Author:
The operation calls the
Grayscale Morphology plugin by Dimiter Prodanov.
Example

Description
The operation closes the greyscale image with a structuring element. It
shrinks background holes in foreground regions and keeps
the original outer shape. It keeps background holes that have
similar shape as the structuring element or that can completely
contain the structuring element and eliminates others. A close is a
dilation followed by an erosion.