# Research on Monocular-Vision-Based Finger-Joint-Angle-Measurement System
## 5 Experimental Verification  
In this study, nine healthy male volunteers aged between 20 and 25 were recruited for the experiment, and three different finger-joint angles were detected using the TS-HOMLDM for visual identifiers with widths of 1.5 mm, 2 mm, and 2.5 mm, respectively, to verify the monocular vision-based finger-joint-angle measurement system (MVBFJAMS) proposed in this paper to measure the accuracy of the test in comparison with the traditional inspection method and to determine the most appropriate visual identifier width. To ensure the reliability of the experiment, we invited professional physicians to measure different volunteer knuckle angles using the traditional method first, after which our group members measured different volunteer knuckle angles using MVBFJAMS. To verify the accuracy of the MVBFJAMS for finger-joint-angle measurement during finger extension/contraction, a control experiment was conducted using the conventional measurement method and the visual measurement method. This paper also verifies the speed of the knuckle detection by the visual inspection method by comparing the time used to detect and record 30 joint-angle data by the traditional method and the visual-inspection method. Table 2 shows the knuckle-joint-retention angles for different volunteers with different markers to verify the accuracy of the visual-detection method. The finger-bone-length data are not given because the actual joint position of the finger was uncertain. The detection method in Figure 3a was adopted for the volunteers, and the detection results for the knuckle accuracy of the different volunteers at different scales of visual markers were obtained, as shown in Table 3. \begin{table}
\begin{tabular}{c c c c c} \hline  & **HSV +** & **Threshold** & **Threshold-** \\  & **HSV +** **Hough Outer-** **and** **Inner-Straight-Line** & **Least-Squares-Fitting-** **Outer-Medial** & **Segmentation +** **Outer-Medial** & **Segmentation +** **Least-Squares-Fitting-** **Knuckle-Angle** \\  & **Method** & **Detection** & **Linear-Detection** & **Line** & **Measurement** \\ \hline MCP & 145.02\({}^{\circ}\) & 144.76\({}^{\circ}\) & 144.95\({}^{\circ}\) & 144.59\({}^{\circ}\) & 145\({}^{\circ}\) \\ PIP & 111.03\({}^{\circ}\) & 109.38\({}^{\circ}\) & 110.48\({}^{\circ}\) & 111.26\({}^{\circ}\) & 110\({}^{\circ}\) \\ DIP & 111.83\({}^{\circ}\) & 114.07\({}^{\circ}\) & 112.09\({}^{\circ}\) & 112.34\({}^{\circ}\) & 112\({}^{\circ}\) \\ Length of & proximal & 26.94 mm & 28.24 mm & 27.37 mm & 27.32 mm & 27 mm \\ phalanx & & & & \\ Length of & 25.53 mm & 25.53 mm & 25.64 mm & 25.26 mm & 26 mm \\ middle phalanx & & & & \\ Mean Angle & 0.407\({}^{\circ}\) & 0.967\({}^{\circ}\) & 0.207\({}^{\circ}\) & 0.670\({}^{\circ}\) & \\ deviation & & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Finger-joint angles measured by different methods. \begin{table}
\begin{tabular}{c c c} \hline  & **MCP (\({}^{\circ}\))** & **PIP (\({}^{\circ}\))** & **DIP (\({}^{\circ}\))** \\ \hline Knuckle-hold angle & 145 & 110 & 115 \\ under each marker & 160 & 130 & 110 \\
150 & 165 & 130 \\ \hline \end{tabular}
\end{table} 
Table 2: Knuckle-retention angles under different markers in different volunteers. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Volunteer**} & **Mark on the** & \multirow{2}{*}{**MCP (\({}^{\circ}\))**} & \multirow{2}{*}{**PIP (\({}^{\circ}\))**} & \multirow{2}{*}{**DIP (\({}^{\circ}\))**} & \multicolumn{2}{c}{**Length of**} & **Length of** \\  & & & & & **Phazanx (mm)** & **Philanx (mm)** \\ \hline \multirow{8}{*}{volunteer 1} & \multirow{2}{*}{2 mm} & 144.72 & 109.31 & 115.42 & 45.52 & 30.23 \\  & & 160.10 & 130.12 & 109.21 & 44.07 & 31.45 \\  & & 149.48 &  
From Tables 2 and 3, the deviations from the mean knuckle angle at different scale markers, shown in Figure 11, can be calculated.