You probably have the wrong idea about what the script does. As the name it creates a layer mask on the active layer using the layer above.
It is just a shortcut, you can do it manually by making a layer mask, then copy and paste from the layer-above (or any other image) into the layer mask. The script saves a few key-stokes and can be useful in certain circumstances such as adding decorative borders.
As an example in a Gimp 2.8
1) Starting off with this image
2) Duplicated the layer which will eventually become the layer mask
3) Manipulate that layer somehow. Might apply threshold for example or something else.
4) Which results in a layer above for the script.
5) Apply the script with the original layer active.
6) It creates a layer mask
7) Set layer visibility's to suit and maybe a little touch-up in the layer mask.
Give some clue as to your requirements and there might be other ways.
Edit: Is it adding a frame / border to an image ? Something like this https://i.imgur.com/UA3RTd0.mp4 ( a bit rough-n-ready - 30 seconds)
It is just a shortcut, you can do it manually by making a layer mask, then copy and paste from the layer-above (or any other image) into the layer mask. The script saves a few key-stokes and can be useful in certain circumstances such as adding decorative borders.
As an example in a Gimp 2.8
1) Starting off with this image
2) Duplicated the layer which will eventually become the layer mask
3) Manipulate that layer somehow. Might apply threshold for example or something else.
4) Which results in a layer above for the script.
5) Apply the script with the original layer active.
6) It creates a layer mask
7) Set layer visibility's to suit and maybe a little touch-up in the layer mask.
Give some clue as to your requirements and there might be other ways.
Edit: Is it adding a frame / border to an image ? Something like this https://i.imgur.com/UA3RTd0.mp4 ( a bit rough-n-ready - 30 seconds)