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Walking on the Moon



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Hi Everyone

Tried NG 281 the other night processed in PI using combined Ha and RGB with Ha as the luminance channel using 13x1000s Ha and 6x600s each of R,G and B.  Used 130pds and Atik383L+

Easy to preserve star colour with this method  -  it appears that the RGB colours get applied to the Ha stars in the combination.  Have I got this right ?  However, the natural red in the nebula gets diluted by adding the Ha as a luminance channel  - although the Ha provides far more detail than a normal L would.  

Still experimenting with how much saturation to apply to the Nebula colour .   Comments on this and anything else would be appreciated  - I guess its a matter of taste ?

Thanks for any comments



ngc281_130pds_383_cc_Hargb_curves 2 hdr.JPG

Edited by halli
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Hi Ian

Some nice data there and well processed but some adjustments could improve - hope the following helps.

Typically you would not want all your HA as part of you luminance layer.  It will always tend to create the salmon colour you are seeing - though as you mention nice star colours so you could keep that.

HA will saturate the lum significantly - you can use colour adjustments to recover but i find the trick is finding the right level of ha to apply.  No rules here - just posted a North America wide field in the forum, this could only take 18% HA when used in conjunction with lum as well.  On its own you may be able to go up to 60-70% but @ 100% the salmon tones will normally always be present.

Have a play and find the balancing ratio, ideally getting as much of the detail as possible is nice so i would aim initially for the point where you notice a major shift from red>salmon.  You can go a few percent beyond this as small colour adjustments will resolve, go to far and adjusting the colour becomes more difficult and often starts to look artificial.

Additionally, as i think you are experiencing it will create a luminosity mismatch causing colourless halos, more easily spotted in the main nebula but present elsewhere.  Getting the blend right will help deal with this (though you can do some masked fixes to the halo's by applying the lum only from the RGB back to the stars, then you may need to also consider the same for adding colour again, as you can see it gets more involved) - a little experimenting should show you the differences.  The ratios to use will vary target to target and if you are really fussy even with a target, you can catch most stars but a few sneak through still and may require some special attention.




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Thanks very much for the information Paddy and apologies for my delayed response !  What you have said makes perfect sense to me.    I had just been using the LRGB combination tool in PI to introduce the Ha instead of luminance and this has always been at 100%.   Now I have taken another look at the tool  in the light of what you said and have noticed there is a waiting of L,R,G and B that can be applied as part of the combination and I will certainly experiment with the amount of Ha I introduce and i'm sure this will help a lot.   My main aim was to use the additional detail in the narrowband data to create almost an improved  conventional LRGB image.  

I am also aware that Ha can be introduced into the red channel in PI using a tool called NRBRGBC  to boost the red content.  This is the method which can easily wash out the star colour though if not used carefully and I dont think you get as much detail improvement in the overall image.  

I need to examine the image again in more detail to understand your comment about the colourless halos.  However thanks again for taking the time to provide your informative and helpful response  - it will certainly push me up the narrowband processing learning curve

Best regards



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