michael.h.f.wilkinson

Sorry to hear you are still out of luck

Just stacked 20 of last night's images, taken with the Canon EOS 80D and the inimitable Sigma 50-100 mm F/1.8 ART zoom, at 100 mm and F/1.8, at ISO 200. I used the EQ3-2 to track on the stars. I do have some more data, but stacking more than 10 minutes at this focal length shows too much comet motion. I might try later to do some starless processing. The is also the issue of some thin cloud starting to invade the FOV, so I am not sure adding more subs will help. I should perhaps have put the nucleus further to the bottom left, or just have used a wider setting on the lens, as the tail just doesn't fit. Very pleased, and I think it is my best comet shot ever.

I will try. I have just finished stacking 20 subs, which gives some nice results, but will do some head scratching on how to best combine the images.

Just a little, shooting at F/1.8 helps a lot, I find, longer exposures or higher ISO might have blown out the nucleus

One of tonight's captures was photo bombed 30 s exposure at 200 ISO, Sigma 50-100 mm F/1.8 at 100 mm.

The comet data will be spread out over all z-planes, but should not show a consistent slope. In this way, small area structures which follow the motion of the comet can be distinguished from the stars. Noise pixels will also show no preferred orientation, which the stars will show.

Just had another idea: These filters work in 3D as well as 2D (all that changes is the number of neighbours). As in this case, I first star align the images in whatever program I like, and indicate to the program where the nucleus is roughly. It then works out the centre coordinates of the bright blob I indicated, and creates a set of images (with stars) aligned on the comet's nucleus. I then treat a stack of these aligned images as a 3D data set. Faint, aligned structures can then be separated from the stars more effectively, because the stars show trails not parallel to the z-axis of the stack of images, and they have a small volume. They will also all have about the same slope in the z direction, making them easy to pick out. You could then separately stack the "straight" comet data from the "skewed" star data. This should not be too hard to code. The current program treats all colours separately. It is also possible to treat this type of data as a luminance data set (simply by adding the signals) and using the colour data separately to reintroduce the colour information. This might be more robust against noise.

This is an area of active research in my group, with the aim of segmenting the signal as accurately as possible into overlapping objects and background. The idea is that we remove the star profile, not represented as a model, but simply "warts and all" with noise included. This leaves a flat area in the remainder, which is a bit ugly, but in this instance they are rather small (<10 pixels). There are ways to mitigate this (including inpainting based on the surrounding pixels, which is rather trivial in these tiny areas), and suitable Poisson noise can be added if desired, for a more natural look. However, this might not be needed if the stars are added back after separate processing, as they will fill the flat areas with their original profile. If you reduce star sizes by some means, you need to have a suitable transition region in order to fill the flat areas up, or you do the inpainting. Again, this is early days, but the initial result is promising.

True, but I think some of the actual signal in the tail has been removed. Currently the filter removes stars simply based on area, so a single-pixel linear structure less than 10 pixels in length is also removed. A simple upgrade could include elongation, to preserve elongated structures. Another approach would be to remove only compact object significantly brighter than the background, leaving any noise (which stacking takes care of). This would only remove stars, rather than noise or wisps of gas and dust. The main result is that the idea itself is sound.

I posted an experimental image with stars removed here:

OK, so back at the office I grabbed my connected filter C code, and the emacs editor to adapt an earlier filter to removing the stars from several NEOWISE images. I added an option to indicate the centre position of the nucleus, and ran the star removal filter, which in this first version already gives results comparable to star-net++ but WAY faster (a few tens of seconds rather than minutes). It should also be easily adapted to floating point data, and run on the linear rather than stretched if you like. It still needs some work (like computing the offsets of the nucleus automatically, perform the starless stacking, and ideally also then stack the stars, but the basic principle shows some promise. This is a stack of 5 images with stars removed, and then stacked in AS!3 on the nucleus. Some stellar residues can be seen, but I think that it the stars are added back, this might not be visible.

Superb detail in the ion tail in particular.

Very nice. Do I spy some NLCs on the left?

In my case there were quite a few stars. AS!3 managed to stack on the comet, however

I did hold the shift key and marked the comet's nucleus, but to no avail.

Very nice indeed

Absolutely cracking shot

Very nice indeed

Really lovely

Nice one. I am not sure imaging with a scope would help. It is big enough to fill the FOV of my 200 mm F/2.8. I found that using my EQ3-2 as tracker for the camera and telephoto worked really well, with longer exposures and lower ISO values.

Still want to see what I get if I stack all 15 minutes' worth of data in the 200 mm case

These are simply short enough stacks that avoid visible comet motion.

Comet and stars doesn't work either. I think it is struggling with the non-stellar nucleus. I can readily think of ways to solve that. I might try some tricks when I get back to the office, and have more serious image processing tools at my disposal

I got the data with a tracking mount, but would like to combine more data than is possible with the time restriction imposed by the comet's motion. I am now trying to stack the comet separately from the stars, and if that doesn't work, I think I will have a go at writing my own code, using so-called connected filtering approaches

I tried comet stacking mode in DSS but struggle with a couple of things. First, DSS seems to butcher colour in the images (checked the right mode, even let it stack full colour fits files produced with APP). When selecting the cometary nucleus it refuses to lock on to the bright spot (which it did manage before in shorter exposures). It probably wants a stellar nucleus, so I found the way of indicating the core using the shift key. It then infuriatingly fails to stack on the comet. Modes "Stars + Comet", "Comet Only", and the default stars option all give the exact same result (with buthered colours added). Has anybody else encountered these issues?