Parallel thinning with two-subiteration algorithms

Two parallel thinning algorithms are presented and evaluated in this article. The two algorithms use two-subiteration approaches: (1) alternatively deleting north and east and then south and west boundary pixels and (2) alternately applying a thinning operator to one of two subfields. Image connectivities are proven to be preserved and the algorithms' speed and medial curve thinness are compared to other two-subiteration approaches and a fully parallel approach. Both approaches produce very thin medial curves and the second achieves the fastest overall parallel thinning.