Figure 3
From: Tracing retinal vessel trees by transductive inference
Notation on the skeleton pixels. Skeleton pixels are classified into the following three types: Body points – Pixels having 2 neighbors; Branching points – Pixels having 3 or more neighbors; Terminal points – Pixels having 1 neighbor, being either root or end pixels. A segment is thus defined as a continuous subset of skeleton pixels starts with a terminal/branching point, and ends with a branching/terminal point.