@eht16 Thank you, I have checked, this is exactly the place where font starts to be blurry. I tried SciTE with `scite "-font.base=font:Monospace Regular,size:12"` and compared Geany, SciTE, Gedit.  Just for my eyes the `I` character in SciTE looks awful. @elextr, @nyamatongwe thank you for explanations! I have to play with some fonts, maybe found good one for Geany.
Thanks for the quick replies. This issue can be closed.