Anyway to resolve dew-related radial gradient?

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xtr33me

New member
I'm wondering if it is a lost cause, but thought I'd post here to get some insight. I have a new ZWO imaging train I have setup. Over past few nights, I have captured a bit of data of the Elephant Trunk, but on many of my 600s subs, I am seeing this strange radial gradient. Some over on another forums stated that it is probably due to dew which has been crazy over the past nights. I was cooling to 0deg and have a dew heater on the lens, but I did find the switch in the ASI Air software was off for the cameras dew heater. So assuming that this is probably the case, but wont be certain until I try again.

All this said, is there a way to correct for the radial gradient in the lights or should I just scrap the data? I have provided a sample below of what I am seeing across many of the subs. Is there a technique I can research or a plugin that helps with this removal?

Thanks!
 

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Well, it is an almost desperate case, but if you can extract a set of good data without the dark spot, you can try to overcome the problem with LocalNormalization.

Since the border of the dark area is quite sharp, you should try to lower the "Scale" parameter well below the 1024 default value.
I would try 256 or less.

The workflow to test the method could be:

  • Select a subset of good frames.
  • Integrate the, into a Reference frame.
  • Use LN on a single defective frame "target mode" to fine tune the Scale value.
  • Finally use LN on your entire set.
Let me know if it works, in could be an interesting case study!

P.S. a complete and updated Documentation on LocalNormalization will be released soon.
 
Thanks astroedo for the workflow. I will see what I can figure out. All my Oiii data has this as well as my LRGB. The Ha and Sii overall seem good, so I'll see if there is some means of using that data set to do something. Thanks again!
 
xtr33me said:
All my Oiii data has this as well as my LRGB.
Click to expand...

This makes all much more difficult: You cannot use LocalNormalization on a set took with a different filter because ih has a very different structure.
One viable option could be to get a new set of good data (let's say at least 5/6 images per problematic channel, the more the better) and use them to correct the "broken" ones.
 
astroedo said:
This makes all much more difficult: You cannot use LocalNormalization on a set took with a different filter because ih has a very different structure.
One viable option could be to get a new set of good data (let's say at least 5/6 images per problematic channel, the more the better) and use them to correct the "broken" ones.
Click to expand...

Yeah you were right...I wasn't able to really achieve the results i was looking for. So I just scrapped the Oiii data and LRGB and used the good data from Ha and Sii and made a SHS combo. Using pixelmath I used percentages of both Ha and Sii but the final result actually came out pretty decent. I really appreciate you taking the time though to try and help me save the data. We've got this hurricane coming so not sure I will be able to get any new data any time soon, but I will recapture other subs at a future time and reprocess.
 
... I have had a similar issue and found that I cooled the camera (QHY268m) too quickly (had to warm the camera up to 10 degrees, wait for the condensation to disappear and then go down in 5 degree steps over 3 minutes
 
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