NIH has (or had) a public domain photo enhancement/analytic package that is (or was) free for the download. It was originally Mac-based, so it's pretty intuitive. I think it's name is "NIH Image" or some such.

It has been ported to PC's.

The source code is also available and so a lot of commercial packages ripped the analysis stuff. But it has analytical lingo rather than Photoshop lingo. But you can get used to it just by playing around with the commands.

I just searched for it and came up with this.

http://rsb.info.nih.gov/nih-image/Default.html