## 3 Results and Discussion  
This section is divided into several subsections. A concise and precise description of the experimental results, their interpretation, and experimental conclusions are provided. The x-axis was a frame, the maximum and minimum sections were cut, and the frames in the section were matched at 100 frames using VICON and 4 DEYE so that the result and graphs could be produced. Subsequently, the interclass correlation coefficient was obtained from the statistical analysis of the results. The y-axis represents the angles of hip flexion, knee flexion, and trunk rotation. The angle of the body was obtained by dividing the frame of the sample motion by a constant time. VICON and 4 DEYE observed that the degree increased as the number of frames increased over time. This result was the same in the subsequent knee-flexion and trunk-rotation analyses, as for hip flexion.  
As a result of comparing motion analysis using IMU sensors and OpenPose-based RGB sensors in previous studies, the kinematic accuracy between the two equipment was consistent as shown in this study [25].  
The three reasons for the differences in angle on the graphs are as follows.  
First, when analyzing the operation with VICON(r) an error may occur from the attachment of an infrared reflection marker because of skin flexion. The length of each segment was measured for the length of the femur in the direction connecting the knee from the hip, and for the length of the fibula in the direction connecting the knee to the  
Figure 3: Multi-view RGB-based 4 DEYE analysis system.  
ankle from the knee, to measure the joint angle of the knee joint. The tension of the skin changed as the body moved, resulting in bending, and the line connecting the two markers did not match the longitudinal direction of the body when the markers were attached to two points starting from the bones protruding into the skin surface in the longitudinal direction of this segment. In addition, the clinical field stipulates that movement occurs because of the fixed axis of the joint when describing the movement of the human body; however, since there is no fixed axis at the center of the joint, the direction of movement may continue to change when actual joint movement occurs. This could lead to an error of several degrees.  
Second, although the trends in statistical and graph angles were very consistent, 4 DEYE shows a smoother graph compared to VICON because it is inferred by calibrating values through AI-learned algorithms in OpenCV.  
Third, the VICON(r) measurement requires a total of four markers to be attached up and down on the chest and back within the sagittal plane of the body (specific attachment positions are up/down of the sternum, protrusions of C7 and T8) in the case of measuring the angle of hip flexion using the difference in the estimation method of the body coordinate system. The directions of the mediolateral, superior-inferior, and anteroposterior axes can be estimated from these four markers. The direction of the body's reference coordinate system is calculated based on the position of the center of the joint to estimate the position of the neck, shoulders, and hip joints within the frontal plane if measuring using 4 DEYE(r). Therefore, the estimated reference coordinate systems of the torso, hip, and knee are different; thus, errors in the vertical degrees can occur as VICON(r) and 4 DEYE(r) have different reference points for estimating the coordinate system. Additionally, if this error is added to the error caused by the first cause described above, it can result in larger errors without offsetting each other.