On Digital Photography (O’Reilly, $40) is a book by photographer Stephen Johnson  that discusses digital in depth — covering its history, the underlying technology, and techniques for achieving better photographs.
As CNET’s Stephen Shankland describes the book: 
Johnson’s perspective has the benefit of history–he’s been guiding Adobe on Photoshop since the product’s inception and has been deeply immersed in digital imagery since the days when that meant scanning film. And he’s paid his pioneer dues: in a 1994 project to digitally photograph U.S. national parks, he’d have to stay awake into the wee hours offloading images from his camera’s hard drive onto tape so he’d have room for the next day’s shots.
On Digital Photography isn’t for the casual snapshotter.
Johnson’s guidance tends toward higher-end matters such as duotones, histograms, archiving, high-dynamic-range images and color-space considerations of printing. When it comes to the book’s practical advice, the ideal audience are people who devote a lot of time and money to photography. Even then, exercise caution: some sections of the book are relatively timeless, but others involving fast-moving technology, such as image repair or raw image processing, are in danger of being rapidly dated.
With those caveats, On Digital Photography  is worth a look.
[tags]On Digital Photography, photography books, scott baradell[/tags]