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Stephan and Deer with more data


DaveS
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I managed to capture some more data on this, so now 30 subs each R, G, B (In G2v calibration) totalling 18 hr 45 min and 72 subs Luminance totalling 12 hr. not sure at the moment how much ended up in the final stacks as I had AstroArt reject subs with elongated stars, fuzzy stars (High FWHM) or high sky background.

The Luminance stack was cropped to remove alignment edges followed by Gradient Removal and DDP with a "soft" High Pass" setting and Richardson Lucy Deconvolution.

The RGB stacks were brought into the Trichromy process and aligned before being cropped and the RGB channels separated for gradient reduction. Again a "soft" High Pass DDP was applied followed by Richardson Lucy deconvolution. Close attention was applied to the histograms during this.

The individual RGB stacks were now brought back into Trichromy before being Coregistered with the Luminance. Several rounds of Histogram Stretch followed to bring the range back to 16 bit before Colour Curves were applied to bring out the Core / Arms difference. There was an Unsharp Mask in there somewhere and a final Histogram Stretch just to bring up the background a touch.

Phew! And I'm still not happy. There are some dark halos that are proving troublesome while still enhancing the detail.

218259973_LRGBSoftHPHSCCCBUM.thumb.jpg.cbd10e5c9cc1004d01048a979c14a478.jpg

C&C welcome, together with any suggestions as to how to proceed from here.

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18 hours ago, DaveS said:

I managed to capture some more data on this, so now 30 subs each R, G, B (In G2v calibration) totalling 18 hr 45 min and 72 subs Luminance totalling 12 hr. not sure at the moment how much ended up in the final stacks as I had AstroArt reject subs with elongated stars, fuzzy stars (High FWHM) or high sky background.

The Luminance stack was cropped to remove alignment edges followed by Gradient Removal and DDP with a "soft" High Pass" setting and Richardson Lucy Deconvolution.

The RGB stacks were brought into the Trichromy process and aligned before being cropped and the RGB channels separated for gradient reduction. Again a "soft" High Pass DDP was applied followed by Richardson Lucy deconvolution. Close attention was applied to the histograms during this.

The individual RGB stacks were now brought back into Trichromy before being Coregistered with the Luminance. Several rounds of Histogram Stretch followed to bring the range back to 16 bit before Colour Curves were applied to bring out the Core / Arms difference. There was an Unsharp Mask in there somewhere and a final Histogram Stretch just to bring up the background a touch.

Phew! And I'm still not happy. There are some dark halos that are proving troublesome while still enhancing the detail.

Looking good, the galaxies certainly have a lot of detail in them. Maybe your stars need a little work on them, they seemed to have lost all their colour. Using a star mask whilst working on the galaxies and background would help retain star colour, or remove the stars altogether. Also a dose of star reduction would certainly help focus attention on the galaxies more.

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I haven't got a clue what you just said Dave but I really like your image!  I noticed when I blow the image up to full size your stars looked a little bit eggy. Is that a focusing thing? Is there any way you can separate the star fields from the galaxies and adjust them individually? If what I've just said sounds a bit thick, I apologise unreservedly!       Gary

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I had another play with the data, applying a star erosion filter to the coregistered RGB channels before anything else, and taking greater care over the processing.

I had to pull some of the sliders down to more gentle levels which has meant that I haven't been able to pull out all the detail in the core of NGC 7331 or else I would be back with dodgy stars again.

I did pull the level of green down using a new "Attenuate Single Colour" tool in AstroArt 8

 

1974316842_LRGBEDDPRLAC.thumb.jpg.5074392f31025b88e8c5369d9574f374.jpg

 

And now I think I will leave it alone.

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 I like the detail of the first and the colour of the second. These are small targets with fine detail - tricky with the foreground stars as any process artifacts are visible on top of the thing you want to look at. The rings around the stars might be deconvolution artifacts perhaps?

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Yep, this is why I'm hitting all around the bullseye. The rings in the first image are a combination of the deconvolution and the high pass filtering in the DDP routine that reveals more detail in the core of NGC 7331.

 

Removing the stars and working on them separately would be logical, but I'm not sure what effect the diffraction spikes would have.

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1 hour ago, DaveS said:

Removing the stars and working on them separately would be logical, but I'm not sure what effect the diffraction spikes would have.

For me using Starnet++ on most occasions the spikes remain and just get sharpened with the rest of the image - I don't mind that - actually prefer  clean spikes. If the star is very bright and the spikes are pronounced then the I usually find blocky artefacts are objectionable.

 

TBH when wanting to look at 1:1 pixel scale I have found that the star removal injects artefacts and you have to be very careful not to amplify them. I am not often successful. One approach that has worked occasionally  was to do a two stage stretch, on the second stage do the star extraction, then go back to the first stage and apply the stars as a mask to work on the image, then add the stars back in later to cover up.

 

I find the outcome is driven by the relative diameter of stars for each filter. If one filter has bigger stars then you have a high chance of bright rings. 

Edited by paul
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