Using APP Calibration Masters in other Programs (in particular, PixInsight) and vice versa  

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Steve
Brown Dwarf Customer
Joined:3 months  ago
Posts: 22
September 10, 2017 17:07  

I share a remote rig with a fellow imager.  I am turning into an APP-guy, but he is a PI-man, through and through.  When we need to download calibration frames, we would like to create the masters on the local machine and simply download these to save some bandwidth on the remote PC network.  APP would be ideal for this - I can (obviously) use them in APP, but the question is - can APP master calibration frames be used by my partner in PixInsight. 

I have tried this and the answer (so far) is no.  I find that I end up with black spots in my PI frames calibrated with APP masters. 

This could be down to me using incorrect settings in PI.  The PI calibration is fine if I just use Bias and Flat masters: it is the Darks that seem to cause the black spots.  These lessen if I unclick the 'Optimize' button in PI, but they do not go away.  If I use a BPM as a Dark in PI, I don't get the issue, but I am not sure that is optimal. 

Of course this is an APP forum and it is not primarily for assisting those trying to use 'some' of APP in another program, but if anyone had any idea what could be causing this (and suggestions for getting rid of it), it would be very helpful.

Steve


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Mabula Haverkamp
Neutron Star Admin
Joined:5 months  ago
Posts: 589
September 11, 2017 19:12  

Hi Steve,

Hmm, I know that PI's flat calibration works differently (other flat-field normalization), especially with DSLR data, so I could imagine that flat calibration won't work. But I would expect a masterdark to just work just like a masterbias. 

One possible reason for incompatibility that I can think of would be the bit depths of the masters relative to the light frames and possible settings for this in PI. APP keeps the masters in the same bit depth as the originals.

I wouldn't expect PI to know how to use APP's BPMs. And loading a BPM as a Dark would normally not work, because a BPM is something completely different ;-).

Mabula

Edited: 1 week  ago

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Steve
Brown Dwarf Customer
Joined:3 months  ago
Posts: 22
September 11, 2017 21:30  

It could of course be that the master flat wasn't working properly either but that the darks issue was more obvious....

Thanks anyway for replying Mabula.


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Steve
Brown Dwarf Customer
Joined:3 months  ago
Posts: 22
September 12, 2017 09:42  

Another thought Mabula.  In PixInsight the (PI) master flat is calibrated with bias and darks.  How is the APP master bias calibrated?  Is it possible that a difference here could cause a double-dark subtraction (and hence the black spots)?

Steve


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Mabula Haverkamp
Neutron Star Admin
Joined:5 months  ago
Posts: 589
September 12, 2017 23:25  

Hi Steve,

In APP the flats are bias or dark subtracted before the flats are integrated. So the masterflat normally is already bias/dark subtracted.

Is you are using both bias and darks for your lights, then the masterdark would be bias subtracted as well.

A masterbias is the most basic and fundamental calibration frame, that is never calibrated by other calibration masters (at least not in APP).

I would need to see your pi masters to answer your question I guess, Maybe you can check at what level the bias pedestal is, and check if it's still there in the masterdark and possibly the masterflat as well, that should answer most questions I would think.

Kind regards,

Mabula

 

 


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Steve
Brown Dwarf Customer
Joined:3 months  ago
Posts: 22
September 13, 2017 09:08  

Thanks again, Mabula.  It is good to know what APP is doing. 

This was a small issue for me and I would not want to take up any of your time with it.  You seem quite busy enough!

 


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Mabula Haverkamp
Neutron Star Admin
Joined:5 months  ago
Posts: 589
September 13, 2017 22:25  

You're welcome Steve 😉

I understand. Different applications approach data calibration differently, especially flat-field calibration works differently in different applications. So mixing master calibration frames could lead to all sorts of strange and different results. So using the masters in different applications is something I would never recommend, calibration of your data is such an important step that you want to be sure that it works correctly ;-).  Best advise would be to both install APP and PI on the computer that gathers the data, and make the masters for PI and APP separately.

Thanks again 😉

Mabula


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Steve
Brown Dwarf Customer
Joined:3 months  ago
Posts: 22
September 13, 2017 23:15  

That is what we will do.  I quite agree - no point trying to 'get cute'!!

 


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