At my City suburban B7/8 location it’s near pointless to image emission nebula in LRGB broadband ( plus I don’t get enough clear nights ) so I worked out a way to use my narrowband acquired data set to produce a “simulated LRGB” image or close as possible to broadband visual spectrum.
I used my recently acquired M17 Swan Nebula SHO data.
Used the Compose module in Startools to map the SHO data set into an LRGB composite as follows -
Luminance Channel ( SHO )
Open Compose module
Load SHO data into RGB channel slots and set Luminance / Color to L+ Synthetic L from RGB, Mono
Save as TIFF
Close Compose module
Red Channel ( Sii + Ha )
Open Compose module
Load Sii data into R channel slot
Load Ha data into G channel shot
Set Luminance Color to L + Synthetic L from RGB , Mono
Save as TIFF
Close Compose module
Open Compose module
Set Luminance Color to L, RGB
Load previously saved Luminance ( SHO ) into Luminance channel slot
Load previously saved Red file ( Sii + Ha ) into Red channel slot
Load existing Oiii data into Green channel slot
Load existing Oiii data into Blue channel slot
Process and Keep
Once you hit the Color module select Color Style - RGB Ratio CIELab Luminance Retention and process accordingly.
The final result was pleasing , definitely not bonafide LRGB but close enough considering my heavy light polluted skies where narrowband is my only option when imaging emission type celestial objects.
It just provides another option and a bit more flexibility in my imaging and processing.
Attached simulated LRGB version in 200kb
Astrobin link below for full resolution……,
https://www.astrobin.com/uf78h5/
Thanks for looking
Comments welcome
Martin