Specifies the area to be filtered in the input image.
This parameter can be set by specifying a window size or a bitmap mask channel.
A window mask is specified as follows:
MASK=Xoffset, Yoffset, Xsize, Ysize
Xoffset and Yoffset define the upper-left starting pixel coordinates of the window. Xsize is the number of pixels that define the window width. Ysize is the number of lines that define the window height.
If no bitmap is specified, the entire layer is processed.