# A Reflective Augmented Reality Integral Imaging 3D Display by Using a Mirror-Based Pinhole Array
## 3 Experiments and Results  
To verify the feasibility of the proposed reflective AR display system, an experimental system was built, as shown in Figure 3. The experimental system consists of a projector, a rear projection screen and a MBPA. The projector with high brightness was used to displace the 2D display screen in order to improve the brightness of the 3D images. According to the projection ratio of the projector we used, the size of the AR display was determined to be \(25\text{ cm}\times 14\text{ cm}\). A \(25\text{ cm}\times 14\text{ cm}\) sized reflective film on which the pinholes were engraved by a laser engraving machine was attached on a transparent acrylic plate to implement the MBPA. The pinholes on the MBPA can transmit the light from the EIA, while the other parts of the MBPA can reflect the light from the real object. The rear projection screen was attached to the other side of the acrylic plate substrate to receive EIA projected by the high luminance projector. From our previous research work [27], the viewing angle was calculated, and the spatial angular resolution referred to the viewpoints number per degree was 0.575. The parameters of the reflective AR display system developed are shown in Table 1.  
Figure 3: The experimental system of the proposed reflective AR display. Figure 2: **(a)** The structure of the mirror-based pinhole array (MBPA), it consists of two parts: pinholes and mirror; **(b)** the 3D image formed by the lights of an elemental image array (EIA) transmitted through the pinholes of MBPA; **(c)** the mirror image formed by the reflected light of the real object reflected by the mirror area of the MBPA; and **(d)** the augmented reality (AR) display of the proposed reflective AR 3D display. As shown in Figure 4a, a 3D scene consisting of eight apples was built up at different depths in 3d Max software, and their depths were \(-4\) mm, \(-3\) mm, \(-2\) mm, \(-1\) mm, \(2\) mm, \(3\) mm, \(4\) mm, and \(5\) mm, respectively. An EIA was generated by using the sparse camera array method [28]. As shown in Figure 4b, the EIA contained \(167\times 94\) elemental images, and each elemental image had \(23\times 23\) pixels. A portion of the EIA in Figure 4b has been enlarged, from which we can see several perspectives on the apple. A 4K projector was used to project the EIA onto the rear projection screen, and the re-projection transformation algorithm was used to align the projected EIA and the pinhole array on the MBPA. A coconut palm tree, which represents the real object, was located in front of the MBPA. Figure 5 shows the different AR views of the reconstructed 3D images and the mirror image. The reference rectangles were drawn in Figure 5 to illustrate that the relative positions of the eight apples and the coconut palm tree changed when the viewpoints moved from left to right. The left four apples and the viewpoints move in the opposite direction, while the right four apples move in the same direction with the viewpoint. This proves that the reconstructed 3D images of the left four apples were located in front of the MBPA, and 3D images of the right four apples were located behind of the MBPA. The apples with large depths moved faster than those with small depths. The experimental results showed that the proposed system can realize a good AR display effect by combining the reconstructed 3D image and the mirror image with the MBPA.