Artefacts in stacked image

Yeah does look like hot pixels. How did you create your bad pixel map exactly? Also, it might be nice to see like 10 frames, 10 darks, 10 flats and 10 bias via wetransfer.com I could have a look at the data and see if something is up. You can mail the link to vincent@astropixelprocessor.com

Thanks Vincent.  I'll arrange the transfer as requested.  I may have been naive in that I simply selected the option to create a BPM in the calibration stage.  I'm relatively new to this and I'm sure its user error.  I should say I have created other images with the same setup and process in APP and this is the only one so far that showed this issue.

Ah, well that probably means it's related to the data itself (if you did the same with the other images). Usually it shows up pretty quickly if we look at the data, so hopefully I can give you an answer very soon after that.

Mmm, I get server errors from wetransfer at the moment. I am on a camp-site, so that might cause a few issues. Do you have it on Google Drive maybe?

No - sorry.  No rush - enjoy your camping!

Thank you. Well, if you could put them in a zip file, that might help maybe..

On its way.  Reduced the size by 50% so hopefully more luck.

Excellent, thanks a lot! Almost there. I'll have a look at it tomorrow.

Sorry, wifi troubles overhere. Will get to it today!

So I'm seeing the same issue indeed. The darks and bias seem ok, bpm as well. Flats can be a point of some issues sometimes, especially if the way they are taken isn't optimal. How do you make them? I see the exposure time is just 0.02 seconds, which is really fast, usually people use a less bright source of light and longer exposure times.

I tried turning the flats off and then the background is suddenly filled with these things. So it seems a weird pattern in the data, I'm now trying to find out if it's indeed within the data. For that, it would be interesting to see what DSS made of it, could you send the result of that to me at vincent@astropixelprocessor.com?

Allright then, upon further testing.. I switched off all calibration frames as playing with the flats didn't make it better. Doing this made the problem go away and I just see a few hot-pixels causing stripes. So this seems to point to an issue with either the bias or darks. Difficult one to diagnose, I might have to get some help from Mabula but he's abroad at the moment so that might take a while (@mabula-admin).

Hi Vincent - thanks for your efforts, apologies was at work so couldn't respond sooner.  I'll send you the DSS stack to deepen the puzzle 😉  OK for it to take awhile - I'll be travelling anyway so won't have access to APP for next week or so.

Mm, the DSS result has a darker background so maybe it doesn't show then. Difficult still. 🙂 I do like APP's cleaner result for the galaxy. Will be continued when Mabula is back.

Thanks Vincent

Hi @scott44 and @vincent-mod,

Thank you Callum, for bringing this issue to our attention.

Can one of you give me a link for download of the data so I can study the data? I will then have a look as soon as possible 😉 to see if I can pinpoint the exact cause of your colored stripes.

Apologies Callum for the delay in solving this issue.

Mabula

Thanks Mabula.  Am away from home today so will send tomorrow evening.  Much appreciated.  Have processed some other data on different targets since from my ASI294MC Pro and Nikon 3100 without any issue so unclear what can be causing it with that dataset.

Hi Mabula, Apologies got back late last night.  What email address can I use for We Transfer to get the files to you?  Thanks Callum

Hi,

I am having a similar problem with an ASI071MC Pro camera as you can see in the screenshot of the attached "overstretched" image.

The problem appears to be in the Master Dark file. I have attached screenshots of the stretched master dark as well as a typical dark sub from the stack used to make the master dark. I am happy to send the actual fits files; and any thoughts would be appreciated.

Thanks,

Steve

Posted by: Callum Wingrove

Hi Mabula, Apologies got back late last night.  What email address can I use for We Transfer to get the files to you?  Thanks Callum

Hi Callum, I would use mabula@astropixelprocessor.com as I'm currently not able to use my computer during a move abroad (again, yes I know.. 😉 ). @Mabula-admin

@backroadrider That's a different issue then what the OP had. It seems to be a problem in your darks indeed, how did you take them and did you set any specific menu options?

@vincent-mod,

The dark subs were taken with CCDAP via TheSkyX (build 12165) using ZWO X2 plugin driver v19.3.6.  Master Dark settings were all default (average, no rejection, kappa 3, 1 iteration).

And I suppose I should add that the darks were taken before dawn with the objective covered by an Alnitak Flip-Flat, and the sensor covered by an opaque filter.

Steve

@vincent-mod

Hi Vincent & Mabula - any update on this.  I sent the data a few weeks ago.  Since then I have been shooting narrowband and not had any issues.  Last night I went back to broadband for Andromeda and got the same problem again.  Attached a crop of an area of the photo.

I should state this was using a ZWO IR cut filter and ASI294MC Pro at -10C.  I stacked 29 x 150s subs.  Aside from the this and some not great stars due to some guiding issues the image is great.  Am going to stack in DSS as that didn't the show the artefacts in the meantime.

An update - stacking in DSS with same data again did not show the issue.  Having said that I prefer the resulting image of the galaxy as rendered by APP over the one generated by DSS 🙂  Just need to understand why these artefacts are being introduced.

Sorry I must have missed your post when I went back to answer a lot of open questions. It is very interesting DSS would solve this and APP not, that would be a first for me. Could you maybe send the relevant data over for me to analyse? It might take a few days as I'm moving to a holiday home, it has wifi but I'm not sure how good it is. 😉

You can send it to APP server using login and password: appuser

Please make a folder first with your name on it, thanks.

@vincent-mod

Hi - I've uploaded the lights and the masters for B/D/F and the BPM.  Have included the output file I get plus the DSS output for the exact same data set.  If you need the underlying B/L/D I can upload those as well.  Thanks kindly.

Found them! Will have a look at them in a few days, thanks!

Hi @scott44 ,

So I processed your data and having the masterdark, bias, flats and BPM loaded, I couldn't see the problem actually. Right click and select to open an image in a new tab to see it at 100%.

1. I had to "force bayer CF" in the RAW (0) tab to get the color data on the lights.

2. In the calibrate tab (2) I selected "adaptive pedestal/reduce amp-glow", not sure if that has any effect as I think that's only used while creating the masterdark, which you already did, but just to get our settings the same.

3. In the integrate tab (6) I selected to stack 87% of frames (14 out of 17) and weights at "quality". I selected to perform LNC 1st degree with 3 iterations and I enabled MBB at 5%. I also selected outlier rejection, MAD sigma clipping, kappa 2.5, 2 iterations. I suggest you dial that back down to kappa 3 and 1 iteration, to the point the problem doesn't show up. Too aggressive will not be great for the data.

4. I performed light pollution correction in the tools tab (9), followed by star color calibration. I switched on saturation on the right, selected to stretch at 20% BG, 5 sigma, 2,5% base, upped the saturation to 0.35, background threshold up to 0.30. Contrast a bit up to 0.038, sharpness to 10.8. After that I got this:

5. Too green to my taste, so I selected HSL selective color and played around with the yellow channel ans shifting the green to magenta and the red channel.