Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Reexamination Certificate
2003-03-03
2004-12-28
Boutsikaris, Leo (Department: 2872)
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
C359S012000, C359S024000, C359S028000
Reexamination Certificate
active
06836348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image display device for projecting an image beam onto a holographic screen to display an image, and to a holographic screen for use in the same.
2. Description of the Related Art
The holographic screens disclosed in Unexamined Patent Publication (Kokai) No. 2000-19937 and Unexamined Patent Publication No. 11-102153 are holographic screens with good color reproducibility.
The above prior art holographic screens can display an image without reproduced colors that appear unnatural, by projecting images at substantially the same angle as a previously set image projection angle.
However, the allowable range of an image beam projection angle that can achieve an image with reproduced colors that appear natural on the holographic screen is narrow. As a result, when the image projection device is to be installed in a shop or the like, precision in the installation is necessary. Consequently, the installation of the image projection device is difficult and the construction time is extended. Also, there is the problem that, depending on the situation, the image projection device cannot be installed in a position that allows a projection angle that can attain good color reproducibility, due to restrictions such as ceiling height and the like.
SUMMARY OF THE INVENTION
The present invention was arrived at in light of the problems inherent in the prior art, and provides an image display device wherein the range of the projection angle of the image beam within which an image with excellent color reproducibility can be displayed is wide, and a holographic screen for use therewith.
According to a first aspect of the present invention there is provided an image display device comprising a holographic screen and an image projection device for projecting an image beam onto the holographic screen at an upward or downward angle, wherein a forward view color difference &Dgr;u′v′ between a chromaticity value (u′, v′) at the center of the holographic screen when a white image is projected onto the holographic screen by the image projection device and a standard chromaticity value (u′
o
, v′
o
) is 0.04 or less when a projection angle of the image beam onto the center of the holographic screen is set to any angle within a specified projection angle range of 20 to 45°.
Next, the operational effects of the present invention will be explained.
In the above image display device, when the projection angle of the image beam is set to any angle within a specified projection angle range of 20 to 45°, the color difference &Dgr;u′v′ is 0.04 or less. Consequently, even if the projection angle of the image display is changed to a relatively large degree, the color difference of the white image changes little. Accordingly, even if the projection angle of the image beam with respect to the holographic screen is not strictly set, i.e. as long as it is set within the above specified projection angle range, an image with excellent color reproducibility can be displayed.
Therefore, the above image display device allows the positional relationship between the above holographic screen and image projection device to be set relatively freely, enabling easy installation.
As described above, according to the present invention, an image display device can be provided wherein the range of the projection angle of the image beam within which an image with excellent color reproducibility can be displayed is wide.
According to a second aspect of the present invention, there is provided a holographic screen for projecting an image beam from an image projection device to display an image, wherein the holographic screen comprises a plurality of laminated holograms. Each hologram is produced by exposing a photosensitive material to an object beam serving as a diffused beam transmitted through or reflected from a light diffuser and a reference beam which is not a diffused beam. The angle of incidence of the reference beam on the center of the photosensitive material during exposure differs for each hologram.
Generally, in a hologram, if the projection angle of the image beam diverges from an angle that is the same as the angle of incidence of the reference beam, the reproduced wavelength changes. If the projection angle of the image beam is greater than the angle of incidence of the reference beam, the wavelength thereof lengthens, and if the projection angle of the image beam is less than the angle of incidence of the reference beam, the wavelength thereof shortens.
Conversely, with the projection angle of the image beam as standard, if the angle of incidence of the reference beam is smaller than the projection angle of the image beam, the wavelength thereof lengthens, as indicated by curve C in
FIG. 25
, and if the angle of incidence of the reference beam is greater than the projection angle of the image beam, the wavelength thereof shortens, as indicated by curve B in FIG.
25
.
If the angle of incidence of the reference beam and the projection angle of the image beam diverge, although there is slight dislocation of the reproduced light diffuser and distortion and the like occur, because the light diffuser normally has a uniform diffusion surface, an observer is not aware of such dislocation, distortion and the like.
The inventor of the present invention has concentrated on the phenomenon and, in a hologram that records a light diffuser having a uniform diffusion surface, has laminated a plurality of holograms having reference beams with different angles of incidence and, by irradiating them with one image beam (i.e. one image beam projection angle), has ascertained that favorable white diffraction beams in which different wavelengths are weighted can be attained. In other words, as shown in
FIG. 25
, the different spectral characteristics A, B and C of peak wavelengths are superposed to produce a white image having a flat spectral characteristic as indicated by curve D in FIG.
26
.
Further, it was ascertained that, because the spectral characteristic is flat even if the projection angle of the image beam is changed, changes in the reproduced color do not easily change, and a hologram having a favorable color reproducibility can be attained with a wide image beam projection angle range.
Accordingly, the holographic screen of the present invention, as described above, is formed by laminating a plurality of holograms in which the angles of incidence of the reference beams on the center of the photosensitive material differ during exposure. Therefore, even if the image beam projection angle changes, color reproducibility on the holographic screen does not change easily.
As described above, according to the present invention, a holographic screen can be provided wherein the range of the projection angle of the image beam in which an image with excellent color reproducibility can be displayed is wide.
According to a third aspect of the present invention, there is provided a holographic screen for projecting an image beam from an image projection device to display an image, wherein the holographic screen is formed by a plurality of laminated holograms. Each hologram is produced by copying a primary master, produced by exposing a master photosensitive material to an object beam serving as a diffused beam transmitted through or reflected from a light diffuser and a primary master reference beam which is not a diffused beam, by superposing it on a photosensitive material for copying and irradiating it with a reference beam for copying. The angle of incidence of the primary master reference beam on the center of the photosensitive material during exposure of the primary master differs for each hologram.
In this case also, a holographic screen that is essentially the same as that in the second aspect can be attained. Also, in the case of the present aspect, by producing a primary master once, and later copying the primary master, the same hologram can be reproduced a number of times. As a result, when a p
Boutsikaris Leo
Nixon & Vanderhye PC
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