Siril Novice Alert !

[Spaced Out]

Hi all

I'm a total newb to Siril, using it for the first time today. Just following a simple processing tutorial on a TIF image (previously stacked using DSS - 16 bit). I've got as far as background extraction and hit a snag, the 'apply' button is greyed out and I can’t work out why. Did a quick google and can't find an answer to this so I thought I'd just ask here. Sure I’m missing something really obvious and will no doubt look foolish, but you've got to start somewhere !

Thanks

 

 

[geeklee]

10 minutes ago, Spaced Out said:

Did a quick google and can't find an answer to this so I thought I'd just ask here. Sure I’m missing something really obvious and will no doubt look foolish, but you've got to start somewhere !

It could be the blind leading the blind here (!) but have you clicked "Compute Background" yet?  

[Spaced Out]

8 minutes ago, geeklee said:

It could be the blind leading the blind here (!) but have you clicked "Compute Background" yet?  

Brilliant ! Thanks. I thought I did but nothing happened. Just restarted and tried it again tho and it has worked ! However, it produced this 🤔 , I'm guessing there is a setting somewhere that I need to work out.

 

...

[geeklee]

7 minutes ago, Spaced Out said:

I'm guessing there is a setting somewhere that I need to work out.

While I doubt this is causing the tunnel effect - Generally I would move a few of the background points off the very faint tails of M51 just to give you the best chance of proper background (I'm being quite coarse here, you may not need to remove/move the same amount).  If you think your background is quite simple, you could also increase the smoothing.  M51 is looking really good and a nice overall FOV!

Otherwise, just make sure the data is calibrated correctly.  When you've calculated the background, if Siril then has a "Show background" option you can assess what it thinks the gradient is.

I'm sure a Siril expert will be along shortly to help though!

Edited February 14 by geeklee

[Spaced Out]

2 hours ago, geeklee said:

While I doubt this is causing the tunnel effect - Generally I would move a few of the background points off the very faint tails of M51 just to give you the best chance of proper background (I'm being quite coarse here, you may not need to remove/move the same amount).  If you think your background is quite simple, you could also increase the smoothing.  M51 is looking really good and a nice overall FOV!

Otherwise, just make sure the data is calibrated correctly.  When you've calculated the background, if Siril then has a "Show background" option you can assess what it thinks the gradient is.

I'm sure a Siril expert will be along shortly to help though!

Thanks, it was my first ever attempt at using a SW 250 PDS the other night so it was more of a test session, setting up coma corrector spacing and the guiding etc, no calibration frames taken unfortunately, it's just stack of about 20x 60 sec subs. Could the lack of calibration frames be the issue ?

I will try deleting some of the points as you've suggested and see what happens.

Interestingly, I just restarted Siril to try again and ran into exactly the same issue of the 'compute background' button not working, nothing happens and then the 'apply' button remains greyed out. 🤔

[Elp]

The rings are because you haven't applied flats to the image prior.

All the menu items in the top should be applied after you've gone through the panes on the RHS left to right in terms of calibrating, registering and stacking but you've done all that within DSS prior.

If you don't have your image calibrated, background extraction will do strange things to your image as it's designed to remove gradients which are linear in fashion and not radial like your uncalibrated image is. To use DBE you left click across your image on areas where there is no star or imaged target nebulosity (ie blank space) to leave small red sample squares/points, you also don't want to place points at the very edges when you haven't pre cropped your image as it'll pick up on your stacking edge artifacts due to field movement, place around 20 points around your image in varying areas of background intensity, press compute background to see the calculated image, then press apply to apply and close the dialog box. It helps to have the console tab in view from the RHS pane when processing as you can see what Siril is doing and whether it throws up any error messages. The RBF algorithm generally is the one to use, if calibrating on a per sub basis to a sequence of images (yes you can pre process per sub) you can use order 1 algorithm normally on a per sub dbe process.

It also helps when you've loaded an image in Siril that hasn't been pre processed/stretched to change the image preview mode at the bottom centre from linear to auto stretch or histogram (this doesn't alter the image, just the way it previews), the latter is a good way to quickly assess the faint nebulosity or dust you have imaged in the stack as well as ensuring when doing DBE you're not placing a sample point where you shouldn't be.

Edited February 14 by Elp

[Spaced Out]

22 minutes ago, Elp said:

The rings are because you haven't applied flats to the image prior.

All the menu items in the top should be applied after you've gone through the panes on the RHS left to right in terms of calibrating, registering and stacking but you've done all that within DSS prior.

If you don't have your image calibrated, background extraction will do strange things to your image as it's designed to remove gradients which are linear in fashion and not radial like your uncalibrated image is. To use DBE you left click across your image on areas where there is no star or imaged target nebulosity (ie blank space) to leave small red sample squares/points, you also don't want to place points at the very edges when you haven't pre cropped your image as it'll pick up on your stacking edge artifacts due to field movement, place around 20 points around your image in varying areas of background intensity, press compute background to see the calculated image, then press apply to apply and close the dialog box. It helps to have the console tab in view from the RHS pane when processing as you can see what Siril is doing and whether it throws up any error messages. The RBF algorithm generally is the one to use, if calibrating on a per sub basis to a sequence of images (yes you can pre process per sub) you can use order 1 algorithm normally on a per sub dbe process.

It also helps when you've loaded an image in Siril that hasn't been pre processed/stretched to change the image preview mode at the bottom centre from linear to auto stretch or histogram (this doesn't alter the image, just the way it previews), the latter is a good way to quickly assess the faint nebulosity or dust you have imaged in the stack as well as ensuring when doing DBE you're not placing a sample point where you shouldn't be.

This is great ! Thank you for taking the time to write this, it has set me on right track. I will try using it from scratch again with a different image/set of calibration frames. Only ever used it a couple of times before, quite a while ago and then I just dabbled with a couple of things. I'm interested to see what it can do.

[PhilB61]

I have had occasional issues with banding although not as prominent as yours, try ticking the Dither box it's supposed to reduce or prevent this type of issue and has worked for me.

[geeklee]

1 hour ago, Spaced Out said:

Could the lack of calibration frames be the issue ?

Yes, if it's not calibrated with flats, I can definitely see why you'd get unexpected results.  Could you take some flats with the rig just now or has it been broken down?  These things (tricky backgrounds) can be brute forced but you always compromise something.  

I see @Elp has provided some specific Siril advice, good stuff 👍

Edited February 14 by geeklee

[Elp]

Siril is quite easy to use one you've done it, I used to use DSS but Siril can do so much more, nearly enough that you don't need Pixinsight (which I don't use), and Siril is free. The remaining finishing touches can be done in PS/Gimp/Affinity or equivalent, GIMP is also free.

[ONIKKINEN]

Some quick tips, might have been already mentioned:

Place samples manually in empty spots, not on stars. Not too many samples either, Elp suggested 20, which sounds good to me but you dont always need even that many.

The dither option can work, but using it is not ideal as it tends to produce more noise (no theory to support this, just what i found in practice).

Have seen this effect a few times with 8 bit stretched or 16 bit stretched or not images, but never for 32 bit stacks. You should consider producing a 32-bit stack for Siril processing. And flats, definitely take flats.

And forgot to mention smoothing, try increasing the value.

Edited February 14 by ONIKKINEN
Smoothing

[Spaced Out]

Thanks everyone for the help and tips ! 👍

[AstroMuni]

17 hours ago, ONIKKINEN said:

Place samples manually in empty spots, not on stars. Not too many samples either, Elp suggested 20, which sounds good to me but you dont always need even that many.

And if you cant be bothered to manually place the markers, use GraXpert AI 🙂

In fact I recommend using this when you have a lot of nebulosity. It does a much better job than RBF.

[Cindyly]

Siril is my primary processing program, but I've not experienced what you did. I hope you can resolve your issue (or have already) because I think you'll find Siril to be a very useful, easy, powerful program. I simply pile my RAW images into their respective folders inside the image file, and Siril converts them , stacks them, and just like magic, a final image pops out ready for processing (still within Siril). I've amended and added a few scripts in order to process files that, for example, lack flats, or similar situations. Overall, it's quite easy to use, very fast, does a bang-up job creating great images, and it's free to boot. If a final product needs any tweaking, I'll just bring it over to Gimp. But most of the time, I am quite happy with the results. Good luck! 

[lock042]

On 14/02/2024 at 15:14, Spaced Out said:

Brilliant ! Thanks. I thought I did but nothing happened. Just restarted and tried it again tho and it has worked ! However, it produced this 🤔 , I'm guessing there is a setting somewhere that I need to work out.

 

...

Hello @Spaced Out. As indicated in the topic, you need to check the dither option. If you made a stack with Siril, in 32bits mode, you wouldn't have needed it, though.

In order to improve the documentation, could you send me your stack output image (WeTransfer), and give me the rights to use it for the Siril documentation?

Edited March 18 by lock042

[lock042]

@Spaced Out: a positive answer could help all the community :).