Getting Anti-aliasing working with an alpha layer

[Reskaillev]

Hi everyone,

So I have this small image consisting of a sine:



and I would like to get a gradient border on it (something like two pixels would be perfect) from the green sine to black.
(Partial transparancy would be nicer but since .gif doesn't support that...and yes I do need it to be a .gif XD)

Problem is...that I can't get any of the filter options to work, they are all disabled. After some tests I noticed that this is because there's an alpha layer that for some reason disables the filters.

So...how to get a gradient (green to black) border on the sine?

thnx in adance,

Reskaillev