Thx for the info. It looks like you've done your homework well.
You might be right about the S3TC-format... it is very similiar, if not the same. I have not tested yet, but it may very well be that it is handled exactly like that. I'm goin' to try it's color calculation method out. If it works, we've got one of the biggest problems off our hands, thanks to you.
That hint on txi-format does make sense. However some of the files do not simply have text at it's end, but an additional number of bytes beforehand, I don't know how to deal with, since the Image ends sooner. Something to research after the color calc. mehtod has been proven right. From looking at the S3TC-format info, it defenitley looks good.
BTW, there's also a 16 Byte - Model described in the ST3C-info I found, and it looks like it also matches up.