Which software/technique for processing comets?

[carastro]

Good luck with all this.  Building your own PC. Wow.  
 

But why did you not take flats?  You go to a lot of trouble to capture the comet, do all the stacking using unfamiliar software and then struggle to process because there are no flats.  
 

If you have to stop imaging  and pack away - leave your camera and scope still attached so you can take the flats afterwards.  I had to do this once when l almost forgot and it worked ok. 
 

In the absence of flats l can only suggest something like gradient exterminator, a photoshop plugin well worth having.  
 

 

Edited February 12, 2023 by carastro

[Elp]

You can apply synthetic flats if you don't have flats, I do it all the time when flats don't quite clean up the image. No need for plugins, but also not a replacement for well calibrated and taken flats.

Edited February 12, 2023 by Elp

[Leo S]

4 hours ago, carastro said:

Good luck with all this.  Building your own PC. Wow.  
 

But why did you not take flats?  You go to a lot of trouble to capture the comet, do all the stacking using unfamiliar software and then struggle to process because there are no flats.  
 

If you have to stop imaging  and pack away - leave your camera and scope still attached so you can take the flats afterwards.  I had to do this once when l almost forgot and it worked ok. 
 

In the absence of flats l can only suggest something like gradient exterminator, a photoshop plugin well worth having.  
 

 

Thanks. I built my first PC more than two decades ago. I do enjoy building PCs, just not the bill at the end! It's actually quite simple, but my memory is not great, so I always follow a guide just to make sure I have not overlooked anything. I like this one, but there are plenty of others to choose from.

As Elp says, there are other ways to deal with vignetting - I saved this link to check out later.

Edited February 12, 2023 by Leo S

[Leo S]

48 minutes ago, Elp said:

You can apply synthetic flats if you don't have flats, I do it all the time when flats don't quite clean up the image. No need for plugins, but also not a replacement for well calibrated and taken flats.

Flats can also be acquired later, so if I struggle with other alternatives, I'll just try taking some flats at some point.

[Leo S]

I'm having second thoughts about going down the Siril route after reading this eye opening thread about Siril and colour over on CN, in particular sharkmelly's post on page 2:

"It should be noted that the workflow using RawTherapee is very different to what is done by Siril, DSS, PixInsight etc.  RawTherapee is designed for normal photography using a DSLR/Mirrorless camera.  So RawTherapee performs all the necessary processing steps to display colours correctly in the chosen target colour space (e.g. sRGB, AdobeRGB etc.)  These processing steps include the colour correction matrix to transform data into the colour space and then to apply the gamma tone curve relevant for that colour space.  Siril, DSS and PixInsight do not perform these necessary steps and therefore their colours are muted.

 

It is certainly possible to take the (linear) raw stacked output from Siril, DSS and PixInsight and apply the necessary colour space transformations so the colours match RawTherapee but it is not straightforward.

 

Mark"

Colour is very important to me, so now looking at how RawTherapee can be incorporated into the workflow. Anyone using it?

[ONIKKINEN]

9 minutes ago, Leo S said:

I'm having second thoughts about going down the Siril route after reading this eye opening thread about Siril and colour over on CN, in particular sharkmelly's post on page 2:

"It should be noted that the workflow using RawTherapee is very different to what is done by Siril, DSS, PixInsight etc.  RawTherapee is designed for normal photography using a DSLR/Mirrorless camera.  So RawTherapee performs all the necessary processing steps to display colours correctly in the chosen target colour space (e.g. sRGB, AdobeRGB etc.)  These processing steps include the colour correction matrix to transform data into the colour space and then to apply the gamma tone curve relevant for that colour space.  Siril, DSS and PixInsight do not perform these necessary steps and therefore their colours are muted.

 

It is certainly possible to take the (linear) raw stacked output from Siril, DSS and PixInsight and apply the necessary colour space transformations so the colours match RawTherapee but it is not straightforward.

 

Mark"

Colour is very important to me, so now looking at how RawTherapee can be incorporated into the workflow. Anyone using it?

That thread is painful to read, i made it to page 10 before i had to tab out from all the nonsense. I recommend that you do not take anything out of it. You definitely should not be applying any daylight color transformation nonsense in astrophotography, especially not in the preprocessing phase to the raw subs!

There is no actual issue with colour calibration done with Siril. You can do whatever you want with the raw data that Siril will stack for you, whereas some kind of daylight colour transformation done on the raw subs will permanently and irreversibly damage it making subsequent processes such as photometric color calibration impossible, because the data is no longer linear. Of course the PCC tool in Siril is not perfect and it can only work if the data fed to it is of sufficient quality. If you feed it a decent integration it will churn out a very nicely balanced colour image in the end, but one you will need to saturate yourself.

Your colours will look "boring" after a photometric color calibration in Siril because they are boring if the image is represented as completely real with no addition of saturation anywhere. You can (and probably should) saturate it afterwards, probably selectively with Photoshop using masks so that you dont saturate the background where just noise exists.

I thought this quite from the Siril dev in that thread was the wisest thing in there:

Quote

In fact, the real problem here is trying to capture Ha photons with a filter that prevents it. It's like trying to catch fish through glass.

 

[Elp]

I think you're reading too much into it, all astro images are post processed even those by the likes of space agencies as they mostly convert numerical data. Considering space is mostly darkness what would you personally constitute as true colour of a deep space object? Is your monitor professionally calibrated and able to display an accurate colour gamut? How do you know what the true colour is supposed to be in the first place? The whole Hubble pallet scheme is visually incorrect in RGB colour space but is deemed as an acceptable way to present images. Most people are happy to produce any sort of image via the effort they put into it.

[Leo S]

Thanks for the input guys. I have not yet got past page 4 on that thread! Just trying to absorb some of what was said early on there.

I realize the output may be naturally muted with software like Siril, but it just sounds like it may be easier to get the colour right using something else like RT, and I trust what sharkmelly says - have been reading his posts for many years.

Regarding getting the colour right. I always shoot with daylight white balance, so with the correct workflow it should be possible to maintain correct/natural colour, despite my monitor not being properly calibrated, if I'm not mistaken?

[Elp]

If you want accurate colour your monitor should be professionally colour calibrated to match the colour workspace specification. A lot of monitors (most) are not able to display full colour gamut in a range of colour profiles so it depends on your equipment, even the majority of consumer colour calibration devices are no good compared to professional devices which obviously cost more.

I'm not sure how it applies for astro images, what would be the colour profile standard as I hinted on previously colour can be subjective.

Edited February 12, 2023 by Elp

[bomberbaz]

Does anyone have a link to the Siril comet stacking workflow, can't seem to find it. 

I found the one for DSS but with 300 frames to stack, a manual job does seem long winded. 

[Elp]

https://siril.org/tutorials/comet/