Banding pattern art...
 
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Banding pattern artifact appears after registration  

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(@cmichaelowen)
Hydrogen Atom Customer
Joined: 4 years ago
Posts: 2
August 14, 2020 08:11  

Hello,

For some time I have been trying to solve a banding artifact occurring in my highly stretched (OIII and SII) data.  I thought for a while that this was an interference pattern between the NB filters and the ASI 1600MM Pro (Mono).

Tonight however I realized that the pattern appears with variation on each individual sub-frame only after registration. Occurs in both normal and mosaic mode, though mosaic produces more curved or even pinwheel artifacts. It is less pronounced but still visible in the masters.

Also less pronounced in other viewers or processing software, but still appears if I stretch far enough

It is not present in the calibrated frame:

Any thoughts?

Thanks,

-Chris


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(@raed)
Brown Dwarf Customer
Joined: 12 months ago
Posts: 7
October 26, 2020 07:00  

Hi,

I have this happening to me now as well.  The images look great (HA-OIII extracts of Ha and OIII).  After registration the image develops vertical banding that are most pronounced in the center of the image, and wither out towards the edges.  I am unable to understand why this is happening.

Have you solved this or has anyone given helpful tips?

thanks

raed

 


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3694
October 28, 2020 12:31  

Interesting. Could you upload the integrations (2 I assume) and the masterbiad, masterdark and masterflat (for me to check) to our server?

Go to https://upload.astropixelprocessor.com and use upload3 as username and upload3 as password.

Create a directory named “raed-stripesafterregistration” and upload in there. Thank you!


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(@cmichaelowen)
Hydrogen Atom Customer
Joined: 4 years ago
Posts: 2
October 30, 2020 03:53  

Raed and Vincent,

After looking into this more I believe it to be moire, an interference pattern introduced by resampling, rescaling, or rotating images.  There are several threads on the cloudy nights forum discussing it.

In my images I notice that a more pronounced moire pattern occurs when the images are zoomed out, but fades when I zoom in, suggesting the resampling artifact is introduced by the display rather than the actual data.

There is a fainter moire pattern that persists, however, and can appear later in post processing when aggressive stretch or noise reduction masking  is applied to the fainter NB channels. This I believe is introduced when the images are resampled for registration.  Zooming in alot I can see stair step aliasing artifacts in bands across some images that correlate.  I will try to post some pictures later.

I have had some luck reducing it if I use a different interpolation method in PI for registration, but I'm not sure how to implement this in APP. 

From what I read, the lancos interpolation is more prone than others to moire, and cubic is suggested.  Also good calibration frames seem to help.

 

Let me know if you have any luck or other insights. 

 

Chris

 


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3694
November 2, 2020 14:18  

Thanks for the insight Chris, I will ask Mabula what he thinks about that.


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