GIMP: How does one use the smaller image in the layer above, to cut out the image in the layer below

Question

I'm using GIMP, and I have a smaller image in the second, above layer. I don't see a way / "Mode" that allows me to use this image to "cut a hole" in the image in the lower layer (matching the shape of the image above).

How do I do this? Thanks.

Answer 1

If the image above is on transparent background:

• with the top layer active: Layer>Transparency>Alpha to selection (this create a selection which is the exact shape of the opaque bits of the top layer)
• with the bottom layer active: Edit>Clear (make sure the layer has an alpha channel if you want the removed part to be transparent)

Answer 2

New answer for Gimp 2.10

In Gimp 2.10, there is an Erase layer blend mode that essentially makes the layer act as a cookie cutter for the layers below it. So if you want to cut a layer to a shape:

• Set the shape at the top, and set to Erase blend mode
• Add the layer to cut through below it
• Put these two in a layer group to restrict the cookie-cutter effect (otherwise it will act on all layers below)

If you want to keep the shape and cut the rest, there is no inverse equivalent of the Erase blend mode, but you use a subgroup to invert the opacity of the shape:

• Add a subgroup
• Put the shape layer in Erase mode at the top of the subgroup
• Add an opaque image-sized layer at the bottom (color indifferent, you just need all pixels to be fully opaque))
• Use the subgroup as the Shape layer in the solution above (so, this subgroup should also be in Erase mode)

The benefits of this technique over the 2.8 one is that changes in the shape layer have an immediate effect on the image without having to repeat operations. In particular, instead of having one shape layer in the group of subgroup, you can have several and toggle their visibility.

Even simpler solution: move the "shape" layer under the layer to cut, and set the Composite Mode of the layer to cut to Clip to backdrop. Put the two layers in their own group so that the "backdrop" is the group contents, and not the whole image. The previous solution may still have its uses in some cases.