I converted RGB file to CMYK:
-image->convert image color space.
-CMYK/8bit/U.S.Web Coated (SWOP) v2 or FOGRA 27 (similar results).
-rendering intent relative calorimetric/black point compensation chcecked.
-export->TIFF with LZW compression.
When i open the file colors are too bright. Here are two examples, first picture - RGB file, second picture (the wrong one) converted via Krita 4.3 (Linux 18.3), third picture is file converted via online https://www.rgb2cmyk.org/ , which shows more or less what the conversion should look like properly. The question is, what causing problem?

First example: https://imgur.com/kiASwnn
Second example:

Does the problem still appears just after the conversion (without saving)? And does it happen if you save the result image as .kra and open?

If the viewing program is not color managed, it may interpret the CMYK file too brightly (basically, the cmyk icc profile is the part which says the colors should be desaturated a bit), so you will need to make sure that the program you are opening the files in is a color managed program.

tymond wrote:Does the problem still appears just after the conversion (without saving)? And does it happen if you save the result image as .kra and open?

No problem after converting before saving. Only after opening the file outside of Krita. After opening the saved kra. look normal, even the open PNG file looks normal if opened with Krita.

PNG file can't be in CMYK, so it's probably converted into RGBA again (when you open the PNG in Krita, you can see the color space on the bottom). However the tiff file should, I think, stay CMYK. If you save into the tiff file and then open it *in Krita*, does it show correct colors? And does it show correct color space on the bottom bar of Krita?

tymond wrote:PNG file can't be in CMYK, so it's probably converted into RGBA again (when you open the PNG in Krita, you can see the color space on the bottom). However the tiff file should, I think, stay CMYK. If you save into the tiff file and then open it *in Krita*, does it show correct colors? And does it show correct color space on the bottom bar of Krita?

Yes, after opening in Krita, TIFF file show correct colors, and correct CMYK color space.

Then it's (most probably) not Krita's problem but the problem of the application that you use to see that tiff file. It probably doesn't understand CMYK properly.