artifacts with astap stacking

[nicolas]

Hi to evervone a week ago i started a new proiect with my non cooled planetary camera (zwo 385mc) with my sky watcher evo star 72ed and my mount: the star adventurer gti all connected to the asi air mini.
veasterday i completed capturing another 4 hours of exposure and i added those getting a total of about 12hours of total exposure on the dumbell nebula (m27)
Usually I stack all my images with astap because I was getting better results compared to the result obtained with dss and all the time i was doing this i didn't have anv artifacts. This time i get on the final image some artifacts only in the blue channel obviously when i do color calibration it apperas on the other channels) and i tried stacking the lights with dss and didn't have the same issue but i have less SNR on the dss result than the
astap final image, can you guys help me please.

The image that i will leave below it's an autostretch with only color calibration and background neutralization and I also removed the stars with starnet++ to highlight the artifacts but they are visible even without the starnet star removal.
file:///Users/nicolastanase/Desktop/m27%2012%20h/starless_no_object,%202023-06-19,%20695x60L,%20EQMod%20Mount,%20ZWO%20ASI385MC_stacked3%20copy.jpeg

[nicolas]

[han.k]

Hi Nicolas,

I like to look but the image is not attached. Can you attach it.

Han

[han.k]

Probably it is also good to share a link to some or all images for inspection. No problem to try to find the cause.. There must be an artifact in the blue channel.

[nicolas]

hi!! i attched a link in the first message to the image, i will attach it again, but i can't attach it to the message beacause the size it's too large to upload here, but the link should work. sorry for my bad english, i'm italian.
file:///Users/nicolastanase/Desktop/m27%2012%20h/starless_no_object,%202023-06-19,%20695x60L,%20EQMod%20Mount,%20ZWO%20ASI385MC_stacked3.tif
^ this is the link of the 12 hours image ^
file:///Users/nicolastanase/Desktop/m27%202/Unsaved%20star%20recomposition%20result.tif
^ this is the 8.5 hours image and if you look better you see the artifact in the left of the nebula ^

(the 12 hours image is a starless version to highlight the artifact)

[nicolas]

if you want i can give you my raw stacked images

[han.k]

That is a link to a local file I can not access. Zip the raw files and upload them e.g. to :

https://ufile.io/

and share the link

Or share a folder of a google drive.

Han

[nicolas]

thank you han! i'll do it right now

[nicolas]

https://ufile.io/5wi98rbe this is the 12 hour image
https://ufile.io/3ehaqwcz and this is the 9 hour image ( i had put this because you can bareliy see the artifacts)

[han.k]

There are some red/brown mark around M27 on the left size. Difficult to say what problem is without seeing the original FITS. Maybe the Flat need to be redone. If it occurs if you add the images from 9th hour to 12th hour then sone light are not correct and need to be skipped. You could use in ASTAP the arrows to scroll trough the images

The image also looks saturated. Colour is missing.

Easiest to correct is to use the ASTAP "copy past tool "function on the stacked fits file. Just stamp the red away with equal parts of the sky. See viewer popup menu. If you hold the CTRL key you can paste many times.

Attached a quick correction for the left mark.

[nicolas]

Hi!! thank you very much. i didn't took the flats because every night i moved in and out my house the telescope so this isn't the problem and also the frames are not the problem because i stacked them too in dss with less detail and snr but the artifacts weren't at all in the image.

[nicolas]

sorry for the stupid question, i was searching how to use the copy and paste tool but idk how to use it because i didn't found articles online, if you can help me i would appreciate.

[nicolas]

i will send you the stacked image with astap that i haven't touched, the stacked log file and the dss one. https://ufile.io/g58l1y54 this is the link for the file.

[nicolas]

https://ufile.io/g58l1y54

[han.k]

The copy & paste tool is in the popup menu of the viewer. Select the area to copy with the mouse while holding the right mouse button down.

To paste many times the same selection hold the CTRL key.

So you can copy & paste the local background over the red/brown areas.

[han.k]

Looking to you FITS image thee red/green marks are at many places. Blue is weaker there. That can't be fixed with copy & paste tool. You can fix most with the "colour replace" tool but it is tricky. See attached.

Better is to fix the cause. Likely it is in the flats. I suspect some pixels are less sensitive to blue. You can see the green/red marks are like a track.It is drifting while guiding is ongoing The three marked areas show the same track pattern due to the guiding. So try to remake the flats (and darks and dark flats) . If it is related to the pixels remaking the flats should still work. But first try the latest development ASTAP:

http://www.hnsky.org/astap.htm#beta_version

Coincidence but I just modified the the flat algorithm to copy better with unequal sensor sensitivity.

Attach also all files in a zip file and upload to ufile.io and share the link so I can have a look.

Han

[nicolas]

thank you very much. i haven't shoot the flats so this is not the problem. i'll try with the new version because mine is a bit old. i will send to you all my results.

[han.k]

No need for development version All ASTAP versions are already updated to version 2023-06-20.

Han

[nicolas]

hi, i was trying to do the colour replace i was having a problem, that i don't know how to import the image in the pixel math to do the colour replace.

[nicolas]

and i will also restart all from zero to see if the problem will come again with another target.

Nicolas

[han.k]

Note I just fixed a problem in the flat routine which was introduced a few weeks ago. Try latest version dated 2023-07-05.

Han

[nicolas]

nice thank you, i will try
now im re capturing another target and i will try stacking the files soon