its possible, but not all that easy, in theory or practice
what it all comes down to is that noone really knows how the whole rendering engine works (yet)
but even then, its a big step to actually make it do what you want
and in the end, its probably not worth it
filtering can only do so much, it wont make that much of a difference
if its done in real-time, expect some simple filtering algorithm like hq4x
modifying the actual background files would require ALOT more work, although that might actually make things look kind-of pretty