union two or more layers without duplication?

[Ofnuts]

(08-12-2019, 11:51 PM)Human3 Wrote: After i match up the layers, i want to combine them without the image becoming more opaque/darker where they overlap.

But what does that mean...Is the result just the more opaque or more transparent of the two? or a normal blend of the two, set to the opacity of the most opaque? For the latter:

* extract the alpha channels of both layers to a new image (add a layer mask on each layer, init to "Transfer alpha channel" and copy/paste the masks as layers in another image). "Undo" to remove the masks.
* merge the two layers in the initial image
* in the "masks" image, set the top layer to "darken only"
* Edit>Copy visible
* Add  mask to the merged layers in the initial image, initialize to "Transfer alpha channel"
* Paste+Anchor the "computed alpha channel": Ctrl-V+Ctrl-H