`Select > Sharpen` "grows" the selection
Environment/Versions
- GIMP version: 2.99 (commit 47a56cf6), also on 2.10.32
- Package: Self-compiled
- Operating System: Kubuntu 20.04
Description of the bug
It is expected that "Select > Feather" followed by "Select > Sharpen" restores more or less the same selection. It did until 2.8 inclusive, but in Gimp 2.10.32 and 2.99, it no longer does. Instead the selection is thresholded at a wrong value
Reproduction
Is the bug reproducible? Always
Reproduction steps:
- Create a 400px wide image (Image precision and gamma seem irrelevant)
- Place a vertical guide in the middle of the image (x=200)
- Make a rectangle selection on the left half of the image, with one side along the guide. The "ants" will be marching along the guide
- "Select > Feather" by 100px: The ants are still along the guide (because AFAIK the feathering is symmetrical around the edge of the initial selection, and the initial selection border is where pixels are 50 selected, which is what is indicated by the ants).
- "Select > Sharpen"
Expected result: The ants remain on the guide, at x=200 (this is what happens in Gimp 2.8)
Actual result: The ants are no longer along the guide, and are around x=223.
Repeating the feather/sharpen cycle shifts the limit 23px at each iteration.