Edge Composite automatically generates an edge matte from an existing alpha channel and allows you to color correct or blur only the edge of the foreground. You can also mix the edge of the foreground with the background. This is very helpful for seamlessly integrating images as well as dealing with aliased mattes.

Composite.

Determines the size of the edge matte.

The edge of the foreground can be color corrected. Go to the Color Correct node to see how the Color Correct controls work.

The edge of the composite is blurred by a fast, quality blur along the X-axis, but only in areas of the edge matte.

The edge of the composite is blurred by a fast, quality blur along the Y-axis, but only in areas of the edge matte.

The horizontal and vertical values can be ganged together.

Mixes the foreground back to the background, but only in areas of the edge matte.