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Old 26-06-2019, 06:00 PM
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Slawomir (Suavi)
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Combining 4 narrowband channels in PixInsight

Hi all,

Last night I tested the Lagoon for NII data and it looks sufficiently different from Ha, OIII and SII that I am tempted to dedicate a clear night to collect NII data and then to use all four channels for a narrowband composite.

Is there a neat way of combining 4 channels in PixInsight into one image, so that all four contribute colour information?
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Old 26-06-2019, 06:15 PM
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codemonkey (Lee)
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That's pretty cool, Suavi.

I have no answers for you, but I'm interested in seeing what others have to say.

Seems like it'd be nice to somehow build a luminance from the normalized masters weighted by the amount of local contrast in a given area... not sure how one might achieve that but it sounds like a good idea :p
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Old 26-06-2019, 06:30 PM
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Atmos (Colin)
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Not sure if it would work but if you input NII into both red and blue it would make a violet.
You’d have to potentially Max() function it in though.
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Old 27-06-2019, 09:01 AM
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Could be done in Photoshop with 4x hue/saturation layers, not sure about PI - be interesting to see what you come up with!
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Old 27-06-2019, 04:22 PM
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rcheshire (Rowland)
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Would the LRGBCombination module do it? Substituting channels?
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Old 27-06-2019, 09:06 PM
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Slawomir (Suavi)
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Thank you all for your suggestions. I have not yet collected the data for the 4th channel for the Lagoon and was interested in what can be done with 4 narrowband channels, and whether itís a worthwhile practice. And now itís cloudy again with rain...
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Old 28-06-2019, 10:14 AM
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AstralTraveller (David)
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That is a very interesting project. I'm not even sure I have heard of NII filters - I'll have to read up on that.

I also can't offer any solution but I can offer a shameless plug for the "PixInsight: More Advanced Topics" workshop at the upcoming NACAA - it sounds as though you could skip the introductory workshop. PixInsight is just one of a variety of workshops to be held over the weekend.

BTW We will be making more announcements once the chair of the Program Committee returns from the TSE in Argentina!

Cheers and Clear Skies,
David
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Old 02-07-2019, 08:03 AM
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Slawomir (Suavi)
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Thanks David for the info

I have decided to try another target for four narrowband channels and attached is a screenshot of 4 single subs of M20 in Ha, NII, OIII and SII.

SNR in those subs is in the ratio of about 4:2:1:1 (Ha:NII:OIII:SII).

I nearly have enough Ha for this image, and pondering on which two I should collect to combine with Ha. Given enough clear skies, I may try collecting all four.

One advantage of getting NII is a possibility of integrating it with Ha for a synthetic Lum and increasing SNR in the LUM, and NII also nicely shows fainter nebulosities around M20, while SII has a weak signal and OIII does not show any gaseous structures surrounding M20, so I would probably not try adding them to the synthetic LUM.

Any advices and opinions will be highly appreciated.

Suavi
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Old 03-07-2019, 08:06 AM
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troypiggo (Troy)
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G'day Suavi,

I recall from way back in 2012 there was a processing challenge posted by Vicent on the PI forum. He had data from something like 23 images/filters. There were a few guys who posted their take, but the most in-depth was, not unsurprisingly, from Juan. He posted a detailed breakdown on his approach. Not sure if it'll be directly translatable to your narrowband data, but might give you some ideas.

I also got to thinking about RGB vs CMYK. Perhaps you could assign a filter to the CMYK and combine along these lines?
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