JP7277328B2 - 3D image display device - Google Patents

Description

The present invention relates to a 3D image display device that displays 3D images.

In recent years, various 3D image display methods have been proposed, including a twin-lens system using 3D glasses. In particular, spatial image reproduction type three-dimensional video display systems such as the integral system have the advantage of being able to reproduce horizontal and vertical parallaxes. This method requires a large amount of image information in order to reproduce light rays in many directions.
In particular, in the case of the integral method, the number of pixels of the 3D image corresponds to the number of element lenses of the lens array. Therefore, in order to improve the resolution of 3D images, it is necessary to miniaturize the lens array.

However, if the lens pitch of the element lenses is reduced, the effect of diffraction by the lenses becomes greater, and at the same time it is necessary to reduce the pixel size of the element images displayed from the rear surface of the lens array. Therefore, there is a limit to miniaturization of the lens array.
Therefore, conventionally, in order to increase the resolution of a 3D image, a method has been proposed in which a plurality of integral type displays for displaying a part of the 3D image are combined and displayed (see Patent Document 1). This method achieves high-resolution 3D video by expanding and combining elemental image groups displayed by multiple displays.

JP 2017-151202 A

In the conventional system, a plurality of displays are combined in order to increase the resolution of the 3D video, which increases the scale of the entire device. Therefore, a new technique for increasing the resolution of 3D images has been desired.
The present invention has been made in view of such a demand, and is intended to increase the resolution of a three-dimensional image displayed by the integral method by displaying different elemental images in time series for each elemental lens of a lens array. An object of the present invention is to provide a three-dimensional image display device capable of

In order to solve the above-described problems, a 3D video display device according to the present invention is a 3D video display device for displaying integral 3D video, wherein a group of element images with shifted viewpoint positions is displayed as a group of element images. 2D video display means for displaying a 2D video with the same display position at a predetermined cycle; polarization switching means for switching the polarization of the light of the elemental image group between two polarization states at the cycle; and the polarization switching. a lens array in which element lenses are arranged at positions corresponding to the display positions of the individual element images of the element image group, arranged on either the light incident side or the light exit side of the means; and a polarization diffraction means for translating the emission direction of the light of the group of elemental images in different directions by diffraction according to the polarization state.

In such a configuration, the 3D video display device uses the 2D video display means to display the group of element images whose viewpoint positions are shifted as a 2D video in which the display positions of the element images are the same at a predetermined period, such as a frame interval. to display. This elemental image group is an image obtained by two-dimensionally arranging a plurality of elemental images for displaying a three-dimensional image by the integral method.
Then, the 3D video display device switches the polarization of the light of the elemental image group between the two polarization states at the cycle of displaying the elemental image group by the polarization switching means.

Further, the three-dimensional image display device is arranged on either the light incident side or the light emitting side of the polarization switching means, and the lens array in which the element lenses are arranged at the positions corresponding to the display positions of the individual element images of the element image group. converts the group of elemental images into reproduced light of the subject. It should be noted that this reproduced light has a different polarization state periodically.
Then, the three-dimensional image display apparatus causes the polarization diffraction means to translate the emission direction of the light of the group of elemental images whose polarization states are switched at a predetermined cycle in different directions by diffraction according to the polarization state.
As a result, the 3D image display device can make the subject of the 3D image visible as subject light reproduced by increasing the number of lenses in the lens array, and can increase the resolution of the 3D image.
For example, a 3D image display device uses a group of elemental images as images corresponding to 1/2 of the lens pitch of a lens array in a predetermined period in an oblique direction. It suffices to shift the light of the elemental image group by 1/4 in parallel.

Further, in order to solve the above-mentioned problems, a three-dimensional video display device according to the present invention is a three-dimensional video display device for displaying integral-type three-dimensional video, wherein element images shifted in an oblique direction by 1/2 pixel a two-dimensional image display means for displaying the group as a two-dimensional image in which the display positions of the element images are the same at a predetermined cycle; a lens array having element lenses arranged at positions corresponding to the display positions of the individual element images of the element image group, arranged on the light exit side of the polarization switching means; and a polarization diffraction means for translating the emission direction of the light of the elemental image group in a ±1/4 pixel oblique direction by diffraction according to the polarization state.

With such a configuration, the 3D video display device can make the subject of the 3D video visible as subject light reproduced by a group of element images in which the number of pixels of the element images is increased, thereby increasing the resolution of the 3D video. can do.

ADVANTAGE OF THE INVENTION This invention has the outstanding effect shown below.
According to the present invention, it is possible to switch and display a group of elemental images with different viewpoint positions in chronological order at the same display position. Therefore, according to the present invention, it is possible to display a 3D image with a high resolution without increasing the size of a display device that displays a group of elemental images.

1 is a perspective view of a 3D image display device according to an embodiment of the present invention; FIG. 1 is a plan view showing the configuration of a 3D image display device according to an embodiment of the present invention; FIG. FIG. 4 is an explanatory diagram for explaining a group of elemental images displayed by the two-dimensional video display means, wherein (a) shows images of odd-numbered frames and (b) shows images of even-numbered frames; FIG. 4 is an explanatory diagram for explaining an example of switching the polarization state by the polarization switching means, in which (a) shows generation of right-handed circularly polarized light and (b) shows generation of left-handed circularly polarized light; FIG. 4 is a front view showing a configuration example of a lens array configured with circular element lenses; FIG. 4A is a diagram showing the diffraction of light rays by the polarization diffraction element, in which (a) shows a case where the incident light is right-handed circularly polarized light, and (b) shows a case where the incident light is left-handed circularly polarized light. FIG. 4 is an explanatory diagram for explaining the relationship between the polarization state and the diffraction direction by a pair of polarization diffraction elements, in which (a) is right-handed circularly polarized incident light, and (b) is left-handed incident light; The case of circularly polarized light is shown. FIG. 5 is an explanatory diagram for explaining the relationship between the diffraction pitch of the polarization diffraction element and the amount of shift; FIG. 5 is an explanatory diagram for explaining the relationship between the center positions of the element lenses and the shifted center positions; FIG. 4 is an explanatory diagram for explaining the effect of increasing the resolution of a 3D image in the 3D image display device according to the embodiment of the present invention; 4 is a flow chart showing the operation of the 3D image display device according to the embodiment of the present invention; FIG. 5 is a plan view showing the configuration of a 3D image display device according to a modification of the present invention; FIG. 5 is an explanatory diagram for explaining the relationship between the center positions of the element lenses and the shifted center positions; It is an explanatory view for explaining the distance between the center position of the element lens and the position where the light beam is shifted in two stages. It is a front view showing an example of the configuration of a lens array, (a) is a diagram of square element lenses, (b) is a diagram of hexagonal element lenses configured in a honeycomb structure, and (c) is a horizontally long lens array. It is the figure which comprised with the rectangular-shaped element lens. FIG. 4A is an explanatory diagram for explaining a chromatic aberration correction method, in which (a) is a diagram showing a mechanism by which chromatic aberration is generated, and (b) is a diagram showing a chromatic aberration correction method. FIG. 11 is a plan view showing the configuration of a 3D image display device according to another modification of the present invention; FIG. 11 is an explanatory diagram for explaining an elemental image group displayed by a 3D video display device according to another modification of the present invention; FIG. 11 is an explanatory diagram for explaining the effect of increasing the resolution of a 3D image in a 3D image display device according to another modification of the present invention; FIG. 10 is an explanatory diagram for explaining how to increase the resolution of elemental images in a 3D video display device according to another modification of the present invention, in which (a) shows light ray paths of pixels of the elemental images; is a diagram showing positions of pixels viewed by an observer.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<<Structure of 3D image display device>>
First, the configuration of a 3D image display device 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG.

The 3D image display device 1 displays an image that allows an observer M to view a 3D image T according to the integral method.
As shown in FIG. 1 , the three-dimensional image display device 1 includes two-dimensional image display means 10 , polarization switching means 11 , lens array 12 and polarization diffraction means 13 .

The two-dimensional image display means 10 displays, at a predetermined cycle, a group of element images whose viewpoint positions are shifted as two-dimensional images in which the display positions of the element images are the same.
This elemental image group is an image obtained by two-dimensionally arranging the elemental images I of the integral method. Also, the elemental image group has different viewpoint positions in a predetermined cycle, for example, a frame cycle in time series.

As shown in FIG. 3, the group of elemental images displayed by the two-dimensional video display means 10 includes m elemental images (m≧2) in the vertical direction (y direction) and m (m≧2) in the horizontal direction (x direction). The image is two-dimensionally arranged with n pieces (n≧2) each.
In addition, the two-dimensional image display means 10 further displays a group of element images with different viewpoint positions in chronological order. Specifically, the two-dimensional video display means 10 displays the element image group (FO _0,0 to FO _m−1,n−1 ) displayed in the odd-numbered frame FO shown in FIG. ), the viewpoint positions are shifted in the vertical and horizontal directions by 1/2 of the elemental images from the group of elemental images (FE _0,0 to FE _m−1,n−1 ) displayed in the even-numbered frames FE shown in FIG. Display an image.
For example, the elemental image _FE0,1 of the even frame FE is an intermediate image of the elemental images _FO0,0 , _FO0,1 , _FO1,0 , _FO1,1 of the odd frames FO.
In this manner, the 2D video display means 10 displays element images having the same arrangement position at the same display position in the element image group having different viewpoint positions in chronological order.

The two-dimensional image display means 10 can be composed of a direct-view display such as a liquid crystal display, an organic EL display, or a micro LED display. Also, a projector or the like that performs diffusion projection can be configured as the two-dimensional image display means 10 by combining it with a lens.

The polarization switching means 11 switches the polarization of the light of the elemental image group to two polarization states at the cycle of displaying the elemental image group of the two-dimensional image display means 10 .
The polarization switching means 11 includes a polarization switching element 110 , a switching control means 111 and a λ/4 wavelength plate 112 .

The polarization switching element 110 electrically switches the polarization of the elemental image group displayed by the two-dimensional image display means 10 . The polarization switching element 110 is arranged in front of the two-dimensional image display means 10 and switches the polarization of the light emitted by the two-dimensional image display means 10 under the control of the switching control means 111 .
For the polarization switching element 110, for example, a liquid crystal polarization rotator or the like can be used.
The polarization switching element 110 normally transmits horizontally polarized light through voltage control by the switching control means 111, and converts the horizontally polarized light into vertically polarized light when a voltage is applied.
The light whose polarization has been converted by the polarization switching element 110 is applied to the λ/4 wavelength plate 112 .
When using an image that is not polarized in one direction as the image (elemental image group) displayed by the two-dimensional image display means 10, a polarizer is placed between the two-dimensional image display means 10 and the polarization switching element 110. It can be inserted and converted into unidirectionally polarized light.

The switching control means 111 switches the polarization switching state of the polarization switching element 110 by voltage control in time division in synchronization with the frame of the image displayed by the two-dimensional image display means 10 . Note that the switching control unit 111 controls polarization switching in the vertical blanking period.
For example, the switching control means 111 does not apply voltage to the polarization switching element 110 in odd-numbered frames (polarization switching switch S1: OFF), and applies voltage to the polarization switching element 110 in even-numbered frames (polarization switching switch S1: OFF). S1: ON).
Thereby, the switching control means 111 can switch the light applied to the polarization switching element 110 to horizontally polarized light or vertically polarized light for each frame.

The λ/4 wavelength plate 112 produces a phase difference of 1/4 wavelength with respect to incident light to convert linearly polarized light into circularly polarized light. Here, the λ/4 wavelength plate 112 is arranged at an angle of 45° with respect to the optical axis so that horizontally polarized light is incident thereon.
As a result, the λ/4 wavelength plate 112 converts the horizontally polarized incident linearly polarized light into right-handed circularly polarized light. Also, the λ/4 wavelength plate 112 converts vertically polarized incident linearly polarized light into left-handed circularly polarized light.

That is, as shown in FIG. 4A, when the switching control means 111 does not apply a voltage to the polarization switching element 110 (polarization switching switch S1: OFF), the light (horizontally polarized light) of the elemental image group is The light passes through the polarization switching element 110 as it is and is converted into clockwise circularly polarized light by the λ/4 wavelength plate 112 . Further, as shown in FIG. 4B, when the switching control means 111 applies a voltage to the polarization switching element 110 (polarization switching switch S1: ON), the light (horizontally polarized light) of the elemental image group is polarized It is converted into vertically polarized light by the switching element 110 and converted into counterclockwise circularly polarized light by the λ/4 wavelength plate 112 .
Thus, the polarization switching element 110, the switching control means 111, and the λ/4 wavelength plate 112 function as the polarization switching means 11 that switches the polarization of light in time series.
The λ/4 wavelength plate 112 irradiates the lens array 12 with the light of the element image group of the polarized light (right-handed circularly polarized light, left-handed circularly polarized light) switched by the polarization switching element 110 .

The lens array 12 is a two-dimensional arrangement of element lenses 120 at positions corresponding to display positions of individual element images of the element image group. For example, as shown in FIG. 5, the lens array 12 has circular element lenses 120 arranged at predetermined intervals in the horizontal and vertical directions. The positions of the element lenses 120 correspond to the positions of the individual element images I displayed by the two-dimensional image display means 10 .

The lens array 12 (element lens 120 ) is arranged apart from the display surface of the two-dimensional image display means 10 by the focal length of the element lens 120 .
The element lens 120 converts the light of the element image I into parallel light and reproduces the light emitted from the subject (subject light). For example, the element lens 120 can be composed of a minute convex lens that is a single lens.
In this way, the individual element lenses 120 of the lens array 12 collimate the light of each pixel of the element image I, so that the observer M observes one pixel of the element image for each element lens 120. be able to.
The lens array 12 irradiates the polarization diffraction means 13 with the light of each pixel of the elemental image I as parallel light.

The polarization diffraction means 13 translates the emission direction of the light (object light) of the element image group incident from the lens array 12 in different directions by diffraction according to the polarization state. The polarization diffraction means 13 comprises two polarization diffraction elements 130a and 130b. The polarization diffraction elements 130a and 130b are large enough to cover at least the entire lens array 12. FIG.

The polarization diffraction elements 130a and 130b diffract right-handed circularly polarized incident light or left-handed circularly polarized light in different directions as ±first-order light according to the polarization state.
For example, as shown in FIG. 6(a), the polarization diffraction elements 130a and 130b transform the incident light into left-handed circularly polarized light in the direction of a previously designed diffraction angle φ when right-handed circularly polarized light is vertically incident. transform and diffract as +1 order light. In addition, as shown in FIG. 6B, when left-handed circularly polarized light is vertically incident on the polarization diffraction elements 130a and 130b, the incident light is converted into right-handed circularly polarized light in the direction of the diffraction angle φ designed in advance. and diffracted as -1st order light.
As the polarization diffraction elements 130a and 130b that change the diffraction direction according to the polarization state of circularly polarized light, known elements may be used. For example, polarization diffraction elements disclosed in JP-A-2008-233539, JP-A-2016-136165, JP-A-2006-106726, etc. can be used.

The polarization diffraction element 130a diffracts the light incident from the lens array 12 according to the polarization state, and outputs the light as +1st-order light or −1st-order light to different positions of the polarization diffraction element 130b, and switches the polarization state. It is.
The polarization diffraction element 130b is arranged in the same direction as the polarization diffraction element 130a and in parallel with the polarization diffraction element 130a. It returns and switches the polarization state.
Observer M observes the light diffracted by this polarization diffraction element 130b.

The polarization diffraction elements 130a and 130b shift the display positions of the elemental images I by 1 of the lens pitch of the elemental lenses in the positive or negative directions of the x-axis and the y-axis, respectively, according to the polarization state of the light incident from the lens array 12. The light is diffracted so as to be displayed at a position shifted by /4.
In FIG. 2, the polarization diffraction elements 130a and 130b cause the incident light from the lens array 12 to be diffracted by Dx/4 in time series in the positive and negative directions of the x-axis with respect to the pitch Dx of the element lenses 120 in the x-axis direction. An example of shifted light is shown.

Here, the positional relationship between the polarization diffraction elements 130a and 130b will be described with reference to FIGS. 7 to 9. FIG.
The shift amount of light rays of each element image by the polarization diffraction elements 130a and 130b is specified by the pitch (diffraction pitch) and inclination angle of the diffraction grating grooves of the polarization diffraction elements 130a and 130b and the distance between the polarization diffraction elements 130a and 130b. be able to. Here, the pitch of the grooves physically formed in the polarization diffraction elements 130a and 130b is described as the diffraction pitch, but if the element has periodicity in diffraction, the period is the diffraction pitch.
Assuming that the wavelength of the incident light is λ and the diffraction pitch of the polarization diffraction element 130a is p as shown in FIG. 8, the diffraction angle φ of the first-order light as shown in FIG. can be expressed as

Further, as shown in FIG. 7, when the distance between the polarization diffraction element 130a and the polarization diffraction element 130b is L1, the diffraction shift amount d can be expressed by the following equation (2).

That is, assuming that the distance between the polarization diffraction element 130a and the polarization diffraction element 130b is L1, as shown in FIG. After being converted, the traveling direction is changed as +1st-order light, and after being shifted by the shift amount d, the polarization diffraction element 130b is irradiated. In addition, the left-handed circularly polarized light that is perpendicularly incident on the polarization diffraction element 130b is converted into right-handed circularly polarized light and diffracted as −1st-order light in the same direction as the traveling direction of the incident light on the polarization diffraction element 130a.

Further, as shown in FIG. 7(b), the left-handed circularly polarized light incident perpendicularly to the polarization diffraction element 130a is converted into right-handed circularly polarized light, changes its traveling direction as -1st order light, and shifts by a shift amount d. After being shifted, it is irradiated to the polarization diffraction element 130b. Also, the right-handed circularly polarized light that is perpendicularly incident on the polarization diffraction element 130b is converted into left-handed circularly polarized light, which is diffracted as +1st-order light in the same direction as the traveling direction incident on the polarization diffraction element 130a.

Here, with reference to FIG. 9, the light ray shift amount d will be further described. FIG. 9 shows the center position (x mark) of the element lens 120 and the position C _O (● mark) shifted by diffracting the light that was originally irradiated perpendicularly to the center position C (x mark) of the element lens 120. and C _E (marked with a circle) on the xy plane.
The position C _O (marked with a circle) corresponds to the shifted position in the odd frame FO. Also, the position C _E (marked with a circle) corresponds to the shifted position in the even-numbered frame FE.
In order to visually recognize the elemental images of the odd-numbered frames FO and the even-numbered frames FE with a uniform light beam density, the center position C It is desirable to shift the light beam to a position shifted by ±Dx/4 in the horizontal direction and by ±Dy/4 in the vertical direction.

Specifically, when Dx=Dy=1 mm, the tilt angle θ from the horizontal axis should be 45°, and the shift amount d=(√2)×Dx/4≈0.35 mm.
In this case, from equations (1) and (2), the diffraction pitch p of the polarization diffraction elements 130a and 130b and the relationship between the polarization diffraction elements 130a and 130b are determined so as to satisfy the relationship of the following equation (3). The distance L1 should be determined.

For example, when the wavelength λ is 550 nm (the wavelength of a predetermined reference color [eg, green]) and the diffraction pitch p is 2.5 μm, the distance L1 is 1.55 mm.
By configuring the 3D video display device 1 as described above, the 3D video display device 1 can change the positions of the elemental images in chronological order and display them. As a result, the 3D video display device 1 can double the number of element images I with respect to the number of element lenses 120, and the resolution of the 3D video T can be improved.

This effect will be described schematically with reference to FIG.
As shown in FIG. 10, the three-dimensional image display apparatus 1 switches the elemental image group and the diffraction direction of light rays in time series so that the observer M can see through the lens center of each elemental lens 120. It is possible to switch the pixels of the element image I to be observed. Thereby, the three-dimensional image display apparatus 1 can form two virtual element lenses 120v in the polarization diffraction element 130b for one physical element lens 120. FIG. This corresponds to doubling the number of element lenses 120, and the resolution of the 3D image T is improved.

≪Operation of 3D image display device≫
Next, with reference to FIG. 11 (see also FIGS. 1 and 2 for the configuration), the operation of the 3D image display device 1 according to the embodiment of the present invention will be described.
In step S1, the switching control means 111 controls the polarization switching state of the polarization switching element 110 for each frame of the element image group. If the frame of the elemental image group is an odd frame, the switching control means 111 does not apply a voltage to the polarization switching element 110, thereby switching the polarization switching element 110 to a state in which the horizontal polarized light is passed as it is. If the frame of the elemental image group is an even-numbered frame, the switching control unit 111 applies a voltage to the polarization switching element 110 to switch the polarization switching element 110 from horizontal polarization to vertical polarization.

In step S2, the 2D video display means 10 displays the elemental image group for each frame.
In step S3, the polarization switching element 110 switches the linear polarization of the elemental image group to horizontal polarization or vertical polarization according to the polarization state controlled in step S1.
In step S4, the λ/4 wavelength plate 112 converts the linearly polarized light that has been switched in step S3 into circularly polarized light. This λ/4 wavelength plate 112 converts the irradiated elemental image group into right-handed circularly polarized light if it is horizontally polarized light, and converts it into left-handed circularly polarized light if it is vertically polarized light.

In step S5, the element lens 120 of the lens array 12 converts the diffused circularly polarized light converted in step S4 into parallel light to reproduce subject light.
In step S6, the polarization diffraction means 13 shifts the subject light reproduced in step S5 in the diffraction direction according to the polarization. Here, the polarization diffraction element 13a of the polarization diffraction means 13 emits incident light as +1st-order light or -1st-order light according to the polarization state of subject light. Then, the polarization diffraction element 130b of the polarization diffraction means 13 returns the subject light diffracted by the polarization diffraction element 130a to the original emission direction. In this manner, the polarization diffraction means 13 shifts (translates) the light of each pixel of the element image to different positions according to the polarization state of the subject light by the two polarization diffraction elements 130a and 130b.

Then, while the 2D video display means 10 is displaying the elemental image group (No in step S7), the 3D video display device 1 returns to step S1 and continues its operation.
On the other hand, when the display of the elemental image group by the 2D image display means 10 is finished (Yes in step S7), the 3D image display device 1 finishes its operation.
By the above operation, the 3D image display device 1 can allow the observer M to visually recognize the 3D image T with high resolution.

<<Structure of Modified 3D Video Display Device>>
Next, with reference to FIG. 12, the configuration of a 3D image display device 1B according to a modification of the present invention will be described.
The 3D image display device 1B displays an image that allows an observer to visually recognize a 3D image according to the integral method.
The 3D video display apparatus 1 described with reference to FIG. 2 displays a double element image by shifting the light rays of the pixels of the element image in two directions in time series.
The three-dimensional video display device 1B displays a quadrupled elemental image by shifting the light rays of the pixels of the elemental image in four directions in time series.

As shown in FIG. 12, the three-dimensional image display device 1B includes two-dimensional image display means 10, polarization switching means 11, lens array 12, and polarization diffraction means 13B. Note that the two-dimensional image display means 10, the polarization switching means 11, and the lens array 12 have the same configuration as the three-dimensional image display device 1 described with reference to FIG. 2, so description thereof will be omitted. 12, only the optical axis of the element lens 120 corresponding to the element image I is illustrated as light rays.

The polarization diffraction means 13B diffracts the light (object light) incident from the lens array 12 according to the polarization state.
The polarization diffraction means 13B includes two sets of polarization diffraction elements 130a and 130b and polarization diffraction elements 131a and 131b, a polarization switching element 132, and a switching control means 133.

The polarization diffraction elements 130a and 130b are the same as the elements described with reference to FIG. 2, so description thereof will be omitted. Here, a pair of polarization diffraction elements 130a and 130b performs a first-stage shift of light rays, and a pair of polarization diffraction elements 131a and 131b performs a second-stage shift of light rays. Here, C ₁ and C ₂ denote light rays with optical axes shifted by the polarization diffraction elements 130a and 130b. Also, C ₁₁ and C 12 denote light rays obtained by shifting the light of the optical axis C ₁ by the polarization diffraction elements 131 a and 131 b , and C ₂₁ denote the light rays obtained by shifting the light of the optical axis C ₂ by the polarization diffraction elements 131 a and 131 _b . , C ₂₂ .

The polarization switching element (second polarization switching means) 132 electrically switches the polarization of incident light. The polarization switching element 132 is arranged between the first pair of polarization diffraction elements 130a and 130b and the second pair of polarization diffraction elements 131a and 131b, and switches the polarization of the light incident from the polarization diffraction element 130b to the switching control means 133. switch by the control of
For the polarization switching element 132, for example, a liquid crystal polarization rotator or the like can be used.
Under the voltage control of the switching control means 133, the polarization switching element 132 normally transmits the circularly polarized light as it is, and when a voltage is applied, it converts the right-handed circularly polarized light into left-handed circularly polarized light. Converts polarized light into right-handed circularly polarized light.
The light whose polarization has been converted by the polarization switching element 132 is applied to the subsequent polarization diffraction element 131a.

The switching control means (second polarization switching means) 133 switches the polarization switching state of the polarization switching element 132 by voltage control in time division in synchronization with the frame of the image displayed by the 2D image display means 10 . Note that the switching control means 133 controls polarization switching in the vertical blanking period.
Thereby, the polarization diffraction means 13B can shift the optical axis of the element lens 120 to four optical axes C ₁₁ , C ₁₂ , C ₂₁ and C ₂₂ in time series.
In this case, as shown in FIG. 13, when the lens array 12 is viewed from the front, light rays are directed to the center positions C of the element lenses 120 for each frame so that the virtual element lenses are uniformly arranged. It is desirable to set the positions _C11 , _C12 , _C21 , and _C22 of the optical axes shifted obliquely (45 degrees from the horizontal axis) as the center positions of the virtual element lenses.

When the pitch of the element lenses 120 is 1 mm, as shown in FIG. 14, the center position C of the element lenses 120 and the optical axis positions C ₁ , The distance (shift amount) _ΔS1 from _C2 is set to 0.35 mm. Also, the distance (shift amount) ΔS ₂ between the position C ₁ (C ₂ ) and the positions C ₁₁ and C ₁₂ (C ₂₁ and C ₂₂ ) of the optical axes shifted to the second stage by the polarization diffraction elements 131a and 131b is 0.18 mm.
In order to shift the light beam in this way, the distance L1 between the polarization diffraction elements 130a and 130b shown in FIG. L2 should be 0.78 mm.

In this way, in order to shift the light beams into four light beams depending on the polarization state, it is necessary to switch the polarization switches S1 and S2 between the polarization switching element 110 and the polarization switching element 132 .
For example, as shown in the state of the polarization switch in Table 1 below, the polarization switch S1 is turned off and the polarization switch S2 is turned off in the F _4n (n is an integer equal to or greater than 0; the same shall apply hereinafter) frame. Also, in the F4n ₊₁ frame, the polarization changeover switch S1 is turned off, and the polarization changeover switch S2 is turned on. Also, in the F4n ₊₂ frame, the polarization changeover switch S1 is turned ON and the polarization changeover switch S2 is turned OFF. Also, in the F4n ₊₃ frame, the polarization changeover switch S1 is turned on, and the polarization changeover switch S2 is turned on.

Note that the two-dimensional image display means 10 may display four elemental image groups whose viewpoint positions are shifted in time series at the same display positions as two-dimensional images in synchronization with the polarization switching switch. In this case, each elemental image group is an image shifted by ⅛ pitch of the elemental lens 120 .
As a result, the 3D image display device 1B equipped with the polarization diffraction means 13B sequentially shifts the light beams of the group of elemental images having different viewpoint positions in the four frames _F4n , F4n ₊₁ , F4n ₊₂ , and _F4n+3 . By displaying, the number of element images can be increased to display a three-dimensional video.
The 3D image display device 1B can allow the observer to visually recognize a 3D image with a higher resolution than that of the 3D image display device 1 .
Although an example in which the light beam is shifted by two stages is shown here, the number of stages may be three or more.

The operation of the 3D image display device 1B is different from the operation of the 3D image display device 1 described with reference to FIG. 11 only in the timing of switching the polarized light, and thus the description thereof is omitted.
Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Various modifications will be described below.

(Regarding the element lenses of the lens array)
In the three-dimensional image display devices 1 and 1B, as the lens array 12, the circular element lenses 120 shown in FIG. 5 are arranged horizontally and vertically. However, the shape of the element lens 120 of the lens array 12 does not necessarily have to be circular.
For example, as shown in FIG. 15A, a lens array 12B may be used in which square element lenses 120B are arranged horizontally and vertically.
Further, for example, as shown in FIG. 15B, a lens array 12C having a honeycomb structure in which hexagonal element lenses 120C are arranged may be used.
Alternatively, for example, as shown in FIG. 15C, a lens array 12D may be used in which oblong rectangular element lenses 120D are arranged in the horizontal and vertical directions. This makes it possible to improve the quality of the horizontal 3D video.
Needless to say, the two-dimensional image display means 10 displays element images at positions facing the element lenses 120, 120B, 120C, and 120D.

(About chromatic aberration)
When the polarization diffraction means 13 shown in FIG. 2 is used, the diffraction shift amount d of the light rays of the elemental image I has wavelength dependence as shown in the above equations (1) and (2). Therefore, the 3D image T to be displayed has chromatic aberration.
For example, when the diffraction pitch p of the polarization diffraction elements 130a and 130b is 2.5 μm and the distance L1 between the polarization diffraction element 130a and the polarization diffraction element 130b is 1.55 mm, and the visible region is 360 to 830 nm, the light beam is diffracted in the direction 0.32 mm. With this degree of spread, there is no visual problem. However, when such chromatic aberration occurs, color fringing due to chromatic aberration may also occur in the three-dimensional image T to be displayed, depending on the coloration pattern or the like. Therefore, it is preferable that the group of elemental images displayed by the two-dimensional image display means 10 is corrected for chromatic aberration in advance.

For example, as shown in FIG. 16A, when the RGB light of a pixel px of the element image I is diffracted by the polarization diffraction means 13, the amount of diffraction differs depending on the respective wavelengths of RGB.
In this case, the light of the pixels should be emitted from the same position of the polarization diffraction element 13b. That is, with a certain color (for example, G) of the elemental image I as a reference, the display positions of the other colors of the elemental image I may be shifted.
Specifically, as shown in FIG. 16B, the G light of the pixel px is shifted by E by the polarization diffraction means 13 . This shift amount E is represented by the following equation (4).

Here, p is the diffraction pitch of the polarization diffraction elements 130a and 130b, L1 is the distance between the polarization diffraction element 130a and the polarization diffraction element 130b, and _λe is the reference wavelength (for example, the wavelength of G light; 550 nm).
For other colors (for example, R and B), pixels (pxr, pxb) shifted by ΔE shown in the following equation (5) from the pixels (here, px) containing the color of the reference wavelength. Display as color. λ indicates the wavelength of colors (R, B) other than the reference wavelength.

As a result, the 3D image display device 1 can suppress the occurrence of chromatic aberration and allow the observer to visually recognize the 3D image.
In the three-dimensional video display apparatus 1B described with reference to FIG. 12, the two-step shift is performed, and it is preferable to correct in advance the chromatic aberration caused by the two-step shift for the group of elemental images to be displayed.

(Types of polarization diffraction elements)
Here, the three-dimensional image display devices 1 and 1B use the polarization diffraction means 13 and 13B to diffract right-handed circularly polarized or left-handed circularly polarized incident light as ±first-order light according to the polarization state, A polarization diffraction element that changes the direction of circularly polarized light (clockwise or counterclockwise) was used.
However, the polarization diffraction means 13 and 13B diffract vertically or horizontally polarized incident light as ±1st-order light according to the polarization state, and change the direction of linearly polarized light (vertically or horizontally). may be used.
In this case, the 3D image display device 1, 1B can omit the λ/4 wavelength plate 112 from the configuration.

Incidentally, such a polarization diffraction element that diffracts vertically polarized or horizontally polarized incident light as ±1st-order light according to the polarization state is disclosed in Japanese Unexamined Patent Application Publication No. 2008-233539 and Reference 1 below. A known polarization diffraction element may be used.
(Reference 1: http://optik.nagaokaut.ac.jp/azo_dye_doped.html)

(Regarding the size and shape of the polarization diffraction element)
Here, the three-dimensional image display devices 1 and 1B use polarization diffraction elements 130a, 130b, 131a, and 131b, which are large enough to cover the entire lens array 12, as the polarization diffraction means 13 and 13B.
However, the polarization diffraction means 13 and 13B need not be configured as one element, and may be configured by two-dimensionally arranging polarization diffraction elements having small areas corresponding to the size of the element images. When two-dimensionally arranging small-area polarizing diffraction elements in this way, it is preferable to arrange them densely in order to suppress the influence of the joints of the tiling.
Moreover, the polarization diffraction element may have any shape such as a rectangle or a circle as long as it can cover the entire lens array 12 .

(Regarding the arrangement of the lens array)
Here, the lens array 12 is arranged between the polarization switching means 11 and the polarization diffraction means 13 . However, the lens array may be provided between the two-dimensional image display means 10 and the polarization switching means 11 as long as it is separated from the display surface of the two-dimensional image display means 10 by the focal length of the element lens 120. . Further, the lens array 12 may be configured such that each element lens 120 is a plano-convex lens, and the plane side is in contact with the light incident side or the light emitting side of the polarization diffraction element 130 a of the polarization diffraction means 13 .

(Improving depth reproducibility)
The 3D video display device 1 displays, in time series, a group of elemental images shifted by 1/4 pitch of the element lens 120 (1/8 pitch in the case of the 3D video display device 1B), thereby virtually By increasing the number of element lenses, the resolution of 3D images has been increased.
However, the resolution of the 3D video may be increased by virtually increasing the number of pixels of the elemental images.
In this case, as shown in FIG. 17, the lens array 12 is arranged on the light exit side (observer M side) of the polarization diffraction means 13 in the same configuration as the three-dimensional image display device 1 (FIG. 2). , a three-dimensional image display device 1C.
Then, the two-dimensional image display means 10 of the three-dimensional image display device 1C, for example, for the element image _IL having the number of horizontal pixels of 2W×the number of vertical pixels of 2H shown in FIG. An elemental image group composed of elemental images _IO of horizontal pixel number W×vertical pixel number H from which pixels are extracted is displayed as an odd-numbered frame. Further, the two-dimensional video display means 10 is arranged to extract element images _IE of horizontal pixel number W×vertical pixel number H obtained by extracting pixels of even-numbered rows and odd-numbered columns indicated by x marks from elemental images _IL . Display the images as even frames.
That is, the 2D video display means 10 displays the group of elemental images shifted in the diagonal direction by 1/2 pixel as a 2D video in which the display positions of the elemental images are the same at a predetermined cycle, for example, a frame cycle.
Further, the polarization diffraction means 13 of the three-dimensional image display device 1C sets the shift amount of the light beam of the element image I to the amount obtained by shifting the pixels of the element image I in the diagonal direction of ±1/4 pixel.

By switching the group of elemental images and switching the direction of diffraction of light rays in time series, the three-dimensional image display device 1C can display the viewer M through the lens center of each elemental lens 120 as shown in FIG. It is possible to switch the pixels of the element image I to be observed. Thereby, the three-dimensional image display device 1C can make the observer M visually recognize an elemental image of 2W×2H pixels with one elemental lens 120 . This corresponds to doubling the resolution of the elemental images in the horizontal and vertical directions, and the resolution of the 3D image T is improved.

A state in which the resolution is doubled by the 3D video display device 1C will be described by enlarging the elemental images with reference to FIG.
FIG. 20( a ) shows the path of light of each pixel (px ₁ , px ₂ , . . . ) of the elemental image I passing through the lens center of the elemental lens 120 . For example, the light of pixel px ₁ is diffracted in time series by the polarization diffraction elements 130a and 130b to become light rays L ₁₁ and L ₁₂ . Similarly, the light of pixel px ₂ becomes light rays L ₂₁ and L ₂₂ .
Conversely, when the observer visually recognizes the light (rays L ₁₁ , L ₁₂ , L ₂₁ , L _{22 ,} etc.) that have passed through the lens center of the element lens 120, as shown in FIG. The pixel positions are observed by extending the light beams L ₁₁ , L ₁₂ , L ₂₁ , L _{22 ,} etc. in the opposite direction (one-dot chain lines and two-dot chain lines in FIG. 20). That is, originally, the pixel pitch becomes v _pg (=p _g /2) virtually by interposing the polarization diffraction elements 130a and 130b with respect to the pixel pitch pg of the element image _I. FIG. This doubles the resolution of the elemental images.
By increasing the resolution of the elemental images in this way, the 3D video display device 1C can improve the depth reproducibility of the 3D video.

Reference Signs List 1, 1B, 1C three-dimensional image display device 10 two-dimensional image display means 11 polarization switching means 110 polarization switching element 111 switching control means 112 λ/4 wavelength plate 12 lens array 120 element lens 13, 13B polarization diffraction means 130a, 130b polarized light Diffraction elements 131a, 131b Polarization diffraction element 132 Polarization switching element (second polarization switching means)
133 switching control means (second polarization switching means)

Claims (7)

A three-dimensional image display device for displaying an integral three-dimensional image,
2D video display means for displaying the group of elemental images with shifted viewpoint positions as 2D video in which the display positions of the elemental images are the same at a predetermined cycle;
a polarization switching means for switching the polarization of the light of the element image group between two polarization states at the cycle;
a lens array in which element lenses are arranged at positions corresponding to the display positions of the individual element images of the element image group, arranged on either the light incident side or the light exit side of the polarization switching means;
polarization diffraction means for translating the emission direction of the light of the group of elemental images whose polarization state is switched at the cycle to a different direction by diffraction according to the polarization state;
A three-dimensional image display device comprising: The elemental image group is an image corresponding to a shift in a predetermined direction of 1/2 of the lens pitch of the lens array in the period, and the polarization diffraction means shifts ± of the lens pitch in the predetermined direction in the period. 2. The three-dimensional image display device according to claim 1, wherein the light of said elemental image group is translated by shifting by 1/4. The polarization diffraction means has a pair of polarization diffraction elements arranged facing each other, and the light diffracted by one polarization diffraction element as +1st-order light is diffracted by the other polarization diffraction element as −1st-order light. 3. The three-dimensional image display device according to claim 1, wherein the light diffracted by the polarization diffraction element as -1st order light is diffracted by the other polarization diffraction element as +1st order light. The polarization diffraction means includes a set of polarization diffraction elements arranged in multiple stages, and a second polarization switching means for switching the polarization state of the light of the element image group at the cycle between each set of polarization diffraction elements. 4. The three-dimensional image display device according to claim 3, characterized by: A three-dimensional image display device for displaying an integral three-dimensional image,
a two-dimensional image display means for displaying a group of elemental images shifted obliquely by 1/2 pixel as a two-dimensional image in which the display positions of the elemental images are the same at a predetermined cycle;
a polarization switching means for switching the polarization of the light of the element image group between two polarization states at the cycle;
a lens array in which element lenses are arranged at positions corresponding to display positions of individual element images of the element image group;
polarization diffraction means for translating the emission direction of the light of the group of element images whose polarization state is switched at the cycle in a ±1/4 pixel oblique direction by diffraction according to the polarization state;
A three-dimensional image display device comprising: The polarization switching means switches the polarization state of the light of the element image group to right-handed circularly polarized light or left-handed circularly polarized light at the cycle,
6. The three-dimensional image display apparatus according to claim 1, wherein the polarization diffraction means diffracts the light of the elemental image group according to the polarization state. The polarization switching means switches the polarization state of the light of the element image group to horizontal polarization or vertical polarization at the cycle,
6. The three-dimensional image display apparatus according to claim 1, wherein the polarization diffraction means diffracts the light of the elemental image group according to the polarization state.

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