Requesting testers for CMYK Mode in GIMP

[CmykStudent_]

Hi! I've been working to add a full CMYK mode to GIMP (as in, you can create and edit images directly in CMYK mode rather than the current CMYK -> RGB -> CMYK late-binding conversion). I'm at the point where it's functional, and now I need to start bug-hunting and finding areas that haven't been implemented yet.

After my last few "big" projects (non-destructive filters, vector layers, etc), I've always received a bunch of bug reports after release because of all the different uses I or our internal testers didn't think of. So I'm hoping to cut down on that by getting more testing from more people, earlier!

If you're willing to try it out, you can download either a Windows installer or AppImage from the merge request: https://gitlab.gnome.org/GNOME/gimp/-/me...te_2750929

Feel free to post any issues you have here or in the merge request - and thanks!

[rich2005]

Ok first whinge from me.  Using the appimage.  Open -> New, default A5 and CMYK Color set in Advanced Options .

The color profile in Preferences is not used in the new canvas, CMYK image with default Gimp sRGB profile.  The same if you set up View -> Colour Management and Soft Proofing. EDIT: OK I forgot to set the profile in File -> New -> Advanced Options but really for a CMYK image it should default to the preferred profile.

   

With that A5 canvas a large brush is so laggy as to be unusable. Typically a large mypaint watercolour brush but a regular large .vbr as well.  As far as I guess, at least 4 times slower than in my regular 3.2.4 appimage.

[CmykStudent_]

rich2005: Thanks! I can improve the routing of prefered CMYK profiles be the default profile - that shouldn't be too difficult.

The performance does seem to be an issue. My guess is that there's internal conversions to RGBA that I'm missing which are causing the lag. I'll ask Jehan and Pippin if they have ideas.

[Tas_mania]

Hi, I'm using from the AppImage. Cannot covert RGB image to CMYK without a color profile. Would it be possible to have a default profile? If not which one to use?

[CmykStudent_]

Tas_mania: Hi! That's currently a topic we're discussing. CMYK printing is normally done for a specific printer, so they should supply you with a CMYK profile for use.

For testing though, you can grab one from here: https://registry.color.org/profile-registry/

[Tas_mania]

Hopefully you get testers that can use this ability. I'm audio-video orientated and regard printers more for docs.  

[rich2005]

(Yesterday, 12:06 AM)CmykStudent_ Wrote: Tas_mania: Hi! That's currently a topic we're discussing. CMYK printing is normally done for a specific printer, so they should supply you with a CMYK profile for use.

For testing though, you can grab one from here: https://registry.color.org/profile-registry/

Not always, I occasionally use a local printer for 10 colour inkjet printing and they prefer a RGB image. (with a caveat that some colours might change).

However, I think one set of users might be for  Kindle desktop publishing, who recommend a color profile for the best print results is  Coated FOGRA39  or Gracol 2006  maybe one of those as a default. You can get a sort of generic cmyk.icc, (looks very similar to the old PS5 cmyk icc to me)

More goes with the appimage, this time using a graphics tablet. 8 bit or 32 bit fp much the same with brush lag.  Converting from CMYK to RGB and back with out-of-gamut colours nicely converted. Text works ok, a bucket fill is quick. Beats the old soft-proofing 

[Tas_mania]

I'd like to see is the same image in RGB mode compared to CMYK mode so people can see the difference?
Is that doable?

[rich2005]

What you can try:

Make an image in CMYK mode using the colours that suffer from out-of-gamut (1) Typically bright colours.
Change the mode to RGB and use the same colours (2)
Now go back to CMYK and those out of gamut colours show as they would print (3)
It is a one way conversion. RGB -> CMYK no going back to the original RGB colours.