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(@gogonfa79)
White Dwarf Customer
Joined: 7 months ago
Posts: 11
October 27, 2021 17:19  

@vincent-mod

Hello Vincent, that is exactly what I have seen during my image processing of this specific session. During the Mosaic integration (based on a previous integrated stack for each panel) something seems to be going wrong in neutralize background function or in the LNC.

I do not think that my calibration frames are the reason for that behavior, I used APP for other Mosaics without any problems! There is only one thing, which is different to all my previous work! It is the large dynamic range of the single panels, which is also not the same for all frames! In the center the galaxy is quite bright and towards the edge, the brightness decreases strongly (this counts for the images, diagonally above and below M31)! In addition to that, the images vary alternately in the brightness strongly! While the other two images (along the galaxy axis) are much brighter, it could be maybe difficult to neutralize and adapt the background with the LNC algorithm correctly in this scenario. 

Regarding my Flats:

In general, I use a dedicated cooled astro camera (the QHY268C) for all my images. I make my flats automatically with N.I.N.A (Nighttime Imaging 'N' Astronomy). This tool has a flat wizard that allows you to specify how the flats should be made. I always specify a histogram mean target of 32768 (for my 16-bit camera) with a mean tolerance of 5%. So, I never had any problems with my flats! But I know, that some CMOS cameras do have a strange behavior when it comes to short exposure times and the sensor is not working in a linear mode! I know that my camera works fine above 0.1s (Sensor linearity test in Sharp Cap) but for the future, I will take care of longer exposures around 1-2s. If the flat correction is wrong, you would see it in an under- or over-correction in the stacked single frames.

 

Let me know if you need more pictures, I really love to work with APP and I support you as good I can to make that tool better 🙂

 


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(@gogonfa79)
White Dwarf Customer
Joined: 7 months ago
Posts: 11

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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3961
October 27, 2021 18:04  
Posted by: @gogonfa79

@vincent-mod

what was the problem in this thread https://www.astropixelprocessor.com/community/main-forum/normalization-failure-in-mosaic-mode/#post-13298

 

No idea as of yet, I asked Mabula to have a look at it as I've not seen such an issue before. I'm suspecting something in the lights or a weird combo of data and the LNC that goes wrong.

edit: Doh, scratch that. 🙂 That does look similar, but he never answered I believe. So your data can be very helpful, it doesn't happen often so it is interesting to see.

 


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(@mabula-admin)
Universe Admin
Joined: 5 years ago
Posts: 2747
October 27, 2021 18:33  

Hi Michael @gogonfa79,

Thank you very much for sharing your issue and your data. I will have a good look myself this evening and will let you know my findings later today.

I suspect the issue could be that you apply Light Pollution Correction on the individual mosaic frames. It seems logical to do so, but in fact it is not the best workflow in my experience, because it will only work if you do Light Pollution Correction perfectly. And on your High Dynamic Range object M31, chances are big you did not do it perfectly end thereby introduced a complication for the LNC algorithm in the mosaic integration proces. Anyway, only speculating now... I will try to see if I can get a better result and give you an explanation why it did not work well for you in APP.

Mabula


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(@mabula-admin)
Universe Admin
Joined: 5 years ago
Posts: 2747
October 27, 2021 23:07  

Hi Michael @gogonfa79,

The best result I get is with using 5) advanced normalization, 6) MBB set to 10% and no LNC at all...

Advanced Normalization MBB10 noLNC

If you turn on LNC on your mosaic, things start to look bad indeed. The reason is the little amount of overlap that you have between the frames... The current LNC algorithms work very well if you would use more overlap when you plan a mosaic. Your mosaic only has 10% overlap and this is just very little in general. If you would use 15-20% things should work perfectly in my experience. Of course, in due time we will release an updated LNC algorithm that should work also with so little overlap.

The fact that M31 is an object with a high dynamic range is clearly a bit too difficult for LNC with so little overlap. On objects with smaller dynamic range, it would still work normally though.

Mabula


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(@gogonfa79)
White Dwarf Customer
Joined: 7 months ago
Posts: 11
October 27, 2021 23:53  

@mabula-admin

Hello Mabula,

thanks for your time and your fast reply! I understood, that it is much better to have a more overlap between the individual frames in a mosaic. Does it mean that all frames have to overlap with at least >15-20% or would it also helpful to add additional data e.g. an image frame where the M31 core is centered in the middle (like that picture below)? 

M31 Andromeda Galaxy 21072021

 Thanks 🙂

Michael


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3961
October 28, 2021 11:50  

Yes that should work I think, then the mosaic has plenty of overlap. I hope this is the issue, nevertheless it's going to be improved upon so your data is definitely helping us there. Thanks!


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(@mabula-admin)
Universe Admin
Joined: 5 years ago
Posts: 2747
October 29, 2021 13:34  

Hi @gogonfa79,

Indeed, adding a mosaic panel in the center would definitely help a lot for sure !


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