Fig 7. Pixels of a typical junction and three associated terminal points showing the counting of adjacent skeleton pixels.

Highlighted are pixels representing (i) terminal points at the end of the line or branch, each adjacent to only 1 pixel, (ii) contiguous points along the line, each with 2 neighbour pixels, and (iii) junction points where three or more branches meet, having 3 or more neighbour pixels. Similar to minesweeper games, the number of adjacent pixels determines the value of each skeleton pixel.