Vignetting correction

In case I click on "show corrected image" following result appears:

Yes, the model is not right here, it’s very much over correcting. You did calibrate with bias and such?

@vincent-mod Thanks for reply. My calibration frames may be not perfect. I use QHYCCD163M first time, QHYFW3 first time, NINA first time and APP first time. There are many firsts. Flat frames were taken with white T-Shirt. Yesterday I just finished my DIY flat panel and took new flat frames. I hope they will help better.

But, With a vignetting correction tool, I was expecting an image, even if looks bad. Facing that kind of mask surprised me and would like to know if there is a bug in v.1.081.

My final image processed with APP without vignetting correction but remove light pollution tool is attached. As I said calibration frames especially flats are not ideal. I'll process same image with new taken flats.

I think the vignetting tool is expecting a well corrected background as it uses that to determine a correct noise background and such (I’m not a mathematician though, so this is how far I dare to go 😉 ). It is a bit of a tricky tool though, I seem to get some over correction with it as well sometimes, it’s best to then use LP correction like you did here and indeed real proper flats.

ps. great result for all those firsts!

Hi, I'm having the same problem, I would say it's definitely a bug, or some major weakness in the algorithm if it routinely over-compensates. Are the developers going to look into it?

I agree this is a bug. For sure Mabula will solve it.

I don't think it's a bug, I've seen this been discussed before but can't find it unfortunately. I'll tag Mabula to see what he says about it (@mabula-admin).

@vincent-mod Dear Vincent, I do follow this topic to learn Mabula's answer and/or advices. If this is not a bug, what do I do wrong and how can I fix my mistake? On the other hand, in case this is a bug, is it working on it to correct? Because Mabula's tutorial on a previous version, vignetting correction works great. If other users have a clue and advice, I'm appreciated any help and advice. Thank you.

This is an old post, but it also mentions it’s important to have a good correction and a workflow that might actually solve this issue; https://www.astropixelprocessor.com/community/tutorials-workflows/how-to/#post-449

Now, what might be wrong in the above posts I’m not sure (if it’s not the workflow), for that I would need to have a look at the calibration data. But I’ll also discuss this with Mabula, he’s a bit busy with the comet feature at the moment. @mabula-admin

@vincent-mod Thank you. I read all posts in the topic. I can sent flats, darks, biases and lights as sample if necessary. There are always a purple effect, which I can not fight only with light pollution tool, in my photos. I was hoping to correct it with vignetting correction but it's totally useless for me and really want to know why and fix my mistakes. Maybe I couldn't express my thoughts saying "purple effect". You can find 2 sample pictures below, perhaps they tell more clear than I did.

Ah ok, that’s a different question, might have more to do with the data. It’s best if I can take a closer look indeed.

If you can please upload some of the relevant subs to our server;

Go to https://upload.astropixelprocessor.com and use upload1 (or upload2 till 5) as username and password will then be the same as the username.

Create a directory named “volkanovun-pinkintegration” and upload in there. Thank you!

@vincent-mod Thank you. I uploaded darks, biases, dflats (Ha-SII-OIII), flats (Ha-SII-OIII) and lights 5 frames of each, under the directory volkanovun-pinkintegration. Please notice, lights completed in three nights, so each filter taken in different night. Because of that I checked "multi session" box while processing.

Thanks again

Thank you! I'll download them tonight and hopefully have a clue tomorrow.

@vincent-mod Hi Vincent, could you take a look at the frames and have a clue?

Of course, sorry it's busy down here I will get to it.

Ok working on it, to start with.. I'm not seeing any extreme vignetting that would require the artificial flat. The regular flats seem to work fine.

I integrated the lights and used some LP correction on the Ha, SII and OIII and that looked fine. As this is narrowband data, the way the color comes out will be depending on how you combine the data in the RGBCombine tool. Narrowband data alone won't have "natural" colors as it's not broadband RGB data, so you would need to pick a combination that you like and tweak the colors manually and will depend on your liking. I'm guessing you combined the above in the tool with the RGB formula?

I did have to crop it a lot as the frames were not the same.

For instance here I used a different combination formula (R: 50% H-alpha, 50% SII, G: 20% H-alpha, 80% OIII, B: 100% OIII).

Posted by: @vincent-mod Ok working on it, to start with.. I'm not seeing any extreme vignetting that would require the artificial flat. The regular flats seem to work fine.

 I'm guessing you combined the above in the tool with the RGB formula?

Thanks for your effort. No, not RGB I combined HSO1 formula. I was expecting a little more and distinct, clear blue arond the core. A purple color become instead blue. On the other hand, I don't know how to set percentage H-a, OIII, SII...

Yes that would be possible when you change the formula there. So in the combine tool, you (taking the example of my formula above) simply use the RGB sliders for every data-channel. So If you want 50% Ha and 50% SII in the red channel, you slide the R of the Ha data to 50 and the same for SII.

Here are some settings I used to tweak the colors to what I think you have in mind a bit; You may need more OIII data to get that to add to the blue more, with this I needed a bit of the Halpha in the blue mix.

@vincent-mod Thank you Vincent. I'll play with these settings. But, it seems my calibration procedures/settings were also not ideal. Because at this step my combined frame looked much worse. That's why I was needing to use vignetting correction. You got this result with Ha,SII and OIII only 5 frames of each, but I use 20 of each. Seems I need more information, more experiment on calibration-analysing, registraton, normalising steps and their settings. Need more tutorial video and user manual.

Well I didn't do anything out of the ordinary, the data already looks quite good. For the stacking I just used the automatic settings and switched on LNC and MBB in the integrate tab. I didn't do multi-session as there was no calibration data for each session that would require that. The user manual is still in the works, I agree that has been promised for too long, we also learn from that.

Oh and I also switched on saturation and stretched more on the right hand side of APP's window.

Thank you Vincent. I'll play with it. Thanks for your effort and concern.

No problem, if anything is unclear please get back to me, happy to help.

I guess this is the most close to my wish. Selection of MBB changed a lot. But, a blue circle ( green on some) on stars looks unnaturel. I'm not sure probably it's called "star halos". How can I fix it?

If some of the channels are slightly misaligned, you can correct for that by saving the frames with the “align channels” in the calibration tab. Then loading those and continue-ing the process from there. If that doesn’t help it’s likely just the way the data is and can only be fixed with post processing in other packages, but usually that’s a lot of work.