# High-Speed Dynamic Projection Mapping onto Human Arm with Realistic Skin Deformation +
## 4 Experiments
### Results  
Figure 2 (first and second rows) presents the projection results obtained before and after accuracy compensation. Black patterns were projected on the forearm surface, which contained five black crosses drawn using an ink marker as the ground truth of skin deformation. The misalignment between the projected patterns and black crosses in the first row of the figure is clear. The second row of the figure shows the improvement in projection accuracy achieved by applying the proposed compensation method, which suppresses the misalignment. We evaluated the accuracy before and after accuracy compensation by counting the numbers of crosses between the projected black patterns in the time sequence. The evaluation was conducted for 5 s, with 150 frames. The user performed wrist supination and pronation once during the evaluation. The more the crosses between the projected black patterns, the higher the accuracy. Figure 2 (bottom) presents the evaluation results. All of the five black crosses stay between the projected black patterns before wrist supination and pronation. Before accuracy compensation, the number of crosses between the projected black patterns drops to 2 and 0 after wrist supination and pronation, respectively. After accuracy compensation, the number of crosses remains 5 in both movements of wrist supination and pronation.  
The developed system achieved a rate of 360 fps, with a bottleneck being caused by the tracking cameras. The tracking part causes a latency of 4 ms, obtained by the OptiTrack software [47]. The rendering part causes a latency of 3 ms, measured directly in the program. The projection part causes a latency of 3 ms, mentioned in [52]. Therefore, by simply adding the latency in each part, we can deduce that the overall latency between motion and projection was approximately 10 ms. At the achieved latency, users could hardly notice the misalignment between the projected image and arm surface, as illustrated in Figure 7. Thus, the proposed system provides fast and accurate projection.  
Figure 8 presents an example of tattoo image projection on the forearm with varying skin deformation using the developed system. The projected image can be selected by the user freely and is deformed realistically as the wrist and elbow joints rotate. The developed system can also enable flexible on-body user interfaces because both sides of the arm surface can be used. In the left photograph of Figure 9, the inner side of the forearm serves as a menu panel, and, in the right photograph, the outer side of the forearm serves  
Figure 7: Projection of tattoo images on the forearm. The user can hardly perceive any misalignment between the projected image and the arm even during high-speed rotations (first row) and translations (second row).  
as a music player interface. Figure 10 presents another example of wound effects using a physical-based rendering texture.  
Figure 8: Proposed system projecting tattoo images (first row) onto the forearm surface under skin deformation (second to fourth rows).  
Figure 9: Both sides of the arm surface serving as on-body interfaces. The inner side of the arm serves as a menu panel (**left**), and the outer side serves as a music player interface (**right**).