3x3 decomposition of circular structuring elements

@InProceedings\{VaV1996,
  author       = "Maria Vanrell and Jordi Vitria",
  title        = "3x3 decomposition of circular structuring elements",
  booktitle    = "IEEE International Conference on Image Processing (ICIP 96)",
  volume       = "3",
  pages        = "5--8",
  month        = "Sep",
  year         = "1996",
  publisher    = "IEEE CS Press",
  address      = "Laussane (Switzerland)",
  url          = "http://cat.cvc.uab.es/Public/Publications/1996/VaV1996"
}