[RCC] M17 Swan Nebula in Narrowband Requests for constructive critique · Antha Adkins · ... · 32 · 1422 · 11

Antha Adkins:


Thanks to all for your suggestions and links.  I am learning a lot!  Here is a new version, where I have done the following: - Used LinearFit to normalize the images to the same median value prior to NBColourMapper using Ha as the reference.  This made a huge difference.- Ran NBColourMapper to make a SHO version and a HOS version, using background neutralization.  I didn’t need to do anything to the input histograms since LinearFit had taken care of that.- Played with using BackgroundNeutralization and DBE after NBColourMapper.  I liked what DBE did – made the background blacker, and running BackgroundNeutralization after DBE didn’t seem to have much effect.  So this image used DBE.- Tried using SPCC in narrowband mode.  This seemed to want to push the nebula back to the original colors – very green for SHO and red and gold for HOS (I really liked the latter).  This image did not use SPCC.- Tried using ColorCalibration.  This brought out the reds and golds in the SHO image, so this image includes that effect, though I liked it without ColorCalibration as well.- Ran StarXterminator.  Stretched the stars and used ChannelExtraction to make a luminance channel and then used ChannelCombination to make a RGB image so the stars would be white.  I thought that looked better than the magenta SHO stars.- Stretched the nebula. - Ran HDRMT on the nebula to pull out details in the core.- Ran Curves on the nebula for a final stretch. - Used PixelMath to add the stars back in. What do y’all think?  Any more suggestions? Thanks so much!! Antha

Andy 01:
I did this one in photoshop using selective colour. Here is a tutorial that may help. http://bf-astro.com/hubbleP.htm

Dan Kearl:
Your OP was better.
Keep it simple. The color mapper seems unnecessary, It creates crazy unreal colors IMO.

Jon Rista:
The key curves that help you adjust color are Hue, obviously, but also the a* and b* curves as well. Sometimes it takes multiple passes of the CurvesTransformation tool to fully shift colors the way you may want them, as a single pass will often run into the limitations of the tool. Hue also sadly has an intrinsic limitation at the red<->magenta transition...you actually cannot adjust across that point (one is in the lower left corner and the other the upper right corner of the tool, and those points cannot really be adjusted properly if you want to, say, shift red into magenta...which ironically is exactly what we as astrophotographers may want to do (i.e. Hydrogen gas overall, will often emit more pinkish than reddish when you account for its other emission lines)).

A first pass with Hue, followed by a second (and maybe even third, etc.) can progressively shift tones, and give you more opportunity to separate or spread out colors than a single pass. Same goes for the a* and b* curves.