just tested another dataset with 16 very similar dithered, calibrated and aligned subs. the noise in a few subs chosen at random varied from 4.55 to 5.5 with a mean of about 5. A stack without any rejection produced a noise level of 1.24, which is almost exactly 1/4 of the average sub noise levels  as it should be for 16 subs. I am not seeing any gain at all over the expected sqrt(n).
ie, I get Stacknoise = Subnoise/sqrt(n)
A stack of the unaligned subs had noise about 25% higher than that from the aligned stack  assume that this indicates some residual FPN.
Last edited by Shiraz; 04122016 at 08:15 AM.
