JP2023114881A - Image display device and head mount display - Google Patents

Abstract

To provide a technology for avoiding deterioration in quality of a display image due to a diffraction phenomenon in a laminated light field image display device.SOLUTION: Disclosed is a light field type image display device 1 in which two or more displays are laminated with a medium layer 30 sandwiched between each display. In at least one set of displays arranged adjacent to each other, an aperture size of pixels of the display closer to the front face is larger than the aperture size of the pixels of the display farther from the front face. The aperture size of the pixels in all displays increases monotonically from the side far from the front face toward the side close to the front face.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image display device, and more particularly to an image display device using light field technology. A head-mounted display including this image display device will also be referred to.

In recent years, attention has been focused on light field technology for controlling light rays emitted from an image display and incident on a user's eyes. A human being can see an object by the rays reflected by the object entering the pupil. Light field technology artificially reproduces this reflected light on an image display, and as a result can provide a sense of depth similar to what people see in the natural world.

Several modes of image display devices using light field technology are known, and typical examples include a microlens array system and a lamination system.
In the microlens array method, an array having lenses with diameters on the order of micrometers is attached to the surface of the display panel. In the microlens array method, a microlens array decomposes light emitted from a display into bundles of rays oriented in specific directions and guides them to the viewer's eyes.

The other stacking method has a structure in which two display panels are stacked with a medium layer interposed therebetween, as described in Patent Document 1. The first display panel positioned farther from the viewer has a backlight or the like and has a function of emitting light. The second display panel located on the side closer to the viewer does not have the function of emitting light and is illuminated by the light emitted from the first display.
In the stacking system, a light ray emitted from a pixel of the first display panel passes through a pixel of the second display panel and enters the viewer's eye, and the combination of pixels through which the light ray passes causes the light ray to pass through. controlling.

In the microlens array method, since one microlens covers a plurality of pixels, in principle, a decrease in display resolution cannot be avoided.
On the other hand, the lamination method is advantageous in that although the first display panel and the second display panel must be sufficiently aligned, it is not so difficult to increase the resolution. State-of-the-art displays have been reported with 900 or more pixels per inch.

Japanese Patent Publication No. 2020-521174

The inventors have found that when the pixel size is reduced in the lamination method, the quality of the displayed image deteriorates due to the light diffraction phenomenon. The inventors solved this problem and completed the present invention.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a technique for avoiding degradation in display image quality due to a diffraction phenomenon in a laminated light field image display device.

A first aspect of the present invention is a light field image display device in which two or more displays are laminated with a medium layer interposed between the displays.
In at least one pair of displays arranged adjacent to each other, this image display device has a pixel aperture size of a display closer to the front than a pixel aperture size of a display farther from the front. , the aperture size of the pixel increases monotonically from the side farther from the front to the side closer to the front.

A second aspect of the present invention is a head-mounted display comprising the image display device according to the first aspect, and an eyepiece arranged on the front side of the image display device with the light incident surface facing the image display device. be.

INDUSTRIAL APPLICABILITY The present invention contributes to avoiding deterioration of display image quality in a laminated light field image display device.

1 is a schematic cross-sectional view showing an image display device according to one embodiment of the present invention; FIG. It is a schematic cross section showing a conventional image display device.

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG.
FIG. 1 is a diagram schematically showing an image display device 1 according to this embodiment. The image display device 1 is a light field image display device, and includes two liquid crystal displays, a first display 10 and a second display 20 .
The front side of the image display device is the second display 20 side, and the user views the displayed image from the front side.

The first display 10 has a backlight 11, a liquid crystal layer 12, and a color filter 13 arranged in this order, and has substantially the same structure as a known color liquid crystal display. In this embodiment, the pixel 15 of the first display 10 includes a first sub-pixel 15a in which the red filter R of the color filter 13 is arranged, a second sub-pixel 15b in which the green filter G of the color filter 13 is arranged, and a third sub-pixel 15c in which the blue filter B of the color filter 13 is arranged.

The second display 20 comprises a liquid crystal layer 22 and color filters 23, but no backlight. In this embodiment, the pixel 25 of the second display 20 includes a first sub-pixel 25a in which the red filter R of the color filter 23 is arranged, a second sub-pixel 25b in which the green filter G of the color filter 23 is arranged, and a third sub-pixel 25c in which the blue filter B of the color filter 23 is arranged.

The aperture size of the pixels 25 of the second display 20 is larger than the aperture size of the pixels 15 of the first display 10 . That is, the aperture size of the first sub-pixel 25 a in the color filter 23 of the second display 20 is larger than the aperture size of the first sub-pixel 15 a in the color filter 13 of the first display 10 . Similarly, the aperture size of the second sub-pixel 25b is larger than the aperture size of the second sub-pixel 15b, and the aperture size of the third sub-pixel 25c is larger than the aperture size of the third sub-pixel 15c.

Although a schematic cross-sectional view is shown in FIG. 1, in the present embodiment, the front view shape of the first display 10 and the second display 20 is a rectangle or square with the same dimensions. The first display 10 and the second display 20 are arranged so that their four sides match each other when the image display device 1 is viewed from the front of the second display 20 side.

The first display 10 and the second display 20 are arranged with the medium layer 30 interposed therebetween. That is, the first display 10 and the second display 20 are arranged substantially parallel with a distance corresponding to the thickness of the medium layer 30 .
A typical example of the medium layer is an air layer, but argon (refractive index 1.000281), carbon dioxide (refractive index 1.000449), helium ( A layer composed of hydrogen (refractive index 1.000140), nitrogen (refractive index 1.000297), oxygen (refractive index 1.000276), etc., or a layer composed of a mixture thereof can also be used. Furthermore, a vacuum layer (refractive index 1.0000) can also be used and is included in the medium layer in the present invention.

The paths of light rays in the image display device 1 will be described.
First, light rays are emitted from the backlight 11 of the first display 10 . The emitted light travels through the liquid crystal layer 12 , the color filter 13 , and the medium layer 30 toward the second display 20 .

FIG. 2 shows a conventional image display device 100. As shown in FIG. Like the image display device 1, the image display device 100 is a laminated light field display, but the two displays 110 and 120 have the same sub-pixel size.
In the image display device 100, light rays from the display 110 pass through sub-pixels in which color filters of the same color are arranged. For example, a light ray emitted from the display 110 through the green filter G passes through the sub-pixel in which the green filter G is arranged among the sub-pixels of the display 120 and enters the viewer's eye, as shown in FIG. and is seen as green.

In order to improve the display resolution of the stacked light field display, the pixel size of the two displays should be reduced. For example, if the aperture size of the sub-pixels forming each pixel is reduced to 1/3, the display resolution is theoretically tripled.

However, the inventors' studies have revealed that there is an optical limit to such improvement in resolution. This is due to the interference of light incident on adjacent pixels on the display 120 closer to the viewer. That is, it has been found that the diffraction limit due to the interference of light causes blurring of the image, resulting in deterioration of the quality of the displayed image.

The diffraction limit is described below, simplified by the example of a circular aperture. Consider the case where two circular apertures of diameter D are located a distance from each other's circle centers. When these two apertures are illuminated with incoherent light, a diffraction image at the apertures can be represented by superposition (interference) of light passing through the two apertures. Here, when diffraction images from two apertures interfere with each other, the limit of distance resolution at which the two images can be distinguished as two points is the diffraction limit. Although there are various definitions of the diffraction limit, the most famous one is the Rayleigh diffraction limit, which is expressed by Equation 1 below.

In Equation 1, λ is the wavelength of light, and 550 nm, which is highly sensitive to the human eye, is mainly used. Also, L is the rear side distance from the opening. The coefficient is 1.22 when the shape of the aperture is circular, but the coefficient is 1 when the shape of the aperture is rectangular.

If the distance between the diffraction images is δ or more, the diffraction images from the two apertures can be separated and identified. Conversely, if it is smaller than δ, the diffraction images from the two apertures appear as one point, deteriorating the quality of the displayed image. The diameter s of the Airy disk of the diffraction image at the rear side distance L is expressed by the following equation (3).

The inventors paid attention to this phenomenon, and found that the distance between the two displays, which is roughly determined by the medium layer, and the diameter of the Airy disk, which can be calculated from the aperture size of the pixel 15 of the first display 10, are smaller than the diameter of the pixel 25 in the second display 20. We succeeded in avoiding the diffraction limit by enlarging the aperture size.
Specifically, the aperture size of each sub-pixel in the pixel 25 of the second display 20 on which light rays emitted from the pixel 15 of the first display 10 enter is defined as the aperture size of each sub-pixel in the pixel 15 of the first display 10. By making it larger than , we realized the avoidance of the diffraction limit in the adjacent pixels of the second display. This allows light rays entering pixel 25 through pixel 15 to pass optically through pixel 25 without obstruction, and also avoids diffraction limitations due to adjacent pixels in the second display. As a result, it is possible to display a good quality image without blurring.

As described above, the image display device 1 according to the present embodiment can suppress deterioration of image display quality due to the diffraction limit.
Furthermore, by maximizing the pixel aperture size of the second display located in front, the range of diameter values of the Airy disk that does not cause the diffraction limit can be increased, increasing the degree of freedom in the distance between the displays, and configuring the display device. It also has the advantage of making it easier.

In this embodiment, the number of stacked displays is two for the sake of simplicity of explanation, but this is only one aspect of the present invention, and other configurations are also possible. For example, in the case of a three-layer laminated light field display structure, in addition to the first display and the second display, the third display located on the side closest to the front of the user is arranged, and the number of pixels in the first display is increased. The pixel aperture size of the display closest to the user, with the smallest aperture size, the second smallest pixel aperture size in the second display, the largest pixel aperture size in the third display, and so on. is the largest, and the aperture size of the pixel becomes smaller as the distance from the user increases.

Alternatively, the pixel aperture size in the first display is the smallest, and the pixel aperture size in the second display and the pixel aperture size in the third display are the same and the second smallest, and so on, whichever is farthest from the user. A structure may be adopted in which the aperture sizes of the pixels in the displays other than the display are all the same and are larger than the aperture size of the pixels in the display farthest from the user.
As described above, in the display device according to the present embodiment, it is sufficient that the pixel aperture size monotonically increases from the display furthest from the front toward the display closest to the front, and a plurality of displays having the same aperture size are provided. It works even if there is.

The image display device according to the present invention will be further described using examples and comparative examples. The technical scope of the present invention is not limited based only on the specific content of the examples.

(Example)
Two IPS (In-Plane Switching) liquid crystal display panels of the same size and rectangular in front view were prepared. One display was attached with a backlight and a color filter to form a first display, and the other was attached with only a color filter to form a second display.
The display resolution of the first display is 200 pixels per inch (200 ppi) and the aperture size of each sub-pixel is 42.3 μm.
The display resolution of the second display is 100 pixels per inch (100 ppi) and the aperture size of each sub-pixel is 84.7 μm.

The image display device according to the example was obtained by completely overlapping the first display and the second display with a gap of 7 mm in front view and fixing this state. This image display device has an air layer with a thickness of 7 mm as a medium layer.

An eyepiece lens was attached to the image display device according to the example, and a head mounted display (HMD) according to the example was produced.

With respect to the image display quality according to the example, the presence or absence of display blur was visually evaluated using an HMD.

In an example, the diameter of the Airy disk at the position of the second display is 78.0 μm from Equation 3 above. On the other hand, the pixel aperture size in the second display is 84.7 μm.
As described above, in the HMD of the embodiment, since the aperture size of the pixel of the second display and the diameter of the Airy disk satisfy the above conditions, it is theoretically shown that the deterioration of image display quality due to diffraction can be avoided. .
Actually, the HMD image according to the example was good with no blurring of the display when viewed visually.

(Comparative example 1)
An image display device and an HMD according to Comparative Example 1 were manufactured in the same procedure as in Example, except that the display resolution of the second display was 200 pixels per inch (200 ppi).
In Comparative Example 1, the diameter of the Airy disk at the position of the second display is 78.0 μm as in Example 1. On the other hand, the aperture size of each sub-pixel of the second display is 42.3 μm, which is the same as that of the first display, which is smaller than the diameter of the Airy disk.
From the above, it is theoretically shown that the HMD according to Comparative Example 1 cannot avoid the diffraction limit.
In fact, in the visual evaluation of the quality of the HMD image, blurring of the display was observed, and the quality was not good.

(Comparative example 2)
An image display device and an HMD according to Comparative Example 2 were manufactured in the same procedure as in Example, except that the distance between the first display and the second display was 3.5 mm.
In Comparative Example 2, the diameter of the Airy disk at the position of the second display is 90.9 μm. On the other hand, the pixel aperture size in the second display is 84.7 μm, which is smaller than the diameter of the Airy disk.
From the above, it is theoretically shown that the HMD according to Comparative Example 2 cannot avoid the diffraction limit.
In fact, in the visual evaluation of the quality of the HMD image, blurring of the display was observed, and the quality was not good.

Although the respective embodiments and examples of the present invention have been described above, the specific configuration is not limited to this embodiment, and includes modifications and combinations of configurations without departing from the gist of the present invention.

For example, in the present invention, means for imparting a light-emitting function to the display is not limited to the above backlight. That is, when a self-luminous display is used as the display, various known structures such as an organic EL (OLED) display, mini-LEDs, micro-LEDs, etc. that emit light from the sub-pixels themselves can be employed. In this case, for example, red, green, and blue mini-LEDs or micro-LEDs may be provided so that the first display does not have a color filter.

Furthermore, the image display device itself may not have a light emitting function, and may have a configuration in which an image can be displayed by separately arranging a light source behind it.

The display device according to the present embodiment is capable of color display as a whole if one of the multiple displays is configured to be capable of color display. The color capable display can be located anywhere.

In a monochrome display, each aperture functions as an independent pixel and there are no sub-pixels. Even when the display device according to the present embodiment includes a monochrome display, by setting the size relationship between the individual apertures and the apertures of the sub-pixels of the display provided with the color filter as described above, the same effect can be obtained. Effective.

In the image display device according to the present invention, as shown in the embodiment, the diameter of the Airy disk is calculated, and based on this, the aperture size of the sub-pixel of the second display, and By determining the interval of , it is possible to freely set the aperture size of each display constituting the display device, and to exhibit the effect.

1 image display device 10 first display 11 backlight 15a, 25a first sub-pixel (pixel)
15b, 25b second sub-pixel (pixel)
15c, 25c third sub-pixel (pixel)
20 second display 30 medium layer

Claims (4)

A light field image display device in which two or more displays are stacked with a medium layer interposed between the displays,
In at least one pair of the displays arranged side by side, the pixel aperture size of the display closer to the front is larger than the pixel aperture size of the display farther from the front;
Aperture sizes of all pixels of the display monotonically increase from a side far from the front to a side close to the front.
Image display device. the pixel aperture size of the display closer to the front is larger than the diameter of the Airy disk formed by the pixel aperture of the display farther from the front;
The image display device according to claim 1. The display farthest from the front has a light emitting function,
3. The image display device according to claim 1 or 2. an image display device according to any one of claims 1 to 3;
an eyepiece arranged on the front side of the image display device with a light incident surface facing the image display device;
comprising
head mounted display.

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