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It's been a while but I'm back with DBE questions

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#1 Becomart



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Posted 23 January 2021 - 11:16 AM

Hi All,

Haven't been around for quite a few months as we haven't had a full clear night now in the UK since last October and I was starting to feel a bit despondent about imaging. However, I'm starting to see a few possible clear nights appearing on the horizon so am doing a bit of processing to make way for new data.


Was playing around with DBE settings and wondered what other people thought on placement options when nebulosity in the field is quite full. In the screen shot image below, I have tried 3 different models. The first one on the far left has small placement points (size 15) placed strategically into the darkest areas of the image only, the second one has larger sample points (size 40) using sample generation with those that fall on significant nebulosity removed and the last one has the same largest sample points but placed around the edges of the image though still avoiding the nebulosity.


As you can see, there are subtle difference - the first one has more nebulosity with less contrast whilst the last one reverses this difference. I am heading towards the middle version but am interested in what you think?



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#2 StephenW



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Posted 23 January 2021 - 11:31 AM

Yeah, DBE when your image is all nebulosity is a challenge.  I think as you have seen, it ends up being a personal preference on what result you like best.  In the three images you shared I'd also lean towards the middle option.


One thing though: I primarily use DBE to remove, or at least try to remove :), gradients.  Not clear from the images you posted, but do you actually have gradients to remove?  In any image of the Crescent, where there is nebulosity everywhere, I think DBE will inherently be destructive in that it will eliminate some of the real signal.  So if you don't have gradients (or some other problem you're trying to solve), I'd use DBE sparingly.

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#3 bobzeq25



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Posted 23 January 2021 - 12:04 PM

This is why you look at the background image PI provides.  It gives you valuable clues about when you're removing a true gradient, and when you're impacting signal.


It's the explanation why the default correction is "none".  PI expects you to trial ABE and DBE, look at the background, decide what is the best true gradient removal, and _then_ actually apply the correction, as a final step.  PI is all about preserving data, more interested in the process than the final result.


It's also related to the fact that PI does not automatically process better, it hands you the tools so that you can process better.

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#4 Becomart



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Posted 23 January 2021 - 12:16 PM

Well now that's the big question isn't it...is it signal or is it gradient. For the record Bob, I always look at the background image. As it's Ha under bortle 5 skies, I suspect there is a slight gradient. Certainly, the image background using both ABE and DBE shows a slight brightening in the top left and bottom right. Whether that is true gradient or not is a difficult call so I'm inclined not to go too heavy with the tool.

#5 Cfreerksen



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Posted 23 January 2021 - 12:18 PM

When doing narrow-band I really don't see a lot of gradient any way. When the field is just nebulosity I just skip it. 



#6 jonnybravo0311


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Posted 23 January 2021 - 12:18 PM

Given your three results, I'd pick the one on the far left. Honestly, unless I was dealing with a gradient issue that was plainly evident in the original image, I'd probably just skip DBE altogether. No need to extract real signal just for the sake of running a process because "you're supposed to use DBE after you crop". I can apply contrast and punchiness later in the editing process if I want. That's my 2 bits :)

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#7 Madratter


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Posted 23 January 2021 - 01:21 PM

At least in my skies, there is rarely any significant gradient when doing narrowband. At least in my case, I'm more likely to do harm than good by using it. Because of the way DBE works, if you insist on doing gradient reduction on narrowband, I would suggest using ABE instead with low function degree.


I have said before and I'll say again, in my opinion the ability to use ABE type function fitting within DBE would be a significant improvement in some situations over either in their current state.

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#8 PhotonHunter1


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Posted 24 January 2021 - 12:19 PM

+1 to jonnybravo. I prefer the image on the far left. You can address contrast later in the processing sequence.

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