anchor.diff:    2*size+1 gives the total width and height of the mask.
   "
     (let ((mask (if mask mask (apply #'generate-mask pattern))))
  -    (binary-morphological-filter image :or mask fill)))
  +    (binary-morphological-filter image :and mask fill)))
   
   
   (defun dilation-filter (image &key pattern mask (fill '(0)))
     "Returns a binary GRAYSCALE-IMAGE produced by a morphological filter
  -  with an AND operation on the given mask kernel.
  +  with an OR operation on the given mask kernel.
   
     The mask may be either specified by PATTERN or provided by MASK, a
     2-d array of (unsigned-byte 8) values set to 0 or 1.
  
positive.code: 
  (defun erosion-filter (image &key pattern mask (fill '(0)))
    "Returns a binary GRAYSCALE-IMAGE produced by a morphological filter
    with an OR operation on the mask kernel.
  
    The mask may be either specified by PATTERN or provided by MASK, a
    2-d array of (unsigned-byte 8) values set to 0 or 1.
  
negative.code: "
    (let* ((mask (if mask mask (apply #'generate-mask pattern))))
      (binary-morphological-filter
       (binary-morphological-filter image :or mask fill) :and mask fill)))
  
  
  
  