Huge difference when converting sRGB to CYMK with Separate+ Plug-In

[Luax]

Hello community,

today I tried to export a GIMP image created in the standard sRGB color profile to a CMYK color profile by using the separate plug-in. This is required by the printing house to avoid color deviations between the design and the final print. Unfortunately, when converting it with the separate plug-in, a massive color difference can be seen. Maybe you can tell me what I am doing wrong?

    sRGB
    CMYK
    separate settings

Looking forward for your assistance!

Software used:
GIMP 2.10.30
Separate+ for GIMP 2.10.6


Yours,
Luax

[rich2005]

10-out-of-10 for getting separate+ working with Gimp 2.10 AFAIK it does not work and that might explain the difference in colours you have.
Just out of interest, where did you get your Separate+ for Gimp 2.10.6 I would like a copy for my archive.

Separate+ does work in Gimp 2.8 and looks like this as a 'pseudo cmyk' https://i.imgur.com/65rRYbU.jpg the layer masks providing an estimation. That image if I save as a Gimp xcf file then open in Gimp 2.10 https://i.imgur.com/tw3N0xR.jpg

There is a conversion tool that works with Gimp 2.10 'CYAN' looks like this: https://i.imgur.com/nHmewAw.jpg

This the CYAN output as a cmyk jpeg opened in Gimp and you might see the muted blues. https://i.imgur.com/ivPh6VR.jpg This is because the CMYK profile gamut is less than RGB. I would think that result 'not too bad' Bright greens and blues are muted.

I recommend trying CYAN http://cyan.fxarena.net/ No need to use the Gimp plugin extension utility unless you are planing on lots of use. CYAN does work on its own. Export as cmyk .jpg or .psd (.tif is broken) CMYK files are much larger than RGB.

An alternative is the graphics application Krita which can convert between color spaces. Big application just for that purpose
or
There are on-line conversion sites https://www.rgb2cmyk.org/

[PixLab]

Just to let people know
I wanted to try this "CYAN" plugin for Linux, then I removed the plugin from the plugin directory ➤ /usr/lib/gimp/2.0/plug-ins , but I got stuck with it like it installed somewhere else without telling me...
Restating GIMP kept the Cyan in the main menu (on that note, I hate that people program like this and you got additional menu between filters/whatever and so in the main menu, IMHO it's a lack of user's respect)
Anyway even removed from the path above still there

   

Indeed, It did install a cyan.py in ➤ /home/patrice/.config/GIMP/2.10/plug-ins without asking me!
Yep... I did freaked out with a mix of being upset (few seconds) before to find out where it did install

[rich2005]

There speaks a user with FX-Foundry (not many of those good for Gimp 10 , Script-Fu (I really hate scripts that register there even the useful ones) , Video (GAP also not too good in Gimp 10).

Not the worst I have seen, there are users around with everything+kitchen-sink installed.

Since it is a python plugin there is always the option to change the registration, I do this with some of the script-fu while updating the old style registration, but cyan is easy, something like

Code:

"<Image>/Tools/Cyan/Export Image",

Quote:Yep... I did freaked out with a mix of being upset (few seconds) before to find out where it did install

Of course it is well behaved and installs in the User profile plug-ins folder As a linux user you can always disable it by removing permissions, again I have several plug-ins that only get used once in a while and disabled until required. Just a pain that a Gimp restart is needed but keeps the menu structure tidy. Scripts are easier using Ofnuts resource manager.

[rich2005]

@Luax

Just a note about file size. Cyan will embed the icc profile in the image file.  PSOcoated is a large .icc and makes the image file that bit larger.
Some Printing Services ignore the embedded profile anyway or if you know that PSOcoated is used by the Printer, then use Krita where saving the cmyk converted file has an option to embed / or not the icc profile.

edit: There is also a command line option ImageMagick (IM) http://www.imagemagick.org for the conversion. Use the -strip option to lose the icc profile or without -strip to embed it. 

Code:

magick  sRGB.png  -colorspace cmyk -profile PSOcoated_v3.icc  -strip im-cmyk.jpg

Going back to the original question, the big difference in colours, I think that both Magenta and Black (K) channels are missing.  just as an example the IM jpeg of that little clip attached.

   

and a screenshot of the pseudo-cmyk with  no M & K