JPH06110131A - Projection screen - Google Patents

Abstract

PURPOSE:To reduce the effect of indoor illumination light and to utilize a projection screen in a bright room by providing a control means turning a diffusion plate into a diffusing state when illuminance is low and a transparent state when the illuminance is high. CONSTITUTION:An observer can use projection screens 5a and 5b as a simple diffusion plate in such a manner that repetition is attained at a frequency so as to hardly feel a flicker by the control means 9 based on information detected by an illuminance detecting means 7. In the (a), when detecting that the illuminance by the indoor illumination light is comparatively low, the projection screen 5a is turned into a diffusion plate state and at this time, projected light L1 from a projector 1 is diffused/transmitted by the projection screen and becomes transmitted light t1D. Then, part of the transmitted light L1D is made incident on the eye of the observer 13 and the observer 13 can observe picture information by the projected light L1. In the (b), when detecting that the illuminance by the indoor illumination light, is high the projection screen 5b is turned into a transparent plate state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection screen used in videophones, video conferences and the like.

[0002]

2. Description of the Related Art In recent years, in an image communication apparatus such as a videophone or a videoconference, a line-of-sight matching technique for talking with each other while looking at each other's faces, that is, a line-of-sight matching, is from a human interface point of view. It is emphasized. For example, there is one that is realized by disposing a semi-transparent mirror inclined at 45 degrees in front of the camera and aligning the optical axes of the camera and the monitor. However, this method requires a large space because a mirror is used, and has some drawbacks such as not being suitable for large-screen display. Further, a combination of a projection display method and a time-division imaging method has been proposed as a line-of-sight matching method suitable for large-screen display. this is,
This is a time-division system in which a camera is installed behind the display screen to synchronize the screen operation and the shooting operation. In the operation sequence of this apparatus, first, the shutter is photographed by the video camera periodically, and then the screen is driven based on the periodic signal of the photographing period to keep the screen in a transparent state for a certain period of time. If the shutter photographing is performed synchronously when the screen is in a transparent state, the screen appears to be always transparent when viewed from the video camera, although the screen is opaque when viewed from the observer.

A typical example of the transmissive projection screen is a combination of a Fresnel lens and a lenticular lens, and a transmissive projection screen (Japanese Patent Application No. 3-60104) having a simple structure is known. Also, two lenticular lenses that are used by crossing them vertically (Japanese Patent Application No. 3-
No. 42432), there is one using a diffuse transmission plate. Further, a typical reflection type projection screen uses a diffuse reflection plate, but there is also known a reflection type projection screen in which directivity is used for reflection to increase the gain around the normal direction. Furthermore, there is a projection screen for a line-of-sight matching display device that switches the projection screen between two states of a diffusion plate and a transmission plate (Technical Report of the Television Society, Vol. 16, No. 1).
0, p.37,). This is to make it possible to match the line of sight of the other party on the projection screen when a videophone is manufactured by combining projection type (projection type) display and time-division imaging using this projection screen.

In this conventional eye-gaze matching type display device, the projection screen is switched between a transparent state and an opaque state in a time division manner, and in the transparent state, image information including an observer on the front surface of the screen is arranged on the rear surface (rear surface). By taking a picture with such a camera and acting as a transmissive diffusion plate when it is in an opaque state, an observer in the front can observe the projection light projected from the projector arranged on the rear with a wide field of view. By repeating the transparent state and the opaque state at a frequency that does not cause flicker, it is an opaque plate that acts as a mere transmission type diffusion plate projection screen for the observer, and it is possible to continuously observe the projection light from the projector. I can.

Hereinafter, this method will be described with reference to FIGS. 8 and 9. In FIG. 8A, when the projection screen is in the state of a diffusion plate, the projection light L101 from the projector 101 is diffused and transmitted by the projection screen 105a and becomes an arrow L101D, a part of which is the observer 13
When entering the eye, the observer 13 can observe the image information by the projected light. Further, the indoor illumination light L102 to the projection screen 105a by the halogen lamp 111 is diffused and reflected by the projection screen 105a and becomes an arrow L102R, and a part of this is incident on the eyes of the observer 13, and the observer 13 is indoors. Observe the background light of the projection screen 105a due to illumination. Therefore, the observer 13 must observe the image information with poor contrast accompanied by the backlight light. Therefore, in general, image information is observed in a dark room, that is, in a room with low illuminance due to indoor illumination light. Further, the indoor illumination light L103 to the object 115 by the halogen lamp 111 is reflected on the object 115 and the reflected light L103R is incident on the eyes of the observer 13, so that the observer 13 can observe the indoor object 115.

In FIG. 8B, the projection screen 10
When 5b is a transparent plate, most of the room illumination light L104 is transmitted through the projection screen 105b, most of it is absorbed inside the housing, and part of the reflected light is reflected again on the projection screen 105b. It passes through and enters the eyes of the observer 13. Further, the arrow L104R that is partially reflected by the projection screen first also enters the observer 13's eye. However, the brightness of light by these arrows L104S and L104R is
It is much smaller than the arrows L101D and 102R in FIG. 8A, and in reality, the observer 13 does not pay much attention to observe them.

FIG. 9 shows changes in these states with time as described above. For example, FIG. 8A and FIG. 8B
Corresponds to the state at time points (a) and (b) on the t-axis in FIG. 9 (a). Specifically, the range from 0 to 1 / 2t1 corresponds to the transparent state in FIG. 8B, and the range from 1 / 2t1 to t1 corresponds to the diffused state in FIG. 8A. Furthermore, FIG.
Is the illuminance of the projection screen by the room illumination light, the transparent state of the projection screen, the diffusion state, the illuminance of the projector light,
This is a graph showing the temporal change in the brightness at which the observer observes the screen. The line 25 shown in FIG. 9A is the illuminance of the room illumination light from the halogen lamp 111, and the illuminance Mave is constant and has a size of 1.5 in arbitrary units. Areas 26a, 26b, and 26c shown in FIG. 9B indicate the transparent state of the projection screen in arbitrary units, and it is assumed that 1 is completely transparent and 0 is completely diffused. Areas 27a, 27b, 27 shown in FIG.
c indicates the diffusion state of the projection screen in arbitrary units, 1
When it is, it is assumed that it is completely diffused, and when it is 0, it is not diffused at all. In the projection screen, it is assumed that the diffuser plate and the transparent plate are alternately changed at the same time in a cycle t1. Figure 9
Areas 28a, 28b, and 28c shown in (d) are the illuminance of the projection light from the projector, and are the illuminance Mp and have a size of 2 in arbitrary units. Projection light is (1/2) at cycle t1
It is assumed that the projection is performed when the projection screen is the diffusion plate for the time of t1. Areas 29a, 29b, 2 shown in FIG.
9c indicates the brightness Ls of the projection screen.

Generally, the brightness L of transmitted light or reflected light when light of illuminance M is incident on a certain substance is represented by L = k × M, and the projection screen is a perfect diffuse reflection surface or a perfect diffuse transmission surface. , L = (1 / π) × M. In the case of projection from the rear surface, there is no problem if a projection screen that is close to a perfect diffusion transmission surface is used, but in reality, there is no perfect diffusion surface with a spectral transmittance close to 1, and generally for transmitted light. The closer to the perfect diffusion surface, the lower the transmittance, and at the same time, the closer to the perfect diffusion surface to the reflective surface. Next, the contrast in the conventional projection screen will be described. For simplicity of explanation, it is assumed that the projection screen has a spectral transmittance of 50% and a spectral transmittance of 50%, respectively, so as to be completely diffused. If the illuminance by the transmitted light of the projected light is Mp, the illuminance by the reflected light of the room illumination light is Mave, and the brightness 30a by each light is Lp and 30b is Lave, the incident time of each light is equal, and Lave = If k1 × Mave Lp = k2 × Mp, then k1 = k2 = 1 / 2π, and Ls = Lave + Lp = k1 × Mave + k2 × Mp = (1 / 2π) (Mave + Mp).

Therefore, the ratio of the illuminance of the projection light to the projection screen and the illuminance of the room light directly becomes the brightness on the projection screen. In this case, the contrast K2 of the projector is used.
Is 1: K1 = Lave: Ls = Mave: (Mave + M
p) = 1.5: (1.5 + 2) = 1: 2.33. However, the contrast of the image by the projection light from the original projector was set to 0: 1. Further, the reflected light from the inside of the housing and the reflected light on the projection screen in the state of the transparent plate are set to 0.

For the projection screen described above, a light control glass in which a polymer liquid crystal is sandwiched between glass plates can be used.
For example, there is "Liquid Crystal Miracle Screen" manufactured by Sharp Corporation, which can drive at about 100 Hz.
This is because it works as a diffusion plate by utilizing the light scattering by the liquid crystal. As the diffusivity is increased, scattered light is generated to the same extent on both the incident side and the opposite side of the light, which results in a low light utilization efficiency. Further, the lenticular lens used in a recent rear projection type projector of about 50 inches is different from the one using the above-mentioned polymer liquid crystal in that the light is diffused by the lens, so little light is reflected in the opposite direction to the incident light. The efficiency of light utilization is high, and by providing a black stripe, it can be observed even under normal room light.

As described above, when the transmission type diffusion plate projection screen utilizing scattering is used, the observer must observe the projected light and at the same time the diffused light of the light incident on the projection screen from the front surface and the rear surface. I have to. This diffused light becomes the background light, and if you do not use the projected light that gives a very bright brightness to observe in a normal room,
The contrast of image information due to the projected light is lowered, and it is generally difficult to observe. Further, in a rear projection type projector in which a projector is arranged on the rear surface, it is possible to reduce the light from the rear surface by housing the projector and the projection screen in an integrated housing, but to prevent the influence of indoor illumination light from the front surface. Is difficult. Further, in a front projection type projector in which a projector is arranged on the front surface, it is basically difficult to prevent the influence of the room illumination light because the projection light of the projector and the room illumination are incident on the projection screen in the same direction. For this reason, a projector using a diffuse transmission plate or a diffuse reflection plate that normally utilizes scattering is used in a darkened room.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a projection screen which can easily reduce the influence of indoor illumination light and can be used in a bright room.

[0013]

To achieve the above object, the first invention of the present application is, in a projection screen under an illumination environment in which the illuminance changes periodically, transmits a diffusion state in which the projection light from the projector is diffused and the illumination light. It is characterized by comprising a diffuser plate which can be in a transparent state, and a control means which brings the diffuser plate into a diffused state when the illuminance is low and a transparent state when the illuminance is high. Further, a second invention of the present application is to provide an illumination unit that emits pulsed light, a projector that projects projection light relating to image information, a diffusion state that diffuses the projection light from the projector, and an illumination light from the illumination unit. It is characterized by comprising: a diffuser plate which can be in a transparent state which is transparent, and a control means which makes the diffuser plate in a transparent state only when the illuminating means emits pulsed light.

Further, a third invention of the present application is to provide a lighting means which uses a phosphor having a short afterglow and whose illuminance is periodically changed, a projector which projects projection light relating to image information, and a projection from the projector. A diffusion plate capable of taking a diffusion state of diffusing light and a transparent state of transmitting illumination light; and a control means for setting the diffusion plate to a diffusion state when the illuminance is low and a transparent state when the illuminance is high. It is characterized by having. Furthermore, a fourth invention of the present application is, in a projection screen in an illumination environment where illuminance changes periodically, a projector that projects projection light relating to image information, a diffusion state that diffuses the projection light from the projector, and the illumination light. A diffusion plate that can be in a transparent state that transmits light, an image pickup unit provided on the projector side with respect to the diffusion plate, and a diffusion state when the illuminance is low, and a transparent state when the illuminance is high. And a control means for imaging the subject by the imaging means when the diffusion plate is in a transparent state.

The present invention having the above configuration has the following operation. In the projection screen of the first invention of the present application, the state of the diffusion plate is set to the diffusion state in which the projection light from the projector is diffused when the illuminance is low, and is set to the transparent state in which the illumination light is transmitted when the illuminance is high. Since the reflection of the indoor illumination light on the diffusion plate is reduced, the influence of the indoor illumination light is reduced, and the indoor illumination light can be used in a bright room. Second application
The projection screen of the invention of 1) obtains the same operation as that of the first invention of the present application by using the illumination means that emits the pulsed light as the indoor illumination light. The projection screen of the third invention of the present application obtains the same effect as that of the first invention of the present application by using a short-afterglow phosphor as the room illumination light and using an illumination means in which the illuminance changes periodically. is there. In the projection screen of the fourth invention of the present application, an image pickup unit is provided on the projector side with respect to the diffusion plate, and the image pickup unit picks up an image of the subject when the diffusion plate is in a transparent state.

An embodiment according to the present invention will be described below with reference to the drawings. 1A and 1B are configuration explanatory views of a projection screen according to the present invention. FIG. 1A is when the projection screen is in a diffusion plate state, and FIG. 1B is when the projection screen is in a transparent plate state. Is. In FIG. 1 (a),
The projector 1 is a projection screen 5 in the state of a diffusion plate.
The projector 1 and the projection screen 5a, which are arranged on the back side of a, are housed in a housing 3 whose interior is black and matte coated. The observer 13, the fluorescent lamp 11, the object 15 on the observer side, and the illuminance detection means 7 for indoor illumination light are arranged on the front side of the projection screen 5a. The projector 1 and the projection screen 5 are controlled by the control means 9. Further, the projection light L1 from the projector 1 to the projection screen 5a and its transmitted light L1D, the room illumination light L2 from the fluorescent lamp 11 to the projection screen 5a and its reflected light L2R, the room illumination light L3 from the fluorescent lamp 11 to the object 15 are shown. And its reflected light L3R are shown respectively. In FIG. 1B, the projection screen 5b is in the state of a transparent plate, and the room illumination light L4 from the fluorescent lamp 11 to the projection screen 5b and its transmitted light L4T and reflected light L4R, and the fluorescent lamp 11 to the object 15 are shown. The room illumination light L5 and its reflected light L5R are shown.
The observer 13, the object 15, the housing 3, and the fluorescent lamp 11 are in the same room where light does not enter from the outside.

By repeating the states of FIGS. 1A and 1B based on the information detected by the illuminance detecting means 7 by the control means 9 at a frequency at which flicker is less likely to be felt, the observer The projection screen can be used simply as a diffuser. In FIG. 1A, the projection screen 5a becomes a diffuser plate by detecting when the illuminance by the room illumination light is relatively small. At this time, the projection light L1 from the projector 1 is diffused and transmitted by the projection screen. It becomes light L1D, and a part of this transmitted light L1D enters the eyes of the observer 13, and the observer 13 can observe the image information by the projection light L1. In addition, the indoor illumination light L4 to the projection screen 5b by the fluorescent halogen lamp 11
Is diffuse-reflected by the projection screen 5b and diffuse-reflected light L
It becomes 4R, and a part of it enters the observer 13's eye,
The observer 13 observes the background light of the projection screen 5b by the indoor illumination.

Therefore, the observer 13 must observe the image information with poor contrast accompanied by the backlight light. However, since the projection screen 5a is a diffusion plate when the illuminance by the room illumination light 11 is small in advance, this embodiment can reduce the backlight light and improve the contrast. Further, the room illumination light L3 to the object 15 by the fluorescent lamp is the object 15
The reflected light L3R is incident on the eyes of the observer 13, and the observer 13 can observe the object 15 in the room. In FIG. 1B, when the illuminance by the room illumination light is relatively high, the projection screen is set to the transparent plate state,
At this time, as in the case of FIG. 3B, most of the room illumination light L4 is transmitted through the projection screen to become transmitted light L4T, which is almost absorbed by the matte coating inside the housing 3, The reflected light L4s that is partially reflected again passes through the projection screen 5b and enters the eyes of the observer 13. In addition, the reflected light L4R that was first partially reflected by the projection screen
Also enters the eyes of the observer 13. However, the brightness of the reflected light L4s and the reflected light L4R is much smaller than that of the transmitted light L1D in FIG. 3A, and the observer 13 does not actually pay attention to observe these. Further, the room illumination light L5 to the object 15 by the fluorescent lamp is reflected on the object 15 and the reflected light L5R enters the eyes of the observer 13, and the observer 13 can observe the object 15 in the room.

FIG. 2 shows the changes over time in these states. For example, FIGS. 1 (a) and 1 (b) show the time points (a) and (b) on the t-axis in FIG. 2 (a). Corresponds to the state.
FIG. 2 shows temporal changes in the illuminance of the projection screen by the room illumination light, the transparent state of the projection screen, the diffusion state, the illuminance of the projector light, and the brightness at which the observer 13 observes the screen. Waveform 15 shown in FIG.
Is the illuminance of the room illumination light by the fluorescent lamp 11, and the illuminance M changes in the cycle t1. Generally, a fluorescent lamp has a periodical change of 100 Hz or 120 Hz (twice of 50 Hz or 60 Hz, respectively) in a normal commercial AC power supply, and the state of this change greatly changes depending on the structure of the electrode of the fluorescent lamp or the kind of the fluorescent substance. . In general, the central portion of the fluorescent tube has a beautiful periodic change of 100 Hz or 120 Hz, but the end portion of the fluorescent tube generally has a distorted light change depending on the electrode structure. This is because there is a difference in the spread and intensity of the light between the cathode negative glow light and the anode light, so that the light sometimes changes at 50 Hz or 60 Hz. Efforts are being made not to manufacture a fluorescent lamp that causes such a phenomenon, because the frequency itself makes it easier to perceive flicker as illumination light.

If the central portion of the fluorescent tube is used,
Since room illumination light that periodically changes at 100 Hz or 120 Hz is obtained, in this embodiment, for the sake of simplification of the description, the periodic change at a frequency of 100 Hz, that is, the cycle t1 =
10 ms. At this time, the illuminance by the indoor illumination light is
Maximum value Mmax = 2 and minimum value Mmin = in arbitrary units
1 and the average value Mave = 1.5. Square waves 16a, 16b, and 16c shown in FIG. 2B indicate the transparent state of the projection screen in arbitrary units, and are assumed to be completely transparent when 1 and completely diffused when 0. Square waves 17a, 17b, 17c shown in FIG. 2 (c)
Indicates the diffusion state of the projection screen in an arbitrary unit, and it is assumed that 1 indicates complete diffusion and 0 indicates no diffusion. In the projection screen, it is assumed that the diffusion plate and the transparent plate are alternately changed at the cycle t1. At this time, the time in the state of the transparent plate is set to (3/4) t1, the time in the state of the diffuser plate is set to (1/4) t1, and the state in the diffuser plate is set so that the illuminance by the room illumination light is near the minimum. , Here, the time (5
/ 8) t1 to (7/8) t1. Figure 2
The square waves 18a, 18b, and 18c shown in (d) are the illuminance of the projection light from the projector, which is the illuminance Mp and has a magnitude of 2 in arbitrary units. The projected light has a period of t1 (1 /
4) It is assumed that the projection is performed when the projection screen is the diffusion plate for the time of t1. The square waves 19a and 19 shown in FIG.
Reference numerals b and 19c represent the brightness Ls of the projection screen.

In this case, in order to simplify the description of the illuminance change shown in FIG. 9 (a), M = 0.5 × sin (2π × t / t1) +1.5, and the projection screen in FIG. 2 (e) is set. Assuming that the illuminance of the projection light and the illuminance of the room illumination light are directly proportional to the brightnesses 20a and 20b on the projection screen, the contrast K2 of the projector is from t = (5/8) t1 to (7/8)
Considering by integrating up to t1: 1: K2 = {(3/8)-(2 / 4π)} t1: [{(3/8)-(2 / 4π)} t1 + (1/2) t1] = 2.91. Therefore, the contrast can be improved by 25% as compared with the conventional contrast K1. Further, the contrast can be improved as the time during which the projection screen is the diffusion plate and the time during which the projection light is projected in synchronization with the diffusion screen are shortened with respect to the cycle. In this case, if the projection light is projected in a very short time around t = (3/4) t1, then 1: K3 = Mmin: (Mmi
It can be increased up to n + Mp) = 1: 3.0.

However, if the illuminance of the projected light is constant as the period in which the projection screen is the diffusion plate and the time for projecting the projected light in synchronism with it are shortened with respect to the cycle,
Since the substantial brightness observed by the observer decreases, it is necessary to take care to increase the illuminance of the projected light in advance. In addition, even if a projection screen like the conventional example can increase the illuminance of the projection light without using room lighting that periodically changes the illuminance, such as a fluorescent lamp, the projection light is projected in a very short time. Projecting in synchronization with the screen is effective in increasing the contrast. Further, these methods are similarly effective when the projection screen is used as a reflection type instead of a transmission type, and the contrast is increased. Also, when an illumination that gives a periodical change in illuminance is provided on the rear surface of the transmissive screen and the change of the projection screen is synchronized, when observing an object on the rear surface by superimposing an image with image information depending on the projected light. The contrast of can be increased.

Further, even if the illuminance detecting means 7 is not provided, the fluorescent lamp 11 can be previously moved to the projection screen 5 by the control means 9.
The same effect can be provided by making it possible to control in synchronism with the change of.

As the fluorescent lamp 11, it is preferable to use a fluorescent lamp having a large change in illuminance. Also,
When using a plurality of fluorescent lamps, it is desirable to align these phases to some extent. Of course, the illuminating means that gives this periodic change in illuminance does not have to be a fluorescent lamp. For example, a halogen lamp may be controlled by a shutter element, or laser light may be modulated. Further, this projection screen may be other than the one using polymer liquid crystal, as long as it can change the transparent plate and the diffusion plate,
For example, it is also effective to use an array of liquid crystal microlenses. FIG. 3 shows an embodiment in which the room illumination light and the projection screen, which are slightly different from those in FIG. 2, are synchronized.
FIG. 5 shows temporal changes in the illuminance of the projection screen, the transparent state of the projection screen, the diffused state, the illuminance of the projector light, and the brightness at which the observer observes the screen due to the indoor illumination light. For example, in FIGS. 1 (a) and 1 (b),
This corresponds to the state at time (a) between 5 / 8t1 and 7 / 8t1 on the t-axis in FIG. 3A and (b) between 0 and 5 / 8t1.

The waveform 31 shown in FIG. 3A is the illuminance of the room illumination light by the fluorescent lamp 11, and the illuminance M is the period t1.
The illuminance by the room illumination light is a maximum value Mmax = 2, a minimum value Mmin = 1, and an average value Mave in arbitrary units.
= 1.5. The square waves 32a, 32b, 32c shown in FIG. 3 (b) indicate the transparent state of the projection screen in arbitrary units, and are completely transparent at 1,
When it is 0, it is assumed that it is completely diffused. Figure 3 (c)
The square waves 33a, 33b, and 33c shown in (1) indicate the diffusion state of the projection screen in arbitrary units, and are assumed to be completely diffused when 1 and not diffused when 0. In the projection screen, it is assumed that the diffuser plate and the transparent plate are alternately changed at the cycle t1. At this time, for a cycle t2 that is twice the cycle t1 of the illuminance change of the room illumination light, the time in the transparent plate state is (5/8) t2, and the time in the diffuser plate state is (1/8). ) T2, and the state of the diffuser plate is near one of the minimum illuminances due to the indoor illumination light. Here, from time (5/16) t2 = (5/8) t1 to (7 /
16) t2 = (7/8) t1.

The square waves 34a, 34b shown in FIG.
34c is the illuminance of the light projected by the projector, and is the illuminance Mp, which is set to 2 in an arbitrary unit. The period of the projected light is a period t1 and a time of (1/8) t2, and projection is performed when the projection screen is a diffusion plate. Areas 35a and 35b shown in FIG. 3 (e) show the luminance Lp of the projection screen. This is effective when the frequency of periodic fluctuations in the room illumination light is large and considering the frequency at which flicker does not occur, it is not necessary to match the fluctuation frequency of the room illumination light with the frequency of the projection light of the projection screen or projector. is there.
Further, for example, the fluctuating frequency of the room illumination light of 300 Hz is given, and the vertical scanning wave number is 60 Hz and P of the NTSC system.
It is also possible to support both 50 Hz of the AL system.

The second embodiment will be described in detail below. FIG. 4 shows an embodiment in the case of using illumination that emits pulsed light for an illumination device that gives indoor illumination light. FIG. 4 shows the illuminance of the projection screen by the indoor illumination light, the transparent state of the projection screen, and the diffusion state. , The illuminance of the projector light, and the luminance with which the observer observes the screen with time. For example, FIGS. 1 (a) and 1 (b) correspond to the states at time points (a) and (b) on the t-axis in FIG. 4 (a). Square waves 36a, 36b, 36c, 36d shown in FIG.
Is the illuminance of the projection screen by the room illumination light of the illuminating device that gives the pulsed light, and the illuminance interval is (1 /
4) At t1, it changes at cycle t1. The illuminance by the indoor illumination light is set to a maximum value Mmax = 2 in arbitrary units. Figure 4
Square waves 37a, 37b, 37c, 37d shown in (b)
Indicates the transparent state of the projection screen in arbitrary units, and is assumed to be completely transparent when 1 and completely diffused when 0.

The square waves 38a, 38b shown in FIG.
Reference numeral 38c indicates the diffusion state of the projection screen in arbitrary units, and it is assumed that 1 indicates complete diffusion and 0 indicates no diffusion. In the projection screen, it is assumed that the diffuser plate and the transparent plate are alternately changed at the cycle t1. At this time,
With respect to the cycle t1 of illuminance change, the time in the state of the transparent plate is (1/2) t1, and the time in the state of the diffusion plate is (1
/ 2) t1 and the state of the diffuser plate is near the center when the room illumination light is not emitted.
/ 2) From t1 to t1. Square wave 3 shown in FIG. 4 (d)
Reference numerals 9a, 39b, and 39c denote the illuminance of the projection light from the projector, which is the illuminance Mp and has a size of 2 in arbitrary units. The projected light is projected when the (1/4) t1 time projection screen has a period of t1 and is a diffusion plate. Figure 4
Square waves 40a, 40b, 40c shown in (e) indicate the brightness Ls of the projection screen.

In this case, since the room illumination light does not enter the projection screen in the state of the diffusion plate, the room illumination light is not reflected by the projection screen and enters the eyes of the observer. The wave 49a is not affected by the brightness of the room illumination light, the background light is eliminated, and the contrast becomes 0: 1, so that the contrast of the projection light of the projector can be observed as it is. In reality, although it is a little reflected light from the inside of the housing and the contrast of the original projector, the same contrast as that normally observed in a dark room can be secured. Even if the pulsed light of the room illumination light and the state of the diffuser plate overlap with each other for a certain time, the contrast is only lowered by that amount, and therefore it is not necessary to completely separate them. Further, the illuminance given by the pulsed light of the room illumination light does not have to be a perfect square wave as shown in FIG. 4A, but may be a mountain-shaped waveform as shown in FIG. Although it may have a shape, it is necessary that the state where the illuminance is 0 or close to it is within a period with a certain length. At this time, the brightness observed by the observer 13 is greatly reduced because not only the brightness due to the projection light but also the brightness due to the indoor reflected light is not continuous, so that it is necessary to observe the object 15 in front of the projection screen. It is necessary to prepare room illumination light that emits only bright pulsed light.

The third embodiment will be described below with reference to the drawings. FIG. 5 shows the present embodiment in which a short afterglow phosphor is used in an indoor lighting device having a periodical change in illuminance. FIG. 5 shows changes over time in these states. For example, FIGS. 1 (a) and 1 (b) show t in FIG. 5 (a).
This corresponds to the states at the times (a) and (b) on the axis. Figure 5
Is the illuminance of the projection screen by the room illumination light, the transparent state of the projection screen, the diffusion state, the illuminance of the projector light,
This is a graph showing a temporal change in the brightness at which an observer observes the screen.

A waveform 42 shown in FIG. 5 (a) is the illuminance of the room illumination light by the fluorescent lamp of the short afterglow phosphor, and the illuminance M changes in the cycle t1. Conventionally, a phosphor having a relatively long afterglow is used to reduce flicker. Therefore, for example, as shown in FIG. 2A, the illuminance does not become 0 even by the AC voltage, and Mmin = 1. Although this depends on the brightness of the human eye, it is generally 50Hz to 60H.
This is because the flicker is not felt at z or more, but it is for preventing the stroboscopic effect of observing a slightly blurred virtual image from appearing on a rapidly moving object. For this reason, using the fact that flicker is rarely felt at 100 Hz or higher,
By using a short afterglow phosphor for the fluorescent lamp, it is possible to obtain an illuminance as shown by the waveform 42 in FIG. Actually, it is difficult to obtain the illuminance completely like at t = (3/4) t1 point, and the characteristics of rising and falling are different, and the characteristics are different between the central part and the end part of the fluorescent tube. In order to simplify the description, here, the central part of the tube is used to make a periodic change with a frequency of 100 Hz, that is, a period t1 = 10 ms, and the illuminance by the room illumination light is a maximum value Mmax = 3 and a minimum value in arbitrary units. The value changes with the value Mmin = 1 and the average value Mave = 1.5, and M = 1.5.times.sin (2.pi..times.t / t1) +1.5.

The square waves 43a, 43b, shown in FIG.
43c shows the transparent state of the projection screen in arbitrary units, and is assumed to be completely transparent when 1 and completely diffused when 0. Square wave 44 shown in FIG.
Symbols a, 44b, and 44c indicate the diffusion state of the projection screen in arbitrary units, and it is assumed that 1 indicates complete diffusion, and 0 indicates no diffusion. The projection screen has a cycle t
It is assumed that the diffusion plate and the transparent plate are alternately changed in 1.
At this time, the time in the state of the transparent plate is (3/4) t1, the time in the state of the diffuser plate is (1/4) t1, and the state of the diffuser plate is such that the illuminance by the room illumination light is near the minimum. Here, the time is from (5/8) t1 to (7/8) t1. Square waves 45a, 45b, 45c shown in FIG.
Is the illuminance of the light projected by the projector, and is the illuminance Mp.
Then, the size is set to 2 in an arbitrary unit. The projected light has a cycle t1
Then, it is assumed that the image is projected when the projection screen is a diffusion plate for a time of (1/4) t1.

The square waves 46a, 46b shown in FIG.
46c indicates the brightness Ls of the projection screen. This Figure 5
The illuminance of the projection light and the room illumination light on the projection screen in FIG.
Assuming that it is proportional to 47b, the contrast K4 of the projector is integrated by considering it from t = (5/8) t1 to (7/8) t1: 1: K4 = {(3/8)-(32 / 4π)} t1: [{(3/8)-(3 2 / 4π)} t1 + (1/2) t1] = 1: 14.38. For this reason, the contrast can be increased by about 4.9 times as compared with the contrast ratio 2 of the first embodiment. Also, because of this, a high contrast ratio can be obtained even if the time for which the projection screen is left in the diffuser state is extended,
The brightness of the projected light to the observer can be substantially increased. Further, it is also effective to lengthen the afterglow characteristic of the fluorescent material and reduce the flicker, instead of reducing it to the required contrast. Further, if the fluorescent lamp is driven with an AC voltage having a frequency twice that of the normal frequency, it is possible to make flicker unnoticeable.

Next, a fourth embodiment will be described. 6 and 7, FIG. 7 is a schematic view of the projection screen.
In FIG. 7A, the area (a) is when the projection screen is in the state of the diffusion plate, and the area (b) is when the projection screen is in the state of the transparent plate. In FIG. 6A, the projection screen 55a is in the state of a diffusion plate, and the camera 51c is arranged on the back side of the projection screen 55a. The indoor lighting device 61 is capable of emitting pulsed light, and the control means 59 includes the projector 51p and the camera 5.
1c, the projection screen, and the interior lighting device 61 can be controlled. Arrows L6 and L6T respectively represent the projection light from the projector 51p to the projection screen 55a and the transmission light thereof. In FIG. 6B, the projection screen 55b
Is in the state of the transparent plate, and the wavy line is the visual field of the image information input through the projection screen in the state of the transparent plate. Figure 6
The observer 13 uses the projection screen 55 as a simple diffusing plate by repeating the states of (a) and FIG. 6 (b) by the control means 59 while synchronizing the respective operations at a frequency at which flicker is less noticeable. At the same time
The camera 51c can use the projection screen 55 as a simple transparent plate to input image information outside the housing.

In FIG. 6A, the illuminance is set to 0 by the indoor lighting device 61 without emitting the illuminating light, and in synchronization with this, the projection screen 55a is set to the diffusion plate state, and at this time, the projection from the projector 51p is performed. Light is projected onto the projection screen 55a, and this projection light L6 is emitted from the projection screen 5a.
The light is diffused and transmitted by 5a and becomes an arrow L6T, a part of which is incident on the eyes of the observer 13, and the observer 13 can observe the image information by the projection light. At this time, the camera 51c closes the shutter and does not input image information.
Further, since the indoor lighting device 61 does not emit light, the observer 13 cannot observe the object 15 in the room.
In FIG. 6B, the indoor lighting device 61 emits illumination light and synchronizes it with the projection screen 55b into a transparent plate state. In synchronization with this, the shutter of the camera 51c is opened and image information is input. At this time, FIG. 1 (b)
Similarly to the above, the brightness of the lights of the interior lighting L9 and L13 is as shown in FIG.
It is much smaller than the arrow L3 in (a), and it is rare that the observer 13 actually pays attention to observe these. Further, the indoor illumination light L13 to the object 15 by the indoor lighting device 61 is reflected by the object 15 and the reflected light L13R enters the eyes of the observer 13, and the observer 13 can observe the object 15 in the room. From the indoor lighting device 61 to the observer 13, the indoor illumination L9 is reflected by the observer 13 and the reflected light L11 is input to the camera 51c as image information. At this time, the camera 51c can input the image information of the field of view indicated by, for example, a wavy line by sampling the projection screen 2b as a transparent plate at a frequency that changes the projection screen 55 into a transparent plate of a diffusion plate.

This frequency is a frequency at which flicker is less likely to be felt with respect to the projection screen 55 or the image information projected on it, and this is the frequency at which the image information is output and observed even when it is input. It is convenient because it matches the frequency where flicker is hardly felt. In this way, the image information projected by the projector 51p on the projection screen 55 can be observed in a bright room, and at the same time, the image information around the observer can be input by the camera 51c on the rear surface of the projection screen 55, which makes the image brighter. Since it is a room, it is possible to observe objects in the room.
Conventionally, the room illumination light that is incident on the observer 13 for image input is incident on the projection screen 55, and the contrast of image information by the projection light of the projector 51p is lowered.

FIG. 7 shows the changes over time in these states. For example, FIGS. 6 (a) and 6 (b) show the times of the regions (a) and (b) on the t-axis in FIG. 7 (a). Corresponds to the state of. FIG. 7 is an embodiment in the case of using illumination that emits pulsed light for an illumination device that provides indoor illumination light. FIG.
It shows the illuminance of the projection screen by the room illumination light, the transparent state of the projection screen, the diffused state, the illuminance of the projector light, the brightness at which the observer observes the screen, and the temporal change of the opening and closing of the shutter of the camera 51c. For example, FIGS. 6A and 6B are (a) and t on the t-axis in FIG.
This corresponds to the state at the time of (b). The square waves 53a, 53b, 53c, and 53d shown in FIG. 7A are the illuminance of the projection screen by the indoor illumination light of the illumination device that provides the pulsed light, and the interval at which the illuminance is provided is (1/4) t1 and the cycle t1
Changes. The illuminance by the room illumination light is set to a maximum value Mmax = 2 in arbitrary units.

The square waves 54a, 54b shown in FIG.
Reference numerals 54c and 54d indicate the transparent state of the projection screen in arbitrary units, and it is assumed that 1 is completely transparent and 0 is completely diffused. Square wave 55 shown in FIG.
Reference characters a, 55b, and 55c indicate the diffusion state of the projection screen in arbitrary units, and it is assumed that 1 is completely diffused and 0 is not diffused at all. In the projection screen, it is assumed that the diffusion plate and the transparent plate are alternately changed at the cycle t1. At this time, with respect to the cycle t1 of the illuminance change, the time in the state of the transparent plate is (1/2) t1, the time in the state of the diffusion plate is (1/2) t1, and the state in the diffusion plate is The time when the room illumination light is not emitted is near the center, and here, it is between time (1/2) t1 and t1. The square waves 56a, 56b, and 56c shown in FIG. 7D are the illuminance of the projection light from the projector 51p, and are the illuminance Mp and have a magnitude of 2 in arbitrary units. It is assumed that the projection light is projected when the projection screen is the diffuser plate for a period of (1/4) t1 in the cycle t1. Square waves 57a, 57b, 57c shown in FIG.
Indicates the brightness Ls of the projection screen. The square waves 58a, 58b, 58c, and 58d shown in FIG.
1c indicates opening / closing of the shutter, 1 indicates opening the shutter to input image information, and 0 indicates closing the shutter.

By performing the operation as shown in FIG. 7, it is possible to input the image information of the observer with the camera 51c provided on the rear surface of the projection screen and use it for the videophone with the same line of sight. Further, at this time, the camera 51c is preferably arranged near the position of the line of sight of the assumed partner. Further, it is effective to determine the cycle t1 for performing these operations in accordance with the transmission method of the image information to be reproduced. For example, NT
If you use an ordinary TV projector of SC system,
A period corresponding to a vertical scanning frequency of 60 Hz or a frequency corresponding thereto is preferable.

[0040]

As described above, in the projection screen of the present invention, the state of the diffuser plate is set to the diffusion state in which the projection light from the projector is diffused when the illuminance is low, and the transparent light which transmits the illumination light when the illuminance is high. Since it is set in the state, it is possible to reduce the influence of the indoor illumination light and use it in a bright room.

[Brief description of drawings]

FIG. 1A and FIG. 1B are configuration diagrams showing the configuration of an embodiment according to the present invention.

2A to 2E show temporal changes in illuminance of the projection screen shown in FIG. 1 due to room illumination light, a transparent state, a diffused state, illuminance of projector light, and luminance observed by an observer on the screen. FIG.

FIG. 3 is a diagram showing the temporal illuminance of the indoor illumination light of the projection screen, the illuminance of the indoor illumination light of the projection screen, the transparent state, the diffusion state, the illuminance of the projector light, and the luminance observed by the observer on the screen when the indoor illumination light and the projection screen are synchronized. The figure which shows change.

4 (a) to (f) are illuminances by the room illumination light of the projection screen, the transparent state, the diffused state, the illuminance of the projector light, and the observer when the illumination that emits pulsed light is adopted as the room illumination light. FIG. 6 is a diagram showing a temporal change in luminance observed by the screen.

5 (a) to 5 (e) are illuminance by room illumination light of a projection screen and a transparent state when a short afterglow phosphor is used for illumination having periodic illumination changes in room illumination light; FIG. 3 is a diagram showing a temporal change in a diffusion state, illuminance of projector light, and brightness observed by an observer on a screen.

6A and 6B are configuration diagrams showing the configuration of another embodiment according to the present invention.

7 (a) to 7 (f) are illuminances of the projection screen shown in FIG.
FIG. 4 is a diagram showing a temporal change in a transparent state, a diffused state, an illuminance of projector light, and a luminance observed by an observer on a screen. The block diagram which shows the schematic structure of a prior art example.

8A and 8B are configuration diagrams showing a configuration of a conventional example.

9A to 9E are illuminances of room illumination light of the projection screen in the conventional projection screen shown in FIG. 8, a transparent state, a diffused state, an illuminance of projector light, and a brightness observed by an observer on the screen. FIG.

[Explanation of symbols]

1 projector, 3 housing, 5 projection screen, 7 indoor illuminance detection means, 9 control means, 11
Fluorescent lamp, 13 observer, 15 observer side object,

Claims (4)

[Claims] 1. A diffusing plate capable of being in a diffusing state for diffusing projection light from a projector and a transparent state for transmitting illuminating light in a projection screen under an illumination environment where illuminance changes periodically, and the diffusing plate. And a control means for setting the state to a diffusing state when the illuminance is low and a transparent state when the illuminance is high. 2. A lighting unit that emits pulsed light, a projector that projects projection light relating to image information, a diffusion state that diffuses the projection light from the projector, and a transparent state that transmits the illumination light from the lighting unit. And a diffusion plate that can take
A projection screen, wherein the diffusion plate is in a transparent state only when the illuminating device emits pulsed light. 3. A lighting unit which uses a short afterglow phosphor and whose illuminance changes periodically, a projector which projects projection light relating to image information, and a diffusion state which diffuses the projection light from the projector. A diffusion plate that can assume a transparent state that transmits illumination light, and a control means that makes the state of the diffusion plate a diffusion state when the illuminance is low and a transparent state when the illuminance is high,
A projection screen comprising: 4. A projection screen in an illumination environment in which the illuminance changes periodically, a projector that projects projection light relating to image information, a diffusion state in which the projection light from the projector is diffused, and the illumination light are transmitted. A diffusion plate which can be in a transparent state, an image pickup means provided on the projector side with respect to the diffusion plate, and a diffusion state when the illuminance is low and a transparent state when the illuminance is high. And a control unit that captures an image of a subject by the image capturing unit when the diffusion plate is in a transparent state.