Contents 1. Introduction
We have previously proposed a thin natural three-dimensional (3D) display system based on the ray reconstruction method [1], [2]. It is one type of realtime one-dimensional integral imaging display system. It consists of an LCD panel and a holographic lens array sheet. Its notable feature is the ability to display natural 3D images, like holography, which are visible to multiple viewers at the same time without the need for special glasses. The viewing angle of this display is 15 deg, and each 3D pixel reconstructs 24 parallax rays. 3D images can be displayed in a range from 10 cm in front of the display to 15 cm behind the display in the prototype thin 3D display. However, since this display can be observed from one direction (in front of the display), it has a disadvantage for cooperation working. To solve this problem, some omnidirectional displays have developed [3], [4]. However, the display area size in the depth dimension of these displays is not enough for cooperation working. In order to overcome this problem, we propose a flatbed-type bidirectional 3D display system for multiple users as an improved version of a previous thin natural 3D display. This is a tool for communication around a 3D image among a small number of people. It is a flatbed-type autostereoscopic 3D display system based on the ray reconstruction method. It consists of one flat panel display and an improved bidirectional holographic lens array sheet. Its notable feature is the ability to display natural 3D images which are visible to multiple viewers at the same time. Reconstructed 3D real image floats over the proposed flatbed-type display. Moreover, front and back sides of a reconstructed image can be observed from two directions. Thus, proposed display allows two or more people surrounding it to simultaneously observe floating 3D images from their own viewpoints. The prototype of proposed display consists of an LCD panel and an improved holographic lens array sheet. The size of the holographic lens sheet is ., This holographic lens array sheet includes elemental holographic lenses, and the size of each elemental lens is which corresponds to pixels of the LCD panel. Thus, the number of the 3D pixels about unidirectional holographic lens array is , and each 3D pixel reconstructs 24 parallax rays. The viewing angle of the holographic lens array sheet is about 23 deg. The holographic lens array sheet reconstructs two 3D images, and these 3D images are superimposed over the display. The reconstructed 3D image can be displayed from 72 mm in front of the display to 72 mm behind of the display. The proposed 3D display is useful for applications in which several people work together to perform tasks or enjoy entertainment with a multiplier effect. This paper describes a flatbed-type autostereoscopic 3D display system, and also describes the experimental results.
