Brushes are one of Aperture's most powerful features. Brushes are thought of as being Aperture's way of performing selective adjustments, but a better way to think of them is as a way to mask individual adjustments. As one can have a great number of adjustments, each of these adjustments can be masked so that they only apply to a portion of your image.
You can add a brush mask for almost any adjustment, with the exception of the RAW Fine Tuning brick and the Exposure brick. See the following steps:
To add brushes to an adjustment we need to carry out the following steps: