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asi 1600 integration problem/grid in stack

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#1 Ruthlessaz

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Posted 21 March 2018 - 12:17 AM

hi all,

 

I use startools and APP. StarTools required the least amount of fancy stuff done to the integration, so I though I would try deep sky stacker again (I have had this issue before...) I stacked over 9 hours if Ha (and am stacking the same frames in APP now with flats and darks to see their results

 

here is a screengrab and the stacked file as well...anyone see this grid pattern before or know what causes it???

thank you for your help!!!!

Adam

 

https://drive.google...1k0EXdMvvGhlTd4

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  • grid.jpg


#2 Jon Rista

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Posted 21 March 2018 - 12:31 AM

At first glance, it looks like a registration artifact. Do you know what kind of interpolation algorithm was used during registration?

 

You can also prove whether it is registration, or native in the data, by checking individual subs. Do they have any similar pattern, or are they clean? 

 

Also check your flats, and see if the flats have any similar kind of pattern, as the flats can introduce micropatterns like this when they are applied to the lights. I suspect a registration issue, though, especially given the amount of rotation you seem to be demonstrating there. 



#3 Ruthlessaz

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Posted 21 March 2018 - 07:37 AM

Hi Jon
I think it's registration also. I used DSS for this stack, I tried w/ APP again w/ limited settings ( as StarTools like no bells and whistles) and long story short, after unchecking all the " bells and whistles", the stack looks to be without any grids... hoping this is the case...funny thing is, when I took the stack into APP after all stacks were integrated, there were no grids...weird. thanks!

#4 Jon Rista

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Posted 23 March 2018 - 03:09 PM

Yeah, it has to do with the interpolation algorithm used during registration. Different algorithms can result in different artifacts. Sometimes the artifacts reinforce through stacking, sometimes they do not. More aggressive dithering helps here, but it is not always a solution. 



#5 TimN

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Posted 23 March 2018 - 04:03 PM

APP can be used just for stacking. The bells and whistles that you refer to are various stacking options - that is up to number 6 - Integration. So, if you just want calibration and stacking set all the options that you want on the left side up to and including Integration. Save the output but untick the stretch option or APP will apply a stretch. The processing functions are under number 9 - tools. They are also on the right hand side of the screen. This may be what you meant by bells and whistles but I'msending this note in case you meant the options in 1-6.


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#6 freestar8n

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Posted 23 March 2018 - 04:53 PM

I have my own code for aligning and stacking and the asi1600 seems prone to grid effects like these.  I'm not sure why.

 

One way this can happen - as a registration artifact - is by making parts of the image "more smoothed" than others.  In that case it isn't a matter of a bright grid with dark squares in it - but a noisy grid with more smoothed squares in it - and the parts with more noise - and higher standard deviation - just appear brighter to the eye.  But what's really happening is the stack ends up with a pattern with varying noise.

 

If that is the case there is no way to flatten it by subtracting or dividing out a flat.  The mean value across the image is correct - but the noise varies.

 

The asi1600 may be more prone to it because it has low read noise or something.  I'm not sure.

 

I don't think the flats play a role because flats mainly impact the bright parts of an image - but this artifact happens in the dark parts.

 

Other stacking methods may show the effect less - but I would make sure they aren't just smoothing the image more under the covers - which is undesirable if you want max detail.

 

Frank



#7 Ruthlessaz

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Posted 23 March 2018 - 07:43 PM

I tried stacking that one in DSS. I stacked in app and unchecked normalise, I didn't do lnc mbb, or anything like that ( to take to StarTools). If I am processing and stacking in APP, I will use all that stuff.i like to try and processing both programs which is why I need to stack twice sine StarTools likes he least amount of stuff when stacking. App much better than DSS :)

#8 Ruthlessaz

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Posted 11 April 2018 - 05:24 PM

APP can be used just for stacking. The bells and whistles that you refer to are various stacking options - that is up to number 6 - Integration. So, if you just want calibration and stacking set all the options that you want on the left side up to and including Integration. Save the output but untick the stretch option or APP will apply a stretch. The processing functions are under number 9 - tools. They are also on the right hand side of the screen. This may be what you meant by bells and whistles but I'msending this note in case you meant the options in 1-6.


So part of the integration is mbb, and lnc, and other things....will those messages up the stack if wanting to use in StarTools? Super weird that my stacks from app never have that banding, but in dss, they do...

#9 Ruthlessaz

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Posted 12 April 2018 - 11:57 PM

I tried stacking again in dss with only one nights of sub frames instead of 2, grid pattern was gone. I tried stacking in 2 groups ( 2 different nights of data) and grid came back. Not sure why dss shows this grid when APP doesn't. Think I'll stick with APP :) great program by the way

Edited by Ruthlessaz, 12 April 2018 - 11:58 PM.


#10 Konihlav

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Posted 13 April 2018 - 03:47 AM

try bilinear interpolation instead of the default bicubic :-)



#11 Ruthlessaz

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Posted 15 April 2018 - 08:27 PM

Thanks I'll try it :)

#12 szg

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Posted 16 April 2018 - 10:42 AM

Looks familiar to me, check my thread.



#13 freestar8n

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Posted 16 April 2018 - 05:26 PM

Be careful with different interpolation methods to make sure you aren't using detail as a result.  This is a good example where oversampling has extra benefit - because you can do processing that involves a form of blurring without losing captured detail.

 

You can check the fwhm and profiles of stars by different methods to see if anything is being lost.

 

Frank




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