The Opacity controls the density or strength of the stroke. A value of 0 (%) effectively disables the slider and prevents the application of the mask, while 100 (%) applies the maximum amount. In most cases, the setting can be left at 100 (%).
The Flow setting controls the rate at which the Opacity is applied, with 0 (%) effectively disabling the application of the mask and 100 (%) being the maximum amount that can be applied per stroke to an area.
When the Airbrush option is enabled, provided that the mouse button remains depressed (or if using a pressure-sensitive pen, the nib remains in contact with the tablet surface), the opacity will reach the value set, including any selected Hardness or feathering (i.e. to the outer edge) of the brush.
As an example, when the Opacity is set to 100% and 20% Flow is selected, 20% of the opacity of the mask is applied per stroke until the maximum 100% level is reached. This can be achieved through additional strokes (four more in this instance), or when the Airbrush option is enabled through continued pressure of the mouse or pen. No number of strokes or pressure after that can increase the Opacity beyond 100%.
- Select the Brush icon in the Layers tool or from the Cursor toolbar.
- Click on the Brush Settings button (slider icon) or Ctrl/Right-click anywhere in the Viewer for quick access. The Brush Settings panel opens.
- Adjust the opacity of the brush stroke; drag the Opacity slider to the right to increase the amount. You can view the effect on-screen in case the option to view the mask is enabled.
- Adjust the rate or Flow slider as required.
- Drag the cursor on-screen to start applying the mask to the layer (unless selected, an Adjustment layer will be created).
- To draw a perfectly straight line, hold down the Shift key and draw.
- To draw a straight line between two points, click on the first point, then release and Shift-click on the second.