De/re-polarisze

Hi y’all,

Things are ticking along nicely in my vvvv self-education, but on one matter I’ve hit a little snag.
I’ve been looking at ways to do image distortions and stuff, when I fell upon “polar co-ordinates fx”. What I’d really like to do is turn a circular image straight. My bet is that I should reservse-engineer the fx plugin but I just don’t have the brain-might.
Can anyone figure out a method?

Hannah.