Jpeg > A8R8G8B8 > save in which ectension?

[cocopascal]

I have jpeg photo's which are converted to A8R8G8B8 because I need an alpha channel. In which extension should the resulting image be saved so quality is preserved best? Or should I convert to another format?

[Galfar]

PNG would be the best I think (it's most widely supported).
You can try JNG (than's Jpeg with alpha channel - if you want to keep the file size very small) but not many programs support it.