https://discuss.pixls.us/t/astro-stacking-with-gmic/1957
This thread is very similar to what I want to do as well. However, I feel as though I am placing more emphasis on foreground than was done in this post. The images I provided aren’t the best example of this, but they were readily available.
I can find lots of options out there for aligning/stacking images containing sky only, but finding one that allows you to define a sky region and a land region so that it handles them differently has been impossible to find. On windows I used Sequator, which was a handy tool that automated this process. Mac has a similar program called Starry Landscape Stacker. I was hoping I could get down the workflow in gimp, and then eventually work it into a semi-automated script.
However, I’m not having a ton of luck. I was able to get OK results by remapping the images in hugin to get their alignment close (it didn’t seem to get them all perfect for a stack of 20). Then I opened these as layers in gimp and manually fixed any alignment issues. Finally I individually changed each layer’s oppacity to emulate and averaging filter, because G’mic seemed to be treating my layers as though I hadn’t gone in and manually fixed their alignment when attempting their Layer (Median) filter.
I hope to keep playing with things as I have time. I’m sure there has got to be a good way to do this. I just don’t know my way around the tools well yet.