So far, we've been learning about primary color corrections. These are corrections that affect the entire image. However, very often you only want to affect a certain range within an image, whether it's a certain range of colors or a certain physical area of the frame. Correcting or grading a limited selection within a clip is known as secondary color correction. FCPX's secondary color correction capabilities come in the form of color masks and shape masks.
A shape mask allows us to isolate a region of the frame and make adjustments to it. It is often used to make exposure adjustments on an interview subjects' face if they were poorly lit, for example.
A color mask allows us to isolate a color (or more likely a range of color) and perform adjustments on just that selection. We'll learn about both of these types of masks in the following two recipes.