Aha you're right, I think I can omit that part!  I always do that when developing to check that the resulting PS is purely real to machine precision (if the centre isn't at 0,0 then you get a sinusoidal complex phase factor that corresponds to the centroid shift).  But here I take the `abs()` anyway.  I'll tell you what I'll do: I'm going to put the timings in and then check to see what is faster: leaving it in and taking the `real` part only, or doing `abs` and omitting it... Shouldn't take a sec...