fig2

Figure 2. An example of judging detection IoU of human surgeon. The standard answer for common bile duct is “d4:e5” (shown in the blue rectangle with shadow). If the surgeon chose an answer(s), which could not form a rectangle, such as choosing e2, e3, f3, d4, and f4 (shown in yellow tick) simultaneously, it was converted into the horizontal rectangle to include the answer(s) below. Therefore, the IoU would be {[Intersection (shown in green shadow)/Union = 1/9 ≈ 0.111]} in this circumstance.