超多视角显示

Multi-projection of lenticular displays to construct a 256-view super multi-view display Yasuhiro Takaki* and Nichiyo Nago Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho Koganei, Tokyo 184-8588, Japan *ytakaki@cc.tuat.ac.jp Abstract: A new super multi-view (SMV) display system that enables the number of views to be increased is proposed. All three-dimensional (3D) images generated by multiple multi-view flat-panel displays are superimposed on a common screen using a multi-projection system. The viewing zones of the flat-panel 3D display are produced in the pupils of the projection lenses and then imaged to the observation space by a screen lens. Sixteen flat-panel 3D displays having 16 views were used to construct a SMV display having 256 views. The 3D resolution was 256 × 192. The screen size was 10.3 inches. 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Iwase, “The D-ILA device for the world’s highest definition (8K4K) projection systems,” in Proceedings of International Display Workshop (IDW’08), pp. 203– 206 (2008). 1. Introduction A natural three-dimensional (3D) display is one that does not conflict with the human 3D perception so that it is free from visual fatigue. A super multi-view (SMV) display [1–4], which has a large number of views, was proposed as a glasses-free and natural 3D display. A high-density directional (HDD) display [5–10], where the viewing zones are generated at infinity, was also proposed. The important point regarding these two techniques is to increase the number of views to evoke the accommodation responses and to provide smooth motion parallax. In the present paper, a new SMV display system that allows the number of views to be increased is proposed. Conventional 3D displays have two problems with respect to human 3D perception. One of these problems is the accommodation-vergence conflict [11,12]. Accommodation causes the eyes to focus on an object, and vergence perceives the depth of an object from the rotation angles of both eyes. Conventional two-view and multi-view 3D displays project different images to the left and right eyes. When two different images are presented to the left and right eyes, vergence correctly perceives the depth position of a 3D image. However, because both images are displayed on the display screen, accommodation makes the eyes focus on the display screen and not on the 3D image. Since there is a close interaction between vergence and accommodation, this conflict causes visual fatigue. The second problem is the absence or imperfection of motion parallax. Motion parallax is the change in a retinal image resulting from the movement of a viewer’s eye position. Two-view 3D displays do not generate motion parallax, and multi-view 3D displays generate discontinuous motion parallax because a retinal image does not change until the eye moves to an adjacent viewing zone. The detailed analysis of the viewing zones and the motion parallax of multi-view 3D displays is given in Ref. 13. This reduces the presence and realism of 3D images perceived by viewers, because humans unconsciously predict the retinal image change due to their movement. A natural 3D display is defined as free from these two problems. The SMV display technique makes the interval between viewing zones smaller than the pupil diameter, so that two or more rays passing through the same point in space pass through the eye pupil simultaneously [1–3]. Therefore, the eyes can focus on that point. The HDD display technique samples ray proceeding directions with a small angle pitch to allow two or more rays to pass through the pupils simultaneously [7]. The SMV display technique produces a large number of parallax images (perspective projections of 3D scenes) into the corresponding viewing zones. The HDD display technique projects a large number of directional images (orthographic projections) with nearly parallel rays proceeding in the corresponding directions. The display systems developed to construct the SMV and HDD displays are explained in Sec. 2. A head-mount-type SMV display also has been proposed [14]. Using this technique, the required number of views is not large. However, glasses-free observation is impossible. The SMV/HDD displays described above provide horizontal parallax. The possibility of realizing full-parallax natural 3D displays using the integral imaging technique was investigated [15]. The number of views of the glasses-free SMV/HDD displays has been increased. However, this increase results in difficulties with the previous display systems. In the present study, a new SMV display system that combines the multi-projection system and the flat- panel system is proposed to achieve a further increase in the number of views. A prototype SMV display with 256 viewpoints is also demonstrated. #123746 - $15.00 USD Received 3 Feb 2010; revised 19 Mar 2010; accepted 12 Apr 2010; published 13 Apr 2010 (C) 2010 OSA 26 April 2010 / Vol. 18, No. 9 / OPTICS EXPRESS 8825 2. Previous SMV/HDD display systems Several systems have been used to construct autostereoscopic displays [16]. A multi- projection system and a flat-panel system have been used to construct the SMV and HDD displays. An SMV display with 30 views was constructed using a fan-like array of projection optics (FAPO) [4]. HDD displays with 64 and 128 ray directions [5,7,10] were constructed using a two-dimensional (2D) array of projection systems. HDD displays with 30 and 72 ray directions [6,8,9] were constructed using a flat-panel system that consists of a lenticular lens and a flat-panel display. Besides the above two systems, the display system using the focused light-source array (FLA) was developed to construct the first SMV display with 45 views [1–3]. However, development of the FLA system has not been continued. The multi-projection system consists of a large number of projection optics and a common screen. The number of projectors is equal to the number of views. The advantage of the multi- projection system is that the resolution of 3D images and the number of views can be increased independently. The resolution can be increased by using higher resolution projectors. The number of views can be increased by using more projectors, i.e., the multi- projection system is scalable. Disadvantages of the multi-projection system include the system complexity and the system size. In addition, a large number of optical components are required, in addition to a long projection distance. The flat-panel system consists of a high-resolution flat-panel display and a lenticular lens. Advantages of the flat-panel system include its simplicity and thickness. One disadvantage of the flat-panel system is the trade-off between the 3D resolution and the number of views. The resolution required for the flat-panel display is the product of the 3D resolution and the number of views. In order to increase the number of views, a large number of projectors are required for the multi-projection system, and an ultra high-resolution flat-panel display is required for the flat- panel system. 3. Proposed SMV display system In the present study, we propose a new SMV display system that does not require a large number of projectors and an ultra high-resolution flat-panel display in order to increase the number of views. The proposed system is shown in Fig. 1. Several flat-panel systems are combined by a multi-projection system. The flat-panel systems are arranged in a modified 2D arrangement. In the modified 2D arrangement, all of the projectors are arranged two-dimensionally with different horizontal positions. All 3D images produced by the numerous flat-panel systems are projected on a vertical diffuser, which is a common screen. A lenticular lens of the flat-panel systems generates multiple viewing zones at a certain distance. In the proposed system, the multiple viewing zones of each flat-panel system are generated on an incident pupil plane of its corresponding projection lens. Each projection lens projects the display surface of its corresponding flat-panel system on the common screen. Each projection lens is appropriately shifted transversely along its optical axis so that all projected images are superimposed at the same position on the common screen. A screen lens, which is located on the common screen, images the exit pupils of all of the projection lenses at a certain distance from the common lens to generate viewing zones for observers. A vertical diffuser enlarges the viewing zones in the vertical direction. #123746 - $15.00 USD Received 3 Feb 2010; revised 19 Mar 2010; accepted 12 Apr 2010; published 13 Apr 2010 (C) 2010 OSA 26 April 2010 / Vol. 18, No. 9 / OPTICS EXPRESS 8826 Fig. 1. SMV display system that combines multiple flat-panel systems by a multi-projection system. Figure 2 shows the horizontal sectional view of the proposed system. The lenticular lens is shifted spatially on the flat-panel display in order to generate viewing zones on the incident pupil of a corresponding projection lens. As explained previously, the projection lenses are appropriately shifted to superimpose 3D images produced by all flat-panel systems on the common screen. The screen lens images the viewing zones of the exit pupils of the projection lenses onto the observation space to generate massive viewing zones for observers. Figure 3 shows the vertical sectional view of the proposed system. The vertical diffuser on the common screen diffuses rays in the vertical direction so that the viewing zones generated by the projection lenses are enlarged vertically. The enlarged viewing zones overlap one another to produce a common vertical viewing zone for observers. The arrangement of the projection lenses is illustrated in Fig. 4. The projection lenses are also arranged in the modified 2D arrangement. The lenticular lens of the flat-panel system produces pseudoscopic viewing zones, i.e., the multiple viewing zones are repeated horizontally. The projection lenses of the proposed system have rectangular apertures to block the light that passes through the pseudoscopic viewing zones. The modified 2D arrangement makes the transparent areas of the pupils of all of the projection lenses to be continuous in the horizontal direction. Therefore, the multiple viewing zones produced by the flat-panel systems are imaged at a fixed distance from the common screen without any gaps in the horizontal direction. #123746 - $15.00 USD Received 3 Feb 2010; revised 19 Mar 2010; accepted 12 Apr 2010; published 13 Apr 2010 (C) 2010 OSA 26 April 2010 / Vol. 18, No. 9 / OPTICS EXPRESS 8827 Fig. 2. Horizontal sectional view of the proposed SMV display system. Fig. 3. Vertical sectional view of the proposed SMV display system. Fig. 4. Arrangement of projection lenses and viewing zones in lens apertures. The proposed SMV system is compared with the multi-projection system and the flat- panel system. The purpose of the proposed SMV system is to increase the number of views. The resolution and the number of flat-panel displays required for the three systems are shown in Table 1. The target number of views of an SMV display is denoted by V, and the target 3D resolution is denoted by X × Y. The number of flat-panel displays used in the proposed system is denoted by L. For the multi-projection system, the required number of flat-panel displays is equal to the number of views, and the same number of projection optics is required. For the flat-panel system, despite the fact that only one flat-panel display is required and no projection optics is required, the resolution required for the flat-panel display increases in proportion to the number of views V. For the proposed SMV display system, the required number of flat- panel displays is less than the number of views, and the resolution required for flat-panel displays is proportional to V/L. Therefore, the proposed SMV display system can be constructed using a moderate number of flat-panel displays of moderate resolution. #123746 - $15.00 USD Received 3 Feb 2010; revised 19 Mar 2010; accepted 12 Apr 2010; published 13 Apr 2010 (C) 2010 OSA 26 April 2010 / Vol. 18, No. 9 / OPTICS EXPRESS 8828 Table 1. Requirements for flat-panel displays Resolution Number of panels Multi-projection system X × Y V Flat-panel system X × Y × V 1 Proposed system X × Y × V/L L In the above explanation, the flat-panel system uses a lenticular lens to produce multiple viewing zones. A parallax barrier can also be used instead of a lenticular lens. In the proposed system, the combination of offset multiple projectors and a vertical diffuser is used. This combination was previously proposed in Ref. 17 to construct multi-view displays. The proposed system uses a 2D array of lenticular displays. The combination of a one-dimensional array of time-sequential multi-view displays and a multi-projection system was previously proposed in Ref. 18. The 3D displays that the authors previously developed employed either the multi- projection system [5,7,10] or the flat-panel system [6,8,9]. The new 3D display system proposed in this manuscript combines both systems in order to increase the number of views. To the authors’ knowledge, the combination of the multi-projection system and the lenticular system has not been proposed in any other study. 4. Prototype system We constructed an SMV display with 256 views (SMV256) using the proposed SMV display system. Sixteen flat-panel systems with 16 views were combined by a multi-projection system. The 16-view flat-panel system consisted of a lenticular lens and a liquid-crystal display (LCD) panel with a special subpixel layout referred to as the slanted subpixel arrangement [19]. The 2D resolution of the LCD panel was 1,024 × 768 and the screen size was 2.57 inches. The photograph of the subpixel structure of this flat-panel display is shown in Fig. 5. Since the subpixel arrangement is slanted, the lenticular lens is not required to be slanted. The conventional multi-view displays are usually constructed by slanting the lenticular lens [20], because the subpixel layout of conventional flat-panel displays is generally the RGB stripe layout, i.e., the subpixel arrangement is not slanted. In the slanted subpixel arrangement, one of the vertical edges of one subpixel and the opposite vertical edge of another subpixel of the same color in the adjacent row occupy the same horizontal position. Therefore, ray-emitting areas of subpixels are continuous in the horizontal direction for each color. The use of the slanted subpixel arrangement has two advantages. One is that the viewing zones are produced along a horizontal line, and the other is that the crosstalk among viewing zones is theoretically zero. Using the slanted lenticular technique, the viewing zones are aligned along a slanted horizontal line, and there is considerable crosstalk among viewing zones. Fig. 5. Photograph of the subpixel structure of an LCD panel with a slanted subpixel arrangement. #123746 - $15.00 USD Received 3 Feb 2010; revised 19 Mar 2010; accepted 12 Apr 2010; published 13 Apr 2010 (C) 2010 OSA 26 April 2010 / Vol. 18, No. 9 / OPTICS EXPRESS 8829 In order to produce 16 viewing zones, a group of 12 × 4 subpixels (4 × 4 subpixels for each R, G, and B colors) corresponds to one of cylindrical lenses that constitute the lenticular lens. The 3D resolution of the flat-panel system was 256 × 192. The lenticular lens was designed to produce 16 viewing zones in the horizontal width of 21.0 mm at a distance of 200 mm from the lenticular lens. The horizontal pitch of the viewing zones was 1.31 mm. The lens pitch of the lenticular lens was 0.202 mm. Next, the design issue of the multi-projection system is described. The display screen size and the pitch of the viewing zones are important parameters for designing the multi-projectio