A technique of synthetically displaying images from a plurality of directions using an image display surface, and making the image appear three-dimensional according to a viewpoint of an observer is proposed as a three-dimensional display system using a two-dimensional plane display.
As the three-dimensional display system, existing techniques may use a binocular stereoscopic system which displays two images observed in viewpoints of right and left eyes, and a multi-view system which displays many images observed in a plurality of viewpoints. Moreover, there exists an Integral Photography method (IP method) which synthetically displays images in an image display surface to many directions, without respect to a particular viewpoint.
As a method to select the image, a method using a pinhole array or a slit array having masked parts and aperture parts, and a method arranging a lens array or a lenticular array on the image display surface, and making an image-formation position of a lens a pixel position, are known. It is more desirable to use the lens array since display brightness is reduced using techniques relying on masked parts.
In order to display the two-dimensional image and the three-dimensional image alternatively on a same display, various proposals of techniques for have been made. One method using a lens array utilizes a selection display technique switching an existence of a lens effect by making the lens into a refractive index variable layer, has been previously disclosed, for example, in Japan Patent Application KOKAI No. 2000-102038. Here, it is said that a liquid crystal lens which is controlled by an alignment of liquid crystal by voltage, as a refractive index control means. By switching the existence of a lens effect, in case the two-dimensional image is displayed, it becomes possible to display an image in the original resolution of the two-dimensional display.
Moreover, as a realization method of a liquid crystal lens, a method of enclosing liquid crystal material between a convex or a concave lens and a substrate has been disclosed in S. Sato, J. J. App. Phys. Vol. 18, NO. 9, (1979) p. 1679-1684. A method of using a Fresnel-lens has been disclosed in S. Sato et al., J. J. App. Phys. Vol. 24, NO. 8, (1985) p. L626-L628. A method of using a diffractive lens which gives modulation of refractive index to an inside of a plane of incidence has been disclosed in S. T. Kowel et al., App. Optics Vol. 23, NO. 2, (1984) p. 278-289. A method of using a refractive index profile lens which gives modulation of refractive index to an inside of a plane of incidence and a propagation direction of light has been disclosed in T. Nose et al., Liquid Crystals Vol. 5, NO. 5, (1989) p. 1425-1433.