Channels & Masks Video Lesson 8: "Found Masks"
In Lesson 8 from Photoshop CS4 Channels & Masks One-on-One, Deke proves that not all masks require arduous, meticulous hand work and complicated sets of steps. (I know, I can't believe this is our same Deke, either.) Here, Deke gives your brain (and fingers) a bit of a rest by showing you how to use "found" channel information to create masks with very little effort. This example uses the same image to create both a density and luminance mask by repurposing channel information almost pixel-for-pixel. If you like what you see, there's more in Lesson 8 of the book, including other found masks like edge masks, depth masks, corrective masks, and color-based masks.