I did this and it works pretty well now, and it isn't that slow. My only
problems right now is not from pygame but from PIL, which raises
exceptions sometimes when it doesn't like the image it is loading, for
ridiculous reasons like 3 bytes missing. Anybody can recommend other
libraries that will let me do high-quality resizing?
Pygame can do filtered "proportional" scaling with the
pygame.transform.rotozoom() function. This does good quality resizing, but
doesn't let you alter the aspect ratio (aka the proportions). If you are
already using PIL you can load with pygame and send to PIL with the
pygame.image.tostring() function.