It might be worthwhile to think about not supporting `p0 == 0`, since that is just a min filter. 

But I think you're right @stefanv, these are all float values. There's enough wiggle there that using `>` everywhere might be a better choice to minimise complexity. I guess one issue might be if this implies `p0==0.5` would no longer return a median filter. I can see how that would piss some people off.

So I guess what I'm saying is, maybe! LOL