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Creating and applying an artificial flat to generate and share calibrated light frames


(@pete_xl)
White Dwarf Customer
Joined: 5 years ago
Posts: 30
Topic starter  

Hi,

I often did not use flats in the past because I had no problems with dust and the very weak vingnetting in my system could easily be removed with the great light pollution remove tool in tab #9.

Actually I am taking part in a coordinated project and need to share old data as calibrated data to the other partners who use a different software. So I tried making artificial flats with the "correct vignetting" tool which delivers nice flats as it seems. As it is important to share the best quality possible I would be glad if someone would check wether or not the following workflow is correct:

01 load the uncalibrated lights
02 load masterdark (MD)
03 load masterbias (MB)
04 load bad pixel map (BPM)
05 calibrate lights with masterdark and masterbias in tab #2
06 save dark-calibrated files in tab #2
07 remove light frames from list
08 load dark-calibrated files
09 choose one representative sub
10 apply the "correct vignetting" tool in tab #9
11 save with option"save artificial flat" checked
12 remove the lights from the file list
13 load the uncalibrated lights
14 calibrate the lights in tab #2 with MF(art.), MD, MB, BPM in place
15 save calibrated files in tab #2
16 share calibrated light only, no need to share the calibration files

Many thanks in advance 🙂

CS Pete


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4727
 

So Mabula once shared the following advice regarding the creation of an artificial flat:

On all lights if you make an artificial master flat, select "create artificial flat". This will save the correction model as an artificial Master Flat. You can then use this Master Flat, just like an original master flat to correct the vignetting.

To get the most accurate result, first calibrate the lights with a master dark or master bias (create masters & assign to lights button, tab 2). Save these calibrated files (tab 2 all the way down). Then clear APP or reload APP and make the artificial flat using one of the calibrated frames (load in 1 of the calibrated lights). Then load in all the calibrated lights and add the artificial flat, calibrate again and see if that works.

Thing is though, if you don't need flats and it looks fine already, I'd say that is better than adding an artificial flat maybe.

 

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(@pete_xl)
White Dwarf Customer
Joined: 5 years ago
Posts: 30
Topic starter  

Thank you very much for the fast response, Vicent!

So your advice is to calibrate the already (pre-)calibrated subs using only the artificial flat (using no master dark and master bias). That makes much sense if the flat does not contain any readnoise by its nature. In that case the calibration warning that APP generates does not apply and can be ignored?

You wonder why I try to make artificial flats while my images look fine without flats. For me the processing was fine without flats because I could use the gradient removal tool on the integrations of only my own data. The plan here is to stack and combine different sets of data from different imagers. Some will work in APP, otzers in PI. So I worry that my data that are shot without flats would inject gradients and/or make problems for the others. That is why I'd like to share calibrated data - ready to use so to say.

Thanks again!

Pete

T


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4727
 

Yes, it should work like that indeed. Do have to say I never use an artificial flat, so if anything doesn't work out, let me know. 🙂

Yes, when sharing data it's nice to have the best data you can get indeed. Point taken.


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