TLDR: Does anybody know a (preferably free) tool that is capable of properly editing PNG files with an alpha channel?
The long story:
I strived for creating some achievement icons for the new achievements recently added to Bionic.
What I planned to do is extract a section of the appropriate size of the Exo portraits available with the game and maybe tinker with their colors a bit.
Problem is that I would like to copy a section of the original image which contains pixels that are set to be completely transparent. I can copy the respective piece just fine, but unfortunately the alpha channel of the pixels does not seem to be copied as well, leading to the unwanted background being visible.
So what I would need is a tool that either allows me to edit these pixels back to fully transparent or, even better, takes care of properly preserving the alpha channel when copying data.
Usually I am doing my image processing stuff using XnView. But in this case I seem to have left its feature scope.
Any tools out there you can recommend?