stacking normalisation

General discussion about StarTools.

stacking normalisation

Postby alacant » Tue Jul 03, 2018 11:47 am

Hi everyone

I've just migrated to Linux and have started using Siril [1] for stacking dso images:

I'm not sure about normalisation as I think we want as linear as possible (?). Apart from multiplicative normalisation for flat frames, would it be advisable to choose no normalisation for everything else?

TIA and clear skies,

[1] Hey, it would be great to add Siril to StarTools to enable a one stop stacking-post processing package for Linux:)
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Re: stacking normalisation

Postby admin » Wed Jul 18, 2018 12:00 pm

Congrats on moving to Linux!

Looking at the documentation for Siril, the relevant page seems to be 43.
If one of these items is selected, a normalization process will be applied to all input images before
stacking. Normalization matches the mean background of all input images, then, the normalization is processed by
multiplication or addition. Keep in mind that both processes generally lead to similar results but multiplicative normalization is
preferred for image which will be used for multiplication or division as flat field. Scale matches dispersion by weighting all input images.
This tends to improve the signal-to-noise ratio and therefore this is the option used by default with the additive normalization.
The offset and dark masters should not be processed with normalization. However, multiplicative normalization must be used with flat-field frames

I would probably just turn it off when stacking your lights. The mean background matching might be innocuous, but there really should be no need for it and Wipe will take care of the bias/offset with a better handle on the real, less noisy background (given it is now stacked).
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