Optical: systems and elements – Holographic system or element – For producing or reconstructing images from multiple holograms
Reexamination Certificate
1997-06-13
2001-05-22
Chang, Audrey (Department: 2872)
Optical: systems and elements
Holographic system or element
For producing or reconstructing images from multiple holograms
C359S024000, C359S025000, C359S026000, C359S022000, C359S030000
Reexamination Certificate
active
06236475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image recording method and apparatus for recording a stereographic image on a holographic stereogram and an image reproducing method and apparatus for reproducing a stereographic image from the holographic stereogram.
2. Description of the Related Art
A holographic stereogram is produced by sequentially recording a large number of images, obtained on sequentially shooting an object from different viewing points, as original images, as strip- or dot-shaped hologram elements, on a sole recording medium.
For example, in a holographic stereogram having the parallax information only in the transverse direction, plural original images
301
a
to
301
e,
obtained on sequentially imaging an object
300
from plural viewing points in the transverse direction, are sequentially exposed to light and recorded on a recording medium for hologram
302
as strip-shaped hologram elements.
With the present holographic stereogram, since the picture information obtained on sequentially imaging an object from plural viewing points in the horizontal direction is sequentially recorded in the transverse direction as strip-shaped hologram elements, the two-dimensional pictures as viewed by left and right eyes of a viewer if the holographic stereogram is viewed by the viewer with both eyes. This the observer feels the parallax so that a three-dimensional image is reproduced.
However, with the conventional holographic stereogram, an optimum reproduced picture cannot be produced. Specifically, with the conventional holographic stereogram, a reproduced image is unclear, dark and poor in contrast, while the reproduced image has a narrow angle of visibility.
For enabling an optimum picture to be produced from a holographic stereogram, it is necessary to completely fix a recording medium for hologram during light exposure of the recoding image to prevent minute vibrations even of the order of the light wavelength. During production of the holographic stereogram, the recording medium for hologram is moved little by little for sequentially recording an extremely large number of hologram elements. For providing a practically useful picture recording device used for producing a holographic stereogram, the recording medium for hologram needs to be transferred quickly during fabrication of the holographic stereogram. Therefore, means for holding and transferring the recording medium for hologram needs to be such a device in which not only the recording medium for hologram can be transferred quickly, but also no vibrations of the recording medium for hologram are allowed after completion and halting of the recording medium for hologram.
For example, if the recording medium for hologram is transferred using an ordinary electrically driven sliding stage, the time of the order of 2 seconds is required until the vibrations of the recording medium for hologram are attenuated, after transfer of the recording medium for hologram, to the extent that the hologram elements can be formed. Therefore, if the recording medium for hologram is transferred each time the hologram element is formed using the electrically driven stage, an extremely long time is consumed until completion of a sole holographic stereogram.
The present inventors have conducted searches into holding and transfer means capable of suppressing the vibrations of the recording medium for hologram more quickly. Thus it has been found that, by loading an elongated recording medium for hologram between two parallel rolls, holding the recording medium for hologram by a torsion coil spring for producing a pre-set tensile force and by causing an object light to fall on the recording medium for hologram placed between the two parallel rolls, the vibrations of the recording medium for hologram can be suppressed more promptly. By employing this method, the time until attenuation of the vibrations after transfer of the recording medium for hologram has been reduced to less than one fourth that when the electrically driven sliding stage is used. However, if this method is employed, the vibrations cannot be suppressed completely. Thus, it has been desired to develop a method and apparatus capable of further suppressing vibrations of the recording medium for hologram.
In a usual hologram, an illuminating light source for reproducing a three-dimensional picture and a hologram are spatially separated from each other. Thus, in a usual hologram, a broad spacing is required for reproduction. On the other hand, for reproduction under an optimum condition, the relative positions of the hologram and the illuminating light source need to be set under a pre-set condition. This applies for a holographic stereogram made up of plural hologram elements.
If the illuminating light source and the hologram are unified with each other, the spacing for illumination becomes unnecessary to make it possible to reduce the size of the apparatus. Moreover, since the relative positions of the hologram and the illuminating light become always constant, reproduction can be performed at all times under optimum conditions. As a hologram for realizing this, there is known an edge-lit system hologram in which recording and/or reproduction is carried out with a recording medium bonded to a transparent light-inlet block.
With such edge-lit system hologram, the optical system for reproduction can be reduced in size and reproduction can be performed at all times under optimum conditions by unifying the light source for the reproducing illuminating light and a light inlet block. Also, since the angle of incidence of the reproducing illuminating light is increased with the edge-lit type hologram, an image is not reproduced by the light incident from outside the light inlet block. Thus the edge lit type hologram is in use in a field in which it is not desirable for an image to be reproduced with, for example, the sunlight, such as in a head-up display device.
For producing a transmission type hologram in which a three-dimensional image is reproduced by the light transmitted through the recording medium, a recording medium for hologram
311
is bonded to a surface
310
a
of a light inlet block
310
formed of a glass plate or a synthetic resin plate of a suitable thickness, as shown in FIG.
2
. At this time, the recording medium for hologram
311
is bonded via an index matching liquid
312
to the light inlet block
310
. An object light beam
314
from an object
313
is illuminated from an other surface
310
b
of the light inlet block
310
towards the recording medium for hologram
311
, while a reference light beam
315
is illuminated from an end face
310
c
of the light inlet block
310
towards the recording medium for hologram
311
. This completes a transmission type edge-lit hologram.
For reproducing the thus produced transmission type edge-lit hologram, the hologram
321
is bonded on an end face
320
a
of the light inlet block
320
via an index matching liquid
322
and a reproducing illuminating light beam
323
is illuminated from the end face
320
b
of the light inlet block
320
towards the hologram
321
. The light transmitted through the hologram
321
is diffracted at this time by the hologram
321
. A reproduced image
325
is generated by a diffracted light beam
324
so as to be viewed by a viewer
326
.
For producing a reflection type hologram in which a three-dimensional image is reproduced by the light reflected by the recording medium, by the edge-lit system, a recording medium
332
is bonded via an index matching liquid
331
on one surface
330
a
of a light inlet block
330
, as in the case of producing a transmission type edge-lit hologram, as shown in FIG.
4
. For the reflection type hologram, an object light beam
334
from an object
333
is illuminated from the side of bonding the recording medium
332
towards the recording medium
332
, while a reference light beam
335
is illuminated from an end face
330
b
of the light inlet block
330
. This completes the edge-lit reflection type h
Kihara Nobuhiro
Shirakura Akira
Chang Audrey
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
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