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Diagonal Lines in Edit

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#1 LIGISTX

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Posted 19 May 2024 - 07:10 PM

I have been relatively successful with DSS and editing in the past, but a few weekends ago I shot M51 and once I got the stacked image into Photoshop and started to really pull data out of it I started to notice diagonal lines in the image which are preventing me from stretching it very far.

 

This is a way oversimplified "cranked the exposure" in photoshop just to quickly and easily show what I am talking about.

 

Does anyone have any idea what is causing this? I shot over 2 nights, a good bit of light polution in Bortle 6 skies, ran an L-pro filter. This is 141 3 minute subs with ~20-30 each of darks, bias and flats. I use a AVX, I threw out about 1/5th of all exposures that looked to be non-circular stars. I also autoguide and was dithering and did 3x drizzle in DSS. Shot on Nikon D850. I have not experienced this before and am unsure what might be causing this.

 

As a result, I was only able to push M51 enough to get this out of it... which considering the light polution and extremely small size this appears on my ~450mm telescope, it isn't horrible. But I know there is more data that I just can't pull out of it due to running into issues with this banding. Current edit: https://flic.kr/p/2pRbw54

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Edited by LIGISTX, 19 May 2024 - 07:12 PM.


#2 DanMiller

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Posted 19 May 2024 - 07:51 PM

What is your camera?  I only ask this because Canon is known for this.  All though, the banding usually goes from left to right.  Also, try GraXpert. It is stand alone and free. https://www.graxpert.com/  It actually is pretty good, so it might be able to clean this up for you.  Doesn't hurt or cost anything.

 

Dan



#3 LIGISTX

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Posted 19 May 2024 - 08:28 PM

What is your camera?  I only ask this because Canon is known for this.  All though, the banding usually goes from left to right.  Also, try GraXpert. It is stand alone and free. https://www.graxpert.com/  It actually is pretty good, so it might be able to clean this up for you.  Doesn't hurt or cost anything.

 

Dan

Camera is Nikon D850, and I have not noticed this in any of my previous images... but I have not historically used a Light Polution filter or dithered. I have done both previously without this tho. 



#4 bignerdguy

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Posted 19 May 2024 - 09:02 PM

That looks like walking noise and the image is overexposed a bit.  Dark frame and flat frame subtraction should remove most of this in post processing.


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#5 LIGISTX

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Posted 19 May 2024 - 09:09 PM

That looks like walking noise and the image is overexposed a bit.  Dark frame and flat frame subtraction should remove most of this in post processing.

This is after stacking with darks and flats. 

 

I would agree, I should have exposed for shorter time especially considering the amount of LP (I don't know why I picked 180 seconds... I meant 120, oops....).

 

What exactly is walking noise? 



#6 LIGISTX

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Posted 20 May 2024 - 01:25 AM

What is your camera? I only ask this because Canon is known for this. All though, the banding usually goes from left to right. Also, try GraXpert. It is stand alone and free. https://www.graxpert.com/ It actually is pretty good, so it might be able to clean this up for you. Doesn't hurt or cost anything.

Dan


That seems to have helped. Not entirely, but I was able to pull more data out before it degraded. https://flic.kr/p/2pS81Y8

Thanks for the advice!
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#7 bignerdguy

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Posted 20 May 2024 - 01:27 AM

What exactly is walking noise? 

Check out this thread:

 

https://www.cloudyni...ise-what-is-it/

 

Apparently if i read it right if you dither your frames this should eliminate this noise.


Edited by bignerdguy, 20 May 2024 - 01:29 AM.


#8 LIGISTX

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Posted 20 May 2024 - 01:37 AM

Check out this thread:

https://www.cloudyni...ise-what-is-it/

Apparently if i read it right if you dither your frames this should eliminate this noise.


Hmm, I was dithering, but maybe by not enough pixels… and only in RA. Maybe that is the cause? Good info, I may have to play with dither settings.
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#9 LIGISTX

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Posted 21 May 2024 - 10:16 AM

One more thing to add to this, I split up the R G and B signal and the diagonal lines are much more present in the R.

Any thoughts as to why?

#10 sharkmelley

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Posted 21 May 2024 - 01:34 PM

One more thing to add to this, I split up the R G and B signal and the diagonal lines are much more present in the R.

Any thoughts as to why?

During white balancing of the D850, the red channel must be boosted by more than the blue, relative to the green.  Hence the red noise may become more apparent.



#11 LIGISTX

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Posted 21 May 2024 - 02:11 PM

During white balancing of the D850, the red channel must be boosted by more than the blue, relative to the green. Hence the red noise may become more apparent.


Ah, that makes sense.


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