While on last week's MacMania cruise, my wife and I had two scuba dive days. (We're both occasional (at best) divers, and took a refresher course before leaving Portland.) I took along my aging-but-still functional Canon PowerShot S30, mainly because we have a 100' underwater case for it (there's a picture of the case in the linked review). Now, I'm far from a good underwater photographer, as the evidence will show -- this was actually only the second time I've been able to take our Canon out diving, so maybe I'll improve with experience.
One thing about shooting underwater is that you lose a lot of color -- red, in particular, gets filtered out, even with a flash. So there's lots of post-processing involved using the tool of your choice. I switched between iPhoto and Photoshop, but it's a tedious job. It seems you have to play with the color balance, saturation, brightness, contrast, etc. in every image to make them look their best.
Then, on the last day of the cruise, during the last session of the day, O'Reilly's Derrick Story passed along, almost in passing, an amazing tip ... one that I wish I had known many editing hours earlier. Derrick takes a lot of photos while snorkeling, and admits to having tried just about every kind of post-processing tool he could find to work with the images. Through all of that, he's discovered the best way to fix underwater images is to do this:
Click the Enhance button in iPhoto!
That's all there is to it. I tried it on the 200ish images I shot during our dives, and it really does a great job, as you can see by the before/after image to the left of this hint. (If you prefer, I created 800x600 versions of the before and after images, so you can see just how the image was adjusted.)
As Derrick pointed out, it seems that the author of the Enhance feature is an underwater photography buff. Note that there were a few images where this worked very poorly, but those were the rare exception rather than the rule. Thanks, Derrick, for the wonderful timesaver!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061106143338736