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Advice on how to add Ha to an LRGB of Andromeda?

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#1 oneredpanther

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Posted 30 November 2021 - 12:03 PM

I have some great LRGB data on M31, and additionally some hours of H-alpha.

 

I'm wondering if anyone has some tips on how best to add the red of the stellar nurseries into the resultant LRGB mix? 

 

I'm using APP and Photoshop only. 

 

Thanks!



#2 happylimpet

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Posted 30 November 2021 - 12:07 PM

I was wondering this exact same thing last night. I can manually add it in to the mono red channel before combining the channels in photoshop, but i want to do it in photoshop so i can adjust it.



#3 FrostByte

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Posted 30 November 2021 - 12:28 PM

You can kind of do it in APP, but I prefer to do it in GIMP (which should pretty much work the same way in PS). First, I open the RGB image in GIMP and decompose it into R, G, and B channels. Then copy the red channel into a new image. Open the H-a channel as a new layer on top of the red layer and adjust the opacity until the blend of the two channels looks the way I want. Then make a new layer from visible, copy it, and paste it back into the red channel of the decomposed version. Recompose into RGB, and done. You can use the channel mixer or adjust the individual channels in the curves tool to adjust, but this is basically what I've been doing.


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#4 bobzeq25

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Posted 30 November 2021 - 01:40 PM

These combined broadband/narrowband images are the kind of thing where PixInsight truly shines.

 

As usual with PI, you have a number of options about how to do it (a PI strength).  I like the NBRGBCombination script.  Narrowband RGB Combination.  Simple, unusually intuitive for PI, but very (and easily) adjustable to fit specific data.

 

In one new version, PI tried to delete the script, since there were other newer methods.  Popular demand brought it back.  <smile>


Edited by bobzeq25, 30 November 2021 - 01:42 PM.


#5 Dean

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Posted 30 November 2021 - 09:11 PM

A simple way to do it in Photoshop is to create two layer groups - Luminance and RGB and change the Luminance group mode to "Luminosity". Copy your lum into the Luminance group and RGB into the RGB group then copy the HA into both groups. For the HA in the RGB group, go to blending options and under Advanced Blending, uncheck the G & B channels (leaving R checked) - That adds the Ha to the red channel. In both groups, set one of the layers to "Lighten" mode. Then you can tweak each separately.

post-7030-14072454544454.jpg


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#6 Huangdi

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Posted 01 December 2021 - 03:50 AM

I made a tutorial on this a while back. It's by no means the best or a perfect way to do this, but it does the job nicely :)

https://youtu.be/LwuiS8N1A-E

Hope this helps!

#7 happylimpet

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Posted 01 December 2021 - 04:00 AM

I'm using APP and Photoshop only. 



#8 imtl

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Posted 01 December 2021 - 04:40 AM

A simple way to do it in Photoshop is to create two layer groups - Luminance and RGB and change the Luminance group mode to "Luminosity". Copy your lum into the Luminance group and RGB into the RGB group then copy the HA into both groups. For the HA in the RGB group, go to blending options and under Advanced Blending, uncheck the G & B channels (leaving R checked) - That adds the Ha to the red channel. In both groups, set one of the layers to "Lighten" mode. Then you can tweak each separately.
post-7030-14072454544454.jpg

If I understand what you are suggesting correctly then you are trying to blend Ha directly with Lum. That is not a good way to do this. If I'm wrong the I'll be happy to know

#9 Dean

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Posted 01 December 2021 - 12:56 PM

If I understand what you are suggesting correctly then you are trying to blend Ha directly with Lum. That is not a good way to do this. If I'm wrong the I'll be happy to know

Blending Ha to the Lum in "Normal" mode would be bad as that would really mess up the stars and any other non Ha sources. But using "Lighten" mode means only the brighter parts of the two layers contribute to the final lum ie: stars from the original luminance layer and emission nebula from the Ha layer. Using "Lighten" mode to blend the Ha to the red channel does the same thing - only adds red to the emission nebula but not the stars, reflection nebula and any other non Ha sources.

 

By doing it this way, you are matching the red from the emission nebula Ha to the emission nebula Ha in the lum. Otherwise you would be trying to match the red from the Ha to the broadband lum which can actually be more difficult, although just blending the Ha to the red channel with "Lighten" mode can make it easier and may be all you need or want. But having 4 channels in 2 groups gives you more flexibility and control over blending in the Ha.


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#10 imtl

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Posted 01 December 2021 - 01:12 PM

Blending Ha to the Lum in "Normal" mode would be bad as that would really mess up the stars and any other non Ha sources. But using "Lighten" mode means only the brighter parts of the two layers contribute to the final lum ie: stars from the original luminance layer and emission nebula from the Ha layer. Using "Lighten" mode to blend the Ha to the red channel does the same thing - only adds red to the emission nebula but not the stars, reflection nebula and any other non Ha sources.

By doing it this way, you are matching the red from the emission nebula Ha to the emission nebula Ha in the lum. Otherwise you would be trying to match the red from the Ha to the broadband lum which can actually be more difficult, although just blending the Ha to the red channel with "Lighten" mode can make it easier and may be all you need or want. But having 4 channels in 2 groups gives you more flexibility and control over blending in the Ha.


Thanks, I use PI and not photoshop and that's why I asked. Now it's clear


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