Why is Inkscape changing the colours as I type them?

[athalyba]

I just have a clue to explain wthat is going on: something related with translating the RGB color to CMYK.

I guess that Inkscape is RGB native and try to convert to CMYK color space "on the fly". In that process, the program tries to find it's way applying some kind of GCR - Gray Component Replacement or UCR - Undercolor Removal method like Photoshop do, but in a messy or at least obscure way.

I'm using Ubuntu 15.04, Inkscape 0.91. That's the scenario:

1) I draw something
2) Applied a colour with gray component like C27 M100 Y27 K27
3) Deselect the object
4) Select it again: now the colour value is C0 M100 Y0 K47

So, it's a kind of colour management for printing (apparently UCR) but I didn't find where to turn it off and put the colour value that *I* want.

Can someone can give me a hint to solve it ?

[brynn]

I'm not sure if I misunderstand your questions, or if you possibly have a misunderstanding about Inskcape's abilities. 

Are you using this extension?  http://wiki.inkscape.org/wiki/index.php/ExportPDFCMYK  Or some other technique to produce CMYK color model, such as using Scribus?  http://libregraphicsworld.org/blog/entry/getting-cmyk-colors-from-inkscape-to-scribus

Inkscape doesn't have any native, true CMYK ability.  Even though in the Fill and Stroke dialg, there's a type of color called CMYK, it's not the true color print model.  I never have understood exactly what it is.  I guess it's just a different way use color.

The effect you're seeing where you set specific values for R, G, or B or C, M, Y, or K, and other values change automatically, is seen with all of Inkscape's color controls.  I'm not very knowledgeable about the technical aspects of color, and I don't know if that's a bug, or expected behavior.  In general, and in my opinion, printing is not one of Inkscape's strong points.

There is a way to set up Inkscape to use the same color profile as your monitor.....I think I said that right     Anyway, have a look at Inkscape Preferences > Input/Output > Color Management.  Maybe that will get you closer to your goal?

Or if you do need true CMYK print color, you could try the PDF/CMYK Export extension, or use Scribus and the tutorial, both linked above.

And of course, we can always consult the manual:  http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Attributes-Fill-Stroke.html#Attributes-Color

and possibly the Tweak tool could help you http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Tweak-Colors.html

Let me know if I've misunderstood, and I'll try again.  Or maybe one of our other members will have the answer

[athalyba]

Hi Brynn !

Thank you very much for your words ...

We gave up to understand what happening and quiting Inkscape for in the parts of the workflow in our studio because have total control over colour management for printing  is a very important issue for us. We gonna continue to study Inkscape at the beginning of the design process but unfortunately we have to quit it's use as a primary design tool for printing till we could solve this problem.

Yes, it's a problem, huge problem for us because we're printing oriented studio.

Please, if you find more info about this, share it with us :-)

One more time, thank you !

[brynn]

Yes!  The lack of professional printing capability is a big obstacle for many using Inkscape.  I'm not sure what prevents developers from providing it.  Maybe I will ask....  Yes, I'll ask on the mailing list, and post the answer here.  I guess it won't help very much, but after answering the question so often, I'm getting curious.  I don't use printing myself, so I've never asked.

[brynn]

Oh, I see that ~suv has anticipated my question!  http://www.inkscapeforum.com/viewtopic.php?f=5&t=18732&view=unread#p73011