Foreground Select - Any Way to Save and Resume Editing Laterme

[TMORT]

I have a high resolution and kind of large picture.  It is a panorama  made from several pictures.

I'm trying to use the foreground select to turn the background to alpha.  I thought I had it done, and when I went to preview it a message box popped up saying calculating unknown pixels and the hard drive was active for quite a while and then GIMP crashed.

I think this may have been because the background was basically the sky and I just put my foreground select lines along the edges of where the background and the foreground intersected.  However, it did mask the photo and allow me to use the brush tool, etc.

I thought I'd see if I could do it in stages and do just one corner, but I see the mask extended beyond where I had my Foreground Select lines.  So it doesn't look like that is an option.  I also tried a different picture and did connect all the foreground select lines and had brushed only part of the picture and then saved it.  It  did save, but I could resume editing where I left off.  Maybe I can but I am missing something.

I guess I could use Foreground Select on the individual pictures the panorama is stitched together from.

I'm wondering if there are any good techniques for doing this?

TIA

for what it's worth, I'm running GIMP 2.10.20 on a new install of Linux Mint 20. I installed the new GIMP because I couldn't find the image tool menu on the earlier version when I tried to use the fuzzy select tool.  It is the menu that has feather edges, mask and some other settings.  I couldn't find it on the new version either.  Maybe I just don't know how to display it.

[Ofnuts]

Good panorama stitching uses non-trivial deformations where the individual images overlap, so I doubt that you could work on individual images first. Depending on how accurate you want the mask to be, you could create a foreground selection on a smaller image and then copy it to size tot the initial image, something like this:

1) Scale a copy of the image by a factor of two (or three, or four, depending on accuray and CPU/RAM). This divides the number of pixels by 4 (or 9, or 16...).
2) Use the foreground select on the scaled down copy
3) Select>Save to channel to save the foreground selection to a channel
4) Scale back the image to its original size, this will scaled up the selection you did
5) Open the Channels list, and drag the saved selection channel to the canvas of the original image. This will create a B&W layer on that image
6) Select the initial image, an din the channels list, drag any of the R/G/B layers (that should all be your foreground selection) to the channels list below. This will copy it.
7) Reselect the channel that you dragged (because selecting it for dragging had the side effect of deselecting it). If you omit this step, you won't alter the value of that channel in your later edits, leading to funky color results.
8) Right click the copied channel, and Channel to selection
9) In the Layers list you can delete the dropped layer

[TMORT]

Thanks for the reply.

I thought that trying to stitch together images with a lot of alpha might be tricky. I figured if I tried it I'd just use two pictures first to test it. You saved me that work.

I have heard about masking as a way of doing this but never really looked into it or tried it, but it sounds like it will probably work well for what I'm up to. It is a landscape sort of thing and the trickiest details are leaves in some trees. They are somewhat distant and not the main focus so I probably don't need great accuracy to get some good results for what I'm up to.

I've used GIMP on and off for quite a few years, but I only do it occasionally. I've used many features as well, but never really often enough to get a real handle on how to use it or remember it the next time. Thanks again.