Quote:
Originally Posted by SamD
However, I'm pretty sure that resampling does lose resolution, so you don't get anything for free!
For example, take a single pixel star on the original sub and resample at 0.5px in x and y. It would get smeared over surrounding pixels.
On the other hand, if the pixels in the original sub were of a uniform background, it's exactly this smearing effect that reduces the noise and improves SNR.
I think, that the lose of resolution in stacking will often explain why stack FWHM is usually less than individual sub FWHM.
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Well I generally don't see any loss in resolution from stacking resampled frames, nothing obvious at least.
But the question does make me think, is resampling a reversible process? Unlike binning which permanently loses resolution (unless you invoke different math such as deconvolution which sorta gets some resolution back).
If it is reversible then no information is lost and you could not see any improvement in SNR, but if the correlated noise in the adjoining pixels is "mixed" then it is not reversible and your hypothesis may be correct. However I feel the improvement would be nowhere near 1.5x and again would be due to FPN reduction. Uncorrelated noise would just redistribute itself to the four target pixels leaving the whole thing where it started and you could undo it although the exact noise signature would not be restored, the average noise would stay the same.
Cheers,
EB