I have tried many ways using a layer mask (such as this one) to accomplish this but could not get the result I expect. I have this image:
I would like to make the square outline semi-transparent say alpha=0.5 but leave everything else unchanged. The steps I took were:
- open image in GIMP
- duplicate layer
- add layer mask initialized as black
- select upper layer & use magic wand to select the gray square outline
- select layer mask & use bucket fill tool to make selection gray (#7f7f7f)
But the outline remains solid gray instead of 50% opaque gray. Why is that & how can I get the result I want? What am I missing? Thanks