This note describes the rules used for the ``binary thinning'' which is applied to the edge images (found using the SUSAN edge detector - see [9] or [8]) after non-maximum suppression has taken place. The rules are simple and quick to carry out, requiring only one pass through the image. Similar text originally appeared in Appendix B of [7].
Much work has been done on the thinning of ``thick'' binary images, where attempts are made to reduce shape outlines which are many pixels thick to outlines which are only one pixel thick. (For examples and reviews of work on ``skeletonization'' see [6], [4], [1], [2] and [5].) However, because of the non-maximum suppression which is applied before thinning in edge detectors such as SUSAN, this kind of approach is not necessary.