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Histogram stretching in stacked result in siril

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#1 srvkmr

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Posted 13 February 2024 - 06:28 AM

hello,
I used a tutorial (https://www.youtube....uS7jenU&t=1224s) to create images of M42 and andromeda galaxy.

That time I was using a normal tripod without tracker, a dslr and a telephoto lens.

Now I have bought an AM5 mount. I tried my hand again on M42 using AM5 mount, dslr and same telephoto lens. I clicked 40 lights for 5 secs, 10 dark frames, 10 flats and 10 bias frames. But this time when I saw my final stacked result in the siril, it looked like this https://imgur.com/a/UVeLcwu.

I also ran the preprocessing again with just 2 flats but the result was again same.

Can anyone help me understand what's going wrong?

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Edited by srvkmr, 13 February 2024 - 06:29 AM.


#2 Jlex

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Posted 13 February 2024 - 06:52 AM

Have you tried the background extraction yet?

 

5 second subs sound way to short, is that all that your conditions/equipment will allow?



#3 srvkmr

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Posted 13 February 2024 - 07:15 AM

Have you tried the background extraction yet?

 

5 second subs sound way to short, is that all that your conditions/equipment will allow?

I tried background extraction. I tried same thing with 120 sec x 40 exposure but with similar results. And yes 2 sec subs are way short but why there is an over exposure?



#4 BQ Octantis

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Posted 13 February 2024 - 07:20 AM

You're evaluating with Histogram preview mode, which stretches the image to the extreme. Autostretch is much better for evaluation. It looks like the flat did not get applied properly.

 

Post a raw light, dark, and flat, and we can see if the captures are the problem.

 

BQ


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#5 sharkmelley

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Posted 13 February 2024 - 07:22 AM

Which camera are you using?

 

It's pretty clear that your flats are not working (or have not been applied correctly) because you have obvious vignetting and dust shadows.  Does Siril store a log which might help determine whether or not the flats were used?


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#6 srvkmr

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Posted 13 February 2024 - 07:45 AM

To clear the clouds of doubts, the attached screenshot of the result of stacked orion nebula, I clicked with normal tripod (no tracker), dslr and telephoto lens. We can clearly see there is a big difference in "histogram" mode stretch preview in siril of the two images.

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#7 srvkmr

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Posted 13 February 2024 - 07:48 AM

Which camera are you using?

 

It's pretty clear that your flats are not working (or have not been applied correctly) because you have obvious vignetting and dust shadows.  Does Siril store a log which might help determine whether or not the flats were used?

 

 

You're evaluating with Histogram preview mode, which stretches the image to the extreme. Autostretch is much better for evaluation. It looks like the flat did not get applied properly.

 

Post a raw light, dark, and flat, and we can see if the captures are the problem.

 

BQ

In this scenario what is the solution to apply flats? To add to the information, lights, darks and bias frames were clicked using asiair plus whereas flats were directly clicked from camera. I converted the raw files into fits and put them in the final folder. If the flats were not included in the stacking, the siril would give an error. Won't it?



#8 sharkmelley

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Posted 13 February 2024 - 07:58 AM

To clear the clouds of doubts, the attached screenshot of the result of stacked orion nebula, I clicked with normal tripod (no tracker), dslr and telephoto lens. We can clearly see there is a big difference in "histogram" mode stretch preview in siril of the two images.

It's clear that the flats worked well for this image of M42.  For the image in the original post it is clear that flats did not work.

 

 

In this scenario what is the solution to apply flats? To add to the information, lights, darks and bias frames were clicked using asiair plus whereas flats were directly clicked from camera. I converted the raw files into fits and put them in the final folder. If the flats were not included in the stacking, the siril would give an error. Won't it?

Never mix DSLR raw files and asiair fits files, even if you convert your DSLR raws to fits.  This is because you don't know how asiair is generating the fits and so the DSLR raw files converted to fits may not be compatible.  If you are going to uses asiair fits files then make sure all your files (lights, flats, bias, darks) are generated through asiair.

 

P.S. I'm assuming you are using a DSLR.  If not, ignore my comment.


Edited by sharkmelley, 13 February 2024 - 08:27 AM.

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#9 BQ Octantis

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Posted 13 February 2024 - 09:37 AM

In this scenario what is the solution to apply flats? To add to the information, lights, darks and bias frames were clicked using asiair plus whereas flats were directly clicked from camera. I converted the raw files into fits and put them in the final folder. If the flats were not included in the stacking, the siril would give an error. Won't it?

 

Don't know.

 

The flat application is simply

 

(light-dark)/(flat-bias)

 

but I would use Siril's calibration tab, and I would extract the bias from the EXIF header. The ASIAir does not save the header, so I'll need a bias frame if the flat doesn't have it.

 

If this calibration works, then the problem is in the scripts.

 

BQ



#10 srvkmr

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Posted 13 February 2024 - 10:13 AM

It's clear that the flats worked well for this image of M42.  For the image in the original post it is clear that flats did not work.

 

 

Never mix DSLR raw files and asiair fits files, even if you convert your DSLR raws to fits.  This is because you don't know how asiair is generating the fits and so the DSLR raw files converted to fits may not be compatible.  If you are going to uses asiair fits files then make sure all your files (lights, flats, bias, darks) are generated through asiair.

 

P.S. I'm assuming you are using a DSLR.  If not, ignore my comment.

I will generate flats through asiair and give it a try.

 

Edit : I generated flats through ASIAIR, put them in stacking folder and yes it worked. Thank you.  :D


Edited by srvkmr, 14 February 2024 - 01:45 AM.

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