[TimoJ]

 That's odd - cause the gui shader does this conversion already. Make sure if you toy with dirtyregion stuff, most of them make no sense anyways. When debugging such issue make sure that the complte viewport is always repainted - which is the default DR mode.If you want to save power use <gui><smartredraw>true</smartredraw></gui> instead  

I removed that dr-setting, so it's default. But when I enable limited range, shouldn't the interface go brighter? Now it goes darker. It's like gui shader is converting the levels to a wrong direction. Or something, I'm not a programmer...      

 As I explained before - this setting only makes sense in combination (xrandr, TV) setting. Think what would happen if TV is limited, xrandr is Full (remember: kodi set to limited with driver set to limited makes no sense at all): then with kodi on full kodi would assume black is 0 and white is 255, means if your tv just cuts them out, you neither have blacks nor whites -> washed out completely. Now if you enable Use Limited, kodi sends 16 as black and 235 as white -> perfect picture.

Test it with a gray ramp to see what I mean.     

But it doesn't seem to do that for the user interface, only for the video content. For the user interface it seems to send black as 0.
So I have to raise TV brightness to compensate this and also adjust Kodi's video brightness to a lower value to compensate raised TV brightness. And now my other videosources connected via the same input thru my AVR have too much brightness.

I watched a greyscale test card picture (jpg) and with Kodi set to full range 16 was black and with Kodi set to limited range 20 was black. Surely it shouldn't be this way? TV limited and xrand full.
Or maybe I'm just too dense to understand this, I'll have to think about this..