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Old 04-12-2016, 11:14 AM
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Shiraz (Ray)
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Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,821
just did some more testing - seems I missed the point in my last posting.

Since the key operation is the alignment interpolation, reasoned that it should apply equally well to a single sub and thereby get around the FPN issue. So I tried a single sub and aligned it to another dithered sub using a variety of interpolations in PI. results for both noise and FWHM are:

original sub: noise = 5.53, FWHM = 3.73
bilinear interpolation: noise = 3.17, FWHM = 3.97
Lanczos3 interpolation: noise = 4.74, FWHM = 3.72
bicubic bspline: noise = 2.73, FWHM = 4.07
Mitchell: noise = 3.13, FWHM = 3.96
CatmulRom: noise = 3.65, FWHM = 3.84

conclusions:
- As Sam noted, there is a smoothing effect. It depends on the algorithm chosen (and presumably on the nature of the noise).
- The smoothing may be accompanied by an increase in FWHM, depending on interpolation algorithm.
would be nice to have results from other datasets if anyone can spare the time.

Thanks very much for the insight Sam.

regards Ray

Last edited by Shiraz; 04-12-2016 at 02:40 PM. Reason: get it right!
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