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NGC 1893: My first try at HaRGB

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#1 Der_Pit

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Posted 14 December 2019 - 11:06 AM

The data is already somewhat older (Nov 22/23), but it took me a while to test and decide how to combine Hα and the RGB data.  This is what I've finally settled to:

  • Generate standard RGB image with low stretch

  • run StarNet on it

  • subtract the starless from the full image, do some color smoothing and deconvolution in LAB space

  • generate monochrome (medium stretched) Hα image, run StarNet on it

  • Clean the starless Hα from last star artifacts, then use it as luminosity layer for the (RGB) starless nebula

  • Again some color/sharpness work on the nebulosity part

  • Re-combine it with the stars (addition mode)

Stacking done in IDL, all layer/LAB processing in GIMP (and of course StarNet).

 

Initial data was 120 subs @30s for RGB, 120 @60s for Hα.

A-P Stowaway (old) with ASI1600MM Pro, Astronomik 31mm filters (Deep sky RGB, 6nm Hα) in EFWmini

CEM60EC guided with ASI290MMmini in ZWO OAG

Acquisition software: KStars/EKOS and PHD2

 

Full size on Astrobin

 

NGC1893_1500.jpg

All acquisition and processing done in Linux


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#2 Dynan

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Posted 14 December 2019 - 11:22 AM

Looks like you got the CEM60-EC working quite well. Great shot!



#3 gunny01

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Posted 14 December 2019 - 12:50 PM

  I think you did a pretty good job on this and  using Ha for the lum data.  Only thing I might do is reduce the red halos on some of those smaller stars and try to bring out that background nebulosity.  Like your work flow also.



#4 kathyastro

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Posted 14 December 2019 - 01:12 PM

Nicely done!



#5 elmiko

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Posted 14 December 2019 - 06:21 PM

Very nice image!



#6 Der_Pit

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Posted 15 December 2019 - 05:30 AM

Thanks Kathy & Mike!

 

  I think you did a pretty good job on this and  using Ha for the lum data.  Only thing I might do is reduce the red halos on some of those smaller stars and try to bring out that background nebulosity.  Like your work flow also.

I had tried also using Hα for star luminosity, which gives very nice&small stars - but intensities are all wrong.  Might try deconvolving r/g/b separately?  How do you do such a reduction?  Didn't want to stretch the faint stuff too much, as it's still quite noisy.  If I remove the Hα stars anyhow, I might go for some really long exposure frames - so far I'm conservative trying not to saturate stars too much, which leaves me far away from read noise swamping crazy.gif

 

Looks like you got the CEM60-EC working quite well. Great shot!

Thanks.  Yes, the CEM60EC has basically vanished.  It just works, and unless there's strong wind (above 10m/s) guiding RMS (total) is .5-.7", without wind even as low as .35 cool.gif


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#7 gunny01

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Posted 15 December 2019 - 09:28 AM

Thanks Kathy & Mike!

 

I had tried also using Hα for star luminosity, which gives very nice&small stars - but intensities are all wrong.  Might try deconvolving r/g/b separately?  How do you do such a reduction?  Didn't want to stretch the faint stuff too much, as it's still quite noisy.  If I remove the Hα stars anyhow, I might go for some really long exposure frames - so far I'm conservative trying not to saturate stars too much, which leaves me far away from read noise swamping crazy.gif

 

Thanks.  Yes, the CEM60EC has basically vanished.  It just works, and unless there's strong wind (above 10m/s) guiding RMS (total) is .5-.7", without wind even as low as .35 cool.gif

  Have you tried to use the star mask generator in starnet?  I've not had a problem using the Ha data and painting the stars using PS as a separate layer.  Another thing that you might try is extracting the luminance from the rgb image.  HTH


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#8 Der_Pit

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Posted 15 December 2019 - 10:23 AM



  Have you tried to use the star mask generator in starnet?  I've not had a problem using the Ha data and painting the stars using PS as a separate layer.  Another thing that you might try is extracting the luminance from the rgb image.  HTH

Not sure what you refer to confused1.gif .  My current starnet++ doesn't have any mask generator.  The original python version did create a binary mask, but that is/was only a thresholded version of the (full - starless) image, and I'm not sure how I would make use of that...

Or do you refer to this post (running starnet through a mask)?  TBH I never understood that one either blush.gif



#9 gunny01

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Posted 15 December 2019 - 10:55 AM

Hi Der,

 

  The newer version of starnet++ for PI does have a check  box for generating a star mask.  Sounds like you may be using the older version.  A lot of folks are using that mask, along with the starless tiff of the lrgb image to create a hybrid of the two.  That mask can also be used in PS, but to me it is complicated to use as I'm not very adept at using masks in pi.

 

  If you can, get the updated version of starnet++ for pi.  I think you'll like the results and what that link you refer to above can accomplish.


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#10 Der_Pit

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Posted 15 December 2019 - 04:32 PM

Ah thanks - but I don't use PI, so I have to live with the standalone version of StarNet....

Generating (binary) star masks is easy though, so I'll play around with those a bit.  Thanks again for the feedback waytogo.gif


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#11 Jim Thommes

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Posted 21 December 2019 - 11:46 PM

Very cool image. Nice color on the Ha nebulosity and the RGB stars.


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#12 Roberto Marinoni

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Posted 22 December 2019 - 09:21 AM

It is a good result on this nebula, with nice colors on both nebula and stars.

I'm also trying to shoot it for a narrow band version, but due to bad weather here in Nothern Italy till now I've done only Ha, I miss OIII and SII.


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