JP2007148451A - Computer hologram - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a computer hologram for displaying a three-dimensional multicolor (full-color) pattern, in particular, for displaying a bright image of high picture quality in accurate colors with reduced noise upon displaying a multicolor three-dimensional image which gives a parallax only in the horizontal direction. <P>SOLUTION: The hologram has a long slit in a horizontal direction as a structural unit consisting of interference fringes computed for light at a desired wavelength, and the hologram comprises a plurality of slit groups, wherein each slit group includes a plurality of the above slits corresponding to various wavelengths arranged in the vertical direction, and each slit group is controlled in such a manner that a product of the wavelength and the main spatial frequency in a vertical direction of the interference fringes constituting the plurality of slits is constant. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a computer generated hologram obtained by forming information on the wavefront of light from each point on a displayed object on a substrate in the form of interference fringes.
In particular, the present invention relates to a computer generated hologram having parallax only in the horizontal direction and displaying a multicolored display image.

  Based on the calculated results, such as calculating interference fringes by adding coherent reference light based on the complex amplitude distribution of light from each point on the object to be recorded using a computer, etc. A “computer generated hologram (CGH)” obtained by forming interference fringes on a substrate so as to have a function of diffracting light is known.

  Computer holograms can be formed on a substrate by directly drawing interference fringes with a high-resolution drawing device such as an electron beam drawing device, or by using a low-resolution image output device. A method of optically reducing and recording an image is known.

Here, the interference fringes are calculated as a two-dimensional pattern and formed on the substrate.
Depending on the formation method and recording material, interference fringes can be distributed on the substrate (transmittance or reflectance distribution) or phase modulation amount distribution (such as the distribution of minute irregularities on the surface and the refractive index distribution). Or a combination of these.

  When predetermined light is incident on such a computer generated hologram, the above density distribution and phase modulation amount distribution diffract the light, and an image recorded by the first-order diffracted light is reproduced. When the first-order diffracted light enters the observer's eyes, the recorded image can be observed as a three-dimensional image.

Computer holograms intended to display stereoscopic images often have a parallax only in the horizontal direction for the purpose of reducing the amount of calculation.
This is because, when a stereoscopic image is displayed under normal observation conditions, it is sufficient that only the horizontal parallax can be reproduced (recognized stereoscopically by binocular parallax). At this time, a computer generated hologram having parallax only in the horizontal direction can be considered as a computer imitating a rainbow hologram photographed using light interference.

In addition, when performing multicolor display in a computer generated hologram, a method of calculating interference fringes for wavelengths corresponding to R, G, and B suitable for multicolor display, and superimposing these interference fringes coherently, and incoherent There is a method of overlaying.
In any of these methods, the final interference fringes are formed on the substrate as a two-dimensional pattern as described above.

In this case, when coherently superimposed, interference components between the complex amplitudes of the light that generates the image of each wavelength are recorded, and noise light other than the light that reproduces the desired image appears at the time of observation. become.
On the other hand, when superimposed incoherently, diffracted light caused by moire components between interference fringes superimposed incoherently occurs and is also observed as noise.
Furthermore, in the latter case, since the density patterns of a plurality of interference fringes are superimposed incoherently, the interference fringes cannot be properly recorded in a region where the two interference fringes are shifted from each other by about ½ period. There is also a problem.

  The occurrence of the above “noise” not only affects a simple S / N reduction, but also part of the light energy to be used for image reproduction is distributed to the noise component, so that the observed image is It also leads to the problem of darkening.

  In addition, when the reconstructed image from the computer generated hologram is multicolored, sufficient consideration has not been given to color reproducibility, and there are color changes depending on the height on the display image, and the saturation of the display image There was a problem of causing a drop.

  The present invention is a computer generated hologram intended for displaying a three-dimensional multicolor (full color) pattern, particularly when displaying a three-dimensional image having parallax only in the horizontal direction in a multi-colored manner, reducing noise and improving image quality. The purpose is to display a bright image with accurate color.

The present invention
In a computer generated hologram with parallax only in the horizontal direction,
A slit unit composed of interference fringes calculated for light of a desired wavelength is used as a constituent unit.
A plurality of slits corresponding to different wavelengths are arranged vertically to form a slit group,
In the slit group, the product of the main spatial frequency in the vertical direction of the interference fringes constituting the plurality of slits and the wavelength is constant,
The main feature is that a plurality of slit groups are formed.

  Further, the present invention is characterized in that each of the plurality of slit groups includes slits made of interference fringes corresponding to the same wavelength (R, G, B, etc.).

<Action>
On the computer generated hologram, the interference fringes corresponding to the wavelength of the desired light are formed in the slit that is long in the horizontal direction (parallax direction) without including the components related to the other wavelengths. It is possible to reproduce a continuous wavefront of light in the horizontal direction, display a high-quality three-dimensional image having parallax in the horizontal direction with little noise, no parallax skipping, and little blurring of the image.

In the slit group, by making the product of the main spatial frequency in the vertical direction of the interference fringes constituting the plurality of slits and the wavelength constant, each slit constituting the slit group emits light of a desired wavelength. It is possible to reliably enter the eyes of an observer at a desired observation distance.
Thereby, additive color mixture display by a desired wavelength from each slit constituting the slit group is possible, and a multicolor image can be displayed with an accurate color over a wide color gamut. (Claim 1)

In the following, the reason for this will be described in detail, and other actions will be mentioned.
Note that the computer generated hologram of the present invention is not limited to the one that exactly corresponds to the definition of the hologram, but a general display (kinoform) that calculates the wavefront of light from an object using a computer and reproduces the image by light diffraction. Etc.).
Therefore, the “interference fringes” constituting the slits of the computer generated hologram of the present invention refer to optical diffraction patterns including not only interference fringes in a strict sense but also phase modulation patterns of kinoform.

First, the interference fringes constituting the inside of the slit will be considered.
In general hologram observations, the standard condition is that white illumination light is incident from above the observer's head and the reproduced image from the hologram is observed near the front of the hologram. The spatial frequency (reciprocal of the period) in the vertical direction of the stripe corresponds to the wavelength of light observed by the observer.
Therefore, in the computer generated hologram according to the present invention, by appropriately setting the spatial frequency in the vertical direction of the interference fringes in the slit, it is possible to arbitrarily select the color (additive color mixture with light of a plurality of wavelengths) in which the slit group is observed. it can.

  Here, the correspondence relationship between the spatial frequency in the vertical direction of the interference fringes of the computer generated hologram and the preset wavelength of light is simply expressed by the following equation.

  Where f is the spatial frequency, λ is the desired wavelength, θ is the incident angle of the preset illumination light on the computer hologram surface, and h is the height of the slit with the center of the computer hologram as the origin (the upward direction is positive) ), D is a preset observation distance. (See Figure 8)

That is, when the incident angle and the observation position of the illumination light are determined, in one slit group at an arbitrary height on the computer generated hologram, (f × λ) of the interference fringes in each slit should be a constant value. For example, light of each set wavelength can be made incident on the observer's eye from each slit, and additive color mixing of a desired wavelength can be realized.
Furthermore, when this is realized in all the slit groups on the computer generated hologram, pattern display with accurate color reproduction can be performed on the entire surface of the computer generated hologram. (Claim 2)

  As the wavelength to be set in advance, any wavelength can be selected, and if at least two wavelengths are appropriately set in the slit group, a desired color in the slit group can be obtained by additive color mixing of at least two wavelengths of light. Can be expressed.

At this time, on the computer generated hologram, a plurality of slit groups each include a slit made of interference fringes corresponding to the same wavelength. It is possible to easily express the entire surface. (Claim 3)
By selecting three or more appropriate wavelengths as a plurality of wavelengths to be set in advance, it becomes possible to express an arbitrary color distribution within the slit group, and a full-color image corresponding to a wide color gamut can be obtained. It is possible to display the entire computer generated hologram surface.

  In particular, when wavelengths corresponding to R, G, and B are selected as the three wavelengths, a full color image can be expressed by additive color mixture of R, G, and B, and digital image data created on a computer can be easily obtained. It is possible to display. (Claim 4)

  On the other hand, when four or more wavelengths are selected, it is possible to accurately represent a wider color gamut than the display using the normal three primary colors of R, G, and B. (Claim 5)

  Here, by using only one type of vertical spatial frequency in one slit, generation of an interference fringe pattern is facilitated, and noise is reduced due to the absence of extra components in the interference fringes, and diffraction is performed. It can be a bright computer hologram with high efficiency. (Claim 6)

Next, consider the length of the slit in the horizontal direction.
A stereoscopic image displayed by a computer generated hologram can be handled as a collection of minute points (hereinafter referred to as “object points”). At this time, when the distance d _p from the computer generated hologram to the object point and the viewing area θ _{− to} θ ₊ of the computer generated hologram are used, the corresponding size L on the computer generated hologram is expressed (see FIG. 5).

Angular width of the viewing zone θ = θ _{+ +} θ _- and when, if theta is relatively small, can be approximated by the following equation.

If a slit having a length of L or more is used in the horizontal direction on a computer generated hologram, continuous wavefront information of light from an object point can be recorded within the slit length.
(Claim 7)
Thus, within the set viewing zone, an object point of depth d _p can be displayed with ideal wavefront information, that is, having a continuous parallax for the observer and focusing. In addition, it is possible to display a stereoscopic image that sufficiently satisfies physiological effects required for stereoscopic vision such as convergence.

  If the horizontal length of the slit matches the horizontal length of the display surface of the computer hologram, the maximum viewing area and / or the maximum display area of the computer hologram having the display surface of that size The depth can be displayed. (Claim 8)

Finally, consider diffraction due to the vertical width of the slit.
In the vertical direction, the spread of diffraction caused by the width b of the rectangular slit is expressed by the following equation when expressed by the width Δy between the first dark lines at the center of the diffraction pattern at the observation distance.

Here, the observation distance is d ₀ and the wavelength is λ.
If Δy becomes too large, the amount of light incident on the observer's eyes with respect to the designed wavelength decreases, and light of a wavelength other than the designed wavelength also enters the observer's eyes. descend.

  If the slit width in the vertical direction is 10 μm or more, Δy at the observation position is several to tens of mm or less under general observation conditions, and an image can be displayed with a highly saturated color. (Claim 9)

  On the other hand, if the width of the slit becomes too large, it is recognized as a horizontal stripe during observation, which is not desirable. In particular, when multicolor display is performed using slits of interference fringes having three kinds of spatial frequencies such as R, G, and B in the vertical direction, it is desirable that the slits such as R, G, and B cannot be recognized.

  Specifically, when the observation distance is 500 mm, a width of about 150 μm or less may be used so that an observer with a visual acuity of 1.0 cannot recognize the slit. (Claim 10)

  When using a slit group consisting of a set of three slits, in order to make the arrangement of each slit group unrecognizable by the observer, the width of the slit group should be less than this value, that is, 150 μm or less. Good. By designing in this way, an image with sufficient resolution can be displayed.

  As described above, in order to set an optimum condition regarding the width in the vertical direction of the slit, it is better to consider the lower limit due to the diffraction phenomenon due to the slit width and the upper limit due to the eye resolution depending on the observation conditions. For example, in the example in which the above three slits of R, G, and B are used as a slit group, the optimum slit width is about 50 μm. By setting the slit width in the vertical direction in this way, a multicolor display image can be displayed with high quality (with sufficient resolution and sufficient color expression).

As described above, as in the present invention, a computer generated hologram has a horizontally long slit composed of interference fringes calculated for light of a desired wavelength as a constituent unit, and a plurality of slits corresponding to different wavelengths are vertically aligned. By arranging the slit group side by side, the product of the main spatial frequency in the vertical direction of the interference fringes constituting the plurality of slits in the slit group and the wavelength is constant, and by arranging the plurality of slit groups,
When displaying a multicolor stereoscopic image with parallax in the horizontal direction, it is possible to display a spatially smooth image in the depth direction, minimizing noise, and realizing accurate color reproduction over a wide color gamut. A high-quality multicolor stereoscopic image can be displayed.

FIG. 1 is an explanatory diagram showing an example of a computer generated hologram according to the present invention.
FIG. 2 is an explanatory view showing, in an enlarged manner, a slit group constituting the computer generated hologram of the present invention having a vertical spatial frequency corresponding to each of R, G, and B wavelengths.

In the present invention, a computer generated hologram is formed by arranging a plurality of slits and slit groups as shown in the upper part of FIG. 1 or enlarged in FIG.
The slit is composed of interference fringes, and the main spatial frequency component in the vertical direction of the interference fringes in each slit corresponds to the observed wavelength, and the spatial frequency component in the horizontal direction corresponds to parallax.

Therefore, in order to ensure a smooth depth and a continuous viewing zone of the display image, the slit has a sufficient length in the horizontal direction.
On the other hand, since the width of the slit in the vertical direction can be considered as the size of the pixel of the display image, an image having a sufficient resolution cannot be displayed unless the width is less than a certain level. Therefore, the slit needs to be long in the horizontal direction as shown in the figure.

  In the figure, the interference fringes are expressed by a binary density modulation (by transmittance modulation, reflectance modulation, etc.) pattern, but the interference fringes may be expressed by gradations, and the density modulation pattern. The pattern is not limited to the above, and may be a phase modulation (by refractive index modulation, thickness modulation, etc.) pattern or a pattern in which both density and phase are modulated.

  Here, an image can be expressed with an accurate color by appropriately setting the wavelength corresponding to the slit constituting the slit group. In particular, if three slits of R, G, and B are used as a slit group, a full color image can be expressed by additive color mixture of R, G, and B, and digital image data created on a computer can be easily displayed. Become. On the other hand, when four or more wavelengths are selected, it is possible to accurately represent a wider color gamut than the display using the normal three primary colors of R, G, and B.

FIG. 3 is a cross-sectional view showing the emission directions of the 0th-order diffracted light and the 1st-order diffracted light when illumination light is incident on the reflection type computer generated hologram.
For an arbitrary wavelength, the basic diffraction phenomenon by the diffraction grating is expressed by the following equation (5).
d = mλ / (sin α−sin β) (5)
However, d is the grating | lattice space | interval (reciprocal number of a spatial frequency) in the focused direction, m is a diffraction order, (lambda) is the wavelength of illumination light, (alpha) is the emission angle of the 0th-order diffracted light (transmitted light and regular reflected light) in the said direction, (beta) Is the emission angle of the m-th order diffracted light in this direction.
Usually, first-order diffracted light (that is, m = 1) is used to reproduce a stereoscopic image. The exit angle of the 0th-order diffracted light is the same as the incident angle of the illumination light, or the sign is only reversed.

  In the case of a transmission type computer generated hologram, the same handling is possible for 0th-order diffracted light and mth-order diffracted light.

FIG. 4 is an example of an enlarged view of interference fringes constituting a conventional computer hologram in which interference fringes having a plurality of types of spatial frequencies are recorded in the vertical direction.
As described above, in the conventional hologram, moire fringes are formed when multiple exposure is performed, and diffracted light or the like is generated by the moire component, which causes noise when a display image is observed. Therefore, in the conventional computer generated hologram, when an image is displayed in multicolor, the generation of noise or the like cannot be avoided.

FIG. 5 is an explanatory diagram showing the viewing area of the computer generated hologram and the size on the hologram surface corresponding to the viewing area.
The minimum value L of the horizontal slit length of the computer generated hologram of the present invention can be calculated by using the equations (2) and (3) for each of the object points constituting the stereoscopic image displayed by the computer generated hologram.
At this time, if a slit having a length of L or more in the horizontal direction is used on the computer generated hologram, continuous wavefront information of light from an object point can be recorded within the length of the slit.
As a result, an object point of depth d _p can be displayed with ideal wavefront information within the range of the set viewing zone, that is, the observer has continuous parallax and is required for stereoscopic vision such as focus adjustment. A stereoscopic image that sufficiently satisfies the physiological effect can be displayed.

  On the other hand, a slit having a length of L or less or a discontinuous slit does not provide a sufficient viewing zone, or the viewing zone is lost in continuity, and the position of an object point cannot be accurately displayed, Problems such as differences in depth information from eye functions such as adjustment and the depth of displayed object points occur.

  If the horizontal length of the slit matches the horizontal length of the display surface of the computer hologram, the maximum viewing area and / or the maximum display area of the computer hologram having the display surface of that size The depth can be displayed.

However, when the horizontal length of the slit is made sufficiently long, it is not necessary to record interference fringes over the entire length of the slit.
The range where the interference fringes exist is only required to be the minimum value L of the length of the slit, and recording the interference fringes longer than that is a noise when there are many object points to be expressed in one slit. It is not preferable because it causes an increase in the above.

Here, the diffraction caused by the vertical width of the slit is considered.
In the vertical direction, when the spread of diffraction due to the width b of the rectangular slit is represented by the width Δy between the first dark lines at the center of the diffraction pattern at the observation distance, Δy can be calculated by Equation (3).

If Δy becomes too large, the amount of light incident on the observer's eye for the designed wavelength decreases, and light of a wavelength other than the designed wavelength also enters the observer's eye, so the color saturation of the display image Also decreases.
Therefore, in general, it is better to set Δy at the observation position to 10 to several mm or less. In order to satisfy this condition, the vertical slit width needs to be 10 μm or more.

As a specific example, when the observation distance d ₀ = 150 mm and the observation wavelength λ = 500 nm, the slit width b must be 15 μm or more in order to make the width Δy between the first dark lines at the observation distance 10 mm or less. There is.
It is also practical to treat the half-value width with respect to the center maximum of the diffraction pattern as the width of the diffraction pattern. In this case, the width Δy _1/2 between the first dark lines at the center of the diffraction pattern at the observation distance is equal to the above Δy. It becomes about 0.7 times.

Δy _1/2 = 0.7 × (2λd ₀ / b) (6)
It is also effective to design the slit width based on equation (6) based on this concept.

On the other hand, when the vertical width of the slit group becomes too large, it is recognized as a horizontal streak during observation, which is not desirable. In order to avoid this, for example, when the observation distance is 500 mm, the slit group should be approximately 150 μm or less in width so that an observer with a visual acuity of 1.0 cannot recognize the configuration within the slit group. It ’s fine.
Thereby, the structure of the slit group is not identified by the observer, and an image having a sufficient resolution can be displayed.

  In particular, when multi-color display is performed using three types of slits of interference fringes having spatial frequencies corresponding to R, G, and B in the vertical direction as a group of slits, a condition in which the observer cannot recognize the arrangement of each group of slits In order to achieve this, the slit may have a width of 1/3 or less of this value (that is, a width of 50 μm or less).

  As described above, in order to set an optimum condition regarding the width in the vertical direction of the slit, it is better to consider the lower limit due to the diffraction phenomenon due to the slit width and the upper limit due to the eye resolution depending on the observation conditions. For example, in the example in which the above three slits are the slit group, the optimum slit width is about 50 μm. By setting the slit width in the vertical direction as described above, a multicolor display image can be displayed with high quality (with sufficient resolution and sufficient color expression).

FIG. 6 is an explanatory view schematically showing the state of observation of a computer generated hologram according to the present invention.
That is, when the light source is installed so that the illumination light is incident on the computer generated hologram according to the present invention at a preset angle, an image is displayed within the range of the viewing zone (θ _{− to} θ ₊ ) set by the first order diffracted light from the computer generated hologram. I can observe.

FIG. 7 is an explanatory diagram showing a method of calculating interference fringes in the slit when generating a computer generated hologram according to the present invention.
First, with regard to a certain object point, attention is focused on a slit group at the position of a line where the object point and the set observer's eyes (or a horizontal line at the viewpoint position) and the computer generated hologram plane intersect.

At this time, the complex amplitude distribution of the light in the slit group need only take into account the light having a viewing area spread from the object point in the same plane.
For all the object points to be displayed, the contribution to the corresponding slit group is calculated with respect to the desired wavelength, and the complex amplitude distributions in the same slit group are added together, so that the horizontal direction to be realized as the slit of the computer generated hologram A complex amplitude distribution is obtained.

Calculation for all desired wavelengths yields a complex amplitude distribution at all positions on the computer generated hologram of the present invention.
For example, when the three slits of R, G, and B are color-displayed as a slit group, in the above calculation process, the light from the object point is decomposed into three components of R, G, and B, and the corresponding slits. The complex amplitude distribution at may be calculated.

  Here, as the spread of light from the object point in the above plane, it does not spread uniformly in the angle range corresponding to the viewing zone, but considers three-dimensional occlusion and the angle dependency of the light intensity. In addition, by setting the angle range of the spread from the object point and the intensity distribution of light individually, hidden surface processing etc. is performed, and more diverse and high-quality stereoscopic images that represent metal surfaces etc. can be displayed It becomes.

  Further, the vertical complex amplitude distribution in the slit can be obtained with respect to the observed wavelength (color) from the incident angle of the illumination light and the observer's viewpoint position at an arbitrary position in the slit using the equation (1). What is necessary is just to obtain the interference fringe of a spatial frequency (vertical direction).

Specifically, for a certain wavelength, a plane wave with a wavefront perpendicular to the above plane (or a cylindrical surface wave focused at the observation position) reaches the computer generated hologram plane with the complex amplitude distribution calculated above in the horizontal direction. The interference fringes in the slit can be obtained on the assumption that another uniform plane wave (coherent with the plane wave or the cylindrical surface wave) is incident from the incident angle of the illumination light.
As a simpler method, the interference fringes in the slit can also be obtained by obtaining the spatial frequency of the interference fringes in the vertical direction in advance by the equation (1) and modulating with the complex amplitude distribution in the horizontal direction described above. It is.

FIG. 8 is an explanatory diagram showing a relationship between the computer hologram and the observer's viewpoint position in the vertical direction when illumination light is incident on the reflection type computer hologram.
Depending on the incident angle of the illumination light, the observation distance, and the height of the slit on the computer hologram, if the relationship between the spatial frequency in the vertical direction of the slit and the observation wavelength is designed based on the equation (1), the observation distance When observed from above, the entire surface of the computer generated hologram can be observed with a desired display color.

If not based on this design, the color tone of the display color is not uniform between the upper part and the lower part of the computer generated hologram, and accurate color reproduction becomes difficult.
On the other hand, when the total height of the computer generated hologram is sufficiently small compared with the observation distance, the equation (1) may be approximated as F = 1 / λ. In this case, the entire computer generated hologram surface is related to a specific wavelength. Therefore, the calculation can be simplified and a computer generated hologram can be easily created.

In the above description, the calculation method has been described with respect to a three-dimensional object as the display object of the computer generated hologram according to the present invention. In this case, in the above calculation method, a narrow viewing zone may be set for each changing image.
Note that the computer generated hologram of the present invention can be applied to any type of hologram form such as a phase hologram represented by a surface relief type and an amplitude hologram by density expression.

Explanatory drawing which shows an example of the computer generated hologram (and slit for R, G, B) by this invention. Explanatory drawing which expands and shows an example of the interference fringe of the slit for R, G, B of the computer generated hologram by this invention. Sectional drawing in the orthogonal | vertical direction which shows the emission direction of the 0th-order diffracted light and the 1st-order diffracted light when the illumination light from a light source injects into a reflection type computer generated hologram. Explanatory drawing which expands and shows an example by which the interference fringes of R, G, and B of the conventional computer generated hologram were multiplexed and recorded. Explanatory drawing of the magnitude | size corresponding on the viewing area of a computer generated hologram of this invention, and a computer hologram surface. Explanatory drawing which shows the mode of observation of the computer generated hologram of this invention. It is explanatory drawing which shows the calculation method of the interference fringe in the slit at the time of the computer hologram production | generation of this invention, and represents a mode that the slit of the position which tied the virtual three-dimensional object which should be displayed and a visual line is calculated. Explanatory drawing which shows the relationship between the computer hologram in a perpendicular direction, and an observer's viewpoint position when illumination light injects into a reflection type computer hologram.

Claims (10)

In a computer generated hologram with parallax only in the horizontal direction,
A slit unit composed of interference fringes calculated for light of a desired wavelength is used as a constituent unit.
A plurality of slits corresponding to different wavelengths are arranged vertically to form a slit group,
In the slit group, the product of the main spatial frequency in the vertical direction of the interference fringes constituting the plurality of slits and the wavelength is constant,
A computer generated hologram comprising a plurality of slit groups. 2. The computer generated hologram according to claim 1, wherein the main spatial frequency in the vertical direction of the interference fringes constituting each slit corresponds to f in the following formula with respect to a desired wavelength.

(Where f is the spatial frequency, λ is the desired wavelength, θ is the angle of incidence of the preset illumination light on the computer hologram surface, h is the height of the slit with the center of the computer hologram as the origin (the upward direction is positive) D) is a preset observation distance.)   3. The computer generated hologram according to claim 1, wherein each of the plurality of slit groups includes a slit made of interference fringes corresponding to the same wavelength.   The computer generated hologram according to any one of claims 1 to 3, wherein the slit group includes three slits made of interference fringes calculated for light having wavelengths corresponding to R, G, and B, respectively.   4. The computer generated hologram according to claim 1, wherein the slit group includes slits corresponding to four or more different wavelengths.   6. The computer generated hologram according to claim 1, wherein the spatial frequency in the vertical direction of the interference fringes constituting the slit is uniform in each slit.   The computer generated hologram according to any one of claims 1 to 6, wherein the length of the slit in the horizontal direction is not less than the product of the maximum depth on the display image and the tangent of the angle of the viewing zone.   7. The computer generated hologram according to claim 1, wherein a horizontal length of the slit coincides with a horizontal length of a display surface of the computer hologram.   9. The computer generated hologram according to claim 1, wherein the slit has a width in the vertical direction of 10 [mu] m or more.   The computer generated hologram according to claim 1, wherein the slit group has a width in the vertical direction of 150 μm or less.

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