## 4 Experimental Verification  
To verify the simulation result, we conduct objective and subjective experiments. First, we adopt a camera set (Canon 600D) at different positions in the viewing plane, each time with a single pixel  
Figure 4: Similar factors at different viewing angles in simulation. Figure 3: The relationship between viewing angle and spot sizes in simulation. Figure 2: Simulated eye images (**a–f**), of spots and horizontal cross section of spot intensity distributions at viewing angles of \(0^{\circ}\), \(4^{\circ}\), \(8^{\circ}\), \(12^{\circ}\), \(16^{\circ}\), and \(20^{\circ}\). lightened, to capture the light spot formed at viewing angles from 0\({}^{\circ}\) to 20\({}^{\circ}\) with a 2\({}^{\circ}\) interval in the viewing plane. According to the designed viewing distance of 5 m, the 2\({}^{\circ}\) interval means translate the camera about 174 mm along the \(x_{0}\) axis. Each location of the camera is pre-marked in the line, and we just take the camera from one point to another. Subsequently, the FWHM of every spot is calculated from the captured pictures, as shown in Figure 5. We compare the experimental and simulated results at viewing angles of 8\({}^{\circ}\) and 16\({}^{\circ}\) in Figure 6. It can be concluded that the results are quite in accordance with the simulation results. In addition, as can be seen from the simulation results shown in Figure 2 and the experimental results shown in Figure 5, the difference in spot shape distortion is much less than the difference in FWHM of spots. Thus, we only used the difference of FWHM to evaluate the disparity, which is how the similar factor is defined in Equation (7). The similar factor values at every viewing angle are calculated and compared with the simulation results, as shown in Figure 7. The maximum deviation of the experimental and simulated similar factor is 0.03, and the average deviation is 0.015, which proves the validity of the simulation method. Figure 5: Experimental horizontal cross-section of spots intensity distributions (**a–f**) viewing angles of 0\({}^{\circ}\), 4\({}^{\circ}\), 8\({}^{\circ}\), 12\({}^{\circ}\), 16\({}^{\circ}\), and 20\({}^{\circ}\). Red: Left eye; and blue: Right eye. Figure 6: Comparison of simulated (red) and experimental (blue) left (**a,c**) and right (**b,d**) horizontal cross-section of spots intensity distributions at viewing angles of 8\({}^{\circ}\) and 16\({}^{\circ}\). Red: Simulation; and blue: Experiment. Secondly, a subjective experiment is conducted. Before the experiment, we tested five stereo images shown in Figure 8 by four volunteers. The maximum horizontal disparities of the five stereo images are adjusted to three pixels, which correspond to the maximum SD 1420 mm of the prototype at the viewing distance of 5 m. The farthest 3D point from the display was marked by an indicator, the position of which was decided by the viewer, and the distance from the indicator to the display was measured to be the SD. The average SD value perceived by the four volunteers from the five stereo images shown in Figure 8 are 900 mm, 1000 mm, 710 mm, 1200 mm, and 850 mm, respectively. When loaded the 'lotus', the volunteers can experience the largest SDs, the mean value of which is 1200 mm. The reason is that the 'lotus' pattern has strong geometrical depth feature of occlusion. Thus, we chose the 'lotus' pattern for our subjective experiment. Sixteen viewers of 20 to 25-year-olds moved into different positions along \(x_{0}\) axis as in the simulation part, watching the same stereoscopic picture \"lotus\" (as shown in Figure 9). The mean value of the interpupillary distances of the volunteers is 64.9 mm and the standard deviation is 1.9 mm. The viewing angles at each position are from 0\({}^{\circ}\) to 20\({}^{\circ}\) with a 2\({}^{\circ}\) interval. The experiment results are shown in Figure 10.  
Figure 8: The tested five stereo images: (**a**) ‘stars’; (**b**) ‘dog’; (**c**) ‘fish’; (**d**) ‘lotus’; (**e**) ‘balloons’. Figure 3:0 Comparison of similar factors by simulation and experiment.