in quake 3 the levelshots are very small, but they still look great when the level loads (i'm using 1680x1050).
i guess there's some kind of overlay with noise to make it look that good. there are no jpeg compression artefacts or such things visible.
however if the small levelshots are maximized on my screen they look like crap.
this "noise" is not present in openarena and therefore the images need to be very large and high quality to look good.
which is a waste of space etc. i'm not sure this is the way it works but i guess it is

if someone could take a look at the code for what is displayed when the levelshot is shown we might be able to get this noise effect in openarena too.
(if it is wanted). i tried to look for missing graphics and such but didn't find anyone that matched - and i'm useless at finding things in the code.