## 3 System Introduction
### System Observation Area  
We analyze the observation area of the system according to the two physiological characteristics of human vision: Visual Acuity (VA) and Field of View (FOV). The visual sensitivity of the human eye limits the Pixel Per Degree (PPD) that the human eye can recognize to 60. That is to say, within the range of 1\({}^{\circ}\) viewing angle, the human eye can distinguish up to 60 pixels in one direction. When the PPD is greater than 60, the human eye will not be able to perceive the existence of pixels [34], such as the retina screen used by Apple. Let \(p\) be the distance between two pixels on the display. Let \(w\) be the width of the display screen, and \(h_{r}\) be the horizontal resolution of the display screen, then:  
\[p=\frac{w}{h_{r}}, \tag{1}\]  
Assuming that the distance between the user and the display screen is \(d\), the PPD can be calculated by the following formula:  
\[PPD\approx\frac{d\cdot\tan 1^{\circ}}{p}=\frac{d\cdot h_{r}\tan 1^{\circ}}{w} \geq 60, \tag{2}\]  
Then:  
\[d\geq\frac{60w}{h_{r}\cdot\tan 1^{\circ}}. \tag{3}\]  
The parameters of the 46-inch screen used by the system in this paper are \(w=1.02\) m, \(h_{r}=1920\) px. Substituting them into the above formula, \(d_{min}\approx 1.8\) m. Therefore, when the distance between the user and the display screen exceeds 1.8 m, the user will not be able to perceive the pixels and achieve the best visual effect. In addition, limited by the size of the room, \(d_{max}\approx 4\) m.  
When keeping the eyeballs still, the horizontal FOV of human eyes is about 180\({}^{\circ}\), the vertical FOV is about 130\({}^{\circ}\), and the color perception range is about 100\({}^{\circ}\) according to the spatial distribution of cone cells [35]. The area with the highest visual accuracy is only 5\({}^{\circ}\) from the optical axis. Although the range of visual information that can be recognized with high precision in the visual field is small, the influence of the peripheral visual field on the user's attention should not be ignored. The research work of [PERSON] et al. shows that the working area of the display wall system needs to be carefully designed because the peripheral vision may affect the user's attention and reduce work efficiency [36]. Based on the range that the color perception area can cover on the display wall, we analyzed the observation area of the system, as shown in Figure 2.  
Figure 2a is a side view of the display wall; the bottom baffle \(H_{bottom}=0.3\) m, and is used to install 3 Kinect V2 sensors at the bottom. The height of the 46-inch screen is about 0.58 m, so the height of the display area is \(H_{rad}=0.58\times 5=2.9\) m. The height of the top LED strip is \(H_{top}=0.3\) m. Assuming that the user's height is \(H_{user}=1.8\) m, the user's horizontal line of sight is in the center area of the display screen, and when \(d_{min}\leq d\leq d_{max}\), the display area is all within the color perception range of the human eye in the vertical direction. As shown in Figure 2b, both the bottom baffle and the top LED light bar use dark color panels, while the roof and the ground use light color panels. By visually setting suggestive boundaries, the user's attention can be focused on the interior of the display area. Figure 2c is a top view of the display wall. When the user is at point A, the distance from the screen \(d=d_{min}=1.8\) m, and the user will not be able to distinguish the pixels and achieve good observation effect. However, the user's viewing range is relatively small at this time, and the user needs to turn the head and body in a large range to observe other areas of the display wall. When the user is at point B, the distance from the screen \(d=d_{max}=4\) m, the user can directly observe most areas of the display wall, and only needs to turn the head in a small range to observe the entire display area. Considering the supplementation of the peripheral vision on both sides, the user will obtain the best observation effect at this time.