This is an excellent book for the serious photographer. It does give and introduction on how to use photoshop, but this book would suit you better once you have a grasp of photoshop first.
It is very well written with plenty of examples. I was dissapointed in that it did cater for the very beginner. So if you know your photography and comfortable with photoshop, this book is a must have.
It is written my people who know there subject abd it is well worth the money the money they are asking for.