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Old 18-08-2018, 08:20 AM
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Slawomir (Suavi)
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Narrowband Luminance

Hi all,

For the past few weeks I have been slowly collecting narrowband data for my next image of the Helix Nebula.

So far I got st.dev. for background at 1.5 ADU for Ha master and 1.3 ADU for OIII master.

While I predominantly use Ha for Luminance in my images, I thought that including OIII will help to show more interesting features. I tried doing ImageIntegration without rejection on Ha and OIII masters, and while noise in the background dropped to about 1.1 ADU (st.dev.), strong OIII signal around the core has made some of the knots barely visible. Perhaps when I compose the final colour image, those features will become visible again?

Is there a better way of combining narrowband masters into a synthetic luminance, or perhaps I will be better off with just Ha as a luminance for the Helix? My goal is to show as many structural features as possible, given modest 4" aperture.

The attached image shows synthetic luminance on the left (OIII+Ha) and Ha master on the right.

Any comments and suggestions will be highly appreciated.
Suavi
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Old 18-08-2018, 09:16 AM
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Atmos (Colin)
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Sometimes Pixel Math can be your friend.

What you could try is running a LinearFit on them so that they're on the same playing around. After that running Max(Ha,OIII) which will create an image with the strongest portions of both images.

Typically, more detailed structures have a stronger emission where the detail is so they tend to show through with the Max function.
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Old 18-08-2018, 09:18 AM
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RickS (Rick)
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Hi Suavi,

IMO you have to make a compromise/decision on what features you want to emphasise and build a lum that matches your vision. You can't have it all...or at least I couldn't figure out how to do it last time I processed this puppy.

Cheers,
Rick.
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Old 18-08-2018, 11:27 AM
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codemonkey (Lee)
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I've got no answers for you Suavi, but I have the same question. I'm not sure how to go about doing it, but basically what I think we want is to compose a luminance that is weighted towards the areas with the most local contrast. There's gotta be a way to do it, probably a simple one...
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Old 18-08-2018, 01:51 PM
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Slawomir (Suavi)
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Quote:
Originally Posted by Atmos View Post
Sometimes Pixel Math can be your friend.

What you could try is running a LinearFit on them so that they're on the same playing around. After that running Max(Ha,OIII) which will create an image with the strongest portions of both images.

Typically, more detailed structures have a stronger emission where the detail is so they tend to show through with the Max function.
Thank you Colin for your advice. I was not aware of the Max function - so I also tried Min function

Unfortunately, the resulting image of linear fit (tried both ways) and Max(Ha, OIII) had even less noticeable detail near the core.

Quote:
Originally Posted by RickS View Post
Hi Suavi,

IMO you have to make a compromise/decision on what features you want to emphasise and build a lum that matches your vision. You can't have it all...or at least I couldn't figure out how to do it last time I processed this puppy.

Cheers,
Rick.
I was afraid that this is the case. The thing is that OIII has 2.5 times signal strength near the core and it is smooth/featureless, while Ha is stronger further away from the star remnant. I may need to try adding a bit more integration to Ha and just use master Ha as Luminance.

Quote:
Originally Posted by codemonkey View Post
I've got no answers for you Suavi, but I have the same question. I'm not sure how to go about doing it, but basically what I think we want is to compose a luminance that is weighted towards the areas with the most local contrast. There's gotta be a way to do it, probably a simple one...
I like your idea Lee of weighting towards areas with most localised contrast. We could call this tool WTAWMLCImageIntegration

BTW - I attached a stretch of both OIII and Ha - almost ready to start putting together the final image :-)
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