Creating an "opposite" image

[Krikor]

My understanding of Sally's steps:

1- Colors - Invert;
2- New layer, fill it black;
3- Put this layer to the bottom;
4- On the top layer, make Alpha for selection;
5- Merge the two layers;
6- Delete the selection;

I believe there could still be an under-understood step:

7- With the fuzzy select tool, select and remove the black external area.

My understanding of the steps taken by PixLab:

1- Alpha for selection; (layer #01)
2- Select - Remove holes;
3- Create a new layer (layer #02) and fill it with black; (selection is still active).
4- Select None;
5- Select the first layer (Layer #01) - Alpha to selection;
6- Select - Grow = 1;
7- Disable the visualization of this layer;
8- Select layer #02 - Delete.