27 replies to this topic

[jlado13]

 

Hello all,

 

I am having problems removing background issues in my images after thorough background extractions, etc.  During stretching, I get 45 degree angled striping or banding, but it is not removed using the debanding tool Siril.  I don't think it's camera "banding" I just don't know what else to call it.  My equipment is as follows:

 

Star Adventurer GTI

Canon Rebel T3i (unmodified)

Tamron 70-300mm f4-5.6

 

The attached image is a Starless image of Andromeda after processed in Siril, then levels/curves adjusted in GIMP.  In Siril I cropped, color calibration, background extraction, Generalized Hyperbolic Stretched, reset my black point, denoised with Noise Reduction, etc.

 

90 x 75second lights @ ISO 800

30 darks

30 flats

30 biases

 

What is this and why is it so hard to get rid of?  Shot in Bortle 7 skies, no filters.

 

Thank you,

Jordan

Edited by jlado13, 06 February 2025 - 07:04 AM.

[jlado13]

I’m going to try again tonight with more integration time, hopefully in the 2-2.5 hour range and try to stretch the image less.

Maybe I’m overstretching to the point I can’t get rid of those bands?

[cmanley134]

I have had issues in the past with Siril not properly debayering images during stacking, which can result in some strange grid-like artifacts in the final image. Of course your problem is slightly different but maybe you can try stacking with a different software to see if that solves the issue.

[bignerdguy]

This looks like banding due to the stretching used in Siril and is common to Canon Camera images.  Siril has a script that helps to deal with Canon banding from what i hear.  Try running this and see if it removes the banding pattern from the image.

[rj144]

The banding has to be horizontal (or vertical), I believe for it to work correctly.  Rotate the image, so the banding is horizontal and apply the banding correction.  Then rotate it back.

[jlado13]

Thank you all, I will give those a try.

Also, didn’t even cross my mind to rotate, apply the technique, then rotate back. I’ll give that a shot tonight.l and report back.

Thank you!
Jordan

[jlado13]

 

Ok, down and dirty rotate, unband, rotate back...  Seems to have worked and I'll add this to my workflow in the future.

 

I have an Astro-Tech AT60ED coming this week.

 

Thank you all and Thank You RJ144!

Jordan

Edited by jlado13, 07 February 2025 - 07:30 PM.

[BQ Octantis]

I've shot 20,000 DSO frames with my 600D/T3i, and not once have I had diagonal banding like yours.

 

Sure, Why Not? (click for full size)

 

I would investigate your flats.

 

BQ

Edited by BQ Octantis, 07 February 2025 - 10:38 PM.

[bignerdguy]

 

 

 

Hello all,

 

I am having problems removing background issues in my images after thorough background extractions, etc.  During stretching, I get 45 degree angled striping or banding, but it is not removed using the debanding tool Siril.  I don't think it's camera "banding" I just don't know what else to call it.  My equipment is as follows:

 

Star Adventurer GTI

Canon Rebel T3i (unmodified)

Tamron 70-300mm f4-5.6

 

The attached image is a Starless image of Andromeda after processed in Siril, then levels/curves adjusted in GIMP.  In Siril I cropped, color calibration, background extraction, Generalized Hyperbolic Stretched, reset my black point, denoised with Noise Reduction, etc.

 

90 x 75second lights @ ISO 800

30 darks

30 flats

30 biases

 

What is this and why is it so hard to get rid of?  Shot in Bortle 7 skies, no filters.

 

Thank you,

Jordan

 

Can you post a copy of the original unedited combined image so we can look at it?  Also a copy of the master flat and dark so we can check those for you too?  It may either be the way the file was edited or was a problem with one of the calibration files.

[jlado13]

 

Thank you for the advice.  Here is the original stacked, unedited.  Also the master (stacked) flat and master (stacked) dark.

 

I'm brand new at this, so open to any criticisms/advice.  This was my first attempt at Andromeda and I've only had this mount a week.

 

Jordan

[bignerdguy]

 

 

 

 

 

Thank you for the advice.  Here is the original stacked, unedited.  Also the master (stacked) flat and master (stacked) dark.

 

I'm brand new at this, so open to any criticisms/advice.  This was my first attempt at Andromeda and I've only had this mount a week.

 

Jordan

 

Can you store them somewhere on a drive and then send us the link?  posting them as images on the CN forum doesn't let us look at them correctly.  I would like to try to edit the master light and see what i get as well.  might help us determine if it is in the processing or shooting that was where the issue lies.

[BQ Octantis]

Unless it's a walked pattern, you can usually diagnose the problem in DSLR data with a single raw light, single raw dark, and single raw flat. The pedestal value is in the EXIF header.

 

How did you take your flats? In Bortle 7 at f/5.6, 112 minutes isn't much time. Even in Bortle 3 skies, to minimize the shot noise in the luminance channel I recommend a minimum of 2 hours at f/2.8. That equates to 4 hours at f/5.6. That would still be a noisy starting point in Bortle 7.

Edited by BQ Octantis, 08 February 2025 - 05:38 AM.

[Chopin]

Unless it's a walked pattern, you can usually diagnose the problem in DSLR data with a single raw light, single raw dark, and single raw flat. The pedestal value is in the EXIF header.

 

How did you take your flats? In Bortle 7 at f/5.6, 112 minutes isn't much time. Even in Bortle 3 skies, to minimize the shot noise in the luminance channel I recommend a minimum of 2 hours at f/2.8. That equates to 4 hours at f/5.6. That would still be a noisy starting point in Bortle 7.

Still trying to wrap my head around all the math as I'm new to thinking in the AP domain, but wouldn't 2 hours at 2.8 be 8 hours at 5.6? That's a genuine question. Semantics aside I also suffer from similar banding in all my Canon cameras, so confirming that more time helps to eliminate a lot of this noise is good to hear.

[BQ Octantis]

Still trying to wrap my head around all the math as I'm new to thinking in the AP domain, but wouldn't 2 hours at 2.8 be 8 hours at 5.6? That's a genuine question. Semantics aside I also suffer from similar banding in all my Canon cameras, so confirming that more time helps to eliminate a lot of this noise is good to hear.

 

No, flux goes as the inverse square of the focal ratio. So (5.6/2.8)² = 2² = 4.

Edited by BQ Octantis, 08 February 2025 - 10:35 AM.

[Chopin]

No, flux goes as the inverse square of the focal ratio. So (5.6/2.8)² = 2² = 4.

Okay, thank you. So flux is a new term for me, I thought the reference was regarding exposure. Sorry to the OP if I’m derailing this thread.

[rj144]

No, flux goes as the inverse square of the focal ratio. So (5.6/2.8)² = 2² = 4.

  Correct, so it's 4 times.  You used 2 hours at 2.8, so it's 8 hours at 5.6.

Edited by rj144, 08 February 2025 - 11:33 AM.

[BQ Octantis]

  Correct, so it's 4 times.  You used 2 hours at 2.8, so it's 8 hours at 5.6.

Ohhhh… OF COURSE!    Public math. Yeesh!  

 

BQ

[rj144]

Ohhhh… OF COURSE!    Public math. Yeesh! 

 

BQ

Happens to all of us.

[jlado13]

Can you store them somewhere on a drive and then send us the link? posting them as images on the CN forum doesn't let us look at them correctly. I would like to try to edit the master light and see what i get as well. might help us determine if it is in the processing or shooting that was where the issue lies.

Lemme see what I can do, sorry.. and thank you.. I’ll figure that out and repost the link.

Thanks again.

[jlado13]

Unless it's a walked pattern, you can usually diagnose the problem in DSLR data with a single raw light, single raw dark, and single raw flat. The pedestal value is in the EXIF header.

How did you take your flats? In Bortle 7 at f/5.6, 112 minutes isn't much time. Even in Bortle 3 skies, to minimize the shot noise in the luminance channel I recommend a minimum of 2 hours at f/2.8. That equates to 4 hours at f/5.6. That would still be a noisy starting point in Bortle 7.

I did the t-shirt method over the lens outside in my driveway, pointed straight up. But, it was in the late afternoon rather than early morning if that makes a big difference.

[BQ Octantis]

I did the t-shirt method over the lens outside in my driveway, pointed straight up. But, it was in the late afternoon rather than early morning if that makes a big difference.

The t-shirt method alone makes it quite probable it's the flats. No way to tell without looking at the raws.

[jlado13]

Oooooo K... Sorry still working on the drive thing to post a link; however, I did run another edit thru Siril and GIMP processing ONLY my light frames. There was a little bit of vertical banding to deal with, but nothing like the original post.

This was the result. Obviously there are plenty of other artifacts visible, blotches, vignetting in the upper right, etc.. BUT, this alone leads me to believe the problem definitely lies within my dark and flat frames. I'll reshoot those and report back as well. Also, this Tamron lens was only $30 and I'm just trying to learn, so you can see the CA on practically all the stars..

Just trying to work out my workflow as a beginner.

Thank you all for your help thus far.
Jordan

Edited by jlado13, 09 February 2025 - 02:45 PM.

[BQ Octantis]

Here is a simple Siril troubleshooting workflow:

 

1. Open the flat and calibrate it

  a. use the EXIF black value as the bias

  b. deBayer

2. Set the preview mode to Histogram

3. Run RBF background extraction

 

After that, if there are diagonal bands in the flat, then Bob's your uncle.

 

BQ

Edited by BQ Octantis, 09 February 2025 - 06:20 AM.

[jlado13]

Ok...  I've come to the realization my FLATS were the issue.  I received my AT60ED and took my first photograph with it.  

 

M42

84 x 90s Lights

30 Darks

30 Flats

30 Biases

 

No banding issues.  Walking noise was a PITA, so once I start guiding I'll dither.  However, this was my first "successful" image, so I'll take it for now.  I paid special attention to my FLATS this time and the outcome appeared way better.

 

Thank you again for all your help.  This is gonna be a lot of fun learning over the years to come.

[rj144]

Do you use NINA?