0 0 0 1 1 1 Structuring element used 0 0 0
chouse the image $MMACH/viff/keyb.xv;
perform the negation of this image;
perform the dilation of the input image by a flat structural element;
reconstruct the negation of the input image from its erosion;
subtract the input image from the reconstructed image;
apply a threshold to the last image.