GIMP Version: 2.8.10
Operating System: Mac OS
GIMP Experience: Intermediate Level

---

Although I have not mastered Gimp by any stretch of the imagination, I consider that I am at an intermediate level, in that I can get things to look like I want when I am creating my digital artwork for book covers. However, I have encountered a problem that I can't seem to resolve on my own.

I recently submitted a pdf book template to a popular POD publisher using Gimp artwork. The cover was acceptable with the exception that the CMYK ink percentages were too high. Their equipment/software requirements dictate that the combined percentages do not exceed 240% and recommend the Cyan be at 40%, the Magenta at 40% the Yellow at 100% and the blacK at 60%. I have not been able to determine how to adjust these levels in Gimp. I think I may need a plugin to manipulate the CMYK percentages, but I would like to find out if anyone on the forum have encountered this issue and resolved it to prevent my reinventing the wheel with this problem.

Thanks in advance for any help anyone can be with this issue.

IM Charon

A few quick thought.
The key is to have setup a color management system in Gimp before you begin, example a ICC profile oe littlecms. Your on a Mac so use Adobe ICC, it's probably on your computer already.
A plug-in for export to TIFF, Separate+.
FYI, Separate+ RGB -> CMYK conversion uses littlecms.
Setup Separate+: Image | Separate | Separate (set source & destination profile), check Preserve Pure Black, for clarity try Make CMYK Pseudo-Composite.
Separate+ original author notes.
Info for Linux but worth the read, CMYK support in The GIMP.

Check the link below on Gimp Decompose...
Decomposing an image to CMYK in Gimp.
FYI, Gimp Decompose doesn't use color management profiles.

Thanks, Odinbc. From checking on various Gimp sites Seperate + was what looked like I needed before I came to the forum. Glad someone here could confirm it for me. I'll give it a try and let you know if that resolves the issue.

IM

I have not come across that one before, but then commercial printers are an awkward tribe.

AFAIK Partha version of Gimp for OSX includes separate+

What you would do with it then, I do not know. Tweak the layer masks?

You can decompose to the CMY masks Colors -> Components -> Decompose -> CMY
and there is even an old Saul Goode script to make a psudo image. (a bit old so I will attach it for reference)

Comparison of the two.


I wonder how the OP got the PDF out in the first place, it would be RGB if it came from Gimp.

Very good this link!
Instructive and easy to understand!
Thx Odin