The Spine II
The spine of an 8-connected convex set is the set of cell (i, j) in
rectangle R satisfying at least one of the following conditions:
- ( nf ??j???sl OR wf ??i ? el ) AND Vj > Hi-1, Hi > Vj-1
- ( sf ??j???nl OR ef ??i ? wl ) AND Hi-1 > A-Vj, A-Vj-1 > Hi-1