When Aperture was released by Apple, they also released a great PDF e-book called “Digital Photography Fundamentals”. I printed it off a few days ago and read through the whole thing with a pen in hand. I learned quite a bit about bit depth, the differences of the file types, the way that color is shown through different mediums, etc. My copy is quite marked up and should serve as a great reference.
I admit that I am a beginning photographer, but I do feel comforable with advanced tech terms and examples. This document was full of great information, and Aperture is only plugged a couple times. I enjoyed it quite a bit more than the usual books for beginners that seem too simplified.
You can read the document here, or right click to save it to your computer.