This tool samples the pixel at the center of its tip and uses it as a color key to make pixels similar to it that are within the tip transparent. When used near but outside an object, it has the effect of erasing the background around that object without affecting the said object.
To use this tool, just hold down the left mouse button and drag the pointer such that the tip area runs over the boundary of the object and the center of the tip stays on the background as shown below:
To clean and refine the edges, use the “Clean” option of the Edge Treatment Tool .
This tool is pressure sensitive when using a graphics tablet; the pressure varies the width of the tool tip.
This tool samples the pixel at the center of its tip and uses it as a color key to make pixels similar to it that are within the tip transparent. When used near but outside an object, it has the effect of erasing the background around that object without affecting the said object. 
