• Shape — specifies the shape of the brush tip. You can create a rectangular, elliptical, or angled brush tip by starting with the round or square shape and modifying it with the Thickness and Rotation options.

• Size — determines the size of the brush in pixels. You can adjust the Size value by using the keyboard as well as by setting the Size control in the Tool Options palette. For more information, see To adjust the brush size by using the keyboard.

• Hardness — determines the sharpness of the brush edges. A setting of 100 produces the sharpest edge; lower values produce an increasingly softer, fading edge.

• Step — determines the time interval that elapses between applications of paint, with each application defined as a single, continuous brushstroke. Lower values produce a smoother, more continuous appearance; higher values create a choppier appearance.

• Density — determines the evenness of coverage produced by the brushstroke (or for the Eraser tool, the evenness of the erasure). Higher values produce more even coverage; lower values produce spottier coverage, which resembles a spray-painted effect. When using the Airbrush tool, you should set Density to values lower than 100.

• Thickness — determines the width of the brushstroke. A setting of 100 produces a brush tip that is completely round or completely square, depending on the Shape setting. As the Thickness setting decreases, the brush becomes increasingly narrow.

• Rotation — applies rotation to a noncircular brush tip

• Opacity — determines how well the paint covers the image surface. At 100% opacity, the painted brushstroke completely covers the surface beneath it. At 1% opacity, the paint stroke is almost completely transparent. For the Eraser tool, this setting determines the level of erasing, so that a setting of 100% produces the most transparent result.

• Blend mode — determines how painted pixels are blended with pixels on underlying layers. The blend modes are the same as layer blend modes. With the Paint Behind blend mode, for example, painting is done behind the image on the active layer. No paint is visible when the topmost layer and the active layer are both fully opaque. For more information about blend modes, see Blending layers.

• Rate — determines the rate at which the Airbrush tool applies paint (from 0 to 50). A value of 0 applies a consistent amount of paint even when the speed of the brushstroke varies. Higher values apply more paint when the brush slows down or pauses.

• Stroke — lets you build up paint on existing paint strokes that were applied with the Continuous check box marked. If the Continuous check box is not marked, or if the check box is marked but no strokes have been made, the Stroke button is grayed (unavailable).

• Continuous — specifies whether paint builds up when multiple brushstrokes are applied over the same area with opacity set at less than 100%. If this check box is marked, painting produces a continuous color, and repainting an area has no effect. To repaint an area, you must click the Stroke button. If the Continuous check box is unmarked (the default), each brushstroke over the same area applies more paint; the color darkens until it reaches 100% opacity.

• Wet Look Paint — mimics wet paint, with soft color inside and a darker ring near the edge. The effect is more visible with lower values for the Hardness setting.

• Smart Edge — uses content-aware technology to sample the brush stroke area and apply a brush stroke only to areas that match the underlying pixels. This makes it easier to apply brush strokes to or around specific elements in your image. For example, you can use Smart Edge with retouch brushes, such as the Dodge, Burn, or Sharpen, to help you edit specific areas of the face, lips, or eyes. Note: Enabling Smart Edge can affect the brush speed.