What is Quick Mask?
The Quick Mask tool is not a tool per se, but rather a mode you can enter when you are creating selections. Through this tool, you can isolate areas in a layer you are working on, giving you greater power in using Photoshop. How exactly does the Quick Mask work?
When a painter has to paint a room in a house, the masking tape is an essential tool. If he has to paint the window frame, he puts on masking tape around the area he wants to paint, paints the frame, removes the tape and the glass is paint free. If he wants to paint the door frame, he does the same thing and the rest of the wall remains untouched.
In essence, the Quick Mask works the same way, it's like digital masking tape and assists in getting a good transition between the areas which are selected, and which aren't. Remember the anti-aliasing and feathering features of Photoshop we mentioned in part 3 of this tutorial series? Quick mask works almost the same way, but the difference is that it is more powerful than any of these features. If you want to change a photo's background, or modify areas on a photo without affecting other areas, then this is the tool to use.
Back on the tools panel, at the very bottom (see photo on the left - click any image to enlarge), you will see two view options. The one of the left is the normal view - the standard page you see when you open a photo for editing. To enter the Quick Mask mode, you need to click the icon on the right (encircled in red) or you can press Q to get in and out of this mode.
The difference between Quick Mask and other selection tools such as Marquee and Lasso tools is that it lets you make complicated selections. It is better than the Magic wand tool because you can make selections by changing the opacity of the edges.