EdgeOutline is a tool to create the outline of the alpha of the main input. I found myself several times using this technique or a similar one, so I decided to make it into a tool to allow me to be faster and more efficient.
You can select the way you want to detect your edge and then play with the rest of the values to get what you want. You can also connect a mask to apply it just to one area, or use the Enable Remove button to get an extra input that lets you cut off an area of the final result.
Expand EdgeOutline