Hologram display

Details Hologram display Hologram display

1998-10-27

2001-09-11

Spyrou, Cassandra (Department: 2872)

Optical: systems and elements

Holographic system or element

Using a hologram as an optical element

C359S599000

Reexamination Certificate

active

06288803

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hologram display employing a transparent hologram element as a screen to display images projected from a projector.
2. Description of the Related Art
A transparent hologram screen of a hologram display is known which is attached to, for example, a show window to display moving and still images projected from a projector for advertising or any other purposes. The projector is installed at an upper part or a lower part behind the screen. The screen diffracts and scatters light from the projector toward viewers so that the viewers may see images.
The conventional hologram displays, however, have some problems as follows.
One problem is that the hologram screen provides a peak efficiency in a specific wavelength area in the spectral distribution curve thereof.
As a result, reproduced light from the hologram screen intensely shows a color corresponding to the peak efficiency in the spectral distribution. Namely, the reproduced light from the hologram screen is tinged with the color corresponding to the peak wavelength area, and therefore, reproduced colors on the hologram screen are different from original colors contained in the light projected from the projector.
When the projected light contains halftone colors such as a flesh color, the peak-wavelength color conspicuously affects them.
To solve this problem, it is possible to employ a technique of making a hologram screen by multiple exposures. The hologram screen made by multiple exposures shows a uniform spectral distribution curve having at least two peaks in visible wavelengths ranging from 380 nm to 780 nm.
Multiple exposures, however, take a long time and, therefore, are unsuitable for mass production.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a hologram display capable of correctly reproducing colors and improving productivity.
In order to accomplish the object, a first aspect of the present invention provides a hologram display having a projector, a hologram screen, and at least one filter disposed between the projector and the hologram screen to absorb light having a wavelength at which the diffraction efficiency in the spectral distribution characteristic is a peak in a specific wavelength area.
The filter may be an existing one used with a camera. For example, it may be a color compensating filter for compensating the color of a light source, or a light balancing filter for providing a creative effect on a photographed image.
By providing the above-mentioned filter between the projector and the screen, light projected from the projector and in the specific wavelength area is absorbed by the filter. The light passing through the filter is diffracted and scattered by the hologram screen that does not absorb the light in the wavelength area absorbed by the filter.
Since the filter reduces the power of the light with the peak diffraction efficiency in the spectral distribution curve of the hologram screen, reproduced light from the hologram screen shows a flat spectral distribution curve.
The hologram screen of the first aspect is made without multiple exposure, and the filter arranged for the projector is a standard one, to thereby improve productivity and cut production cost.
In this way, the hologram display of the first aspect is capable of correctly reproducing colors and improving productivity.
A color difference &Dgr;u′v′ between light projected from the projector and light reproduced by the hologram screen is preferably equal to or smaller than 0.03.
If this condition is met, viewers sense no difference between colors reproduced by the hologram display and original colors projected from the projector.
The color difference &Dgr;u′v′ is calculated as follows:
&Dgr;u′v′={(u1′−u2′)
2
+(v1′−v2′)
2
}
½
where (u1′, v1′) is projected light from the projector, (u2′, v2′) is reproduced light on the hologram screen, and u′ and v′ are UCS chromaticity coordinates specified by CIE (International Commission on Illumination).
A second aspect of the present invention provides a hologram screen having a hologram element for diffracting light projected from a projector and a light scattering element having a scattering angle of five degrees or larger.
The scattering element helps the hologram element to correctly reproduce the original colors and to secure a glare preventing effect to be explained with reference to FIG.
32
.
The scattering angle of the scattering element must be at least five degrees. If it is smaller than five degrees, the effect of the present invention will not be secured. An upper limit of the scattering angle is also set as will be explained later. If the scattering angle is larger than the upper limit, too large an amount of the projected components will be scattered to dim the image and deteriorate the transparency of the hologram screen.
The scattering element attached to the hologram element expands the incident angle of the light that enters the hologram element from the projector, so that the hologram element may faithfully reproduce original colors.
The scattering element may be attached to either side of the hologram element.
When white light is diffracted by the hologram element, the light is provided with a peak diffraction efficiency in a blue or green wavelength area by the spectral distribution characteristics of the hologram element. When this light is passed through the scattering element, which is attached to the light exiting side of the hologram element in this case, the light becomes the original white color.
In this way, the hologram screen of the second aspect correctly reproduces original colors.
The scattering element may have a proper distance from the hologram element.
When the scattering element scatters light that enters the hologram element, viewers will see double images one on the hologram element and another on the scattering element. To avoid this, it is necessary to set a proper distance between the scattering element and the hologram element.
The distance, however, must not be too long when the scattering element is positioned in front of the hologram element because, if the distance is too long, a large part of light scattered by the scattering element will miss the hologram element to dim the images formed on the hologram element.
It is necessary to properly set the distance between the hologram element and the scattering element.
The scattering element may be arranged on the same or opposite side of the projector with respect to the hologram element.
In any case, the effect of the present invention is attainable.
The scattering element reduces the glare of zero-order light.
The scattering element may be designed to scatter light whose incident angle is within a specific range, so that the hologram screen may transmit background light and diffract light from the projector.
This maintains the transparency of the hologram screen while correctly reproducing colors of the projected light.
The specific range of incident angles is determined according to the size of the hologram screen and a positional relationship between the hologram screen and the projector.
In
FIG. 22
, light from the projector has an incident angle of “m” at the center of the hologram screen, “n” at the top end of the screen, and “l” at the bottom end of the screen. In this case, the scattering element is required to scatter light whose incident angle is in the range of “l” to “n.”
Projected light that enters the center of the hologram screen usually has an incident angle of about 35 degrees.
In this case, the scattering element must scatter light whose incident angle is in the range of 25 to 60 degrees.
The scattering element may preferably have a perpendicular transmittance of 30% to 100% so that it can transmit background light of the hologram screen, so that viewers may see the background of the hologram screen through the same.
This expands applic

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