(uncheck 'Reduce'/'Enlarge' and keep 'fit' only -> I can't get any HQ when fit zoom is used)
I suppose it's for people who want quality only for "fit" (with fullscreen/windowed/preview) but don't want this CPU drawback while normal zooming...

But I'm not sure this option actually makes sense. What do you think?
XnView 1.90 <x>