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Old 11-10-2017, 08:44 PM
E_ri_k (Erik)
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Thoughts on strange artefact in image

Hi all, I begun an imaging run on NGC 300 last night. I put together what I had so far and found this odd shadow/ghost image overlaid on the top left of the image.

All the subframes look the same to me, so by trial and error I integrated the image several times, omitting One image at a time. I narrowed it down to one frame causing error: frame 6.

Without frame 6 the result is normal.

Thoughts?

Erik
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Old 11-10-2017, 09:03 PM
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PRejto (Peter)
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Erik,

To me it just looks like image 6 is not registering properly to the stack. If you look just above middle left side you can see a bit of the galaxy totally unregistered. If you blink through the stack after aligning is #6 really registered?

Peter
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Old 11-10-2017, 09:31 PM
E_ri_k (Erik)
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Quote:
Originally Posted by PRejto View Post
Erik,

To me it just looks like image 6 is not registering properly to the stack. If you look just above middle left side you can see a bit of the galaxy totally unregistered. If you blink through the stack after aligning is #6 really registered?

Peter
Thanks Peter, I did notice part of the galaxy in the corner also. I'll flick through and have a look. Just curious as to why?

Erik
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Old 12-10-2017, 06:12 AM
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PRejto (Peter)
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I had something like this happen once using CCDStack. I never understood the reason even after getting help on the CCDWare forum. Logically one thinks the images must be the same because they look so similar. But, clearly at a mathematical level there are differences and the software messes up.

Peter
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Old 13-10-2017, 02:16 PM
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sil (Steve)
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I wonder if that frame had a slight glitch when writing or is on a weak part of a HDD. Formats like TIF, BMP and JPG are surprisingly robust when it comes to read/write errors. could just be that frame didn't completely write all its metadata fully in the header information. You could try running the subs through a batch process to resave then to same or different uncompressed format and try those to see if they register/stack properly. That would point towards a read/write issue rather than a registration issue.

If it happens again using the same subs but resaved (this should give you cleanly written files on different hard drive sectors so failing hard drive wont fail the same way with the new files and if it does fail stacking you can look at your registration settings, maybe your camera is starting to get more noisy with age or climate ? its just considering the factors and testing/eliminating to pin down exactly why. obvious suggestion i overlooked, does your software log what it does? you might find information that indicates what caused that file to not register.
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