination, that's just how it is. Then you need to compensate and work around it.

[Dynamic Office]

Maybe i just need to bite the bullet, a part of me is nervous to do it as mentioned it's been drilled into me.

Perhaps the next print job I'll do it.

[c.pfaffenbichler]

You should never convert from CMYK to CMYK - this will among other things cause 100K blacks to convert to 4 color (rich) blacks.

Actually Device Link Profiles do provide the option to keep primary and even secondary CMYK colors pure (so pure black would stay that) but, frankly, they are not part of my workflow as I usually have access to the RGB imagery anyway.

[D Fosse]

Yes, printing houses do use device link profiles when necessary. But it's not part of a standard Photoshop workflow and I have no experience with them. A normal conversion in Photoshop will distribute K-only content to all four plates.

[c.pfaffenbichler]

Yeah, in a standard CMYK to CMYK conversion dragging the image through the profile connection space (basically Lab) will lose that information.

As you stated above separation at pdf-export is the current standard for photographic images.

Mainly when separating for particularly small gamuts (like newspaper ads) it generally seems advisable to check first which Render Intent would provide a preferable result.

But that can be done in Photoshop with soft proofing and the Intent for individual images could still be changed in Indesign.