Well, I looked at the thread, and thought about it a while... then went back and reread it.
It looks like it supports .jp2 files... if you happen to be a hacker and can fix the bugs with it. Oh, and you have a Windows machine. Which... I don't.
Now, it's possible that I haven't properly digested the implications of the discussion. I am not a programmer, and am a step up, perhaps, from a super-user. Sure I have studied some basic programming, even written a few programs... but apparently not enough to help with this.
However, things get easier now that my computer knows how to view these images.
I can strip out individual files from the archive, then open them with Kview to save them in a pcx format, which, hooray(!), my version of GIMP can read. I don't know how much loss one gets from doing that, but it looks good from my initial test. As an added bonus, my system doesn't act like it's digesting a particularly large meal.
I didn't want to try a standard JPG, largely because ginormous files in JPG have lots of cpu overhead, and can cause... problems. Hence, why jp2 was created in the first place. I was thinking of TARGA format, too, because I have heard that it is supposed to be good for large cumbersome files, but I have never tried it.
Ooops, sorry about the (possible) drift. Should I start a new topic before going on a rip about file formats?
If so, I can install a link here in case others want to follow the progression.