Ebook: Photoshop Masking & Compositing

This book is getting a little outdated, but many of the techniques are still very much applicable for CS5. You will be a master of channels and selections after going through all of the lessons in the book. I am an Adobe Certified instructor and use this book to teach an Advanced Photoshop class. I highly recommend this book, even as Photoshop gets better with selection tools, it's always good to know the "old school" techniques. They come in handy when the fancy new tools don't work (which happens quite a bit).