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Looking for help on SHO processing

Processing SHO Request for feedback Deep Sky NGC7635
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Andy Wray avatar
Andy Wray avatar
Below is my first serious attempt at SHO processing.  This is The Bubble nebula, 4.5 hrs total integration using 7nm Ha, Sii and Oiii filters in a Bortle 5 zone.  

I'm looking for feedback on:

* Colour pallette .. I used 40% straight SHO mixed with 60% of the Foraxx pallette with some green SCNR noise reduction to tame it down a bit.  Do you have other suggestions for combining Ha, Sii, Oiii data?
* Stars  ... size, shape and colour.  I have taken RGB, but haven't replaced the SHO stars as yet ... do you think it is worth it?  Also, any techniques to make stars rounder?
* Other general stuff like background level, noise levels, contrast, saturation etc.

Thank you for your time and any feedback you can give me.



Original is here:


The Bubble
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David Redwine avatar
David Redwine avatar
You have a very nice data set, but it does need a little "de-greening".  I like to use curves.

  Using the green curve,  you need to set a control point on the left to control the black point.  On the right side (still adjusting the green curve) you need to do a little bit of de-saturation by bringing the white point (the far right point on the control line) down just a little.  Then grab the middle and pull it down a bit.

Moving to the blue curve, place a point on the left for black point control and another point on the right for white point control.  Place a point in the middle and pull it up a bit.

Repeat adjustments until you have the desired false-colors you like. False colors are not true colors, so there is no right or wrong.  I usual go for maximum contrast.

With respect better stars, you need better guidance or tighter sub rejection criteria. Or just replace them with round RGB stars. 

As far as RGB stars go, it is always a good idea to shoot several short RGB exposures.  Align these RGB  subs with the narrow band data.   Then, de-star the SHO version you have here.  Clone out any star residuals on the RGB and Narrowband layers,  then merge the RGB stars under the SHO image using PS or the equivalent.  Since the stars in the final image were shot with a short exposure you will have smaller rounder stars.  For simplicity you don't really have to calibrate the RGB stars,  just stretch them a little then blend them using "lighten"  or "lighter color"  blending mode (all the noise is dark so it gets covered-up anyway).

CS
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James avatar
James avatar
Color is very subjective.  Some people like to remove all the green from their NB images, some like to leave some in.  I'm in the latter.. I like have some green.  More importantly.. leaving green gives you a lot of flexibility to tweak and manipulate the "non green" colors.  Making use of color and range masks helps a lot too.


I prefer straight SHO.  I can manage the colors from there.

I posted a video on my YouTube channel a couple of months ago that goes over how to work with color.  I'm using pixinsight but the principles apply to colors in general.. so it doesn't matter what software you use.

https://youtu.be/Ex8Jrn2xyp8

As for the stars.. does every sub have oblong stars?  If not, cull the subs that do.. the final stack should have better stars.  As for making them round.. I believe there is a technique using deconvolution in PI that might help.  You would use the "motion blur" tab.. but I've never tried it.

I actually like the color I can get with NB stars and so I've not bothered putting RGB stars in.  It's all personal taste.  What I do is remove the stars with starX after the image has been stretched.  Then for the stars I hit them with morphological transformation and then maybe pull back on curves a little more.  Boost saturation.. and then use scnr to remove green, the invert an remove green again to get rid of the purple stars (or you can use the script).  Then add the stars back.
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Andy Wray avatar
Andy Wray avatar
Thanks for the feedback guys.  I added another two hours of data which gave me a better ability to use SubFrameSelector.  I also tamed the green which does make it look a bit more natural.  My median eccentricity of the final image is now down to 0.39 which I think is acceptable.

Original here:


The Bubble