Quote:
Originally Posted by rogerg
I've found CCDStack can normalize and then stack the exposures weighted according to their exposure time. This sounds very similar except it's basing the weighting on exposure time rather than actual SNR. I suspect there would be some difference in the results from the two methods but stacking weighted by exposure might not end up so bad/different. I will give it a try.
I'm yet to be sure CCDStack doesn't have a similar "weight by noise" feature.
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According to the
CCDStack website, it does have this feature:
Quote:
Normalization:
Normalizing the stack results in all images having similar ADU values for corresponding pixels (and area and features). Normalization mathematically compensates for variations in sky background, sky transparency, exposure times and so on. Such compensation is often necessary to produce optimal data rejection and image combines.
For example, after normalization the average ADU of a 5-minute exposure will approximate the average ADU of a 10-minute exposure (that’s what normalization does). If these images are summed without weights then the 10-minute exposure will contribute the same S/N as the 5-minute exposure, thus resulting in sub-optimal S/N. But a weighted sum preserves this difference to produce optimal S/N.
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