Quote:
Originally Posted by rogerg
Yeap, that was what I was interpreting as "normalize and then stack the exposures weighted according to their exposure time" which I had the impression would be different to what Rick said in PixInsight of .... "using normalization Additive with scaling and weighted by noise evaluation" ?
Perhaps they are the same  but I interpreted that PixInsight bases the weighting on a measure of SNR and interpreted that CCDStack weights based on exposure time (it can't do it based on ADU because it's normalised them....) ? |
My apologies, I was going by your opening post. Normalizing for sky background means additive (moving the histogram left/right but keeping the shape the same), and normalizing for transparency means scaling (stretching the histogram peak so it's wider/narrower but keeping the mean/median ADU the same).
Yes, weighting by evaluated noise is something else again and will also compensate for other things like periods of poor transparency, or an unlucky number of cosmic ray/radiation hits.
PI has a range of options for weighting - based on noise has been giving me the best results so far.