Mosaic Integration Issue
I actually have some problems to combine a 2x2 Mosaic of M31. I proceeded as followed
1.) Correction and stacking of each individual panels (BIAS, DARK, FLAT ), I did a light pollution and background correction --> the single frame result seems to be good!
I saved all panels as 32-bit float FITS-File!
2.) I tried to combine all panels to a mosaic --> result is a bit strange!
That's not my first mosaic, I already did some others without any problems! Could that be a problem with the LNC and the high dynamic range of the panels? Would it be helpful to combine a fifth panel in the center of all others?
Where is my failure? What is going wrong here!
Looking forward to your advice,
Is it correct that I see "no offset" in the Fits headers? You normally do need an offset when calibrating frames. It may be that something is going wrong because of variations in the background of the panels or even black background because of that. Can you check if precious results had no offset as well?
I just checked the fits header of the sub frames and there is an offset available! Same for my calibration files....but that's not that kind of offset you mean or?
In all of the files produced by APP, the offset is always zero...I have checked this on some good pictures!
Ah ok, got it. So then it might be that the frames, even though correcting nicely on their own.,still show a different background signal to each other. Does it help when you use light pollution correction on the mosaic? This is normally a good idea as well. I do agree the differences look a bit extreme here.
No, I tried several times to use the light pollution correction with different settings for the LNC, without success!
But on my last attempt, I turned off the LNC, just out of frustration, and it worked... 🤣
Will now use the LPC to do a final adjustment and I really hope that the SCC will work properly on that mosaic now....
PS: I saved all FITS before as a 16-bit integer FITS
You now what, that is actually a nice find. I'll ask Mabula if this is normal behaviour for APP as well and what might make it so extreme. Regarding bit-depth, especially for calibration data, 32-bit is best to use.
Ok, got answer from Mabula; the problem lies in the fact you used 2nd degree LNC. For mosaics, 1st degree is better for the panels and mosaic (algorithm wizardry that I also don't understand completely yet). 🙂
Ok, thanks for the fast reply! I will try to use the 1st degree LNC now to combine my panels to a mosaic....will also use the 32-bit FITS Files for the integration!
Will share the result with you asap 🙂
Hi Vincent, here is the result of the 1st degree LNC intergration. I started with the standard 3 iterations, but the result was not really good, so I increased the number of iterations to 10...
Not really that what I expected...should I send you the four panels for some tests? (Fits, 32bit, LPC, CBG)
Mmmm, yeah not the result I was hoping for. Yes, you can share your data and I will have a look (bed time now and a busy week ahead, so please allow for a few days);
Go to https://upload.astropixelprocessor.com and for the username and password, use: upload
Create a directory named “gogonfa79-mosaicIssue” and upload in there. Thank you!
@vincent-modHi Vincent, any news regarding the mosaic issue? Let me know if you found a time slot to make some tests...
Sorry Michael, I missed that you uploaded it. I'll have to ask to notify me when uploaded in the future, apologies!
I'll work on it either this evening or tomorrow.
So yes, I checked the files as well and have the same issue. I still think something is wrong in the background, could you upload a few single subs and your master calibration files as well? Thanks!
I wonder if a preview option were possible to check the differences in the Mosaic settings and see which work. I have set of 100+ images to integrate from four sessions. If the program used a subset of the Lights from each session you could more quickly test what worked best. I'm using an iMac Pro and the processing for the last integration takes many hours.
hello Vincent, sorry for my last reply! Will upload my master frames and some lights for each panel tomorrow!
In the meantime I had the chance to test PixInsight, and this tool did not had comparable problems with the mosaic…the result is also not perfect due to some registration artifacts (APP is the best for such things 😉) but it seems that the background normalization is much better… 😅
I used the same files for the mosaic as uploaded (the single stacks made with APP)
Nice result! Yes, I think you used some of the HDR capabilities in PI. This is not implemented as such yet in APP. So for those specific cases it can definitely help. Please notify me when your upload is finished. 🙂
@vincent-mod I uploaded all files, really curious to know what went wrong with my image processing!
regarding the Mosaic with PixInsight, yes I used as a last step the HDR capabilities…but the mosaic and background normalization worked very well and I didn’t had comparable issues with PI
I'll have a look at the data today. Thanks for uploading more frames!
One thing I notice is that your flats are taken at 0.1 seconds and such. They don't look wrong to me, but it's usually advised to aim for 1-2. I used all frames and put them into their own session, with flats for that session applied.
At each subsequent step things seemed normal and I integrated all frames into a mosaic and indeed, LNC seems to still go wrong here. So next up is me trying without any calibration file, just to see if anything there might cause it.
Ok and now without calibration and the effect is the same! How odd, I think there must be something in the lights. I'll notify Mabula about it.