15.5.177 erode

erode(image [, /zeroedge])

Returns a copy of the two-dimensional numerical array image which is eroded using a 3 by 3 square mask. Only the properties "equal to zero" and "unequal to zero" of the data values are regarded. If any of the nine data elements centered on the element of interest are equal to zero, then a 0 is returned for the element of interest, and a 1 otherwise. On the one-element-wide edges a 1 is returned if the element of interest is unequal to zero, or a 0 otherwise, except if /zeroedge is specified, in which case the edges are always set to zero.

See also: dilate