There is a lot of non-image data which is probably being compressed.
But I also suspect:
- mostly uncompressed media
- even if media is compressed, most games group stuff into large files which hold this compressed media, which usually have a lot of redundancy in them (long bits of null padding, structure is almost never compressed)

I can't say that there's a lot of compression across images, if they're already compressed, because entropy coders can affect the output a fair bit, even with a small change in input.  But it's still possible nonetheless.

And PNG is based off deflate, which you can usually compress a tiny bit more using better compression algorithms.  JPEG is probably in the same boat here.

(This post was last modified: 31/08/2010 10:49 PM by ZiNgA BuRgA.)