// AnnularDilation
// uses Gray_Morphology plugin
// G. Landin at bham. ac. uk
// 11 Sep 2010

k=getNumber("Annulus diameter", 15);
c=floor(k/2);
kernel=" ";
for (y=0;y<k;y++){
  for (x=0;x<k;x++){
   d=sqrt(pow((y-c),2)+pow((x-c),2));
   if (d<=(k/2) && d>(k/2)-1)
       kernel+="255 ";
   else
       kernel+="0 ";
  }
}
print (kernel);
run("Gray Morphology", "radius=1 type=[free form] operator=dilate text1=[ "+kernel+" ]");