Determining the critical point of a ST . a) A and C represent the constituent pixels of an arc and a chord of an example ST, and the ring indicates the initial splitting point. b) Indicates DA where all zero elements in blue are seeds and all other elements are neighbors whose values are set based on the chessboard distance to their nearest seed. c) Illustrates DC with zero elements as seeds and neighbor elements. d) DM, which is obtained by adding the matrix in b) to the matrix in c).