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michael.h.f.wilkinson

Different stack of yesterday's Wirtanen data

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Tried registration on comet and stars in DSS, and some postprocessing in APP and GIMP. Not totally convinced by the result, as there is a lot of streaking in the background and still some smearing of the stars going on. Not sure how to improve that.

46P-Wirtanen-CSstack.thumb.jpg.157ea67c7114132cc39e28c46851f628.jpg

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Oh, well thats put a spanner to my plans then! I had high hopes for the "comet registration" mode in DSS. Looks like its done something though. I suppose a composite is possible? But then you'd have a big smear where your comet was supposed to be on your star layer and your comet layer would obviously be too small to overlay over the top.

This challenge could be one for the sketchers!

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You can mess about in P'Shop and presumably gimp and remove the stars, process the comet and stick the stars back on, I cheat and delete the blurred comet and cut and paste an unblurred one on, works OK with ones with no long tail, it's only a comet record image so doesn't need to be an image processing masterpiece :grin:

Might be worth making more effort when you can get the Hyades and Pleiades in the same FOV.

Dave

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Have you reversed the direction of travel?

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I thought about this - two way comet stacking, and this is what I think:

1. Stack on comet and use sigma clip reject - this should remove stars as they are in different position each frame. Depending on how fast the comet is moving you might want to increase rejection threshold to get clean stack of the comet.

2. Stack on stars - this will smear the comet. Sigma clip will not help here much, because of large surface of the coma - not enough background to reject coma.

Take stars stack and extract stars in some way - either aggressive background removal, or some high pass filtering - or whatever comes to mind and works good.

Blend comet stack with result. Fiddle with processing until happy :D

 

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1 hour ago, vlaiv said:

I thought about this - two way comet stacking, and this is what I think:

1. Stack on comet and use sigma clip reject - this should remove stars as they are in different position each frame. Depending on how fast the comet is moving you might want to increase rejection threshold to get clean stack of the comet.

2. Stack on stars - this will smear the comet. Sigma clip will not help here much, because of large surface of the coma - not enough background to reject coma.

Take stars stack and extract stars in some way - either aggressive background removal, or some high pass filtering - or whatever comes to mind and works good.

Blend comet stack with result. Fiddle with processing until happy :D

 

I am looking at it that way. I am also thinking of so-called morphological hyperconnected attribute filters we developed here some years back. They can separate different structures quite neatly based on their properties, such as shape or size.

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5 minutes ago, michael.h.f.wilkinson said:

I am looking at it that way. I am also thinking of so-called morphological hyperconnected attribute filters we developed here some years back. They can separate different structures quite neatly based on their properties, such as shape or size.

That sounds nice, any published papers on that by any chance? Would like to have a read and see what is it about.

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1 minute ago, vlaiv said:

That sounds nice, any published papers on that by any chance? Would like to have a read and see what is it about.

We had a paper in IEEE Transactions on Pattern Analysis and Machine Intelligence

https://ieeexplore.ieee.org/abstract/document/5432219

http://www.cs.rug.nl/~michael/OuzounisWilkinsonPAMI2011fpage.html

We also have some more recent work on so-called viscous hyperconnected filters

https://link.springer.com/chapter/10.1007%2F978-3-319-18720-4_56

https://pdfs.semanticscholar.org/ee31/687a694b2c44b984865bb5dc9e486266fe3d.pdf

 

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I find DSS is working OK for me on processing last night's stack on either comet, or both comet and stars but I did mark the comet position on every frame. The sky for me is the most murky crud and I am trying to make something usable.

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Interesting thread.

I took x33 light frames of the comet on Thursday (13th December) and for the first time used DSS employing it's comet staking options. The option "Comet and stars stacking: "star freeze effect" yields a similar final image to the OP's post with a static comet but ghost streaking to the stars. I did identify the centre of the comet in all the light frames-

14_12_18_Comet_46P_MainPC_Bothstill_Final.thumb.jpg.946c840298a66a13de2fcec952902523.jpg

The images were taken with my Canon 600D DSLR, and Astronomik clip-in UHC filter, 75-300mm lens at 135mm and f/4.5 and ISO 1600. The 120 second images were stacked with x10 temperature matched dark frames and master flat and bias frames from x50 exposures each. The resulting master frame was processed in StarTools.

Cheers,
Steve

Edited by SteveNickolls

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I'm not getting that stuttery star effect, I'm on the new 64bit DSS version. I'll check again my fits file outputs to make sure I didn't miss seeing the stuttering stars. I used kappa sigma clipping.

Edited by happy-kat
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8 minutes ago, happy-kat said:

I'm not getting that stuttery star effect, I'm on the new 64bit DSS version. I'll check again my fits file outputs to make sure I didn't miss seeing the stuttering stars. I used kappa sigma clipping.

Thanks happy-kat. I'm using the 64-bit version. I'd have to check but I'm sure I use kappa sigma clipping setting too. I was intrigued someone else was getting  a similar effect on the final image. Time here is a little hard to come by at the moment but I might have chance this afternoon to recheck the DSS settings and try another run.

Cheers,
Steve

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It would appear there are stutters just they did not show on processing so I assumed there were none.

This is stacked on the comet.

image.png.b321b791c69ce514cb567c2cacb50ecd.png

This is stacked on comet and stars fits file opened in StarTools and a stretch and snip to paste here, not stutters showing.

image.png.3cb8f7a305bf14b5da8d860587fcea39.png

Yet the same fits file opened in fitsliberator shows stutters, I am not getting the stutters when processing the fits file..

image.png.02990a3e4eda81d63461973247ec758a.png

 

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I find the sigma stacking in AstroArt is good for ensuring no star trails when stacking on a comet nucleus.  I leave a 30 second gap between each individual sub acquisition, to try and ensure that each star in the “trail” is a distinct dot, as it were.  That seems to avoid or at least greatly reduce residual trails in the final stack.  Works for me, anyway...

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When selecting the comet in dss, are you all zooming in to really get into the nucleus? That helped reduce the 'stack on comet' smears a lot. But did not remove them entirely, for me. 

 

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Yes I zoom in, but I don't have any smears when processing the fits in StarTools they only show in fitsliberator.

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1 hour ago, skybadger said:

When selecting the comet in dss, are you all zooming in to really get into the nucleus? That helped reduce the 'stack on comet' smears a lot. But did not remove them entirely, for me. 

Thanks for this potential remedy. I will have another try in DSS and take extra effort where the centre of the comet is identified and see how that works out. 🙂 

Happy-kat I have restacked making sure sigma-kappa clipping is correctly used but the result was the same-streaks where the stars are.

 

P.S.

Added- I've just come across this piece of information in the DSS Technical help document relevant to the issue-

Obviously the most demanding algorithm is the Comet and Stars stacking leading to the star freeze effect.
Slow moving comets are leading to hard to detect large objects or big stars and in this case the comet extraction process may be less than perfect.
In all cases, if you take a set of images from the same area without the comet (the day after or before) it will improve a lot the look of the final image.

Best Regards,
Steve

Edited by SteveNickolls

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Think I might have a play with the startools heal and layers module to make a composite from each different stack one on comet the other on stars.

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3 minutes ago, happy-kat said:

Think I might have a play with the startools heal and layers module to make a composite from each different stack one on comet the other on stars.

 

Hi,

I have come across this-

If you go to YouTube and enter "Processing a comet using StarTolls Layers" you will find a host of videos.

Not had chance to experiment with any ideas yet but good hunting!

Cheers,
Steve

Edited by SteveNickolls
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Cheers. My process so far isn't so bad with the limited data I have, just thought to expand practice to see if could do better.

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9 minutes ago, happy-kat said:

heers. My process so far isn't so bad with the limited data I have, just thought to expand practice to see if could do better.

Thanks happy-kat, let me know how you get on, I'll do likewise 🙂

Cheers,
steve

 

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Interesting another imager using 30 second subs for a comet, I'm thinking it is the sweet spot for the comet not becoming elongated as they are going so fast. Yey something I can do (as can't use the barndoor facing east anyway as can't see Polaris).

Must be moving faster then Lovejoy as that didn't streak even on 3 minutes.

Edited by happy-kat
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