JP7481222B2 - Image projection system and screen - Google Patents

Description

This disclosure relates to an image projection system that projects an image, and a screen that displays the image produced by the projected light. Note that in the following disclosure, the "image" to be projected includes both moving images and still images.

In recent years, the use of components that separate spaces, such as window glass, walls, partitions, and blinds, as screens for projecting images has become widespread. For example, Non-Patent Document 1 proposes a window system that dynamically changes the transparency of part of a window, Non-Patent Document 2 proposes a system that changes the transparency of a display to enable communication with the other side, and Non-Patent Document 3 introduces a product made of transparent glass screen.

Publication: "Squama: a programmable window and wall for future physical architectures", by Junichi Rekimoto, Internet address: https://dl.acm.org/doi/abs/10.1145/2370216.2370358 Paper "Tracs: transparency-control for see-through displays", by David Lindlbauer et al., Internet address: https://dl.acm.org/doi/10.1145/2642918.2647350 Product information: "Glass transparent screen Glascene (registered trademark)", AGC Inc., Internet address: https://www.agc.com/products/new_markets/detail/transparent_glass_screen.html

However, when projecting an image onto a transparent surface such as window glass, there is a concern that the image may be unintentionally seen from the opposite side of the projection surface.

In relation to the above, there is also known technology for projecting images onto both sides of a screen, rather than just one side. Although technology for switching the projection surface of a screen when projecting an image can be achieved, for example, by installing projectors on both sides of the screen or by installing displays on both sides of the screen, there is a demand for a simpler, less expensive configuration.

Therefore, in consideration of the above circumstances, the present disclosure aims to make it possible to switch the projection surface of a screen using a simpler and less expensive configuration while avoiding an image showing through to the opposite side of the surface to be projected.

The image projection system according to the present disclosure comprises a screen composed of four layers: a polarizing layer, an opaque layer, a circular polarizing layer consisting of a polarizing plate and a quarter-wave plate, and a semi-transparent projection layer, the four layers being arranged in the order of the polarizing layer, the opaque layer, the circular polarizing layer, and the projection layer along the thickness direction from the light receiving surface side of the projected light, and the polarizing layer and the opaque layer are provided with through holes at corresponding positions along the thickness direction; and one or more projection devices that project at least one of light polarized in the same direction as the polarization direction of the polarizing layer and light polarized in a different direction toward the screen from one side of the screen.

The detailed principle will be described later with reference to the drawings, but in an image projection system configured as described above, the projection surface of the screen can be switched as follows. That is, at least one of light polarized in the same direction as the polarization of the polarizing layer of the screen and light polarized in a different direction is projected from one side of the screen. Of these, if the light polarized in the same direction as the polarization of the polarizing layer of the screen reaches the polarizing layer of the screen instead of the through-hole provided in the screen, it passes through the polarizing layer and is reflected by the opaque layer, so that the image of the light is projected on the front surface of the screen (the surface on which the projection device is provided). On the other hand, if the light (polarized in the same direction) passes through the through-hole, it reaches a circular polarization layer consisting of a polarizing plate and a quarter-wave plate and is absorbed by the circular polarization layer. This allows front projection to be realized while preventing the image from showing through to the back surface.

In addition, if light polarized in a direction different from the polarization caused by the polarizing layer of the screen reaches the polarizing layer of the screen instead of through the through-holes in the screen, it is absorbed by the polarizing layer. On the other hand, if the above light (polarized in the same direction) passes through the through-holes, it reaches a circular polarizing layer consisting of a polarizing plate and a quarter-wave plate, and passes through the circular polarizing layer, where part of the light is reflected by the semi-transparent projection layer and the rest of the light is transmitted, so that the image of the transmitted light is projected on the back of the screen (the side opposite the side where the projection device is installed), and the light reflected by the semi-transparent projection layer is absorbed by the circular polarizing layer due to the rotation associated with the reflection. This allows rear projection to be achieved while preventing the image from showing through to the front.

In addition, the above image projection system is not configured with projectors on both sides of the screen, nor is it configured with displays on both sides of the screen, but rather has a relatively simple configuration with a projector installed on one side of the screen.

As described above, the image projection system according to the present disclosure makes it possible to switch the projection surface of the screen with a simpler and less expensive configuration by controlling the passage of light using the polarizing layer and the circular polarizing layer in the screen, while preventing the image from showing through to the opposite side of the surface to be projected.

In addition, by devising various configurations for the projection device in the image projection system, it is possible to expand the variety of switching options beyond the front and rear projection mentioned above, such as double-sided projection of the same image or double-sided projection of different images. These will be described in detail in the embodiments of the invention.

The present disclosure makes it possible to switch the projection surface of a screen using a simpler, less expensive configuration while preventing an image from showing through to the surface opposite the surface you want to project.

1A and 1B are diagrams for explaining the configuration and operation of an image projection system in a first embodiment. FIG. 4 is a flowchart showing the operation of a control unit in the first embodiment. 11A and 11B are diagrams for explaining the configuration and operation of an image projection system in a second embodiment, where (a) shows a diagram for explaining front projection using a polarizing plate method, and (b) shows a diagram for explaining rear projection using a polarizing plate method. FIG. 11 is a flowchart showing the operation of a control unit in the second embodiment. 13A and 13B are diagrams for explaining the configuration and operation of an image projection system in a third embodiment, in which (a) shows a diagram for explaining front projection using a liquid crystal panel method, and (b) shows a diagram for explaining rear projection using a liquid crystal panel method. FIG. 11 is a flowchart showing the operation of a control unit in the third embodiment. 13A and 13B are diagrams for explaining the configuration and operation of an image projection system in a fourth embodiment, where (a) is a diagram for explaining the case of front projection, (b) is a diagram for explaining the case of rear projection, and (c) is a diagram for explaining the case of double-sided projection. FIG. 13 is a flowchart showing the operation of a control unit in the fourth embodiment. 13A to 13C are diagrams for explaining the configuration and operation of an image projection system in a fifth embodiment. FIG. 13 is a flowchart showing the operation of a control unit in the fifth embodiment. FIG. 2 illustrates an example of a hardware configuration of a control unit.

Various embodiments of the image projection system and screen according to the present disclosure will be described below with reference to the drawings. Five embodiments will be described below, but an overview of each will be provided first.

The first embodiment is an embodiment in which the projection device has two types of projection units, a first projection unit that projects polarized light for front projection and a second projection unit that projects polarized light for rear projection, and switches between front projection, rear projection, double-sided projection of the same image, and double-sided projection of different images. The second embodiment is an embodiment in which either one of a projection device with a vertical polarizing plate or a projection device with a horizontal polarizing plate is used to switch between front projection and rear projection. The third embodiment is an embodiment in which a single projection device equipped with a vertical or horizontal polarizing plate and a liquid crystal plate that can be turned on and off is used to switch between front projection and rear projection. The fourth embodiment is an embodiment in which a single projection device equipped with a vertical or horizontal polarizing plate and a liquid crystal plate that can be turned on and off in a grid is used to switch between front projection, rear projection, double-sided projection of the same image, and double-sided projection of different images. And the fifth embodiment is an embodiment in which a single projection device equipped with a vertical or horizontal polarizing plate and a liquid crystal plate that can be turned on and off is used to realize double-sided projection by switching the liquid crystal plate on and off at high speed.

[First embodiment]
As shown in FIG. 1, the image projection system 1 in the first embodiment includes a screen 10 for displaying a projected image, and a projection device 20 provided on one side of the screen 10 .

The screen 10 is composed of four layers: a polarizing layer 11, an opaque layer 12, a circular polarizing layer 13 consisting of a polarizing plate and a quarter-wave plate, and a semi-transparent projection layer 14. The above four layers are arranged in the order of polarizing layer 11, opaque layer 12, circular polarizing layer 13, and projection layer 14 along the thickness direction (left-right direction in FIG. 1) from the light-receiving surface side of the projected light (left side in FIG. 1). Furthermore, the polarizing layer 11 and the opaque layer 12 are provided with through-holes 15 at corresponding positions along the thickness direction, and light passing through the through-holes 15 reaches the circular polarizing layer 13.

The projection device 20 is composed of one or more projection devices that project at least one of light polarized in the same direction as the polarization by the polarizing layer 11 of the screen 10 and light polarized in a different direction toward the screen 10 from one side of the screen 10. In particular, the projection device 20 in the first embodiment is characterized by including a total of two types of projection units, a first projection unit 20A and a second projection unit 20B. The first projection unit 20A and the second projection unit 20B are not limited to being composed of one projection unit each, and may each be composed of multiple projection units. Among these, the first projection unit 20A includes a first projector 21A that emits light for image projection, and a first projector-side polarizing layer 22 that is arranged on the emission surface side of the first projector 21A and is made of a vertical polarizing plate or a horizontal polarizing plate, while the second projection unit 20B includes a second projector 21B that emits light for image projection, and a second projector-side polarizing layer 23 that is arranged on the emission surface side of the second projector 21B and is made of a polarizing plate having polarization characteristics different from those of the first projector-side polarizing layer 22 out of a vertical polarizing plate and a horizontal polarizing plate. The projection device 20 also includes a control unit 28 that incorporates an image DB 29 that stores image data of an image to be projected, and supplies image data to the first projector 21A and the second projector 21B. The control unit 28 is assumed to hold information regarding the image projection process to be performed (information indicating either front projection, rear projection, double-sided projection of the same image, or double-sided projection of different images) in advance, and determines the image projection process to be performed based on this information. In addition, in the first projection unit 20A and the second projection unit 20B described above, the projector and the polarizing layer do not necessarily need to be in contact with each other, and may be separated by a predetermined distance. The configurations of the control unit 28 and the projection units 20A and 20B described above are the same in the second and subsequent embodiments.

The polarizing layer 11 and the circular polarizing layer 13 of the screen 10, and the first projector side polarizing layer 22 and the second projector side polarizing layer 23 of the projection device 20 have the following two patterns of relationship in terms of polarization characteristics. That is, as a first pattern, when the polarizing layer 11 and the first projector side polarizing layer 22 are vertical polarizing plates, the second projector side polarizing layer 23 is composed of a horizontal polarizing plate, and the circular polarizing layer 13 is composed of a horizontal polarizing plate and a 1/4 wavelength plate for left rotation. On the other hand, as a second pattern, when the polarizing layer 11 and the first projector side polarizing layer 22 are horizontal polarizing plates, the second projector side polarizing layer 23 is composed of a vertical polarizing plate, and the circular polarizing layer 13 is composed of a vertical polarizing plate and a 1/4 wavelength plate for right rotation. However, either of the above two patterns may be adopted.

Next, the operation of the image projection system 1 in the first embodiment will be outlined with reference to Figs. 1 and 2. First, the control unit 28 judges whether the image projection process to be executed is "front projection", "rear projection", "double-sided projection of the same image", or "double-sided projection of different images", and supplies image data according to the judgment result. For example, the control unit 28 judges whether the image projection process to be executed is single-sided projection (front projection or rear projection) in step S1 shown in Fig. 2, and if YES, judges in step S2 whether the process is single-sided projection, front projection or not (rear projection). On the other hand, if NO (double-sided projection) in step S1, judges in step S3 whether the process projects the same image or not (projects different images).

If the image projection process to be executed is front projection, the above steps S1 and S2 are YES, and the process proceeds to step S4, where the control unit 28 supplies image data to be front-projected to the first projector 21A. As a result, the light of the image to be front-projected, shown by the solid line in FIG. 1, is emitted from the first projector 21A, and the light polarized by the first projector-side polarizing layer 22 reaches the screen 10. At this time, when the polarized light reaches the polarizing layer 11, the polarizing layer 11 has the same polarization characteristics as the first projector-side polarizing layer 22, so the polarized light passes through the polarizing layer 11 and is reflected by the opaque layer 12. Therefore, the image (front-projected image) produced by the above light is projected on the front surface of the screen 10 (the surface on which the projection device 20 is provided). On the other hand, when the polarized light reaches the circular polarization layer 13 through the through-hole 15, the circular polarization layer 13 has different polarization characteristics from the first projector-side polarization layer 22, so the polarized light is absorbed by the circular polarization layer 13. This prevents the image (front-projected image) of the light from showing through to the back of the screen 10. As a result, front projection is achieved and the image from showing through to the back is prevented.

If the image projection process to be executed is rear projection, the result is YES in step S1 and NO in step S2, and the process proceeds to step S5, where the control unit 28 supplies image data to be rear-projected to the second projector 21B. As a result, the light of the image to be rear-projected, shown by the dashed line in FIG. 1, is emitted from the second projector 21B, and the light polarized by the second projector-side polarizing layer 23 reaches the screen 10. At this time, when the polarized light reaches the polarizing layer 11, the polarized light is absorbed by the polarizing layer 11 because the polarizing layer 11 has different polarization characteristics from the second projector-side polarizing layer 23. On the other hand, when the polarized light passes through the through-hole 15 and reaches the circular polarizing layer 13, the circular polarizing layer 13 is composed of a polarizing plate and a 1/4 wavelength plate with the same polarization characteristics as the second projector-side polarizing layer 23, so the polarized light passes through the circular polarizing layer 13, and a part of the light is reflected by the semi-transparent projection layer 14, and the rest of the light passes through. Here, the image of the transmitted light is projected onto the rear surface of the screen 10 (the surface opposite to the side where the projection device 20 is provided), thus realizing rear projection. In addition, the light reflected by the semi-transparent projection layer 14 has its polarization characteristics changed by the rotation accompanying the reflection, and is absorbed by the circular polarization layer 13. In this way, the light that reaches the aforementioned polarizing layer 11 is absorbed by the polarizing layer 11, and further, the light reflected by the projection layer 14 is absorbed by the circular polarization layer 13, so that the image of the above light (the image to be rear projected) can be prevented from showing through to the front surface of the screen 10. As a result, rear projection is realized and the image can be prevented from showing through to the front surface.

In the case of double-sided projection of images with different image projection processes to be executed, the results of steps S1 and S3 are NO, and the process proceeds to step S7, where the control unit 28 supplies image data to be front-projected to the first projector 21A and image data to be rear-projected to the second projector 21B. As a result, the light of the image to be front-projected is emitted from the first projector 21A, and the light polarized by the first projector-side polarizing layer 22 reaches the screen 10. At the same time, the light of the image to be rear-projected is emitted from the second projector 21B, and the light polarized by the second projector-side polarizing layer 23 reaches the screen 10. After that, both the operation related to step S4 and the operation related to step S5 described above are executed simultaneously, and as a result, both front projection and rear projection (i.e., double-sided projection) are realized, and the front-projected image is prevented from showing through to the rear and the rear-projected image is prevented from showing through to the front.

If the image projection process to be executed is double-sided projection of the same image, the result is NO in step S1 and YES in step S3, and the process proceeds to step S6, where the control unit 28 supplies image data to be front-projected to the first projector 21A and image data of the mirror image of the image to be front-projected to the second projector 21B. As a result, the light of the image to be front-projected is emitted from the first projector 21A, and the light polarized by the first projector-side polarizing layer 22 reaches the screen 10. At the same time, the light of the mirror image of the image to be front-projected is emitted from the second projector 21B, and the light polarized by the second projector-side polarizing layer 23 reaches the screen 10. After that, both the operation related to step S4 and the operation related to step S5 described above are executed simultaneously, and as a result, both front projection and rear projection (i.e., double-sided projection) are realized, and the front-projected image is prevented from showing through to the rear and the rear-projected image is prevented from showing through to the front. Furthermore, at this time, a mirror image of the image projected in front is projected onto the rear, so the image seen from the rear is the same as the image projected in front, achieving double-sided projection of the same image.

According to the first embodiment described above, a simple and inexpensive configuration in which a projection device is installed on only one side of a screen makes it possible to switch between projection processes among "front projection," "rear projection," "double-sided projection of the same image," and "double-sided projection of different images," while preventing an image from showing through to the opposite side of the surface to be projected.

[Second embodiment]
In the second embodiment, an embodiment will be described in which either a projection device having a vertical polarizing plate or a projection device having a horizontal polarizing plate is used to switch between front projection and rear projection.

Figures 3(a) and (b) show a configuration diagram of an image projection system 1 in the second embodiment. The image projection system 1 includes a screen 10 for projecting a projected image and a projection device 20 provided on one side of the screen 10.

3A shows the configuration for front projection, and the configuration of the screen 10 is the same as that of the first embodiment, so the description will be omitted. The projection device 20 includes a projector 21 that emits light for image projection, a projector-side polarizing layer 22 that is arranged on the exit surface side of the projector 21 and is made of a vertical polarizing plate or a horizontal polarizing plate, and a control unit 28 that incorporates an image DB 29 that stores image data of the image to be projected and supplies image data to the projector 21, and the projector-side polarizing layer 22 has the same polarization characteristics as the polarizing layer 11 of the screen 10. In addition, the polarizing layer 11, the circular polarizing layer 13, and the projector-side polarizing layer 22 of the screen 10 have the following two patterns of relationship in terms of polarization characteristics. That is, as a first pattern, when the polarizing layer 11 and the projector-side polarizing layer 22 are vertical polarizing plates, the circular polarizing layer 13 is composed of a horizontal polarizing plate and a 1/4 wavelength plate to rotate left. On the other hand, as a second pattern, when the polarizing layer 11 and the projector-side polarizing layer 22 are horizontal polarizing plates, the circular polarizing layer 13 is composed of a vertical polarizing plate and a quarter-wave plate to rotate right. However, either of the above two patterns may be adopted.

Figure 3 (b) shows the configuration for rear projection, where the projection device 20 includes a projector 21 that emits light for image projection, a projector-side polarizing layer 23 made of a vertical or horizontal polarizing plate arranged on the exit surface side of the projector 21, and a control unit 28 that incorporates an image DB 29 that stores image data of the image to be projected and supplies image data to the projector 21, where the projector-side polarizing layer 23 has polarization characteristics different from those of the polarizing layer 11 of the screen 10. In addition, the polarizing layer 11, circular polarizing layer 13, and projector-side polarizing layer 23 of the screen 10 have the following two patterns of relationship in terms of polarization characteristics. That is, as a first pattern, when the polarizing layer 11 is a vertical polarizing plate, the projector-side polarizing layer 23 is made of a horizontal polarizing plate, and the circular polarizing layer 13 is made of a horizontal polarizing plate and a 1/4 wavelength plate for left rotation. On the other hand, as a second pattern, when the polarizing layer 11 is a horizontal polarizing plate, the projector-side polarizing layer 23 is composed of a vertical polarizing plate, and the circular polarizing layer 13 is composed of a vertical polarizing plate and a 1/4 wavelength plate for right rotation. However, either of the above two patterns may be adopted.

Figure 4 shows the operation of the control unit 28. When the image projection process to be executed is "front projection" (YES in step S11), the control unit 28 supplies image data to be front projected to the projector 21 (step S12). On the other hand, when the image projection process to be executed is "rear projection" (NO in step S11), the control unit 28 supplies image data to be rear projected to the projector 21 (step S13).

As a result, in the configuration for front projection (FIG. 3(a)), the light of the image to be front-projected, shown by the solid line in FIG. 3(a), is emitted from the projector 21, and the light polarized by the projector-side polarizing layer 22 reaches the screen 10. At this time, when the polarized light reaches the polarizing layer 11, the polarizing layer 11 has the same polarization characteristics as the projector-side polarizing layer 22, so the polarized light passes through the polarizing layer 11 and is reflected by the opaque layer 12. Therefore, the image (front-projected image) of the light is reflected on the front surface of the screen 10 (the surface on the side where the projection device 20 is provided). On the other hand, when the polarized light reaches the circular polarizing layer 13 through the through-hole 15, the circular polarizing layer 13 has polarization characteristics different from those of the projector-side polarizing layer 22, so the polarized light is absorbed by the circular polarizing layer 13. Therefore, it is possible to prevent the image (front-projected image) of the light from being seen through to the back surface of the screen 10. As a result, front projection is realized and the image from being seen through to the back surface is prevented.

In the configuration for rear projection (FIG. 3(b)), the light of the image to be rear projected, shown by the dashed line in FIG. 3(b), is emitted from the projector 21, and the light polarized by the projector-side polarizing layer 23 reaches the screen 10. At this time, when the polarized light reaches the polarizing layer 11, the polarized light is absorbed by the polarizing layer 11 because the polarizing layer 11 has a polarization characteristic different from that of the projector-side polarizing layer 23. On the other hand, when the polarized light reaches the circular polarizing layer 13 through the through hole 15, the circular polarizing layer 13 is composed of a polarizing plate and a 1/4 wavelength plate with the same polarization characteristics as the projector-side polarizing layer 23, so the polarized light passes through the circular polarizing layer 13 and a part of the light is reflected by the semi-transparent projection layer 14, and the rest of the light is transmitted. Here, the image of the transmitted light is projected on the rear surface of the screen 10 (the surface opposite to the side where the projection device 20 is provided), thereby realizing rear projection. Furthermore, the light reflected by the semi-transparent projection layer 14 has its polarization characteristics changed by the rotation accompanying the reflection, and is absorbed by the circular polarization layer 13. In this way, the light that reaches the aforementioned polarization layer 11 is absorbed by the polarization layer 11, and further, the light reflected by the projection layer 14 is absorbed by the circular polarization layer 13, so that the image (the image to be rear-projected) produced by the above light can be prevented from showing through to the front of the screen 10. As a result, rear projection is realized, and the image can be prevented from showing through to the front.

According to the second embodiment described above, a simple and inexpensive configuration in which one projection device is installed on one side of the screen makes it possible to prevent an image from showing through to the opposite side of the surface to be projected, while enabling the projection process to be switched between "front projection" and "rear projection" by switching the polarizers (vertical polarizer or horizontal polarizer) of the projector-side polarizing layers 22 and 23.

[Third embodiment]
In the third embodiment, an embodiment will be described in which a single projection device equipped with a vertical or horizontal polarizing plate and a liquid crystal panel that can be turned on and off is used to switch between front projection and rear projection.

5(a) and (b) show a configuration diagram of an image projection system 1 in the third embodiment. The image projection system 1 includes a screen 10 for projecting a projected image and one projection device 20 provided on one side of the screen 10. The configuration of the screen 10 is the same as that of the first and second embodiments, so a description thereof will be omitted. The projection device 20 includes a projector 21 that emits light for image projection, a projector-side polarizing layer 22 made of a vertical polarizing plate or a horizontal polarizing plate arranged on the exit surface side of the projector 21, a liquid crystal plate 24 that can be turned on and off and is arranged on the exit surface side (i.e., downstream side in the traveling direction of the light) of the projector-side polarizing layer 22, and a control unit 28 that includes an image DB 29 that stores image data of the image to be projected, supplies image data to the projector 21, and controls the on and off of the liquid crystal plate 24. The projector-side polarizing layer 22 has the same polarization characteristics as the polarizing layer 11 of the screen 10. Furthermore, the polarizing layer 11, the circular polarizing layer 13, and the projector-side polarizing layer 22 of the screen 10 have the following two patterns of relationship in terms of polarization characteristics. That is, as a first pattern, when the polarizing layer 11 and the projector-side polarizing layer 22 are vertical polarizing plates, the circular polarizing layer 13 is composed of a horizontal polarizing plate and a 1/4 wavelength plate to rotate left. On the other hand, as a second pattern, when the polarizing layer 11 and the projector-side polarizing layer 22 are horizontal polarizing plates, the circular polarizing layer 13 is composed of a vertical polarizing plate and a 1/4 wavelength plate to rotate right. However, either of the above two patterns may be adopted.

Figure 6 shows the operation of the control unit 28. If the image projection process to be executed is "front projection" (YES in step S21), the control unit 28 turns off the liquid crystal panel 24 and supplies the image data to be front projected to the projector 21 (step S22). On the other hand, if the image projection process to be executed is "rear projection" (NO in step S21), the control unit 28 turns on the liquid crystal panel 24 and supplies the image data to be rear projected to the projector 21 (step S23).

As a result, in the case of front projection, as shown in FIG. 5(a), when the liquid crystal plate 24 is off, the light of the image to be front-projected shown by the solid line in FIG. 5(a) is emitted from the projector 21, and the light polarized by the projector-side polarizing layer 22 passes through the liquid crystal plate 24 without being further polarized by the liquid crystal plate 24 and reaches the screen 10. At this time, when the light polarized by the projector-side polarizing layer 22 reaches the polarizing layer 11, the polarizing layer 11 has the same polarization characteristics as the projector-side polarizing layer 22, so the light passes through the polarizing layer 11 and is reflected by the opaque layer 12. Therefore, the image (front-projected image) of the above light is reflected on the front surface of the screen 10 (the surface on which the projection device 20 is provided). On the other hand, when the light polarized by the projector-side polarizing layer 22 passes through the through-hole 15 and reaches the circular polarizing layer 13, the circular polarizing layer 13 has polarization characteristics different from those of the projector-side polarizing layer 22, so the light is absorbed by the circular polarizing layer 13. This prevents the image produced by the light (the image projected from the front) from showing through to the rear of the screen 10. As a result, front projection is achieved while preventing the image from showing through to the rear.

In the case of rear projection, as shown in FIG. 5(b), when the liquid crystal plate 24 is on, the light of the image to be rear projected shown by the solid line in FIG. 5(b) is emitted from the projector 21, the light polarized by the projector-side polarizing layer 22 is further polarized by the liquid crystal plate 24, and the light polarized by the projector-side polarizing layer 22 and the liquid crystal plate 24 (light shown by the dashed line in FIG. 5(b)) reaches the screen 10. At this time, when the light polarized by the projector-side polarizing layer 22 and the liquid crystal plate 24 reaches the polarizing layer 11, the polarizing layer 11 has the same polarization characteristics as the projector-side polarizing layer 22, but the light polarized by the projector-side polarizing layer 22 is further polarized by the liquid crystal plate 24, so the light that reaches the polarizing layer 11 is absorbed by the polarizing layer 11. On the other hand, when the light polarized by the projector-side polarizing layer 22 and the liquid crystal plate 24 reaches the circular polarizing layer 13 through the through-hole 15, the circular polarizing layer 13 is composed of a polarizing plate and a quarter-wave plate with different polarization properties from the projector-side polarizing layer 22, but the light polarized by the projector-side polarizing layer 22 is further polarized by the liquid crystal plate 24. Therefore, the light reaching the circular polarizing layer 13 passes through the circular polarizing layer 13, and a part of the light is reflected by the semitransparent projection layer 14, and the rest of the light is transmitted. Here, an image formed by the transmitted light is projected on the rear surface of the screen 10 (the surface opposite to the side where the projection device 20 is provided), thereby realizing rear projection. In addition, the light reflected by the semitransparent projection layer 14 has its polarization properties changed by rotation accompanying the reflection, and is absorbed by the circular polarizing layer 13. In this way, the light that reaches the polarizing layer 11 described above is absorbed by the polarizing layer 11, and further, the light reflected by the projection layer 14 is absorbed by the circular polarizing layer 13, so that the image (the image to be rear projected) produced by the above light can be prevented from showing through to the front of the screen 10. As a result, rear projection is realized and the image can be prevented from showing through to the front.

According to the third embodiment described above, a simple and inexpensive configuration in which one projection device is installed on one side of the screen makes it possible to prevent an image from showing through to the opposite side of the surface to be projected, while enabling the projection process to be switched between "front projection" and "rear projection" by switching the liquid crystal panel 24 on and off.

[Fourth embodiment]
In the fourth embodiment, a projection device equipped with a vertical or horizontal polarizing plate and a liquid crystal plate that can be turned on and off in a grid is used to switch between front projection, rear projection, double-sided projection of the same image, and double-sided projection of different images. Here, "on/off controllable in a grid" means that the surface of the liquid crystal plate is divided into a fine grid and each individual division unit (e.g., pixel) can be turned on and off.

7(a), (b), and (c) show configuration diagrams of an image projection system 1 in the fourth embodiment. The image projection system 1 includes a screen 10 for projecting a projected image and one projection device 20 provided on one side of the screen 10. The configuration of the screen 10 is the same as that of the first to third embodiments, so a description thereof will be omitted. The projection device 20 includes a projector 21 that emits light for image projection, a projector-side polarizing layer 22 that is made of a vertical polarizing plate or a horizontal polarizing plate and is arranged on the exit surface side of the projector 21, a liquid crystal plate 25 that can be turned on and off on a grid arranged on the exit surface side (i.e., downstream side in the traveling direction of light) of the projector-side polarizing layer 22, and a control unit 28 that includes an image DB 29 that stores image data of the image to be projected, supplies image data to the projector 21, and controls the on and off of the liquid crystal plate 25. The projector-side polarizing layer 22 has the same polarization characteristics as the polarizing layer 11 of the screen 10. Furthermore, the polarizing layer 11, the circular polarizing layer 13, and the projector-side polarizing layer 22 of the screen 10 have the following two patterns of relationship in terms of polarization characteristics. That is, as a first pattern, when the polarizing layer 11 and the projector-side polarizing layer 22 are vertical polarizing plates, the circular polarizing layer 13 is composed of a horizontal polarizing plate and a 1/4 wavelength plate to rotate left. On the other hand, as a second pattern, when the polarizing layer 11 and the projector-side polarizing layer 22 are horizontal polarizing plates, the circular polarizing layer 13 is composed of a vertical polarizing plate and a 1/4 wavelength plate to rotate right. However, either of the above two patterns may be adopted.

Figure 8 shows the operation of the control unit 28. When the image projection process to be executed is "front projection" (YES in steps S31 and S32), the control unit 28 turns off the entire surface of the liquid crystal panel 25 and supplies image data to be front projected to the projector 21 (step S34). When the image projection process to be executed is "rear projection" (YES in steps S31 and NO in step S32), the control unit 28 turns on the entire surface of the liquid crystal panel 25 and supplies image data to be rear projected to the projector 21 (step S35).

Furthermore, when the image projection process to be executed is "double-sided projection of different images" (NO in steps S31 and S33), the control unit 28 controls the on/off of the liquid crystal panel 25 to form a grid, and supplies image data of the front image and the back image arranged in a grid to match the liquid crystal panel 25 to the projector 21 (step S37). Furthermore, when the image projection process to be executed is "double-sided projection of the same image" (NO in step S31, YES in step S33), the control unit 28 controls the on/off of the liquid crystal panel 25 to form a grid, and supplies image data of the front image and the back image (mirror image of the front image) arranged in a grid to match the liquid crystal panel 25 to the projector 21 (step S36).

In the case of front projection, as shown in FIG. 7(a), when the entire surface of the liquid crystal plate 25 is off, the light of the image to be front-projected shown by the solid line in FIG. 7(a) is emitted from the projector 21, and the light polarized by the projector-side polarizing layer 22 passes through the liquid crystal plate 25 without being further polarized by the liquid crystal plate 25 and reaches the screen 10. At this time, when the light polarized by the projector-side polarizing layer 22 reaches the polarizing layer 11, the polarizing layer 11 has the same polarization characteristics as the projector-side polarizing layer 22, so the light passes through the polarizing layer 11 and is reflected by the opaque layer 12. Therefore, the image (front-projected image) of the above light is reflected on the front surface of the screen 10 (the surface on which the projection device 20 is provided). On the other hand, when the light polarized by the projector-side polarizing layer 22 passes through the through-hole 15 and reaches the circular polarizing layer 13, the circular polarizing layer 13 has polarization characteristics different from those of the projector-side polarizing layer 22, so the light is absorbed by the circular polarizing layer 13. This prevents the image produced by the light (the image to be projected from the front) from showing through to the rear of the screen 10. As a result, front projection is achieved while preventing the image from showing through to the rear.

In the case of rear projection, as shown in FIG. 7(b), when the entire surface of the liquid crystal plate 25 is on, the light of the image to be rear projected shown by the solid line in FIG. 7(b) is emitted from the projector 21, the light polarized by the projector-side polarizing layer 22 is further polarized by the liquid crystal plate 25, and the light polarized by the projector-side polarizing layer 22 and the liquid crystal plate 25 (light shown by the dashed line in FIG. 7(b)) reaches the screen 10. At this time, when the light polarized by the projector-side polarizing layer 22 and the liquid crystal plate 25 reaches the polarizing layer 11, the polarizing layer 11 has the same polarization characteristics as the projector-side polarizing layer 22, but the light polarized by the projector-side polarizing layer 22 is further polarized by the liquid crystal plate 25, so the light that reaches the polarizing layer 11 is absorbed by the polarizing layer 11. On the other hand, when the light polarized by the projector-side polarizing layer 22 and the liquid crystal plate 25 reaches the circular polarizing layer 13 through the through-hole 15, the circular polarizing layer 13 is composed of a polarizing plate and a quarter-wave plate with different polarization properties from those of the projector-side polarizing layer 22, but the light polarized by the projector-side polarizing layer 22 is further polarized by the liquid crystal plate 25. Therefore, the light reaching the circular polarizing layer 13 passes through the circular polarizing layer 13, and a part of the light is reflected by the semitransparent projection layer 14, and the rest of the light is transmitted. Here, an image formed by the transmitted light is projected on the rear surface of the screen 10 (the surface opposite to the side where the projection device 20 is provided), thereby realizing rear projection. In addition, the light reflected by the semitransparent projection layer 14 has its polarization properties changed by rotation accompanying the reflection, and is absorbed by the circular polarizing layer 13. In this way, the light that reaches the polarizing layer 11 described above is absorbed by the polarizing layer 11, and further, the light reflected by the projection layer 14 is absorbed by the circular polarizing layer 13, so that the image (the image to be rear projected) produced by the above light can be prevented from showing through to the front of the screen 10. As a result, rear projection is realized and the image can be prevented from showing through to the front.

When projecting different images on both sides, as shown in FIG. 7(c), the on/off of the liquid crystal panel 25 is controlled by a grid, and the light of the front image and the rear image (light shown by solid lines in FIG. 7(c)) grid-shaped according to the liquid crystal panel 25 is emitted from the projector 21, and the light polarized by the projector-side polarizing layer 22 is further polarized by the liquid crystal panel 25 whose on/off is controlled by a grid. At this time, since the on/off of the liquid crystal panel 25 controlled by the grid and the light of the front image and the rear image grid-shaped are linked, the light of the front image passes through the off-controlled grid of the liquid crystal panel 25 without being polarized and reaches the screen 10. On the other hand, the light of the rear image is polarized by the on-controlled grid of the liquid crystal panel 25, and the polarized light (light shown by dashed lines in FIG. 7(c)) reaches the screen 10.

At this time, when the light polarized only by the projector-side polarizing layer 22 reaches the polarizing layer 11, the polarizing layer 11 has the same polarization characteristics as the projector-side polarizing layer 22, so the light passes through the polarizing layer 11 and is reflected by the opaque layer 12. Therefore, an image (front-projected image) produced by the light is projected on the front surface of the screen 10 (the surface on which the projection device 20 is provided). On the other hand, when the light polarized only by the projector-side polarizing layer 22 reaches the circular polarizing layer 13 through the through-hole 15, the circular polarizing layer 13 has different polarization characteristics from the projector-side polarizing layer 22, so the light is absorbed by the circular polarizing layer 13. Therefore, the image (front-projected image) produced by the light can be prevented from being seen through the back surface of the screen 10. As a result, front projection is realized and the image can be prevented from being seen through the back surface.

In addition, when the light polarized by the projector-side polarizing layer 22 and the liquid crystal plate 25 reaches the polarizing layer 11, the polarizing layer 11 has the same polarization characteristics as the projector-side polarizing layer 22, but the light polarized by the projector-side polarizing layer 22 is further polarized by the liquid crystal plate 25, so the light that reaches the polarizing layer 11 is absorbed by the polarizing layer 11. On the other hand, when the light polarized by the projector-side polarizing layer 22 and the liquid crystal plate 25 reaches the circular polarizing layer 13 through the through hole 15, the circular polarizing layer 13 is composed of a polarizing plate and a 1/4 wavelength plate with polarization characteristics different from those of the projector-side polarizing layer 22, but the light polarized by the projector-side polarizing layer 22 is further polarized by the liquid crystal plate 25, so the light that reaches the circular polarizing layer 13 passes through the circular polarizing layer 13 and a part of the light is reflected by the semitransparent projection layer 14, and the rest of the light is transmitted. Here, the image of the transmitted light is projected on the rear surface of the screen 10 (the surface opposite to the side where the projection device 20 is provided), so rear projection is realized. Furthermore, the light reflected by the semi-transparent projection layer 14 has its polarization characteristics changed by the rotation accompanying the reflection, and is absorbed by the circular polarization layer 13. In this way, the light that reaches the aforementioned polarization layer 11 is absorbed by the polarization layer 11, and further, the light reflected by the projection layer 14 is absorbed by the circular polarization layer 13, so that the image (the image to be rear-projected) produced by the above light can be prevented from showing through to the front of the screen 10. As a result, rear projection is realized, and the image can be prevented from showing through to the front.

As described above, the configuration shown in FIG. 7(c) makes it possible to perform double-sided projection (front projection and rear projection) of different images while avoiding the image showing through to the opposite side of the surface to be projected.

Furthermore, in the case of double-sided projection of the same image, in step S36, the liquid crystal panel 25 is turned on and off in a grid, and image data for the front image and the back image (mirror image of the front image) in a grid that matches the liquid crystal panel 25 is supplied to the projector 21, so that the mirror image of the front image is made into the back image in the same operation as in the case of double-sided projection of different images, and as a result, the same image as the front image is viewed from the back side. Therefore, with the configuration shown in FIG. 7(c), it is possible to perform double-sided projection of the same image by using the mirror image of the front image as the back image while avoiding the image showing through to the opposite side of the surface to be projected.

According to the fourth embodiment described above, a simple and inexpensive configuration in which one projection device is installed on one side of the screen prevents an image from showing through to the opposite side of the surface to be projected, while controlling the on/off of the liquid crystal panel 25 in a grid makes it possible to switch the projection process between "front projection", "rear projection", "double-sided projection of different images", and "double-sided projection of the same image".

[Fifth embodiment]
In the fifth embodiment, an embodiment is described in which a single projection device equipped with a vertical or horizontal polarizing plate and a liquid crystal plate that can be controlled to be on or off is used to achieve double-sided projection by rapidly switching the liquid crystal plate on and off.

Figure 9 shows a configuration diagram of an image projection system 1 in the fifth embodiment. The image projection system 1 includes a screen 10 for projecting a projected image and one projection device 20 provided on one side of the screen 10. The configuration of the screen 10 is the same as in the first to fourth embodiments, and the configuration of the projection device 20 is the same as in the third embodiment shown in Figures 5(a) and (b), so duplicated explanations will be omitted. In the fifth embodiment, in an image projection system 1 with the same configuration as in the third embodiment, the liquid crystal panel 24 is switched between the off state shown in the upper part of Figure 9 and the on state shown in the lower part of Figure 9 at high speed, thereby quickly switching between front projection (upper part of Figure 9) and rear projection (lower part of Figure 9), thereby realizing double-sided projection.

Figure 10 shows the operation of the control unit 28. When the double-sided projection to be executed projects different images on both sides (NO in step S41), the control unit 28 quickly switches between "turning off the liquid crystal panel 24 and supplying image data to be projected on the front to the projector 21 (step S45)" and "turning on the liquid crystal panel 24 and supplying image data to be projected on the rear to the projector 21 (step S46)" until the projection is completed (YES in step S47). The detailed operation has been explained in the third embodiment based on Figures 5 (a) and (b), so it will not be described here. However, the above process executes both the front projection of the image to be projected on the front and the rear projection of an image different from the image to be projected on the front and the rear projection of an image different from the image to be projected on the rear while avoiding the image from being seen through to the opposite side, and as a result, double-sided projection of different images can be realized.

On the other hand, if the double-sided projection to be executed is to project the same image on both sides (YES in step S41), the control unit 28 quickly switches between "a process of turning off the liquid crystal panel 24 and supplying image data of the image to be projected on the front to the projector 21 (step S42)" and "a process of turning on the liquid crystal panel 24 and supplying image data of the mirror image of the image to be projected on the front to the projector 21 (step S43)" until the projection is completed (YES in step S44). The detailed operation has been explained in the third embodiment based on Figs. 5(a) and (b) and will not be described here, but the above process executes both the front projection of the image to be projected on the front and the rear projection of the mirror image of the image to be projected on the front while avoiding the image from being seen through to the opposite side. In the latter rear projection, the same image as the image to be projected on the front is visible from the rear, so that the double-sided projection of the same image can be realized.

According to the fifth embodiment described above, a simple and inexpensive configuration in which one projection device is installed on one side of the screen makes it possible to realize double-sided projection of the same or different images by quickly switching the liquid crystal panel 24 on and off while avoiding the image showing through to the opposite side of the surface to be projected.

[Terminology, variations, etc.]
The block diagrams used in the description of the above embodiments show functional blocks. These functional blocks (components) are realized by any combination of at least one of hardware and software. The method of realizing each functional block is not particularly limited. That is, each functional block may be realized using one device that is physically or logically coupled, or may be realized using two or more devices that are physically or logically separated and directly or indirectly connected (for example, using wires, wirelessly, etc.). The functional blocks may be realized by combining the one device or the multiple devices with software.

For example, the control unit 28 may function as a computer that performs the processing in the above embodiment. FIG. 11 is a diagram showing an example of the hardware configuration of the control unit 28. The above-mentioned control unit 28 may be physically configured as a computer device including a processor 1001, a memory 1002, a storage 1003, a communication device 1004, an input device 1005, an output device 1006, a bus 1007, etc.

In the following description, the term "apparatus" can be interpreted as a circuit, device, unit, etc. The hardware configuration of the control unit 28 may be configured to include one or more of the devices shown in the figure, or may be configured to exclude some of the devices.

The functions of the control unit 28 are realized by loading specific software (programs) onto hardware such as the processor 1001 and memory 1002, causing the processor 1001 to perform calculations, control communication via the communication device 1004, and control at least one of reading and writing data in the memory 1002 and storage 1003.

Although the present disclosure has been described in detail above, it is clear to those skilled in the art that the present disclosure is not limited to the embodiments described herein. The present disclosure can be implemented in modified and altered forms without departing from the spirit and scope of the present disclosure as defined by the claims. Therefore, the description of the present disclosure is intended as an illustrative example and does not have any limiting meaning on the present disclosure.

The processing steps, sequences, flow charts, etc. of each aspect/embodiment described in this disclosure may be reordered unless inconsistent. For example, the methods described in this disclosure present elements of various steps using an example order and are not limited to the particular order presented.

The input and output information may be stored in a specific location (e.g., memory) or may be managed using a management table. The input and output information may be overwritten, updated, or added to. The output information may be deleted. The input information may be transmitted to another device.

As used in this disclosure, the phrase "based on" does not mean "based only on," unless expressly stated otherwise. In other words, the phrase "based on" means both "based only on" and "based at least on."

When the terms "include," "including," and variations thereof are used in this disclosure, these terms are intended to be inclusive, similar to the term "comprising." Additionally, the term "or," as used in this disclosure, is not intended to be an exclusive or.

In this disclosure, where articles have been added through translation, such as a, an, and the in English, this disclosure may include that the nouns following these articles are in the plural form.

In this disclosure, the term "A and B are different" may mean "A and B are different from each other." The term may also mean "A and B are each different from C." Terms such as "separate" and "combined" may also be interpreted in the same way as "different."

1...image projection system, 10...screen, 11...polarizing layer, 12...opaque layer, 13...circularly polarizing layer, 14...projection layer, 15...through hole, 20...projection device, 20A, 20B...projection unit, 21, 21A, 21B...projector, 22, 23...projector-side polarizing layer, 24, 25...liquid crystal plate, 28...control unit, 29...image DB, 1001...processor, 1002...memory, 1003...storage, 1004...communication device, 1005...input device, 1006...output device, 1007...bus.

Claims (9)

A screen composed of four layers, namely, a polarizing layer, an opaque layer, a circular polarizing layer consisting of a polarizing plate and a quarter-wave plate, and a semi-transparent projection layer, the four layers being arranged in the order of the polarizing layer, the opaque layer, the circular polarizing layer, and the projection layer along a thickness direction from a light receiving surface side of the projected light, and only the polarizing layer and the opaque layer are provided with through holes at corresponding positions along the thickness direction;
one or more projection devices that project at least one of light polarized in the same direction as the polarization of the polarizing layer and light polarized in a different direction toward the screen from one side of the screen;
An image projection system comprising: The projection device is
A projector that emits light for image projection;
a projector-side polarizing layer arranged on the exit surface side of the projector and made of a vertical polarizing plate or a horizontal polarizing plate;
A projection device including:
2. The image projection system of claim 1. The projection device is
A projector that emits light for image projection;
a projector-side polarizing layer disposed on the exit surface side of the projector, the projector-side polarizing layer being made of a polarizing plate that polarizes light in the same direction as the polarization by the polarizing layer of the screen;
a liquid crystal plate that is controllably turned on and off and is disposed downstream of the projector-side polarizing layer in the light traveling direction;
a control unit that controls the operation of the projector and the on/off of the liquid crystal panel;
A projection device including:
The control unit is
When projecting a front image, the liquid crystal panel is turned off to emit light of the front image from the projector;
When projecting a rear image, the liquid crystal panel is turned on to cause light of the rear image to be emitted from the projector.
2. The image projection system of claim 1. The projection device is
A projector that emits light for image projection;
a projector-side polarizing layer disposed on the exit surface side of the projector, the projector-side polarizing layer being made of a polarizing plate that polarizes light in the same direction as the polarization by the polarizing layer of the screen;
a liquid crystal plate that is arranged downstream of the projector-side polarizing layer in the light traveling direction and that can be turned on and off in a grid;
a control unit that controls the operation of the projector and also controls the liquid crystal panel to turn on and off a grid;
A projection device including:
2. The image projection system of claim 1. When performing double-sided projection on the screen, the control unit
a grid is controlled to be turned on and off for the liquid crystal panel, and light for a front image and a rear image formed in a grid in accordance with the liquid crystal panel is emitted from the projector;
5. The image projection system according to claim 4. The projection device is
a first projector that emits light for image projection;
a first polarizing layer made of a vertical polarizing plate or a horizontal polarizing plate, the first polarizing layer being arranged on the exit surface side of the first projector;
A first projection unit including:
a second projector that emits light for image projection;
a second polarizing layer arranged on the exit surface side of the second projector and made of a polarizing plate having a polarization characteristic different from that of the first polarizing layer, out of a vertical polarizing plate and a horizontal polarizing plate;
A second projection unit including:
Consists of:
2. The image projection system of claim 1. The projection device is
A projector that emits light for image projection;
a projector-side polarizing layer disposed on the exit surface side of the projector, the projector-side polarizing layer being made of a polarizing plate that polarizes light in the same direction as the polarization by the polarizing layer of the screen;
a liquid crystal plate that is controllably turned on and off and is disposed downstream of the projector-side polarizing layer in the light traveling direction;
a control unit that controls the operation of the projector and the on/off of the liquid crystal panel;
A projection device including:
The control unit is
a control for turning off the liquid crystal panel and emitting light of a front image from the projector, and a control for turning on the liquid crystal panel and emitting light of a rear image from the projector, thereby performing double-sided projection;
2. The image projection system of claim 1. When the same image is projected onto both sides of the screen, the control unit sets a mirror image of the front image as the rear image.
8. An image projection system according to claim 5 or 7. A screen for projecting an image from projected light,
It is composed of four layers: a polarizing layer, an opaque layer, a circular polarizing layer consisting of a polarizing plate and a quarter-wave plate, and a semi-transparent projection layer.
The four layers are arranged in the following order along a thickness direction from a light receiving surface side of the projected light: the polarizing layer, the opaque layer, the circular polarizing layer, and the projection layer;
Only the polarizing layer and the opaque layer are provided with through holes at corresponding positions along a thickness direction.
screen.

Images