Further considerations of a 1-subcycle parallel thinning algorithm

In this paper, we present two improved versions of a pseudo 1-subcycle parallel thinning algorithm which we proposed earlier [1] and describe a twostage structure to realize the 1-subcycle parallel algorithm. The purpose of the first improved algorithm is to produce the P8ET (perfect 8-curve excluding T-junction)-type thin line which is well-defined in general. This algorithm involves local branches containing T-junctions or quasi T-junctions. The second improved algorithm obtains an isotropic skeleton of an L-shape pattern, such that the visual quality of a skeleton is more satisfactory. In this algorithm, another set of thinning conditions especially designed is also involved. We also describe a two-stage structure which consists of a thinning table and a control unit. The thinning table is used to provide the attributes of an input 3×3 local pattern. The control unit is used to check the removal of the center "1" pixel of this local pattern. The inputs of the control unit also comprise the outputs of other neighboring thinning tables. This structure can exactly implement the original 1-subcycle parallel algorithm. The above-mentioned algorithms have been implemented on this realized structure in this paper. Several experiments confirm that the improved algorithms can produce the desired effective thin line, and also show that the realized structure is feasible and practicable.