Tabletop three-dimensional (3D) display can provide natural and realistic terrain scenes for viewers, which has a great application potential in many fields. With the development of advanced real-time terrain rending, it becomes feasible to acquire high definition topography based on massive terrain data. However, traditional 3D displays are hard to reach the harsh requirements of tabletop 3D display. For example, the auto-stereoscopic display based on a lenticular lens array or parallax barrier suffers from a small viewing zone, viewing jumps, and perspective errors due to the lack of vertical parallax. Light field display is considered to be one of the most potential methods to realize ideal realistic 3D display. Through simulating the light rays emitted from each point of the spatial object, light field display can reconstruct the light distributions of the displayed scenes. Former efforts of our group have been devoted to achieving reconstructed high definition light field scenes in recent years. Detailed terrain data is showcased with a horizontal parallax viewing angle of more than 100°. However, if we apply this device to tabletop 3D light field display, the plane of the liquid crystal display(LCD)screen must be set horizontal, thus there are two serious flaws. First, the viewing range of this 3D light field display is only designed for viewing from right above the screen, therefore not suitable for tabletop viewing. Second, a wrong perspective relation occurs due to the lack of vertical parallax. We hope that our strategy and work can be helpful for the design of tabletop light field display with large frontal viewing angles and for the correction of multiple viewer perspective errors.

First, the light field display unit, which consists of collimated light and a linear lens array (LLA) that reversely sticks on the LCD panel with a resolution of 7680 pixel×4320 pixel, is designed to construct a high resolution 3D scene in a large horizontal viewing angle. Then, the direction turning films (DTF) can deflect the viewing range from the top to the front, and the holographic functional screen (HFS) is applied to distribute the thin collimated light beams in a specifically arranged geometry with a specifically spreading function. Therefore a vertical viewing angle is formed and the reconstruction of the discrete sampling light field scenes is realized. After that, the views-segmented image coding scheme is calculated to deduce the mapping relationship between sub-pixels on the LCD and the proposed views-segmented voxel. These voxels divide the whole frontal viewing range into a number of independent viewing zones based on the spatial coordinates of each viewer. In addition, instead of acquisited camera arrays according to horizontal parallax, each part of the acquisition camera array moves synchronously with the viewer in different viewing zones to realize the adaptive perspective correction of multiple viewers in real time rendering.

In our experiment, the proposed light field display unit successfully generates realistic, high definition 3D images within a 100° horizontal viewing angle. The light intensity measurement experiment in two different viewing directions shows that a frontal 90° vertical viewing angle, which is more suitable for tabletop light field display, is well covered based on the light-beam modulation of the HFS (Fig. 2) and the deflection effect of the proposed DTF (Fig. 7). With the appliance of the views-segmented image coding method, the sub-pixel arrangement in each image unit is settled and the views-segmented voxel is generated to provide each viewing zone with different 3D scenes and parallax relationships (Fig. 5). In the experiment of perspective correction, when multiple viewers in different positions (located by the depth camera with facial recognition) are watching the 3D terrain scenes of the tabletop light-field display device at the same time, all corrected perspective relations in different viewing zones are clearly observed (Fig. 11).

Tabletop 3D light-field display with full parallax based on direction-turning films and views-segmented voxels is demonstrated. In this system, the collimated backlight and the lenticular lens array reversely attached to an LCD panel with a resolution of 7680 pixel×4320 pixel are designed to achieve a 100° horizontal viewing angle, and the direction turning films and the holographic functional screen are applied to reconstruct 3D light-field images within a 90° frontal viewing angle. Views-segmented voxels are first proposed to separate the frontal viewing range into some disparate viewing zones according to the spatial coordinates of different viewers, then the views-segmented image coding method and the mapping function between the views-segmented voxels and sub-pixels on LCD are also deduced. Finally, after the real-time adaptive perspective correction in each viewing zone, a full parallax, high-definition tabletop 3D scene is presented to multiple viewers.