## 3 Experimental System  
The experimental system using the proposed technique was conducted to verify the improvement in the resolution experimentally. The experimental system had only a horizontal parallax, i.e., a lenticular lens and a slit array were used as the lens and aperture arrays, respectively. Figure 2: Divergence of rays of the proposed technique. We employed a commercially available flat-panel display and lenticular lens for the experimental system. An 8K liquid crystal panel (UP3218K, Dell Inc., Austin, TX, USA) was used as a flat-panel display and had subpixel and pixel pitches of \(q=0.0303\) and 0.0909 mm, respectively. The slanted lenticular lens from NTKJ Co., Ltd. (Tokyo, Japan) was used to balance the horizontal and vertical resolutions of 3D images [26], and the slanted angle was \(\tan^{-1}\) (1/6). The measured pitch of the lens along the horizontal direction was \(p=0.710\) mm. From the measurements, \(f\) was obtained as 0.947 mm, and the principal plane of the lens was located behind the lens vertex at a distance of 0.125 mm. A photomask was used as the slit array, which was made using photolithography. The measured thickness of the slit array was 0.185 mm. The gap between the flat-panel display and lens array, which determines the magnification of the virtual subpixel images, was adjusted by sandwiching an acrylic spacer between them. In our previous light-field system, using a 0.3 mm thick acrylic spacer caused a gap of \(g_{p}=0.883\) mm and a magnification of \(M_{p}=13.6\). Thus, in the previous prototype, the pitch of the virtual subpixel images was \(M_{p}q=0.413\) mm, and only one virtual pixel image was observed through each lens. In this study, a 0.2 mm thick acrylic spacer (the thinnest commercially available on the market) was used to decrease the magnification. The acrylic spacer was glued to the display panel using an UV resin from Norland Products Inc. (Jamesburg, NJ, USA). Considering the thickness of the UV resin layer and photomask, the gap between the principal plane of the lens and pixel of the display became \(g_{p}=0.799\) mm in this proposed prototype system. Thus, the magnification was decreased to \(M_{p}=6.39\), and the pixel pitch of the virtual pixels also decreased to \(M_{p}q=0.194\) mm. Although the maximum number of virtual pixel images observed through each lens was \(n=3\), the number of subpixel images was limited to \(n=2\) because of the large image distortion around the lens valleys. In this case, the width of the virtual slit images should be \(w^{\prime}_{a}=0.388\) mm, which was not, unfortunately, equal to the lens pitch due to the limited options for the thickness of the acrylic spacers. To produce the virtual images of the slits, the printed side of the slit array was facing the spacer; thus, the thickness of the slit array became \(g_{a}\), and the magnification of the virtual slit image became \(M_{a}=1.34\). Therefore, the aperture width of the slits was set to \(w_{a}=0.290\) mm. The pitch of the slits was equal to that of the lens, and the slits were slanted at the same angle as the lenticular lens. Table 1 presents the display parameters of the constructed resolution-improved light-field system and those of the previous system [7]. In the proposed system, the horizontal resolution was doubled, resulting in an improvement in the imbalance between the horizontal and vertical pixel pitches of the 3D images. The viewing zone angle was slightly widened due to the reduction in the gap between the flat-panel display and lens array. The lateral image resolutions calculated from the spot size were 9.49 and 4.42 mm\({}^{-1}\) for the proposed and previous systems, respectively [19]. Although the lateral image resolution of the proposed system exceeded that of the previous system, the depth of focus of the proposed system was only 0.124 mm, which was smaller than that of the previous system of 0.687 mm. The proposed system also has a larger ray divergence away from the screen plane than the previous system.