JPH02149880A - Projection type multiplex recording device and multiplex recording method - Google Patents

Abstract

PURPOSE:To record a hologram having excellent image quality by superposing plural images on the same part of a recording medium every proper time width and recording them. CONSTITUTION:By using a spatial modulation element 24 which displays the plane image as a variable density pattern where transmittivity or reflectance is modulated with an external signal such as a video signal, etc., and adding the modulation of the time pulse width in accordance with the signal level every picture element, image information temporally different is superposed on the same part of the recording medium 10 every proper time and recorded. Therefore, the hologram having the excellent image quality is recorded by superposing and recording the images which are temporally same or different on the same part of the recording medium every proper time, even in the case of using the spatial modulation element 24 which only displays about eight gradation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a multiplex recording device and a multiplex recording method for recording a large amount of image information with high contrast and high gradations directly or in the form of a hologram, etc. In particular, the present invention relates to a new projection type multiplex recording device and multiplex recording method that record a series of video signals on a hologram and enable clear three-dimensional image synthesis.

2. Description of the Related Art In recent years, information recording and reproducing systems using various electronic, magnetic, optical, or a combination of these media have been developed. Among these, hologram memory, which can record image information with high quality and high density, has attracted particular attention since the 1960s, and its application to computer memory or video memory has been actively researched. Also 3
Research and development of dimensional display technology is expanding to include art, education, and medical fields. For example, a holographic stereogram has been developed in which a three-dimensional object is photographed from each direction and then combined into a sheet-like hologram that can be displayed as a three-dimensional image with parallax. Reproduction using a non-laser light source (white light source is also possible) achieves considerable image quality.

The holographic stereogram will be described below. FIG. 5 is a diagram schematically showing a conventional holographic stereogram hologram recording optical system. First, as shown in Figure 5(a), 3 on the table 1 that can rotate 360 degrees.
A projector 3 projects a dimensional object as a series of two-dimensional images viewed from different angles at a time. Next, the photographed film 4 is irradiated with a laser beam 5 as shown in FIG. 4(b), and the lenses 8, 7. The hologram is projected onto a screen 9 through a slit opening 8 and recorded on a film-like recording medium 10 provided on the back surface thereof. Here, reference light is made to enter from a reference light source 11 located above. Note that the beam passing through the recording medium 10 converges at the position of the straight line 12. FIG. 6 is a diagram showing the principle of image synthesis by forming the recording medium 10 on which the hologram array obtained in this way is recorded into a cylindrical shape. FIG. 6(a) shows a method for reproducing a three-dimensional image from a hologram 14 using a diverging laser beam 13.
When an observer looks at the position indicated by the straight line 15, the reproduced images incident on the observer's eyes 16 and 17 are different, and a three-dimensional image 18 is obtained due to the effect of parallax. FIG. 6(b) shows a method for performing similar three-dimensional image reproduction using a white light source 1θ. In this case, the eye position is designed so that the eyes are positioned slightly behind the hologram 14 so that only a portion of the red, green, and blue diffraction image components 20 to 22 (for example, the central green image 21) that have undergone chromatic dispersion can be seen. be.

Problems to be solved by the invention In conventional holographic stereograms,
A process of photographing an actual three-dimensional object on photographic film is essential, and after the film is developed, a process of converting each frame of the photograph into a hologram is necessary. Furthermore, the procedure used consisted of two completely separated optical systems. Therefore, real-time recording was of course impossible, and the uses of holographic stereograms were also limited. In addition, today, many parts of image processing are processed and recorded as video information, especially video signals, and this is directly processed and recorded as a spatial modulation element (hereinafter abbreviated as SLM).
There is a strong demand for technology that can convert input images into holograms through holograms and effectively utilize reproduced images. Means for solving problems of high image quality such as high contrast and high gradation In the inventions described in claims (1) and (4), in order to solve the above-mentioned problems, a planar image is generated by an external signal such as a video signal. Using a spatial modulation element that displays a light and shade pattern with modulated transmittance or reflectance, temporal pulse width modulation is applied to each pixel according to its signal level, and temporally different image information is recorded at appropriate time intervals. The present invention provides a projection type multiplex recording device and a multiplex recording method for recording holograms having excellent image quality in terms of contrast, gradation, etc. by overlapping recording on the same portion of a medium.

Furthermore, the invention according to claim (2) uses an active matrix type liquid crystal display device in which an a-8i TFT or the like is formed in each pixel as a spatial modulation element, a liquid crystal display device using ferroelectric liquid crystal, etc. While the contrast and gradation of the spatial modulation element itself is obtained by making monochromatic light such as a laser beam into almost parallel light, the multiple images obtained by such a device are transferred to the recording medium at appropriate time intervals. The object of the present invention is to provide a projection type multiplex recording device that records a hologram having performance superior to the contrast and gradation of the spatial modulation element itself by overlapping recording in the same area.

Furthermore, the invention as set forth in claim (6) includes correction processing of an image obtained from a hologram recorded on a recording medium using light transmitted or reflected by the spatial modulation element to an external signal input to the spatial modulation element. The hologram is recorded by feeding back the conversion function for the hologram.

As a working space modulation element, the contrast is Cs1 and the N tone is Ks.
Let us assume a case where a hologram is recorded on a recording medium corresponding to the density of a certain pixel of a spatial modulation element. If photographic film is used as the recording medium, the diffraction efficiency of the hologram is controlled according to the shading of each pixel by dividing the total amount of incident light into each pixel in time and making it incident in an appropriate amount, and the original image is An image corresponding to the desired shading is reproduced. Let Kf be the gradation of the image that is currently being recorded and reproduced, and each pixel of the spatial modulation element has a time interval t.
It is assumed that a desired amount of light is transmitted (or reflected) for each o. By repeating this operation a necessary number of times N, on the film, the sum of the amounts of light accumulated during the time NtO and the desired gradation information of Q are recorded. In this way, the contrast Cf of the recorded image on the film will be Cf2C8, and the tone will be N K f > k s
becomes. Therefore, it is possible to record and reproduce images with a greater number of gradations and better contrast than ever before.

Embodiments Hereinafter, a projection type multiplex recording apparatus and a multiplex recording method according to embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a schematic configuration of a hologram recording device for a holographic fist stereogram according to the present invention. As can be understood by comparing it with FIG. 5 showing a conventional example, a converging lens 23 is located behind a spatial modulation element (SLM) 24, and the SLM 24 is irradiated with parallel monochromatic light (laser light) 25. . With this arrangement, a uniform and large hologram can be recorded without increasing the aperture of the imaging lens 26. In FIG. 1, numerals 7 to 11 have the same structure as the conventional example shown in FIG. 5, and are a lens 7.8, a screen 9, a film-like recording medium 10, and a reference light source, respectively. The SLM 24 uses an external electrical signal source 27 and a box-type liquid crystal panel. In the same figure, 2
8.29 are polarizing plates whose tip axes are almost perpendicular to each other,
On the polarizing plate 29, there is a glass substrate 35 on which nonlinear elements (switching elements) 30 to 33 and an alignment film 34 are formed on one main surface at intersections of pixel electrodes arranged two-dimensionally in a matrix. It is provided. A narrow space is formed between this glass substrate 35, a glass substrate 38 having a counter electrode 3θ and an alignment film 37, and a seal 39, and a liquid crystal such as a twisted nematic (TN) liquid crystal 4 is formed in the space.
Hold 0. Note that 41 and 42 are laser beams that are incident and transmitted and are collimated almost in parallel, and when using a linearly polarized laser, the polarizing plate 29 is not necessary.

As is well known to those skilled in the art, the various performances of active matrix liquid crystal display devices are as follows regarding the contrast Φ gradation.
It currently exhibits the best characteristics among the liquid crystal display devices proposed so far. Under parallel monochromatic light, a contrast of 100 or more and a gradation of 16 or more were obtained. (Reference: Tanaka et al. 3-inch color LCD TV using RA-3iTFT”, National Technical Report, Vol. 33, No. 198
7, pp64-75, etc.).

FIG. 3 is a characteristic diagram schematically showing the dependence of the transmittance of the above-mentioned transmissive active matrix liquid crystal display device on the input signal Vrms. Tmax is the maximum transmittance of the display device, and is shown normalized to 1. Tmin
indicates the minimum transmittance of the display device, and the amount of light leaking out during the time to is WO. The contrast of the display device in this case is Cs = Tmax/Tmin
It is expressed as If this value is 100, the contrast C6 of the display device is defined as 100. If the maximum transmittance T wax of this display device is divided into eight equal parts and the transmitted light amount per to time is W, then in order to transmit the light amount of nxW per to time, input signals S11 S2 ~
It is sufficient to input the signal of Sn in S8. Note that n is a positive integer. To minimize the amount of light per time (WO), input the SO times signal. In this embodiment, in order to simplify understanding, a case will be considered in which the density pattern of an image to be recorded (or recorded/reproduced) changes in proportion to the amount of incident light. In holography, since the recording method uses a carrier wave, such an approximation is generally allowed. Furthermore, in the present invention, an image is considered to be a collection of pixels of various shades of light and shade.

The following description focuses on one pixel of an image to be recorded (or recorded/reproduced).

FIG. 4 is a diagram for explaining the multiplex recording method of the present invention, and shows how the transmittance of one pixel of a display device is temporally controlled. The vertical axis B indicates the amount of light transmitted per unit time of the display device, in other words, the amount of light per unit time incident on the recording medium. The horizontal axis shows time.

Assume that the recording medium is exposed for a time of t:8XtO. Note that the signal input to the display device is changed for each to.

In the case of exposure at the maximum transmittance of the display device, a total amount of light of 64×W is incident on the recording medium in a time of 8×to, as shown in the figure. The black recording level is achieved when the transmittance of the display device is minimized, but the total exposure amount in that case is 8 x WO
become. As mentioned above, the display device's load rating is C5.
= 8 fists W/WO = 100, so the maximum contrast ratio (contrast Cf) of the total exposure amount is Cf = (64-W)/
(8-WO)=8 fists W/WO=Cs=100, and the contrast Cf of the image recorded on the recording medium matches the contrast Cs of the display device.

On the other hand, if the tone of the image you want to record is n when the maximum brightness is 64, then n/8 = n1... With remainder n2, the transmittance of the time display device of n1XtO is set to the maximum 8W, and the period of to Let the transmittance be n2XW, and the remaining period (
8-n 1-L) Control the input signal so that the transmittance of the XtO display device is minimized. In this case, the total exposure amount to the recording medium is n.
W+α·WO (α≦8−n1−1). That is,
When each pixel is controlled by an external signal as described above, eight grayscale patterns are displayed every tO using a display device that displays only eight tones of transmittance per unit time, and the total exposure time is 8·to. As a result, a shading pattern of approximately 64 gradations is recorded on the recording medium. Moreover, the contrast Cf of the recorded image at that time matches that of the display device Cs.

Next, a multiplex recording method according to a second embodiment of the present invention will be explained. This embodiment is also structurally the same as the first embodiment. However, in the first embodiment, the shading to be recorded (recorded/reproduced) changes in proportion to the amount of incident light, and the shading of the recorded (recorded and reproduced) image is approximately proportional to the shading pattern of the recording medium. I mentioned the case. However, a recording medium with such good characteristics that the shading of a recorded/reproduced image and the shading of a recording medium forming a hologram are directly proportional to each other cannot be easily and inexpensively obtained. In practice, special photographic film is often used. moreover,
Images recorded and reproduced holographically are not simply proportional to the density of the recording medium. Therefore, the shading of the recorded (recorded session) image in such a case is not simply proportional to the amount of incident light;
It changes in proportion to a certain function f. Therefore, as a second embodiment, a case will be described in which the density y of a recorded (recorded/reproduced) image changes with respect to the amount of incident light X in the relationship y=f (x). First, the conversion function f for recording is measured in advance. In this measurement, light is incident on a film, which is a medium, and a function f is determined based on the resulting shading. According to this function f, by overlapping exposure of 8 gradation patterns every tO for a period of 8.10, a reproduced image with a gradation nearly 8 times the gradation of the display device (SLM, ) is realized. . In other words, when recording the brightness of n out of 64 equal parts between the bright and dark display states as the degree of image gradation to be recorded (recorded/played), At every tO, the input signal of the display device is controlled so that the transmittance is as explained below. In this case, the density of the recorded (recorded/reproduced) image when exposed for a time of 8·tO so that the transmittance of the display device is minimized is yo=f(8·WO). As a display device, the transmittance is changed in eight gradations (8·W).

Since the amount of change in density of the recorded (recorded/played) image is 7=f(X), the total amount of light incident on the recording medium x=f''(y)
The transmittance of the display device is controlled by an external signal by time modulation so that For example, evaluate in advance how y changes with X.

When exposed for a period of 5-tO at the maximum transmittance set by the display device, the density of the recording medium becomes ymax=f-1(6
4W). Therefore, if f-1 (64W) is set to be the recording density close to the maximum of the recording medium, the contrast Cf of the image to be recorded (recorded and reproduced) will be C
f=f-1(64・W)/f″'' (8-Wo). Photographic film and hologram recording/reproduction have thresholds and noise levels, and with an exposure amount of 8・WO, there will be no exposure or It is easy to set the gradation of the reproduced image so that it does not change.The contrast Cf can be the contrast of the film itself or the contrast of the hologram recording session itself, and can be nearly several hundred.

Therefore, Cf=f-1(64・W)/f-1(8・W
O)>C5=64eW/8・WO=100 can be realized. If you want to obtain the light and shade of n tones out of 64 tones, use x
Read n=l'(n) from the table, x・n/8−W=n
Calculate the remainder n2XW of lXtO, maximize the transmittance of the display device for the time nIXtO, and set the period of to, n2
×W recording density bone transmittance, remaining period (8-nl
-1) XtO controls the input signal so that the transmittance of the display device is minimized.

When this is done, the density of the recording medium is f(8Xn
I XW+n2XW+αXWO)=f Cxn+a
×WO) ~ n, which means that n tones out of 64 tones have been expressed. In other words, the transmittance per unit time is 8
By using a display device that only displays gradations, the transmittance (or reflectance) patterns of eight identical or different display devices are exposed to the recording medium for an exposure time of 8 tO for each to. An image of approximately 841 shades of light and shade is recorded. Further, the contrast Cf of the recorded image at that time can be made larger than the contrast Cs of the display device.

The recording device and recording method of the present invention have been described above, focusing on an active matrix type transmissive liquid crystal display device that can provide relatively high gradations as a display device (SLM), but the present invention also uses another display device. spatial modulation element (SLM)
), for example, reflective type or BS○ (BiSiOx) type SL
M, FROM-8LM1 Liquid crystal display devices other than the active matrix type can also be used. In addition, in the explanation of the embodiment, the explanation was not limited to holographic recording, but if the same recording medium is irradiated with a reference beam that is optically branched from the laser beam used as the incident beam, holographic recording can be made. Needless to say.

Effects of the Invention As described above, according to the present invention, even if a spatial modulation element capable of displaying only about 8 gradations is used, temporally identical or different images can be displayed at the same portion of the recording medium at appropriate times. By superimposing the recording on the hologram, it is possible to record a hologram with superior image quality in terms of contrast 11 tones, etc., compared to a hologram formed using only the tones inherent in the spatial modulation element. Furthermore, the effects of the present invention are enhanced by using an active matrix liquid crystal display device with excellent gradation as a spatial modulation element.

Furthermore, by making the light incident on the liquid crystal display device closer to parallel light, the contrast φ gradation characteristics of the display device can be improved, which is highly effective.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of a projection multiplex recording device according to an embodiment of the present invention, FIG. 2 is a sectional view of an active matrix liquid crystal display device used as a spatial modulation element of the projection multiple recording device, and FIG. The figure is a characteristic diagram showing the input signal dependence of the transmittance of an active matrix liquid crystal display device, Figure 4 is a diagram showing time and exposure conditions for explaining the multiple recording method of the present invention, and Figure 5 (a) , (b) is a perspective view schematically showing the recording system of a conventional holographic stereo duram, and FIGS. 6(a) and (b) are perspective views schematically showing the same conventional holographic stereo duram reproduction system . 7.8.23.26#... Lens, 10... Φ recording medium, 24... SLMl 25 --- Parallel monochromatic light, 27I
Iψ・Image signal generator.

Claims (6)

[Claims] (1) A first device that is a spatial modulation means that displays a two-dimensional gray pattern displayed over time T by an external input image signal as a plurality of light and dark patterns of transmittance or reflectance at each time ti; a second device that irradiates light onto the first device; a third device that projects light transmitted or reflected from the first device; and a record that records the light projected from the third device. 1. A projection type multiplex recording device, comprising: a recording medium, and recording a plurality of temporally gradation patterns displayed by the first device in a manner superimposed on substantially the same portion of the recording medium. (2) The projection type multiplex recording device according to claim (1), wherein the first device is a liquid crystal display device. (3) The projection type multiplex recording device according to claim (1) or (2), wherein the first device is an active matrix type liquid crystal display device. (4) a first device that displays a two-dimensional shading pattern as a shading pattern of transmittance or reflectance according to an external signal; a second device that irradiates light to the first device; a third device that projects light transmitted or reflected from the
and a recording medium that records the light projected onto the third device, wherein a plurality of temporally shading patterns displayed by the first device are placed on substantially the same portion of the recording medium. A multiplex recording method characterized by recording in a superimposed manner. (5) As the degree of shading of an image recorded on a recording medium or a reproduced image pixel k of a shading pattern recorded on the recording medium, the brightness of n out of the total m divisions between the bright and dark display states is calculated. A multiplex recording method for recording as shown in FIG. m, the exposure time is divided into times ti, and the external signal is applied so that the pixel s on the first device corresponding to the pixel k exhibits a predetermined transmittance or reflectance for each time ti. input, and transmits the pixel s to a predetermined transmittance or reflectance so that the total amount x of light that is transmitted or reflected and reaches the recording medium during the entire exposure time is n/m. controlling an external signal input to the recording medium, and temporally superimposing a plurality of grayscale patterns, which are displayed on the first device as a set of pixels s showing grayscale according to each external signal, on substantially the same portion of the recording medium. 5. The multiplex recording method according to claim 4, wherein the multiplex recording method is characterized in that recording is performed by (6) As the degree of shading of a pixel k recorded on a recording medium that exhibits the characteristic that the amount of exposure is expressed by a specific function f relative to the amount of input light, the display state from bright to dark is divided into m equal parts in total. This is a multiplex recording method for recording the brightness of n of the total exposure time, and the pixel s on the first device corresponding to the pixel k has a predetermined transmittance or a predetermined transmittance or inputting the external signal so as to indicate reflectance, and setting the pixel s at the total exposure time to the predetermined transmittance or reflectance, and the total amount x of light transmitted or reflected and reaching the recording medium; When the exposure time is the maximum transmittance or reflectance of the first device and the total amount of light that is transmitted or reflected and reaches the recording medium is Xmax, f(x)/f(Xmax)=n/m The external signals inputted to the first device are controlled so that the relationship of 5. The multiplex recording method according to claim 4, wherein the recording is performed in a superimposed manner at substantially the same location on the recording medium.