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Hot Pixel Artifacts in Mosaic  

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(@neverfox)
White Dwarf Customer
Joined: 4 months ago
Posts: 11
September 21, 2020 19:21  

Today I tried doing a 2-panel mosaic integration (~10% overlap) for the first time, but when I do the mosaic integration, the result has lot of what I can only describe as hot red, green, and blue artifacts (see attached image), all apparently the same shape. I used dark frames from my library that were done at the same exposure time and temp as my new lights and took flats and dark flats after the session. The only changes to default settings were:

  • RGGB
  • Ha-OIII Color algorithm (I also see the artifacts on extract Ha and extract OIII, though they're only readily apparent after combining into RGB).
  • 32-bit masters
  • use dynamic distortion correction
  • 10 scale stop (as recommended)
  • mosaic registration mode
  • 10% MBB (as recommended)

When I go back to normal registration on one panel alone (dropping scale stop back to 5), I do not get these artifacts, so it seems related to doing the mosaic. Should I be trying other settings?

Screen Shot 2020 09 21 at 1.23.17 PM

Happy to provide all data for troubleshooting.


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 2453
September 21, 2020 21:24  

When you do the extract algorithms, did you see if the darks were actually applied to the lights? You can check by loading the lights (with the extract algorithm), adding the masterdark, then switching to "l-calibrated" on top of the window and see if that frame is getting calibrated.


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(@neverfox)
White Dwarf Customer
Joined: 4 months ago
Posts: 11
September 21, 2020 23:04  

Good call. It does appear to get applied because I see hot pixels disappear but it's not getting all of the hot pixels. I guess I need a better BPM that the one automatic produces? That said, if I fully integrate one panel of my lights normally, I see no hot pixels in the final image (outlier rejection?). With mosaic integration, all of those hot pixels not caught by the BPM aren't getting sorted out.


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 2453
September 22, 2020 09:35  

It may help to switch off the automatic setting in the integrate tab to "average" and then the options for rejection can be changed. You can try to lower the kappa high so it rejects more.

Another thing might be the darks, they should contain almost all the hot pixels, so I'm wondering if those are exactly the same iso and such as the lights? For a very good BPM it's a good idea to take a very long dark, like 10 min or so, it will then have as many hot pixels as the sensor might generate and should then correct for those. A BPM is never destructive to your data, so having more pixels in there if your lights are not having them (due to lower exposures) is no problem.


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(@xs4allan)
White Dwarf Customer
Joined: 7 months ago
Posts: 17
September 23, 2020 11:25  

@neverfox

 

Did you manage to get rid of these artifacts? I got the same problem when integrating with drizzle. Also seem to be there when not drizzling only less prominent. Creating a new BPM helped with getting rid of these artifacts 100% with a lower kappa of 2.0 but it introduced pretty bad artifacts around the stars. So not sure what to do now.


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