JPH0554677B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to improvements in projection display devices.

[Prior art] Conventional projection display devices capable of displaying moving images include those using a projection CRT (outlined in Journal of the Television Society vo 1.38, No. 1, (1984) P11), and liquid crystal light valves. (optical vo1.13, No.1,
(1984) on page 52), electro-optical ceramics (PLZT), J.Japan Society of
Appl.Phys.vol.44, (1975) P87) etc. are publicly known. Both simply project and enlarge an image onto a screen.

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, light is irradiated onto a screen placed at an image forming position, and the light is scattered there to localize the image, and ambient light is also reflected onto the screen. is scattered. As a result, the black level increases in bright environments, leading to a decrease in contrast. Furthermore, when using a light valve that emits a light beam that has polarization characteristics, conventional screens designed for light beams that do not have polarization characteristics do not make effective use of the polarization characteristics.

The present invention solves these problems, and its purpose is to provide a projection display device with high contrast.

[Means for Solving the Problems] The present invention provides a projection display device comprising: a light source; a light valve that modulates light from the light source; a projection optical unit that magnifies and projects the light modulated by the light valve;
A projection type display device comprising a polarizing screen disposed at a position where the light enlarged and projected by the projection optical means forms an image, characterized in that a polarized light transmission axis of the polarizing screen is formed in a vertical direction. .

[Function] The polarized light transmission axis of the polarizing screen according to the present invention is formed in the vertical direction. Therefore, according to the present invention, the influence of reflection of horizontally polarized light on the screen can be reduced.

On the other hand, among ambient light such as fluorescent lights that enters the screen from above the room, most of the vertically polarized light is transmitted through the screen, and most of the horizontally polarized light is reflected by the screen.

Therefore, according to the present invention, it is possible to effectively prevent a decrease in contrast due to an increase in the black level of a displayed image caused by reflection of ambient light on the screen.

Another effect of the present invention is that since the screen has polarization characteristics, it effectively absorbs ambient light, lowers the black level, and increases display contrast. Conventional screens that have isotropic characteristics with respect to ambient light (for example, dyed transmissive screens) absorb ambient light uniformly. In contrast, the present invention directs the absorption axis of the screen in the direction of the polarized component of the ambient light that is included in a larger amount, and selectively absorbs this component.

Second, when the output light from the image forming means has polarization characteristics, a screen having polarization characteristics selectively transmits or reflects the output light having polarization characteristics. Therefore, more components harmful to display can be removed than with an isotropic screen, and a high-contrast image can be localized on the screen. Furthermore, if the image forming means emits light that originally has polarization characteristics, an image that is the intensity distribution of the light can also appear on the screen.

[Example] Example 1 Example 1 uses a 90° twisted nematic liquid crystal (hereinafter referred to as
This is an example of a rear projection type display device using a liquid crystal display panel (hereinafter referred to as TFTLCD) that drives a thin film transistor (TFT) array (hereinafter referred to as TFTLCD). FIG. 1 is a diagram showing its configuration. 1 is a light source, 2 is a condenser lens for condensing light, and together with the projection lens 6 and the screen, constitutes a projection optical system. 4 is TFTLCD
Its structure and drive are SID digest (1983)
156, which is equivalent to that described in Nikkei Electronics No. 258 (1981), page 164. 3 is a polarizing plate, and in the example shown in FIG. 1, the transmission axis 5 is in the horizontal direction. Since the screen is of a rear projection type, it is of a transmission type, and consists of a light scattering plate 8 in close proximity to or in close contact with a polarizing plate 7. Polarizing plate 7
The transmission axis 5 of is set to transmit the least polarized component of the ambient light 9. In this example it is oriented vertically.

Next, the effect will be explained. Light from a light source 1 is condensed by a condenser lens 2, and is incident on a TFTLCD 4 through a polarizing plate 3. The source light has all polarized components until it enters the polarizing plate 3, but
The polarizing plate 3 limits the polarization component to the transmission axis 5 . The polarization component of the light beam incident on the TFTLCD 4 is rotated for each pixel according to the displayed image. Up to this point, it is the same as a normal TN liquid crystal display panel. In a normal TN liquid crystal display panel, polarized light components are limited by a nearby analyzer to produce a displayed image, but in this embodiment, after the speed of light passes through the projection lens 6, the screen polarizing plate 7, which is an analyzer, The configuration is such that the light is incident on the The light beam modulated by the TFTLCD and given polarization characteristics is imaged on the light scattering plate 8 by the projection lens. Since the polarizing plate 7 adjacent to the light scattering plate 8 has its transmission axis 5 directed as shown in FIG. 1, the amount of transmitted light is determined here. The screen consisting of the polarizing plate 7 and the light scattering plate 8 acts on the incident light having polarization characteristics to form a projected image. Another function is to absorb ambient light 9 and lower the black level. Reference numeral 10 indicates ambient light that is reflected by the screen without being absorbed, and reference numeral 23 indicates ambient light that has passed through the screen. Further, 11 is an eye representing an observer. In this case, the direction of the transmission axis 5 of the polarizing plate 7 is determined by assuming that the ambient light has many horizontally polarized components. The light scattering plate used here is a milky-white translucent acrylic plate, but it would be even better to use a light scattering plate with a devised flat lens type like the one used in the projection television device using the projection CRT described above. Effective. Note that the polarizing plate is a general one that is commercially available.

Also, in this example as a light valve.
TFTLCD is adopted, but ECB (Electric Field Controlled Birefringence)
Any material having an electro-optic effect capable of modulating polarization characteristics can be used instead.

Example 2 Example 2 is an example of a full-color projection display device using a reflective light valve. Figure 2 shows its configuration. As a light valve as in Example 1
TFTLCD was used. In order to achieve full color, the light source light is divided into red R, green G,
The light is separated into the three primary colors of blue B, and light modulation of each color is performed by the TFTLCD4. The polarizing plate 3 is a reflecting mirror 14
and TFTLCD, and the transmission axis is adjusted to match the LCD panel. The light reflected by the mirror 14 and modulated by the TFTLCD is combined by the dichroic mirror, passes through the projection lens 6, and is combined onto the screen. The screen is composed of a polarizing plate 7 and a light scattering plate 8. Further, 15 is a mirror for bending the light from the light source, and is positioned so as not to interfere with the output light.

In the case of the second embodiment, as in the first embodiment, the screen functions to form and absorb a projected image.
Further, when the optical system has a complicated optical system as shown in FIG. 2, flare such as scattering is likely to occur. However, if the screen has polarizing properties, the polarizing plate 7 can cut out most of the flare that is harmful to the contrast.

Regarding full-color display, there are not only the method shown in FIG. 2, but also a method of installing a color filter for each pixel, a method of projecting the three primary colors onto a screen separately, etc., but the present invention, which has a screen with polarization characteristics, Since the contrast between each color can be increased, a vivid display with high color purity can be obtained.

Example 3 Example 3 is a case where a projection type CRT is used as an image forming means. FIG. 3 shows a cross-sectional view of a system using a transmission screen. Projection type CRT1
The light beam emitted from the projection lens 6 passes through the projection lens 6, is reflected by the mirror 14, and forms an image on the screen 17. Although the ambient light 9 is absorbed by the screen 17,
A reflected component 10 and a transmitted component 23 remain, which causes a decrease in contrast. Using a screen with polarizing properties according to the invention, selective absorption of ambient light 9 takes place. By matching the polarization characteristics to the polarization characteristics of ambient light, it absorbs ambient light more effectively than a device that absorbs isotropically.

Furthermore, a polarizer may be installed in a projection type CRT, which is an image forming means that does not have polarization characteristics, and polarization characteristics may be imparted extrinsically.

Example 4 A transmission screen integrated with a polarizing plate can be used as a projection display device. FIG. 4 shows a cross section of the integrated transmission screen. A polarizing plate 18 dyed with iodine and uniaxially stretched is attached to a roller 1 having a scattering surface shape.
9 is embossed so that the surface scatters light. As a projection type display device, Example 1
It can be configured in the same way as 3.

Example 5 Example 5 is a case where a reflective screen is used. FIG. 5 shows an example of the configuration. Since the projection device 20 can be the same as in Examples 1 to 3, the screen will be explained. A cross section of the reflective screen 21 is shown in FIG. reflective layer 2
A polarizing plate 7 is closely attached on top of 2. The reflective layer must not disturb polarized light and must have diffusive properties. These are contradictory demands, and a compromise must be found. Aluminum foil with a rough surface is suitable for this purpose. In addition, it has a concave mirror-like curve in consideration of directivity. Since the polarizing plate 7 on the front surface selectively absorbs ambient light, it is possible to lower the black level and increase the contrast, similar to a transmissive screen.

[Effects of the Invention] As described above, the projection display device of the present invention has the following effects:
Since the polarized light transmission axis of the screen is formed in the vertical direction, it is possible to effectively prevent a decrease in contrast due to an increase in the black level of the displayed image due to reflection of ambient light on the screen. There is an effect.

[Brief explanation of the drawing]

FIG. 1 is a main configuration diagram of the present invention,
This is a case where TFTLCD is used as an image forming means. FIG. 2 is a block diagram of a full-color display device using a TFTLCD according to the present invention. FIG. 3 is a sectional view of a display device using the projection type CRT of the present invention. FIG. 4 is a diagram simply showing the cross section and manufacturing method of the transmission screen of the present invention. FIG. 5 is a cross-sectional view of the reflective screen of the present invention and a projection system using the same. 4...TFTLCD, 6...Projection lens, 7...
Polarizing plate, 8... Light scattering plate, 16... Projection type CRT,
17... Polarizing transmissive screen, 18... Integrated transmissive screen, 21... Polarizing reflective screen.

Claims (1)

[Scope of Claims] 1. A light source, a light valve that modulates the light from the light source, a projection optical device that magnifies and projects the light modulated by the light valve, and an image of the light that is magnified and projected by the projection optical device. What is claimed is: 1. A projection type display device comprising: a polarizing screen disposed at a position where the polarizing screen has a polarized light transmission axis extending in a vertical direction;