LÖVE

Well, due to my limited english skills i really don't know if "translucent" is the right term... I'd like to "select" a color (like i do for transparent color with irfanview) when saving a .png file so that every gradation from transparent to translucent is displayed by love with decreasing transparency... Anti-aliasing? Like Jasoco's font used to display bombs/arrows... Is there any "free" program that a windows-user like me can download to make this happen?

I'm not sure I understand you. Translucence is a very similar effect to transparency: transparent means you can see everything behind it though tinted to this colour; translucent means you can see light (and so rough shapes) behind it.

What I think you are saying is that you want to be able to pick a background color that will be removed from images and treated as alpha: for example, pink used as a background color on a spritesheet. That said, I don't know how to do this. So.. I'm not much help.

Uh, nope... I can already do that... I want to make sprite border anti-aliased, instead of rough... Uff... I have the concept in my mind, but i can't explain it! What an horrible sensation...

AFAIK, LÖVE can do full-screen antialias, but I'm not really sure if that's what you want. In any case, such feature can be enabled using the config file, by setting the fsaa parameter.

I think what you mean is translucency, which is IIRC having each pixel have RGBA values, for that you need a good (free ) image editor. For example the GIMP or Inkscape. (And yes, you can use them on Windows. )

Yes, that's what i was looking for! Thank you!