Combining Ha and OI...
 
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Combining Ha and OIII from a colour dual narrowband filter  

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(@benursinus)
Molecular Cloud Customer
Joined: 1 year ago
Posts: 4
January 27, 2021 13:19  

Hi,

 

I've recently been imaging with an optolong L-enhance filter using a colour zwo 533 mc pro camera. I have followed some tutorials to extract the Ha and OIII data into two separate mono images and then combining (e.g. HOO). I've tried this with two seperate targets and I feel like the OIII portion of the image remains in mono, with only colour in the Ha channel? The OIII looks very grey to me regardless of the saturation settings. I've attached a screenshot which is zoomed in and shows the coloured red channel but looks like mono behind. Also attached is the basic unedited image (but with saturation and light pollution removal).

The method I'm following is this ( https://www.astropixelprocessor.com/community/postid/7610/).

Do you agree with my thoughts? Am I doing something wrong somewhere?

Thanks,

 

Rosette HOO
combine HOO 2 lpc cbg St

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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3955
January 27, 2021 13:25  

On my monitor that looks blue actually. Not very pronounced, but blue. Maybe you can try to boost the OIII signal a bit by increasing the top slider of the OIII panel in the RGBCombine tool. Besides that you could have a play with HSL selective color and boost the blue's there a bit as well. OIII as signal can be way less intense then Ha, so that is tricky sometimes.


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(@benursinus)
Molecular Cloud Customer
Joined: 1 year ago
Posts: 4
January 27, 2021 13:53  

Hi, thanks for the quick reply. Overall it does look a bit blue to me too, but when I zoom in I get a strange texture which I tried to show in the screenshot. The coloured red (orange) just seem to sit on top of the background, which looks more grey the more I zoom in. I'll have a go boosting the blue in the rgb combine and selective colour and report back. 


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(@benursinus)
Molecular Cloud Customer
Joined: 1 year ago
Posts: 4
January 27, 2021 15:44  

Attached are some more recent attempts - really not good, but I got the blue at least. I am still getting the strange artefact though (see screengrab), where the orange/red seems separate to the blues if that makes sense, if you zoom into the image. I guess it could just be noise, but the standard image seems much smoother colour wise.

combine HOO 2 lpc cbg St PS sm
Rosette Nebula St APP
Rosette HOO 2

 

This post was modified 10 months ago by Ben Ursinus

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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3955
January 27, 2021 15:58  

I think that's just the signal that is now a different color and not very strong in those parts, so it becomes very clear where the seperation occurs. The other, smoother, picture has very similar colors all over and so blends better. More data for OIII (and maybe a bit longer exposures) will help here for sure. What mixing formula did you use?

edit: Maybe upping the upper slider isn't the best in this case either, it depends on what you want of course. So if you set that to 1 and play with the HSL selective color tool, you may also get better results. Possibly.


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(@benursinus)
Molecular Cloud Customer
Joined: 1 year ago
Posts: 4
January 27, 2021 16:15  

Ok great, thanks, I'll give that a go. 

I used the default HOO 2 formula as this gave me the best results. I adjusted the sliders a bit but did not think I got better results so I left it at stock and adjusted in the selective colour. I've not used it before so was a bit trial and error, so ill need to read up on that a bit more. 

This is only 1.5 hrs of data, and sadly my scope was constantly illuminated by a neighbours light, so I did not expect the best data. These are 3 min exposures, would you advise longer?


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3955
January 27, 2021 16:40  

Oh yes, if possible narrowband data gives the best results when exposing for a long time. Think 10-15 min per sub even. That will produce better results than many shorter exposures. Of course when light is really an issue, that may be less so, but still good to try. When you go for regular RGB broadband data and light pollution, shorter exposures will give better results. A true dark site, long exposures are the best as well.


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