"Save as 32 bit" (and Drift limit...)
Posted: Wed Sep 18, 2024 11:40 am
Two question, please. May be I've missed these points...
1). We have two button at the end - "Save as 16 bit" and "Save as 32 bit". I use to choose the second (32bit) and like to stack with Sigma clipping.
Now. Unfortunately even 32-bit saving do not escape data stretching during saving, as we read in guide:
"Save as Raw (32-bit) Stack... when using Sigma Clipped stacking, the 32 bit values will be stretched up to a maximum value of 2^31-1".
(BTW, my stacks often do not stretched to a full range 1..2^32. For example, max value may be 3.3E8. Why?)
So we can't sum rightly two or more stacking with essentially different time integration. For example. We stacked the day before yesterday a DSO object 10min totally. And yesterday we stacked it 60min totally. First stack obviously much more noisy, and direct adding one to other (when they were stretched to the same range) kill the good SNR of the second sum (60 min). But we could add one to other without any SNR degradation were they be not stretched.
My question (if I am right, of course): May be it will be a good idea to add the button "save as 32 bit unstretched" (or something of this kind)?
2). Other. We have Drift Graph - a great and useful feature. But we can't set a Drift limits (on X and Y) for an automatically stop stacking when real drift values goes above these limits. Example. We stacking a good hour or more, and suddenly our friend touch our mount in the darkness by his leg. Touch a little, but it could be sufficiently to shift our field of view as more as a half frame! But stacking algorithm do not lose the part of reference stars and continue to stack. But the result will be corrupt totally if only one or two shifted frame will be added...
Is such Drift limits a good idea to add it in SC?
Anton
1). We have two button at the end - "Save as 16 bit" and "Save as 32 bit". I use to choose the second (32bit) and like to stack with Sigma clipping.
Now. Unfortunately even 32-bit saving do not escape data stretching during saving, as we read in guide:
"Save as Raw (32-bit) Stack... when using Sigma Clipped stacking, the 32 bit values will be stretched up to a maximum value of 2^31-1".
(BTW, my stacks often do not stretched to a full range 1..2^32. For example, max value may be 3.3E8. Why?)
So we can't sum rightly two or more stacking with essentially different time integration. For example. We stacked the day before yesterday a DSO object 10min totally. And yesterday we stacked it 60min totally. First stack obviously much more noisy, and direct adding one to other (when they were stretched to the same range) kill the good SNR of the second sum (60 min). But we could add one to other without any SNR degradation were they be not stretched.
My question (if I am right, of course): May be it will be a good idea to add the button "save as 32 bit unstretched" (or something of this kind)?
2). Other. We have Drift Graph - a great and useful feature. But we can't set a Drift limits (on X and Y) for an automatically stop stacking when real drift values goes above these limits. Example. We stacking a good hour or more, and suddenly our friend touch our mount in the darkness by his leg. Touch a little, but it could be sufficiently to shift our field of view as more as a half frame! But stacking algorithm do not lose the part of reference stars and continue to stack. But the result will be corrupt totally if only one or two shifted frame will be added...
Is such Drift limits a good idea to add it in SC?
Anton