@article{NSJOM_1990_20_2a_3,
     author = {Crombez G.},
     title = {Group theoretical methods 

 in {Gray-scale} mathematical morphology},
     journal = {Novi Sad Journal of Mathematics},
     pages = {31-41},
     publisher = {mathdoc},
     volume = {20},
     number = {2},
     year = {1990},
     url = {http://geodesic.mathdoc.fr/item/NSJOM_1990_20_2a_3/}
}