Kicking the tires on Siril

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bobharmony
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Kicking the tires on Siril

#1

Post by bobharmony »


I live in a bright-sky area (that is the opposite of a Dark-Sky site) and have been dealing with nasty gradients since starting with AP a few years ago. I have never been able to completely eliminate the effects of a gradient that is different from sub to sub as my target moves across the sky as the imaging session progresses. Stacking is not able to eliminate the gradient and post-processing has not be completely effective as the gradients tend to be very complex over the length of a session.

Enter Siril, a stacking and processing tool that claims to provide background (gradient) extraction on a per-sub basis as part of the pre-processing before stacking. This is of GREAT interest to me, particularly for targets in the Northeast, which rise out of Hartford's light dome as the night progresses. Preliminary experimentation indicates that there is some possibility that Siril does what it says.

As an example I provide screenshots of the initial Autodev process in StarTools for a variety of stacks of my recent M101 data in DSS and Siril.

First DeepSkyStacker using Kappa=3, Sigma=8. The presence of the gradient is pretty obvious:
m101 DSS KS38 autodev.jpg
Second DeepSkyStacker AutoAdaptive Weighted Averaging, my first attempt to resolve the issue:
m101 DSS AAWA autodev.jpg
I then moved on to Siril, starting with a standard stack:
m101 siril autodev noBGX.jpg
Finally a Siril stack with the per-sub background extraction applied before stacking:
m101 siril autodev BGX.jpg
This one shows a bit more initial detail, and appears a bit noisier than the others. It also appears that the flats may have over-corrected a bit as the corners are rather too light. I am not surprised at this as the flats are exposed all the way to the right, which was needed by the first three stacks to work completely on the vignetting. I will shoot some shorter flats and stack with those to see if the over-correction can be fixed.

Another this I noticed about Siril is that it is more accurate reporting (and hopefully compensating for) field rotation over the course of the evening. I may also go back to my M33 data from a few years back to see if I can get any gradient relief there.

I am curious to hear if anyone else has tried Siril, and what your experiences with it have been. I will add additional info here as I continue trying it out.

Oh, I noticed the Siril stacks are mirror imaged vertically when opened in StarTools, but not when opened in Siril. I have no idea what that might mean. :)

Bob
Hardware: Celestron C6-N w/ Advanced GTmount, Baader MK iii CC, Orion ST-80, Canon 60D (unmodded), Nikon D5300 (modded), Orion SSAG
Software: BYE, APT, PHD2, DSS, PhotoShop CC 2020, StarTools, Cartes du Ciel, AstroTortilla

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STEVE333 United States of America
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Re: Kicking the tires on Siril

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Post by STEVE333 »


Hi Bob -
Very interesting results! We will be watching with interest.

One comment, I believe the reason the last image appears noisier may be because it has been auto-stretched further because much of the gradient has been removed.

Steve
Steve King: Light Pollution (Bortle 5)
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Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
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Re: Kicking the tires on Siril

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Post by bobharmony »


STEVE333 wrote: Sun Mar 28, 2021 6:22 pm Hi Bob -
Very interesting results! We will be watching with interest.

One comment, I believe the reason the last image appears noisier may be because it has been auto-stretched further because much of the gradient has been removed.

Steve
Thanks, Steve. Your comment on the noisier image has me slapping my forehead and saying "Doh!". It makes perfect sense and helps with my understanding of the workings of StarTools!

Bob
Hardware: Celestron C6-N w/ Advanced GTmount, Baader MK iii CC, Orion ST-80, Canon 60D (unmodded), Nikon D5300 (modded), Orion SSAG
Software: BYE, APT, PHD2, DSS, PhotoShop CC 2020, StarTools, Cartes du Ciel, AstroTortilla

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Re: Kicking the tires on Siril

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Post by SkyHiker »


Keep going Bob, I follow this with interest. The last image is not quite convincing yet. I don't know if the gradient is done based non every individual sub and whether there are problems subtracting when the count goes below zero. Of course the gradient may shift during imaging so from that viewpoint it would be good.
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: Kicking the tires on Siril

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Post by bobharmony »


As a next step, I went back to some M33 data I collected in 2017 to see what Siril might do with some old Canon data. I started out by calibrating with darks, bias, and flats, then stacked without per-sub extraction and did an initial Autodev in StarTools. It looked a lot like the DSS result I got in 2017, so I applied per-sub background extraction with the default of using a 1st degree polynomial. Results were better, but still not where I wanted it to be.

Initial autodev w/o background extraction in Siril:
M33 no BG extraction.jpg
result with 1st degree polynomial:
M33 with BG extraction.jpg
I then reran the stacking process with a 2nd, a 3rd, and a 4th degree extraction to see if any of them would be better.

2nd degree:
M33 with BG2 extraction.jpg
3rd degree:
M33 with BG3 extraction.jpg
and 4th degree:
M33 with BG4 extraction.jpg
Each was a little different and I decided to proceed with the 3rd degree result. A quick and dirty process gave me this:
M33 BGX3 ST.jpg
The remaining background was easier to remove with the ST Filter module (I left a little in the corners intentionally). This result compares favorably to my previous best efforts, which used up to 9 hours of data over several nights. My Siril effort is one nights data with 3 hours of integration time. I will try integrating some of the additional data to see if there are further improvements to be had, once I figure out how to script that process in Siril.

This M33 data also proved that Siril can integrate data from before and after a meridian flip, which was another thing I wanted to validate.

I also will get some different exposure flats for the M101 data and see if I can get that better - also hoping to collect more subs on that target next week if the weather cooperates.

Bob
Hardware: Celestron C6-N w/ Advanced GTmount, Baader MK iii CC, Orion ST-80, Canon 60D (unmodded), Nikon D5300 (modded), Orion SSAG
Software: BYE, APT, PHD2, DSS, PhotoShop CC 2020, StarTools, Cartes du Ciel, AstroTortilla

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Re: Kicking the tires on Siril

#6

Post by STEVE333 »


Looks encouraging Bob. M33 is certainly a tough test for any processing.

Thanks for sharing your results along the way.

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
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