Algorithm 2 Algorithm for straight index finger detection.

Input: range of $\theta$ as ${\theta }_u$ and ${\theta }_l$

Input: range of $\gamma$ as ${\gamma }_u$ and ${\gamma }_l$

Input: index finger joints as $I=[I1,I2,I3,I4]$

1: for i each joint of index finger do

2:  for j = 0 to 180 do

3:   compute $I\left[i\right](Z,Y)$ as the Hough transform of each j degree $⟶H_t(\gamma ,\theta )$

4:  end for

5:  calculate intersection of $H_t(\gamma ,\theta )$ and ${\gamma }_0$$⟶({\gamma }_p,{\theta }_p)$

6:  if ${\theta }_u<{\theta }_p⩽{\theta }_l$ and ${\gamma }_u<{\gamma }_p⩽{\gamma }_l$ then

7:   set index finger straight

8:  else

9:   set index finger not straight

10:  end if

11: end for