Stacking an SHG H-alpha image -- first attempt at stacking a large number of frames

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thesmiths
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Stacking an SHG H-alpha image -- first attempt at stacking a large number of frames

Post by thesmiths »

As I mentioned in a previous post viewtopic.php?t=36895, we are now testing the capabilities of the new version of our SHG software. Stacking has been a goal for awhile for a few users. One issue has been that previous software versions often failed to adequately reconstruct all the SER files. The new version appears to be much more robust so essentially 100% of the data will get processed into a PNG image (there can of course still be failures in the mount scanning and -- the most common error -- USB-traffic camera errors).

The other main issue is that it is so time consuming to "pre-process" the PNG files. The auto-cropping feature we added helps a lot with that. Now the only pre-processing that needs to be done is doing a left-to-right image flip on half the images (since scanning is done in both directions). We will probably add a feature to automatically do this, and maybe also a 90, 180, 270 degree image rotation option.

So here is my first attempt at a large stack. I put 45 PNG images (representing 169 GB of video data) into AutoStakkert and let it chose the best 25% (I also let it do 50%, 75%, 100% -- there was not much difference between 25% and 50%). I then used ImPPG (using the settings L-C Sigma 2.0, Iterations: 70; Unsharp Sigma 2.0, Amount 1.0). In Photoshop I then did a little playing around with the levels and used the "Auto Sharpen" feature. This is a 100% crop of the image and saved in high-quality JPG so there is quite a lot of detail. So click on the image to see at higher resolution or try [right click --> open image in new tab --> left click to magnify] to see at full resolution.

H-alpha, stack of best 25% of 45 SHG images. June 22, 08:25 to 10:11 UTC.
H-alpha, stack of best 25% of 45 SHG images. June 22, 08:25 to 10:11 UTC.
220622-Ha-700mm-stack-imppg-ps.jpg (1.14 MiB) Viewed 620 times

Since I scanned in DEC (which has some advantages in terms of mount issues), the image is rotated by 90 degrees with regards to normal North-South. Also, the image was acquired as a full disk (since we are using our very long slits) but at 700mm focal length (106mm aperture), the edges of the image on the slit are outside the best part of the imaging optics. The lenses in the SHG are only 25mm in diameter and the grating is 30mm square; the image on the slit is around 6.4mm. I therefore cropped off the top and bottom parts since they were a bit out of focus. I think next time, I will scan in RA since typically the solar equator has more features than the poles so discarding the poles is not such a great loss.

For a first attempt at a fairly large stack of H-alpha images, I think this turned out quite well. We will try to streamline and automate the process further. I am not aware of anyone trying SHG stacks greater than 6 previously, and these were usually of hand-picked frames, rather that letting the stacking program select the best ones. See these posts on astrosurf from Jean-Francois Pittet, who collaborated with us on developing our software: http://www.astrosurf.com/topic/154847-s ... tte-72430/, http://www.astrosurf.com/topic/154913-s ... tte-72430/


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Re: Stacking an SHG H-alpha image -- first attempt at stacking a large number of frames

Post by marktownley »

Incredible image!!!!!


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Stacking an SHG H-beta image

Post by thesmiths »

Using our most recent update to our SHG software viewtopic.php?t=36904, we were able to speed up the "pre-possessing" considerably by using a "mirror flip" function to convert the reverse scans to match the forward scans. For H-beta, we only had 20 frames to stack, of which we let AutoStakkert use 25% (so only 5 frames). As before, we then applied ImPPG and a bit of Photoshop. The top and bottom of the image were cropped for the same reasons mentioned above. The videos represented 70 GB of data.

H-beta, 700mm, 106mm aperture, June 22, 07:55 to 08:11 UTC. Best 25% of 20 SHG images.
H-beta, 700mm, 106mm aperture, June 22, 07:55 to 08:11 UTC. Best 25% of 20 SHG images.
220622-Hb-700mm-stack-imppg-ps.jpg (1.36 MiB) Viewed 586 times
Last edited by thesmiths on Tue Jul 05, 2022 9:58 am, edited 1 time in total.


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fulvio.mete
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Re: Stacking an SHG H-alpha image -- first attempt at stacking a large number of frames

Post by fulvio.mete »

Wonderful images, well done, Douglas.

Fulvio


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Re: Stacking an SHG H-alpha image -- first attempt at stacking a large number of frames

Post by p_zetner »

Fabulous results!


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Re: Stacking an SHG H-alpha image -- first attempt at stacking a large number of frames

Post by Montana »

Oh my ***!!! the holy grail :bow :bow :bow Merlin66 (Ken) has dreamed of this for years :hamster:

These images from an SHG are now equal to regular etalons :bow

Alexandra


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