Stacking multiple sessions
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Hello all. Does anybody have any tips as to the best way to stack mutiple nights exposures? I currently have 3 sets of subs from 3 different nights. However the background is different between them. One set is a bit brighter due to having a little bit more moon in the sky. But when I put all 3 sessions into ASTAP and sigma stack, the result has some strange anomolies around the edges. Basically some strips around the edge that are lighter than the rest of the image. I assume this is down to the unequal background brightness/gradient between sessions.
Is there a setting in ASTAP that equalizes the backgrounds of each sub before stacking?
Last edit: michael michael 2023-09-03
I would suggest to stack the bright night separately. Then combine the 2 or 3 stacks in second stack using average stacking.
If you combine a bright night with a dark night frames then the sigma clip will not work very well because there is not good representative average.The average background will be halfway between the dark and bright night.
So do the following:
1) Stack the bright night in mode sigma clip
2) Stack the dark night(s) in mode sigma clip
3) Combine the two stacks using mode average. (if You load them first in the lights tab they will be unchecked but you can just check them again)
Success, Han
Last edit: han.k 2023-09-03
Nice. Thanks for the guidance Han. I'll try that this evening.
I noticed while stacking that im getting a error: "error decoding site longitude and latitude". This is something I've always ignored! But now Im thinking this might also be related? IS this error pointing out something critical or can it be ignored?
Longitude and latitude are only required for asteroid or comet annotation to get maximum accuracy. It is also used for SQM but for stacking it can be ignored. So just ignore it or set default in the asteroid annotion menu. Shortcut CTRL+R. Then save settings In File, Save Settings... and the error should never return.
Thanks Han. That's good to know.
Hi All, I had a similar question (one night dark, one night bright) and followed the stack separately using sigma clip and then combine stacks using average. However, I'm getting a weird repeated pattern of missing pixels (a box pattern and a diagonal pattern). I have a star tracker and manually framed the shots so they are close for both nights, but there is a bit of rotation between them. Do you have any suggestions for settings to smooth out the averaging (using sigma clip there are no holes, but with two "lights" is that just picking one pixel from either frames?). The screen shot is the zoomed in average stack made overly bright to highlight the pattern
(and I have double clicked on teh "Post" button... please remove one of the posts)
Last edit: Mitchell Mysliwiec 2025-01-08
Hi All, I had a similar question (one night dark, one night bright) and followed the stack separately using sigma clip and then combine stacks using average. However, I'm getting a weird repeated pattern of missing pixels (a box pattern and a diagonal pattern). I have a star tracker and manually framed the shots so they are close for both nights, but there is a bit of rotation between them. Do you have any suggestions for settings to smooth out the averaging (using sigma clip there are no holes, but with two "lights" is that just picking one pixel from either frames?). The screen shot is the zoomed in average stack made overly bright to highlight the pattern
Hi All, I had a similar question (one night dark, one night bright) and followed the stack separately using sigma clip and then combine stacks using average. However, I'm getting a weird repeated pattern of missing pixels (a box pattern and a diagonal pattern). I have a star tracker and manually framed the shots so they are close for both nights, but there is a bit of rotation between them. Do you have any suggestions for settings to smooth out the averaging (using sigma clip there are no holes, but with two "lights" is that just picking one pixel from either frames?). The screen shot is the zoomed in average stack made overly bright to highlight the pattern
Combine just two images can create artifacts. Normally they should smoothed out by the software. I suspect the images have a different or and unequal background value. I could have a look if you share them but not in the next days.
Han
Hi Han! Thank you for taking a look. The first night the moon had set, but I only captured 55 minutes (55x60L files) before the clouds covered the sky. A few nights later the first quarter moon was up for the 166 minutes (166x60L files) I was able to capture. Stacking all together with sigma clip (with darks and flats classified by date) results in a pretty heavy bright vignette-type gradient) . Stacking the first night via sigma clip, then the second night via sigma clip, and then stacking those two with average results in the regular pattern on holes in the image.
I'm new to all this, so any pointers are well welcomed and appreciated
I posted the files to a google drive:
https://drive.google.com/drive/folders/14nG9HMaMWNRNkV95-H_XTqEYlZp-MYVo?usp=drive_link
Last edit: Mitchell Mysliwiec 2025-01-11
Hi Mitchell. Your mail was put in the Sourceforge spam folder. I just released it. Is there any problem left?
Han
I have found a solution. Just need some time to test it more.
Fantastic! Thank you for your help.
ASTAP version 2025.01.13 was released today.
I took the opportunity to reorganise the code a lot. If you find any problem please tell me.
Han