ASI294MC + L-extreme + gradients

I think, what he meant is that all your data is mainly in the red channel (H-alpha signal) and that you'd need flats for that. APP has a very nice feature to extract the H-alpha signal from your data (tab 0, extract-Ha algorithm). If you set it to that, then load in the lights and calibration frames (flats included), you should get a mono H-alpha channel from your data which can then be corrected with your flats etc.

Thank you for your answer.

Actually he really meant separate process for every RGB-channel, not for Ha/Oiii-channels - that's Im sure. He told that in Pixinsight there is checkbox "Separate CFA flat scaling factors" but wasn't sure, how to do same in APP. I understood that this gradient problem is relevant in every dual narrowband -filters and this way to process will fix it.

We don't have such a feature (for manual adjustment that is), but the way I described should work perfectly (as many use it like that), APP does a lot of these things in the background. The algorithms in tab 0 are specifically meant for dual- tri-band filters.

@vincent-mod

For me resolution is not perfect - or could be better. I have posted some integration images here. In this example I have used carefully made calibration frames (same temperature, flats with flatbox etc.) and more than normally needed. Lights 30 x 600 s = 5 hours. Notice that these are from bortle 3 skies so everything is more sensitive than in light polluted areas. Your light pollution tool excellent, but I hope that this problem could be fixed without using it. For me it's an emergency function.

These are images using different integration-methods:

Ha-OIII color

Ha-OIII Ha extract

Ha-OIII OIII extract

Ha-OIII mono

Ha + OIII extractions very roughly combined (Ha = red, OIII = green+blue) 

Screenshot from flats (taken by the expert who has advised me). Top left is the red channel, top right is the blue channel and bottom is the green channel.

@tojuliin Since you're shooting with a color camera and an L-eXtreme filter, you'll get an equal amount of exposure time on Ha and OIII. So in order to reach the bottom colored result that you show here, you need to boost the OIII signal a lot since the Ha signal is so much stronger. That will bring out faint background noise in the OIII channel, even if you're shooting from a bortle 1 site. Not sure if it is possible to get a cleaner image without using a mono camera to be honest.

@wvreeven 

I'm not sure what you mean. Yes, Ha signal is often more stronger than Oiii signal. But Oiii signal is as bad or even worse than Ha signal if we look at gradients. Top left corner is red and bottom right corner is blue/green. If I boost more Oiii signal bottom right corner will be even more blue/green than it's now and gradient is stronger. I guess?

Also notice subtle dark and bright "circles" around the object.

This one is OIII extract:

@tojuliin I checked with Mabula and APP always computes three scaling factors, just like PI does when that option is enabled. So whatever the issue is with the gradient, it is not caused by processing with APP but something inherent to your images. If it were possible to remove the gradients by processing, that would imply that the gradient also is present in the flats. Apparently this is not the case so these are genuine gradients. Even in bortle 3 skies, the sky background isn't completely even so gradients can arise even with 3 nm filters.

https://www.cloudynights.com/topic/661685-word-of-warning-asi294mc-pro-and-opt-triad-and-nb/

Maybe this will help.