What are those alpha pictures for?

[Masterlegodude]

On the TGE Demo, they got name.alpha.jpg's of some textures, and they're black with white on them, why is that, and what do they do?

[Ad Bot]

[Space Guy]

Different game engine, same concept: Alpha Masks

Basically, it's to make the edges of a texture partially transparent and blend it with the background so .jpgs and other images with odd-coloured AA "borders" don't show up with a blocky white halo around them.