I used an archaic copy of Photoshop 5 which I got for dirt cheap($20) since I can't have illegal software on my work laptop
Can't remember the exact command(on a different laptop - have 5 for work), but it is a 1-click autolevel adjustment that adjusts for color & contrast levels.
Often the auto-level function "over-corrects" so I have gotten much better at manually adjusting the levels, but it is rather time-consuming. I usually auto-adjust to see the potential of a given photo then work from there.
