Two panel M31 (first mosaic attempt)

I got rid of that sharp discontinuity by (when making the separate panels) setting the LNC to 1st degree and 3 iterations, and setting MBB at 7%. Now I still do not get evenly illuminated combined panels after integration and I wonder if it is my data or my processing. I tried several combinations of LNC and iterations, the best was this set (LRGB and the LRGB-combine):

Especially the luminance panel has a terrible dark region at the centre which clearly shows in the combined panel. But in addition the upper panel is more magenta, while the lower is more towards green.

During imaging I started both panels in the same direction of the sky (they were imaged on two successive nights), but there appears to be quite some difference in sky-quality. The  following image shows the two luminance panels at their original contrast at the left, which shows that the lower panel has more contrast (due to a better sky?). At the right I gave the lower panel only a linear stretch and contrast:

So I wonder: did I do something wrong with normalisation?

In post-processing I managed to squeeze this out of it, but it required very local corrections (i.e. brightening that dark centre due to lum and adjusting the colour for the two panels individually).

Hope you can supply me with some advice.

Thanks

Nicolàs

Hi Nicolàs @infinnity-deck,

Thank you very much for sharing the issue.

It is in fact an issue on our issue list. Especially our LNC implementation can not deal well with having a bright object like M31's core in the overlap area of a mosaic. We need to fix it and it is on our list to do so.

Your data is beautiful for me to have this tested and sorted out going forward. Can you upload the data here:

https://upload.astropixelprocessor.com/

username: uploadData

password: uploadTestData

Please make a folder like InfinityDeck-Mosaic-normalization-LNC-issue

and let me know once uploaded 😉

Mabula

Hi Mabula,

thanks for coming back on this, good to hear that my data can be of use. I have uploaded the dataset to your server. The filenames speak for themselves (I hope), but just to be sure, the four images per panel are identified by "_P1-" and "_P2-" in their filenames.

Looking forward to your findings and hopefully an improved LNC-routine.

Thanks for all your great work on APP!

best wishes,

Nicolàs

I was about to post a similar issue and came across this thread with the exact same problems.

I have imaged a 4 panel mosaic with the Esprit 150 and QHY600. I'm having the same impossible to solve issue of improperly normalized frames - it would seem as a result of having the core of M31 inside the overlaps of the panels.

I am also having and issue where the panel overlaps have duplicated/blurred stars, and one area where there is a swirl in the center of one panel that makes the stars appear to be in a spiral.

Are these all related to the outstanding issue that you mentioned Mabula? I've attached screen caps of my issues, if these data will not be able to be processed in APP at this time then I guess I'll file them for the future, but that is very unfortunate.

Thanks in advance,

Eric

It is indeed an issue for normalization to have the core in the center, not sure if Mabula is able to work around that, but it's best to try and have the core offset.

I ended up using the 'process each frame separately then mosaic combine' method to get a final image. It worked, but a massive amount of extra work in doing so. Since targets like this, and any others that are bright are often framed as the center of an image, I hope that this is on a priority list for getting fixed. I'm gathering LRGB data on this now, that will be a LOT of work!

Thanks to all for the work, love the APP!

https://www.astrobin.com/ffh9xn/

Hi Eric @flywaldo,

Thank you very much for sharing your issue as well.

The issue with normalization is on our list and is an important once for sure, so it is high on our list.

The other issues:

I am also having and issue where the panel overlaps have duplicated/blurred stars, and one area where there is a swirl in the center of one panel that makes the stars appear to be in a spiral.

the swirl can happen when you enable dynamic distortion correction when the data really does not need it, also an issue on our list that will be fixed.

If registration is off in the overlap areas, you normally need to increase the star count in 3) analyse stars to have that fixed.

Mabula

Hi Mabula,

any progress on this issue?

thanks,

Nicolàs

Hi Nicolàs @infinnity-deck,

No not yet, it is on our ToDo list, but we need to finish work on other priorities first. For this issue to be fixed completely, we need to create new and better LNC algorithms and also improve the general normalization I think. Of course, this is important so this is high on our list to improve and fix.

Mabula