Experimented a bit.
A manual process to bevel but it works. Would be nice to automate it possibly using a BgraBmp.
Brightness Relief of Bevel can be set with a TSpinedit.
I found:
If the edges are bright, bevel the Right and Bottom and the rotate 180 degrees and bevel again.
If the edges are dark, bevel the Left and Top and the rotate 180 degrees and bevel again.
The rotation of 180 degrees is quite slow.
Some dark bevel joins at the corners seem to have a 1 pixel white gap at the mitre.
The resulting beveled pngs are what I was after in effect.
Tried to automate the process and got crappy results.
Also tried sampling the brightness of the edges automatically, but that did not work as expected
(but the manual process did work)