@Wandarer
Usually only downscalling is necessary (as all the icons at least 32x32 or 62x64 minimum), and its all usually about downscale bigger icons to the same size.

I for now just check the os4/mos realisations of down/up scalling, and should to say they both are ok. I mean and downscaling and upscalig. Of course i not upscale 32x32 up to 320x320 , as its undersanable will looks bad.

But if someone will in interest to take it up, need to have both, and upscaling and downscaling. Most of times users choice some "almost the same" sizes of icons, and there is no big and detactable differences will be beetwen down and up scalling.

of course only downscaling. Looks good

... or AfA OS.

I could provide a sophisticated icon-scale algorithm.
But of course, only downscaling looks good.

@erbsenbirne
Yeah like on mos/ambient, and the same as on os4/wb too (just different look of settings).

You mean like in Ambient where you set it to 64x64 and then all icons appear in that size?

As for one more bounty idea, will be cool to have in aros global preferences for auto-resizing of icons. Using AROS lately and see screens from active users, i see that icons on their desks always different by size, and its for sure annoing to do all the resizing works manually for every icon, to fit it good to design. Something like on aos4 will be good to implement (i.e. some maximum and minumum size, to which icons will fits).