In Photoshop, brushes are much more than a tool for painting a drawing. Many tools (including the quick select tool, clone stamp, eraser,etc.) use brush mechanics and concepts to operate. A brush is made up of 3 components: size, hardness and a preset shape.
Size and Hardness
Size and hardness can be manipulated in multiple ways. The most accurate is through a dialog box on the left most side of the options bar signified by an image of the brush preset with a number below it.
Brush size is measured in pixels and relates to the diameter of the brush.
Brush hardness is the edge shape of the brush preset. This is generally a blending tool which allows for the pixels of the image or content behind the brush strokes to combine with the content of the brush.
Using Retouching Brushes
Not all brushes are used for adding color over an image. In fact, many utilize the pixel information present in a image to make corrections or alterations. When you make alterations to an image, it is always a good idea to place them on a new layer as to give yourself flexibly to remove them in the future. Lets get some context with an example:
The Healing Brush
This is an incredibly robust tool that combines algorithms and user input to create content within a brush head. It is a great tool for retouching and cleaning up photographs that have small to midsize blemishes. A key component of this tool is the Option-Click command. Option-click allows a user to create a source point from where the computer algorithms will create similar, blended content within the brush space.
The healing brush is one of many retouching tools. If you are interested in retouching tools, please attend a workshop or look at the Additional Resources page.
Creating a brush preset
Brush presets are the foundation of any brush. A brush stroke is basically a rendering of a multiple stamps of the brush preset over distance and time. While these and other factors are fully controllable, a good brush preset is the backbone of a good brush. Learn how to make one with this video: