Postprocessing with alpha background

Hello, I am at war with the post production. My intention is to create animations with effects such as glare node with transparent background (the goal is make post produced atlas animations for a 2D game and convert the frames on gifs to put over a web). It’s like to put the render result with alpha over on a background of solid color made with … pfff Paint for example, and to the result, take that color with the tool “convert color to alpha” of GIMP, leaving the glare as transparent gradient. But if Blender do this by itself would save me a lot of time xD.

For now, when I try to do this, I think that blender applies a mask to apply transparency in areas where there isn’t mesh, so that the effects of postprocessing are hidden behind the mask. :’(

Sorry by my poor english (?) xD.

Thanks :slight_smile: