Masks are one of those areas of Photoshop that you can happily ignore for years and yet still be perfectly productive. Once you start delving into them, though, they can open up a whole new world — a world where selections are easier to make, and where layers become much less cumbersome to work with.
Broadly speaking, masks in Photoshop are used for two distinct purposes. First, they can be used in the same way as selections, allowing you to work on selected areas of your image while masking off, or protecting, other areas from editing. This is a bit like using masking tape to protect areas that you don't want to paint on. Second, you can use them to hide unwanted areas of your image, while still keeping those areas available for later use or editing. Think of adding a sheet of acetate on top of your layer, then painting black onto the sheet.
Photoshop gives you various types of masks to play with, including Quick Masks, alpha channels, layer masks, vector masks, and clipping masks. Quick Masks and alpha channels are more commonly used to make selections, while the other types of masks tend to be used to hide areas of an image. It's important to remember, though, that masks are fundamentally the same, regardless of which use you put them to. You can use a mask as a selection one minute, then use the same mask to hide parts of your image the next.
This chapter takes you through all the different types of masks available in Photoshop, concentrating mainly ...