Shoutbox

by default it's set to a bitmap image (.bmp) Leaving that saves the image with full quality. Selecting the other options on the list alters the compression/quality according to the filetype, For example, when you save it as .gif, it has like dots on  the image.

When you select something from a list, it doesn't add the .xxx extension. If you do it manually, it'll save with bmp quality but as another type.