http://www.douglas-jones.com/ppd.exe
now has a powerful new featu

I added a new button "Edit Alpha Mask".

Alpha channel's controlling factor is intensity, so for best results
one should edit using levels of gray as the selected colors.
Black = totally opaque.
White = totally transparent.

Download and have fun.

Doug

ppd.exe is a stand alone program for editing images.
No install needed. It's very small, about 253k bytes, so put it almost
anywhere on your computer,
BaumBadier suggested one could even take it along on a memory card.