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Old 19-01-2015, 07:53 PM
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multiweb (Marc)
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Comet Tail Processing

I'm sharing this here as it might help a lot of people trying to process those pesky comet shots. I tried different things to extract the tail details from the trailing stars and sky background and just figured out that the easiest way to do it without damaging the tail details too much is to use the motion blur in Photoshop and align the direction with the tail direction. The star trails are almost perpendicular to the streamers so you can blur them out without blurring the tail.

If any of the gurus have a better way to do it by any mean jump in and share your thoughts.
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Old 21-01-2015, 09:23 PM
gb44 (Glenn)
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ImagesPlus software to the rescue

This might help.
Checkout the feature mask tutorial in the list here
http://www.mlunsold.com/ILProcessing.html
Particularly
http://www.mlunsold.com/process/ip5/UFM/UFM.html

An example is at
https://www.flickr.com/photos/laurie...n/photostream/

GlennB
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Old 29-01-2015, 08:58 AM
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Thanks for that Glenn. I'll check it out.
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Old 29-01-2015, 03:58 PM
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i prefer your shot with faint star trails best of the two. I'd have loved to be able to use my better gear and get something similar. Only got shots with a hint of a trail with what i can use.

have you tried a registration of the background stars to bring them out then composite them in? so its got better context? or possibly plate solvable instead of working to isolate it. either way the comet and tail ARE the focus of the shot, so anything to keep the detail would be best, so many comet shots just have a nice comet on the horizon, but rarely do we see the fine detail up close. damn good shot, so jealous!
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Old 29-01-2015, 04:40 PM
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multiweb (Marc)
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Quote:
Originally Posted by sil View Post
i prefer your shot with faint star trails best of the two. I'd have loved to be able to use my better gear and get something similar. Only got shots with a hint of a trail with what i can use.
In hindsight I don't think you need good gear to photograph the comet. The tail was very hard to get on this one. I think the best approach would have been to guide on the comet itself, from a finder or short FL scope and do 5min subs, then wait 1 or 2 minutes, then do another 5min, etc... I suspect that with 20min total integration on the tail you would get some really good SNR.

Quote:
Originally Posted by sil View Post
have you tried a registration of the background stars to bring them out then composite them in? so its got better context? or possibly plate solvable instead of working to isolate it. either way the comet and tail ARE the focus of the shot, so anything to keep the detail would be best, so many comet shots just have a nice comet on the horizon, but rarely do we see the fine detail up close. damn good shot, so jealous!
Yes, that's the plan. I reject the stars with a sigma combine, registering on the comet's core and that takes care of the stars. The issue is read noise. So I'm trying to find an efficient way to clean the tail from this noise before compositing it.

Last edited by multiweb; 29-01-2015 at 06:36 PM.
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Old 02-02-2015, 09:02 AM
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multiweb (Marc)
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PSD layers

Here's a reduced PSD file with uncollapsed layers showing the basic processing flow for the second comet shot C/2014 Q2.

The star mask was generated from the stars stack in Startools and saved as a 16bit TIFF files. One stack was registered on the stars so the comet's core and tail were trailing, then removed with the starmask.

The comet's tail and core were extracted from a stack registered on the comet nucleus, so the stars were trailing and rejected with a sigma algo. The program used to stack the subs and do the data rejection was CCD Stack.

The file is about 4MB. You can download it here. It's saved in Photoshop CS6 format. If you have any issue opening it let me know and I can downgrade it to a lower versions of Photoshop.
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