Hi we had some problems with sprites, where the borders where looking ugly so we made a tool that bleeds the colors of the opaque pixels into the transparent ones, the pixels that are not 100% transparent are not changed, but the transparent pixels get the color of the neighouring pixels. This fixes the interpolation error that usually happens in those pixels.
The tool does this
the left image is the original one rendered over a red background, the middle one is the result with alpha disabled, and the right one is the result image rendered over a red background with alpha enabled.
The projects is available here: https://github.com/gemserk/imageprocessing
and there is a runnable jar in the downloads section.
If you have any question feel free to ask.