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Crab Nebula - What issues can you see in this image?

Processing SHO Request for feedback M1 Messier Objects
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Andy Wray avatar
Andy Wray avatar
I've tweaked my processing of my first SHO image and am looking for any suggestions on how to improve my workflow.  The steps I took after image selection, calibration, registration and stacking were:

* DynamicCrop on individual SHO masters to remove slight registration borders
* DynamicBackgroundExtration on each master image
* LinearFit using the weakest channel as the reference
* MaskedStretch on the individual channels
* Extracted Ha and OIII stars using Starnet++ and also removed stars from SII master
* Combined the 3 channels using ChannelCombination (SHO) to end up with a starless RGB image
* MultiscaleMedianTransform to denoise the new starless RGB image
* ArcsinhStretch on the starless RGB image to give it some punch
* Created a mask using Rangeselection with some bluring and smoothing to work on just the nebula rather than the background
* Applied an SCNR (green) at 35% twice to the nebula
* Removed the mask and applied a 3rd SCNR (green) at 35% to just tweak a bit of green from the whole image including the background
* Combined the Ha and OIII star masks using PixelMath (R=Ha, G=Ha*0.2+OIII*0.8, B=OIII) to create RGB(ish) stars
* Histogram transformation to get my RGB stars to about the level I wanted
* Used CurvesTransformation (Hue) on the stars to just tweak the colour of them a bit as there was still a bit of green in the white stars
* PixelMath to add starless RGB image to stars image
* One final DynamicBackgroundExtraction to remove a slight top to bottom gradient

Please feel free to be hyper-critical as I know have a lot more to learn and I won't take offence.


The full size image is

Crab Nebula SHO using a cheap newtonian
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Eddie Bagwell avatar
Eddie Bagwell avatar
Your image looks nice and it seems you have your PI workflow in order now. It's similar to mine. I haven't tried the ArcsinhStretch on the RGB stars yet. I'll give that a try. Thanks!

I have one other 3 step process that I use to reduce star size I picked up from Shawn Nielson (Visible Dark) on youTube that includes:
Multiscale Transform/Star Mask/Morphological Transformation

Eddie
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Andy Wray avatar
Andy Wray avatar
I have one other 3 step process that I use to reduce star size I picked up from Shawn Nielson (Visible Dark) on youTube that includes:
Multiscale Transform/Star Mask/Morphological Transformation


Thank you!  I will look into that.  I didn't do star reduction on this one as I'm having mixed results and they have ended up looking a bit false with too many artefacts.  I've tried using deconvolution carefully on the stars and that was sort of OK.  I've also tried using the Star De-emphasizer script, but that left me with too many artefacts at my imaging scale.  That's definitely one area that needs a lot of careful handling.
Well Written Concise
kuechlew avatar
kuechlew avatar
Eddie Bagwell avatar
Eddie Bagwell avatar
Do you have your processes ordered and stacked in the right column and saved as a project that you can load when you open PI? It's a wonderful feature.
Well Written
Andy Wray avatar
Andy Wray avatar
Do you have your processes ordered and stacked in the right column and saved as a project that you can load when you open PI? It's a wonderful feature.


I do now.  Very handy; thanks.
Andy Wray avatar
Andy Wray avatar
FWIW:  I've decided to use MultiscaleLinearTransform earlier in the process now for noise reduction; i.e. on the individual linear channels after the linear fit.  I'm using an inverted mask created using a duplicate of each channel that has had the STF applied using HistogramStretch. I think this is a pretty standard approach and one which leaves me with more detail in the nebula whilst removing most of the pesky noise from the background.