Image stitching with balanced brightness
Stacking program, astrometric (plate) solver, fits file viewer
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Hi Han,
I have a two panel mosaic that ASTAP successfully stitches. The problem I have is that by the time I finished capturing the data for the second panel the moon had risen. As a result there is a very noticable difference in background brightness between the two halves of the finished mosaic.
Is there anyway to balance the apparent background brightness? I have tried ticking the equalise brightness box but it makes no difference. The subject is M42 and it fills a substantial amount of the combined image.
Phil
Hi Phil.
Maybe it is possible to improve the second panel with option "remove gradient" first prior to stitching. Can you share the two images via a link so I can have a look myself?
Han
Hi Han,
You can download the panels using the following link. There are 4 fits files. The two with GraXpert have had the gradient removed using GraXpert AI to see whether this would help. The other two are the originals as there were stacked in ASAP and cropped to get clean edges. The data isn't very good I am afraid but I am trying to make the best image I can.
The link is:
https://1drv.ms/u/s!AkrqkHGQhYgHmbFACpoLHCbzRwnP5g?e=00nPvl
Phil
I got the images. There goes something wrong in the stitching process. The west side of M42 is mostly missing. I have to figure out what is happening.
For mode stitching there was a bug in the last versions. This is now fixed in the code. Yes i can see the unequal background. Looks like M42 is disturbing too much. I will tomorrow try to improve the routine.
I also noted that flats are not applied. This makes it difficult to equalize the background since the corners are darker. Do you have flats?
Tomorrow I will continue.
Han
Hi Han,
I did use flats and dark flats. The link below will download the master file ASTAP created.
https://1drv.ms/u/s!AkrqkHGQhYgHmbFCLcjj2kEpZVOAAA?e=9hjMkF
Let me know if you want the original flat and darkflat frames.
The CALSTAT keyword in the stacked files indicates:
CALSTAT = 'DS'
So D=Darks where applied and it is S=Stacked. But F for flat and B for bias are missing.
This doesn't matter so much at the moment. The equalise option in the stitching looks mostly to the background value of the center. With M42 in the center this will not work. I will change to the four corners.
The flat is now difficult to apply since it is different size and orientation. I will do without for the moment.
I have uploaded an improved (Development) version. Download it from:
http://www.hnsky.org/astap_setup.exe
For your images It is important to checkmark "Limit background correction" See attached.
The mosaic is still not perfect. I will atach my result. If you stack again with a masterflat it will be better. Alternatively you could download and use the free Microsoft program ICE Image Composite Editor). It is no longer available from Microsoft but there are some other alternative links. This works better for these difficult images. I will attach the result once this positing is send.
I will attach the ASTAP result and ICE result.
Han
Last edit: han.k 2023-10-14
Nog kleine correctie in ASTAP. Download opnieuw.
Groetjes, Han
I see what you mean about the ICE program. I will try and find a copy. I have tried restacking the original subs with the development version but it keep crashing at 10% with an Access Violation when I try to stack Panel 1.
Thank you for trying though.
Gone back to an earlier version and still getting the Access Violation so it must be something my end.
I have tried uninstalling ASTAP completely (except for the d20 files) and re-installing the development version. I have restarted my machine and still it is throwing an Access Violation. I am running the software on Windows 11 Pro with 32GB RAM.
I have also tried stacking Panel 2 instead of Panel 1 with the same result. What could have changed?
Phil
OK. If I removed the master flat and the files will stack. This might explain why the panels I sent you did not have flats applied.
In case you are interested in finding out what is going on I have zipped up the original data along with the flats and my master dark file. Each panel had a series of 1s subs and a series of 180s subs. I did not have darks at 1s.
This link is:
https://1drv.ms/u/s!AkrqkHGQhYgHmbFFxM18zWFKJCdxig?e=F1sZWR
No problem. I will have a look tomorrow. Must be one of the files.
I stacked the files without problems. See attached. I stretched such that the background is pretty bright to show the stitch. Looks pretty good to me.
Maybe you used "astrometric alignment" Set it to "star alignment" in tab alignment.
I have only used the 180 second exposures. The 1 second exposures are too faint and will introduce only noise. Do not use the one second exposures. I used all flats and bias frames.
The stars have a blue and red side. Strange. Should not happen for OSC image. Is your optics well collimated?
The 180 seconds exposure is too long for such a bright nebula. The center is saturated. You better make exposures of 30 or 50 seconds.
Try it again and tell me if ASTAP works for you.
Han
Hi Han,
Sorry for the delay in getting back to you. You were correct, I had Astrometric Alignment ticked not "Star Alignment". I can now get the individual panels to stack. But when I go to stitch them together it is just creating what appears a large black FITS file.
I will try again tomorrow.
Phil