You can retouch mattes with the paint tool.
A new internal layer has an empty, black layer matte. An external layer's alpha contains the matte information of the incoming image.
Painting on the alpha of an internal layer is accomplished in one of two ways: implicitly or explicitly. Implicit alpha strokes are added when you paint on the layer front. For every stroke added to the layer front, a corresponding stroke is added to the layer alpha. Explicit alpha strokes are added when painting directly on the layer alpha.
Painting on the alpha of an external layer can only be accomplished explicitly. When you add strokes to the layer front, corresponding strokes are not added to the alpha.Strokes added explicitly to the layer alpha will be visible on the layer front (nor in its proxy) in composition view when you commit the stroke(s).
Pen to be removed from image shown in the alpha and the comp.
Unwanted areas can be removed from the image by painting on the alpha of the image.
