Do I want to convert or just tag with the CMYK profile?

Question

I have some images to send to the printer. The printing company wants them in 'CMYK' but doesnt offer any other information. I've read up quite a bit on this but most info that I've found seems to be about the theory of color profiles with not much on the actual procedure.

Currently my image is in sRGB (I'm using the GIMP which I believe uses sRGB, but doesnt embed this color profile in the image). I understand that ISOcoated_v2_300_eci.ic is a good general-purpose CMYK profile.

1) Do I want to convert my image to the CMYK profile or do I just want to add the profile to the image?

2) How can I verify that the above has worked. E.g. if I load the image up with some viewer app and view it on the monitor, how can I tell if it is all correct? I.e. I believe once the image is in the new profile you should be able to preview to get an estimate what it will look when printed (as CMYK has a smaller range than sRGB) and maybe adjust the colors to improve things. Maybe there are some test images showing before and after conversion?

3) Can anyone recommend tools for 1 and 2 (free hopefully). I am on windows 7, but could also use Linux. (Other than Separate+ for the GIMP - I tried it but I'm pretty certain its not working correctly for me as yellow turns into yellow-green).

Answer 1

Currently GIMP has no native CMYK support at all. This may change in future versions. Applying a CMYK profile will not make an image CMYK.

There are (or were) plugins available for exporting an image to CMYK.

I believe Separate+ no longer works in GIMP 2.10. It was designed for GIMP 2.4 and hasn't been updated. Essentially it's defunct. I guess you could install an older version of GIMP to try to get it to work. It used to work in GIMP 2.8 if that's any help to you.

There's another plugin called Cyan - available here: https://cyan.fxarena.net/ - I've tried this, but to be honest I can't get it to work. After doing some more research, it seems the latest version 2 is a standalone app, that no longer works as a plugin inside GIMP. So if you don't mind using another app, then this solution might work for you.

There may be other GIMP plugins, but so far I haven't been able to find any.

If you don't want to mess around with plugins, and want support for CMYK out of the box, try Krita. It's free and Open Source like GIMP, and works on Linux, Windows, and Mac. Unlike these GIMP plugin solutions, you can also edit in CMYK mode directly in Krita. If you need ICC CMYK colour profiles, these are available for free on the International Colour Consortium website at color.org

I have no affiliation with any of the websites I linked to above.

Answer 2

GIMP doesn't do color profile conversion very well AFAICT. Based on what I've read in the past, it still doesn't have full CMYK support. I personally use Photoshop, and for simple color conversion, you can probably just use an old copy of Photoshop (even as old as Photoshop 6.0 if it'll run) that you can pick up pretty cheaply.

You almost always want to convert your colors (Edit>Convert to Profile...) when changing color profiles (unless you mistakenly tagged/assigned the image with the wrong color profile before or received an image with no color profile attached). When you convert to a different profile, there will still be a visible color change, but it will be minimized based on the conversion method you choose (Perceptual, Saturation, Relative Colorimetric, Absolute Colorimetric).

If you're starting with an RGB image, there's no way you can assign a CMYK color profile to it, but Photoshop will still let you change the color mode without using the Convert to Profile... command. Photoshop is still going to do some form of color conversion behind the scenes, but I'm not sure which, and in my experience, the printed results are usually color shifted far more than when you use the Convert to Profile... command.