Open the Layers dialog ("Windows/Dockable Dialogs/Layers"), left-click on the relevant layer in the Layers dialog to make it active then set the "Opacity" field near the top of the layers dialog.

I'm an ex Photoshop user who does astrophotography (AP). In AP we frequently shoot a number of photos that we then stack in layers to reduce noise or create color channels. One problem with stacking is that the sky may move between photos. (It's called field rotation.) This can be corrected if the stack is aligned properly. While Photoshop has a number of automated stitching techniques available, I can't find any of these in GIMP.

I could manually align layers in stacks if I could reduce the transparency of one layer relative to the layer below it. Is this possible?

On Mon, Apr 17, 2017 at 5:30 AM Seldom wrote:

I'm an ex Photoshop user who does astrophotography (AP). In AP we frequently
shoot a number of photos that we then stack in layers to reduce noise or create
color channels. One problem with stacking is that the sky may move between photos. (It's called field rotation.) This can be corrected if the stack is
aligned properly. While Photoshop has a number of automated stitching techniques available, I can't find any of these in GIMP.

GIMP doesn't currently have an automated way to align images, but that doesn't mean that there aren't ways available in Free Software.

A commonly used option is a script that comes with the panorama stitching tool, Hugin: align_image_stack

You can read a little about using it (it's pretty simple) here: https://patdavid.net/2013/01/focus-stacking-macro-photos-enfuse.html#hugin-align-images