In this paper, we describe a single-user glasses-free (autostereoscopic) 3D display where images from a picoprojector pair are projected on to a retroreflecting screen. Real images of the projector lenses formed at the viewer's eyes produce exit pupils that follow the eye positions by the projectors moving laterally under the control of a head tracker. This provides the viewer with a comfortable degree of head movement.
IntroductionThe availability of small and relatively inexpensive picoprojectors has encouraged the authors to develop a 3D display based on these. The principle of using projectors in conjunction with a retroreflecting screen where light is reflected back at the same angle it enters was described by Okoshi in 1976 [1]. A pair of projectors is used to form regions, referred to as exit pupils, in the vicinity of the projector lens so that eyes located in these regions see either a left or a right image over the complete area of the screen.With only a retroreflector as the screen, light would return to the vicinity of the projector lenses and the viewers' eyes could not be located in these regions. In order for the viewer's eyes to be situated within an exit pupil region, and also to enable vertical head movement, the light is diffused vertically at the screen as shown in Figure 1. By itself, this configuration would be inconvenient as the projectors would be located at the same distance from the screen as the viewer's eyes. The use of mirrors as shown in the figure overcomes this problem.It is not comfortable for users to remain in one position and it is preferable to move the exit pupils to follow the positions of their eyes. This can be achieved by determining the eye positions and moving the projectors so that the exit pupils always land on the eyes. This makes the display a head tracked type; these have been under development in different forms for many years with the earliest reference found to date being that of Schwartz in 1985 [2]. There have been many others over the years including those of Sharp [3] and MIT [4]. Microsoft has developed a head tracked 3D display [5] based on the Wedge waveguide technology originally developed at Cambridge University.LG produce a head-tracked 3D monitor [6] and Toshiba a head-tracked laptop [7] [8].
ImplementationThe authors have developed multiuser head-tracked displays in the EU-funded MUTED [9,10] and HELIUM3D [11,12] projects. These are fairly complex as they serve multiple viewers; the relatively simple single viewer display described here has been developed using same tracker technology [13]. Vertically elongated real images of the picoprojector lenses form the exit pupils shown in Figure 1. The lenses of the projectors are only 8 mm diameter and if the retroreflectors had an ideal characteristic narrow exit pupils would be formed with viewers having very little lateral freedom of movement. Fortunately the characteristic of the particular retroreflector material used produces pupils in the region of 60 mm wide at the viewing distance of 1.5 m...