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Light polution tool with too much nebulosity in the picture


(@marcieow)
Molecular Cloud Customer
Joined: 3 years ago
Posts: 4
Topic starter  

I've got data from 2 nights on IC1396, with my modded Canon 500D. So far so good. But I find it hard to remove the light polution, since there are very little places without nebulosity. Maybe I'm nog getting something, but I'm not pleased with the results.

IC1396 19 4 20 110x180ISO800 2

 I know I sould make the boxes in areas with no or little nebulosity, but haven;t got much of those haha. Anyone with a hint or tip is welcome ofcourse!


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4736
 

Yes, that's quite challenging indeed. What helps me in these cases is to first over-stretch the data (on the right-hand side select the box right under the switches for DDP, auto and saturation) to 30% BG. Switch on saturation and then go down the right-hand side and slide the Sat-slider (amount of saturation) to the right and the Sat.TH (saturation threshold, to protect the background from saturating), more to the left. This will show, hopefully, as much of nebulous data as possible and the ares where that signal is the lowest. I then place the boxes there. You can always perform the LP correction, remove the boxes and slightly change them according to what you then see as a result. You can check if the model is somewhat correct by clicking on the big "Show corrected image" button, this will show the gradients APP thinks are in the image, based on the location of the boxes. The correction should ideally be a smooth gradient, or gradients.


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(@tmyers)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 56
 

Vincent, just getting into the BG Calibration and LP removal. I find that BG Calibration doesn't do all that much but the Remove LP works fairly well. From what you have said above, do I understand correctly that these tools will work better with more stretch, more Sat and less Sat TH?

Also with regards to Removing LP, what actually does the "Flexibility" Slider do? I have used it at both extremes and see little to no change in the image.

When selecting boxes, is  it better to use more small boxes or fewer larger boxes. I am having slightly better results with more as in 20 or 30 smaller boxes, much like what would be used in PI and their DBE tool. Sorry didn't mean to swear, I let my PI trial run out, went with you guys instead.


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4736
 

The tools don’t work better, but with over stretching and over saturation you are able to see what the true background is a bit better. And also where the problem areas are. You can then put the boxes on those areas.

The flexibility, I think, relates to how strict the model is in calculating the background. But I’m not a mathematician so that would be one for Mabula. 😉

You can start with a few large boxes, a normal gradient should then already be corrected pretty well. With more gradients in the image or smaller effects, smaller boxes might help in getting a better “resolution” for the model to work with. If that works better depends on the data you have.


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