Can't use Color to alpha on that one

[Ofnuts]

(05-16-2024, 06:57 AM)rich2005 Wrote:

(05-16-2024, 06:27 AM)PixLab Wrote: ...snip...
Although I cannot find out where is that selected pixel...

As you say back to basics

Grow the selection a suitable amount, fill the selection. Look at the center.

For a single small area: Image > Guides > New guides from selection, (with two areas, look in the corners, above two, no joy).

My personal technique: Select > To Path and ofn-path-edits > Path summary gives one line per selected area.