Imagine an image with a free selection with Antialiasing on + Feather edge pixels, copy and paste to new Layer(top), set the top Layer mode to something like Clear/Erase.
I wonder if the following is not possible at all -even with individual pixel adjustments- or technically not possible for a program to automatically predict the desired result?:
I'm looking for a way to extract the difference as a single piece of graphics which I could use like a puzzle stone to get same background image again out of these 2 parts.
Explanation with help of my 4 pictures example collection below:
Picture 2 merged with Picture 3 must together look like the original image(bottom picture 4)
So basically add to the -individual pixels different alpha values- of that red marked border zone(top picture) the appropriate reversed difference of "individual pixel alpha values" from original image pixels to get a 1:1 copy of the original image as result.