@article {15235,
	title = {Centers of sets of pixels},
	journal = {Discrete Applied Mathematics},
	volume = {103},
	year = {2000},
	month = {2000/07/15/},
	pages = {297 - 306},
	abstract = {The center of a connected graph G is the set of nodes of G for which the maximum distance to any other node of G is as small as possible. If G is a simply connected set of lattice points ({\textquotedblleft}pixels{\textquotedblright}) with graph structure defined by 4-neighbor adjacency, we show that the center of G is either a 2{\texttimes}2 square block, a diagonal staircase, or a (dotted) diagonal line with no gaps.},
	keywords = {Center, Chessboard distance, City block distance, Intrinsic distance, Simply connected set},
	isbn = {0166-218X},
	doi = {10.1016/S0166-218X(99)00248-6},
	url = {http://www.sciencedirect.com/science/article/pii/S0166218X99002486},
	author = {Khuller, Samir and Rosenfeld,Azriel and Wu,Angela}
}
