Gifs have binary transparency - a pixel is either 100% transparent or not at all.
PNGs have 8bit transparency - 256 degrees of transparency
To make transparency available to an image:
<right-click>->Layers->Add Alpha Channel
//if the option is greyed out, it's probably available already
To paint transparent use the eraser tool and turn the "Hard Edge" option on.
To make selections transparent: in the properties dialog:turn off the "Antialiasing"
option for the tool your using then delete the selected area in any normal way
if you're paranoid you could save your image as a gif and then open the gif and save
that as a png...if you're paranoid
If you're trying to enforce binary transparency on an existing image: mail me an
example of what you're trying - or If the above doesn't solve your problem...
sometimes it's nice to overkill...
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