JPH0389316A - Projection type video display system - Google Patents

Abstract

PURPOSE:To improve the contrast on the projection surface by allowing a direct light from an indoor illuminating light source to have a polarization characteristic being different from a polarization characteristic of the projection surface. CONSTITUTION:An image reproduced on a liquid crystal panel 1 is illuminated by a projection light source 3, and projected onto the projection surface 6 by a projection lens 2, and in this case, the projection light becomes a polarization state being parallel to a polarizing plate 4 by a polarization characteristic indicated with an arrow 12, therefore, it can nearly pass through the polarizing plate 4. On the other hand, a direct light from an indoor illuminating light source 7 becomes a polarization state being vertical to the polarizing plate 4 by a polarizing plate 8, therefore, it can scarcely pass through the polarizing plate 4. In such a way, even when a person present executes a necessary indoor illumination in order to take a memo, etc., an image having a satisfactory contrast is obtained on the project surface by a video light from a display device.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a projection type video display system, and more specifically, the present invention relates to a projection type video display system, and more specifically, it displays various information using computers, VTRs, etc. to a large number of attendees at conferences, lectures, group education, etc. This invention relates to a projection-type video display system used to present and promote understanding. [Conventional technology] In recent years, the development and spread of combinators has been remarkable, and companies,
In research institutions, educational institutions, etc., text 1 table, graph, etc.
Computers are increasingly being used to create and edit information such as graphics. Also, with the development of television technology,
2. Description of the Related Art With the rapid spread of inexpensive VTRs (video tape recorders), video cameras, and the like, moving images are increasingly being used to present various types of information that involve movement. Computer-generated text, tables, graphs, figures, and other information, as well as video-based moving image information, can be used at conferences, lectures, etc.
Projection-type video display devices have been used to present information to a large number of participants in group education to encourage understanding. Conventionally, this type of projection type image display apparatus is typically constructed as shown in FIG. In Figure 3, 30
31 is a projection light source, 32 is a liquid crystal panel on which information from the information 21130 is reproduced as a video, and 33 is a liquid crystal panel 32. Light source 3
This is a projection lens that projects onto a projection surface 34 using light from 1. A method in which the image is projected from the same side as the one from which the image displayed on the projection surface 34 is viewed is called a front projection type, and a method in which the image is projected from the opposite side is called a rear projection type. Conventionally, overherad projectors with a liquid crystal panel placed on the document surface have also been widely used. A liquid crystal panel suitably used in such a projection type image display device is configured as shown in FIG. 31114, as is widely known. In FIG. 4, a liquid crystal element 42 has a function of changing the polarization characteristics of transmitted light according to the strength of an applied electric field, and upper and lower electrode means are provided to sandwich the liquid crystal element 42. 4° 1.43 forms an arbitrary electric field at an arbitrary location (referred to as a pixel) divided into a mesh of the liquid crystal element 42 according to the video signal to be reproduced from the information source 45. The input side polarizing plate 40 has a function of aligning the polarization direction of the projection light from the projection light source in a fixed direction, and the output side polarizing plate 44 has the function of aligning the polarization direction of the projection light from the projection light source in a certain direction, and the output side polarizing plate 44 has the function of aligning the polarization direction of the projection light from the projection light source in a certain direction. It has a function of selectively transmitting only light having the same polarization direction as the polarizing plate 44. Therefore, among the many pixels of the liquid crystal element 42, the pixels to which an electric field is selectively applied by the upper and lower electrode means 41, 43 so that the polarization direction of transmitted light is the same as the alignment direction of the output side polarizing plate 44 Only the light that passes through the output side polarizing plate 44
At this time, since the electric field applied to each pixel is controlled by the video signal to be reproduced from the information source 45, the video is reproduced on the liquid crystal panel. still. At this time, this image light has the same polarization direction as the polarization direction of the output side polarizing plate 44.

[Problem to be solved by the invention]

By the way, this type of projection video display device is used in places such as conferences. It must be used under adequate lighting so that attendees can take notes and take notes. However, in the above-mentioned conventional example, the liquid crystal panel suitably used in the projection type image display device has a drawback that it is difficult to see when used under illumination because the intensity of the projected light is low. This will be further explained using FIG. 5. In the figure, 50 is an image of bright pixels reproduced on the liquid crystal panel on the projection surface 52, and the intensity of the light is expressed as . Also,
51 is an image of the dark pixel reproduced on the liquid crystal panel on the projection surface 52, and the intensity of the light is I. t, projection surface 52
In addition to the projected light from the liquid crystal panel, direct light (intensity 1o) from the illumination light source and indirect light (intensity ts) resulting from reflection of the light from the illumination light source within the room are incident on the top. Here, indirect light is generally 1/1 that of direct light.
The ratio of transmitted light intensity between bright pixels and dark pixels of a liquid crystal panel is generally 10:1.
to about 50:1 (here, it is assumed to be 20:1). Here, in the first case, the indoor lighting is dimmed and the dark pixel intensity is 11. Assuming that the direct light intensity I and the direct light intensity I are equal, the ratio of the brightness of the bright pixel and the dark pixel on the projection surface 52, that is, the contrast, is as follows. (■.+Io +■.-tl + I * + I a )” (2
0I-rr +I. OIゎ 1/(x, rr L / 10 Io) = (20+1+1/10)/1+l+1/10) Given 10゜In this case, +1/1 + ■. + )/(I Although it is possible to obtain a contrast of If bright pixel intensity!. and direct light intensity! are equal, then the projection surface 5
The ratio of the brightness of bright pixels and dark pixels on 2 is Contrast = (t, s + te + Im) / (
Isrr+j. +1. ) = (20I□g+20Iett+21eer) / (Istr +20I**r+2
I*rr) = 42/2341.8, the contrast is significantly lowered and the projected image is almost invisible. To solve the above problems! In order to obtain the same contrast as in the case of 1!1, the illumination light intensity remains the same as in the second case, and how many times (k) should the projection light intensity be multiplied is as follows: 10.5= (20・k ” 1eer +20 Ie
re+21stt) / (kIott
+2゜f net + 21 o'tt・)=4
20+lO+2)/(k+20+2), so it becomes =22. That is, it can be seen that the intensity of the projection light source needs to be increased by 22 times. If the intensity of the projection light source is increased by 22 times, the power consumption will also increase by 22 times, causing a serious problem such as impractical cooling of the light source. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems by providing a projection-type video display system of the type described above, while providing sufficient indoor lighting for attendees to record memos, etc. An object of the present invention is to provide a projection type video display system that can obtain an image with a high contrast. [Means for Solving the Problems] In the present invention, which achieves the above object, in a projection type image display system that directly projects an image, a first polarization characteristic is provided to the light reaching the projection surface. 1 polarizing means;
a second polarization means for giving illumination light for illuminating the surroundings a second polarization characteristic orthogonal to the first polarization characteristic;
A third polarizing means is provided for imparting a polarization characteristic parallel to the first polarization characteristic to the projection light for displaying an image on the projection surface. [Function] In the present invention having the above configuration, the direct light from the light source for indoor lighting does not reach the projection surface because it has polarization characteristics that are different from the polarization characteristics of the projection surface, while the projected light does not reach the projection surface. Since it has the same polarization characteristics as the light beam, it reaches the projection surface, and this improves the contrast on the projection surface even though the surroundings are bright. [Example 1] Figure 1 is a diagram for explaining the first example of the present invention.
In the figure, 1 is a liquid crystal panel, which reproduces video signals from a computer, video tape recorder, etc. (not shown). The projection light reproduced by the liquid crystal panel l is projected onto the projection surface 6 via the projection lens 2 by the light from the projection light source 3. In Figure 1, 7 is a light source for indoor lighting, 4 is a polarizing plate for giving the projection surface 6 horizontal polarization characteristics (indicated by arrow 5 in the figure), and 8 is a polarizing plate for indoor illumination light. Polarization characteristics of plate 4 (
11 is a polarizing plate that schematically shows the polarization characteristic of direct indoor lighting, and 13 is indirect light of indoor lighting. This figure schematically shows the polarization characteristics of . Furthermore, since the liquid crystal panel 1 has polarizing plates on both sides of the light incident side and the light output side of the projection light source 3 (see explanation in Fig. 4).
, is governed by the polarization characteristic of the polarizing plate on the exit side, which has a polarization characteristic parallel to that of the polarizing plate 4 (indicated by arrow 12), and the polarization characteristic of the projected light is as schematically shown by the symbol IO. becomes. The operation based on the above configuration will be explained. The image reproduced on the liquid crystal panel 1 is illuminated by a projection light source 3 and projected by a projection lens 2.
However, at this time, the projected light is in a polarization state parallel to the polarizing plate 4 due to the polarization characteristics shown by the arrow 12, so that most of the projected light can pass through the polarizing plate 4. On the other hand, since the direct light from the indoor illumination light source 7 is polarized by the polarizing plate 8 at right angles to the polarizing plate 4, the polarizing plate 8
When the light from the indoor illumination light source 7, which hardly passes through the room, is diffusely reflected by various objects in the room and enters the projection surface 6,
Because the indirect light no longer has specific polarization characteristics due to diffuse reflection, it can pass through the polarizing plate 4. In the first embodiment, the polarizing plates 4 and 8 have a transmittance of 90% for light in the same polarization direction as the polarizing plates, a transmittance of 1% for light in a direction perpendicular to the polarizing plates, and natural light (unpolarized light). light)
A polarizing plate with a transmittance of 25% is used, a liquid crystal spring is used in which the intensity ratio of bright pixels to dark pixels of the liquid crystal panel 1 is 20:] as in the conventional example, and furthermore, there are no polarizing plates 4 and 8. When the intensity of the direct light from the light source 7 for indoor lighting is
(The intensity of the indirect light is set to be 1/10 of the direct light as in the conventional example described above.) When the polarizing plates 4, 8, etc. are used under such setting conditions (these conditions are not special but general), the contrast on the projection surface 6 is as follows. Contrast = (1,, +I.+Is) / CI@
tt +Io +Ia) = (201,tt xo, 9+20 1*rt xQ, 25XO,t+ 2I□f Xo, 25X0.2 5)/ (I.tt xQ, 9+2 0■.tt xQ, 25xO, 1 +21att 25XO. 25) = (18+0.5+0.125)/(0.9+0.5+0°125)41・2.2 This value is considered to be sufficient as it provides more contrast than when the indoor lighting was dimmed in the conventional example. Vine. In this way, according to the IT embodiment, the contrast on the projection surface 6 can be made sufficient while making the indoor lighting sufficiently bright. Here, as mentioned above, the brightness of the indoor lighting is reduced to 25% due to the presence of the polarizing plate 8, so the intensity of the indoor lighting is reduced to 4.
Consider what happens when you double the amount. In this case, the contrast is "Contrast" (201-tt xQ, 9+80ra
texQ, 25XO, 1+ 81 oee X O-25") / (Ierr
XQ, 9+80 ratexQ, 25xO-1+8
I-r, xo, 252) = (18+2+0.5)/(Q, 9+2+0.5) The contrast is 6.0, and although the contrast is slightly lower, a sufficiently good contrast can be obtained. In actual operation, the reflected light from the projection surface 6 is further seen through the polarizing plate 4, and since the polarization direction is almost preserved in this reflection, the projected light 10 is reflected after being reflected from the projection surface 6. Nearly 90% of the light passes through the polarizing plate 4. On the other hand, the illumination light is reflected by the projection surface 6 and then attenuated by the polarizing plate 4 again. Therefore, the contrast when actually viewing the projection surface 6 is better than the above calculated value. FIG. 2 shows a second embodiment of the present invention. The second embodiment is a rear projection type system, and in the figure, 22 is a liquid crystal panel for reproducing video signals from a computer, video tape recorder, etc. (not shown). The reproduced video signal is projected by light from the projection light source 21 through the projection lens 24 onto the projection surface 25 from the back side (the surface opposite to the viewing side). Further, 26 is a polarizing plate for imparting polarization characteristics to the projection surface 25, and has a polarization direction perpendicular to the paper surface.
is a polarizing plate on the exit side of the liquid crystal panel 22, which, like the polarizing plate 26, imparts polarization characteristics perpendicular to the plane of the paper to the image light 29; 27 is a light source for indoor lighting; and 28 imparts polarization characteristics to the indoor illumination light. It is a polarizing plate for light and has polarization characteristics in the direction parallel to the paper surface. In the second embodiment, the reproduced image projected onto the projection surface 25 is transmitted to the polarizing plate 26 by the output-side polarizing plate 23 of the liquid crystal panel 22.
Since the light has the same polarization characteristics as the light, it can pass through the polarizing plate 26 as it is. On the other hand, the direct light from the indoor illumination light source 27 is set by the polarizing plate 28 so that it has polarization characteristics perpendicular to the polarizing plate 26, so it hardly passes through the polarizing plate 26. Since there is no direct light incident due to illumination, the contrast on the projection surface 25 is improved. The projection surface 25 uses the same polarizing plates 26 and 28 and the liquid crystal panel 22 as in the first embodiment, but without the polarizing plates 26 and 28.
If the direct light from the indoor lighting light source is set to have the same intensity as the bright pixels of the liquid crystal panel 22, the contrast will be as follows. Contrast = (Ian+Io +IM)/(t
. rr+I. +l5) = (20I.et +201ott XO, 25xO,
1+2I. ,. xo, 25”)/(1°ft+201, rf Xo, 25X0°1+21.rr The light from the illumination light source 27 passes through the polarizing plate 2 twice in total, once when it is incident on the projection surface 25 and once when it is reflected.
However, the projected light 29 only passes through the polarizing plate 26 once when it is projected onto the projection surface 25 and exits. Therefore, there is an advantage that the reduction in the intensity of projected light due to the polarizing plate 26 is small. By the way, in the above embodiment, a liquid crystal panel was used as the projection light for displaying images on the projection surface, but various other display devices (for example, those using electro-optic crystals, plasma display panels, etc.) may be used as display devices. It's coming. [Effects of the Invention] As explained above, according to the configuration of the present invention, even if the room is illuminated to allow attendees to take notes, the image light from one display device can provide a good image on the projection surface. An image with contrast can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention, FIG. 2 is an explanatory diagram of a second embodiment, FIG. 3 is a diagram of a conventional example, FIG. 4 is a diagram of an example of a liquid crystal panel, and FIG. FIG. 5 is a diagram for explaining the problems of the conventional example. 1.22...Liquid crystal panel, 2.24...Projection lens, 3.21...Projection light source, 4.26...
...Polarizing plate (first polarizing means), 6.25...
Projection surface, 7.27...Light source for indoor lighting, 8.2
8...Polarizing plate (second polarizing means), 23...
・Output side polarizing plate (third polarizing means)

Claims (1)

[Scope of Claims] 1. In a projection type image display system that projects an image on a projection surface, a first polarization means for imparting a first polarization characteristic to light reaching the projection surface, and a first polarization means for illuminating the surroundings. a second polarizing means for giving the illumination light a second polarization characteristic orthogonal to the first polarization characteristic; and a second polarization means for giving the illumination light a second polarization characteristic orthogonal to the first polarization characteristic, and a polarization parallel to the first polarization characteristic to the projection light for displaying an image on the projection surface. A projection type image display system equipped with a third polarization means for imparting characteristics. 2. The projection type video display system according to claim 1, wherein the projection light is produced by illuminating a liquid crystal panel with light from a light source.