Algorithm 1 Magnetic Ring Location Algorithm

1: Given a grayscale torus image $H\in R^{M\times N}$.

2:  Use sub-region gray threshold segmentation to obtain a binary image $G_{\mathrm{h}}$.

3:  for I = 0, …, M do

4:     Scan $G_{\mathrm{h}}$ from top to bottom.

5:     Count the number $\delta$ of black dots.

6:     if $\delta >T_l$

7:         Get the up position $up=i$.

8:     end

9:  end

10: for I = 0, …, M do

11:   Scan $G_{\mathrm{h}}$ from bottom to top.

12:   Count the number $\delta$ of black dots.

13:   if $\delta >T_l$

14:     Get the down position $down=i$.

15:   end

16:  end

17: Output the location result $up$ and $down$.