WO2024042828A1 - Surface shape diffusion sheet for reducing black level degradation, reflective screen, video display system, and video display method - Google Patents

Abstract

The present invention provides a surface shape diffusion sheet for reducing black level degradation, a reflective screen, a video display system, and a video display method.　A surface shape diffusion sheet 1 comprises a surface shape anisotropic diffusion layer 2 and a substrate 3 that is an underlayer for said surface shape anisotropic diffusion layer, the diffusion angle of the surface shape anisotropic diffusion layer 3 in the in-plane up-down direction is within the range of ±14° (half-width), and, inside or on the surface of the substrate 3, a transmittance T is within the range of 0.5 to less than 1 in the visible light wavelength band. The video display system calculates a black level degradation amount Lb (= 255 × black luminance / white luminance) of video, and corrects a reduction in brightness observed in the brightness range Lb ≤ L < 2Lb of a brightness L of each element of the video.

Description

Surface shape diffusion sheet, reflective screen, video display system, and video display method that reduce black floating

The present invention relates to a surface shape diffusion sheet that reduces black floating applied to a reflective screen, a reflective screen equipped with this diffusion sheet, a video display system equipped with this reflective screen, and this reflective screen (hereinafter referred to as The present invention relates to an image display method using an image projection device (also simply referred to as a screen) and an image projection device.

The reflective screen referred to here is a screen that diffuses and reflects the image light from an image projection device (also called a projector) on the front side of the screen (observer side) to the front side and emits it, and the surface of the screen This refers to types in which the image light incident on the screen is diffused and reflected on the surface of the screen, and types in which it is diffused on the surface of the screen and reflected by an internal reflective layer.

Reflective screens suffer from a phenomenon called a hot spot, where incident image light appears as a bright spot on the surface of the screen, and a phenomenon called hot spot, where the brightness of ceiling lights and windows near the screen is reflected on the surface of the screen. There is a phenomenon called.

In order to prevent these phenomena, conventionally, a surface-shaped diffusion layer having an uneven surface with a pitch of several micrometers to several tens of micrometers is provided on the screen surface to diffuse hot spots and reflected light on the screen surface and make it less noticeable. (See Patent Document 1). The combination of the surface shape diffusion layer and the underlying substrate is called a surface shape diffusion sheet.

However, if the surface of the surface shape diffusion layer is the screen surface, not only the image light from the projector, but also external light from ceiling lights, floors, walls and windows in front of the screen (unwanted light other than the image light) light) is also diffused on the surface of the screen. A part of the light is reflected to the front side by the surface of the screen, and the rest reaches the reflective layer inside the screen, is reflected, and is emitted to the front side. These so-called external light diffuse reflection lights are superimposed on the image light, so they generate so-called noise light and deteriorate the image quality of the image to be observed.

This phenomenon is called "black floating" because it particularly increases the brightness of black in the image.
When black floating occurs due to external light, the contrast, gradation expression, and color reproducibility of the image are significantly impaired, resulting in images that lack sharpness, blacks that are not sharp, and look like gray, and the overall colors of the image become less vivid. Instead, the image appears thin and blurry, making it difficult to reproduce a clear image.

This black cast depends on the intensity of outside light, so it can be prevented by turning off the ceiling lights in the room and blocking the windows with curtains to prevent outside light from entering the screen. However, in school classrooms, corporate conference rooms, etc., it is also important to look at large displays, check each other's facial expressions, view materials at hand, and take notes. If these actions become impossible by making the room dark, the efficiency of classes and meetings will be significantly reduced.

On the other hand, there are ways to use liquid crystals, OLEDs, or microLEDs with less black floating as large displays for classes and meetings, but these require large displays of 80 inches or more. Mass production of these products requires large manufacturing equipment and a large amount of chemicals, water, electricity, etc. in the manufacturing process, resulting in an excessive environmental burden from the perspective of SDGs (Sustainable Development Goals). Furthermore, since the size, weight, and power consumption of the display body are large, it is difficult to transport and install, and furthermore, the price is high, making it difficult to popularize it widely. Due to the above-mentioned circumstances, there is an increasing need to develop an image display system using a reflective screen that can reproduce high-quality images even in bright environments affected by external light.

Patent No. 5971742

As mentioned above, when black floating occurs due to external light, the contrast, gradation expression, and color reproducibility of images displayed on a reflective screen are greatly affected. Contrast is expressed as the ratio of white luminance to black luminance, and therefore deteriorates by the amount that black luminance increases due to black floating. Similarly, since gradation expression is determined by the value of the difference between white luminance and black luminance, the luminance range of gradation expression becomes narrower as the black luminance increases.

Regarding the above-mentioned problems with contrast and gradation expression, a conventional measure has been to increase the brightness of white on the projector side by the amount of black floating. Currently, the video light output of projectors for schools and offices currently on the market is becoming high, with a maximum light intensity of around 4,000 lumens.

On the other hand, at present, almost no countermeasures have been taken regarding the deterioration of color reproducibility due to black floating. Even with reflective projection displays using high-output projectors, there is a problem that the original colors cannot be reproduced in bright environments affected by external light, and color reproducibility deteriorates in proportion to the brightness of black floating. Remaining.

SUMMARY OF THE INVENTION Therefore, the present invention provides a surface-shaped diffusion sheet that reduces the deterioration in image quality caused by external light from ceiling lights, which has the greatest effect on the above-mentioned black floating, and all external light in the bright environment of a reflective screen. Provides a reflective screen with Furthermore, the present invention provides a video display system and a video display method that can reduce the deterioration of the color reproducibility of the video on the reflective screen and correct the deteriorated color reproducibility of the video.

In order to solve the above problem, the present inventors have made extensive studies, and have made the surface shape diffusion layer of the surface shape diffusion sheet an anisotropic surface shape diffusion layer that limits the diffusion angle in the vertical direction, and We have found that lowering the transmittance of the substrate underlying the anisotropic diffusion layer in the visible wavelength band is an effective solution. Furthermore, the present inventors have found that the deterioration in color reproducibility of an image can be quantified by expressing black floating using numerical values of an RGB color model.

Based on the above knowledge, the present inventors conducted further studies and completed the present invention. That is, the present invention is as follows.
[1] A surface shape diffusion sheet provided on the surface of a reflective screen that diffuses and emits image light from an image projection device,
surface shape anisotropic diffusion layer,
A flat substrate is provided as a base of the surface shape anisotropic diffusion layer,
The diffusion angle of the surface of the anisotropic surface shape diffusion layer in the in-plane vertical direction is within the range of ±14° (half width),
A surface shape diffusion sheet for reducing black floating, characterized in that the inside or surface of the substrate has a transmittance T in the visible wavelength band of 0.5 or more and less than 1.
[2] A reflective screen equipped with a diffusion sheet on the surface,
The diffusion sheet is the surface shape diffusion sheet described in [1] above,
A reflective layer, a protective film, and a retaining plate are sequentially arranged and bonded from the substrate to the back side,
a bonding surface between the reflective layer and the substrate serves as a surface that reflects the image light;
The protective film is a film that covers the reflective layer,
A reflective screen characterized in that the holding plate is a plate that maintains flatness of the substrate.
[3] Further, a lens layer disposed and bonded between the substrate and the reflective layer,
The lens layer is made of a Fresnel lens having a reflective surface shape on the back side,
The reflective screen according to [2], wherein a joint surface between the reflective layer and the lens layer serves as a surface that reflects the image light.
[4] For the focal length f of the Fresnel lens, reflect the image light from the iris surface of the projection lens of the image projection device that is a distance away from the surface that reflects the image light, and )+(1/b)=1/f The reflective screen according to [3], characterized in that the spatial imaging iris surface is formed at a position separated by a distance b that satisfies the relationship: )+(1/b)=1/f.
[5] An image display system comprising the reflective screen according to any one of [2] to [4], an image projection device, a luminance meter, a black float amount calculation means, and a brightness adjustment means. There it is,
The image projection device projects image light,
The luminance meter measures black (R=0, G=0, B=0) and white (R=255, G= 255, B=255) to obtain the respective measured values Kmin and Kw,
The black floating amount calculation means calculates the black floating amount Lb as an integer part of the value of the formula: 255×Kmin/Kw,
The brightness adjustment means corrects a decrease in brightness observed within a brightness range Lb≦L<2Lb of the brightness L of each element in the black-to-black image (R=Lb, G=Lb, B=Lb). A video display system characterized by:
[6] In place of or in addition to the brightness adjustment means, an image light output adjustment means is provided,
The video display system according to [5], wherein the video light output adjustment means increases the brightness of the white color from Kw to Kw×(1+2Lb/255) to reduce black floating.
[7] An image display method using the reflective screen according to any one of [2] to [4] and an image projection device that projects image light,
Projecting black (R=0, G=0, B=0) and white (R=255, G=255, B=255) in an RGB color model from the image projection device onto the reflective screen;
a step of measuring the luminance of the black and white colors under external light to obtain respective measured values Kmin and Kw;
Calculating the black floating amount Lb as the integer part of the value of the formula: 255 x Kmin/Kw;
A brightness adjustment step of correcting a decrease in brightness observed within the brightness range Lb≦L<2Lb of the brightness L of each element in the image where the black becomes black (R=Lb, G=Lb, B=Lb). A video display method characterized by comprising:
[8] Instead of or in addition to the brightness adjustment step, the image light output adjustment step increases the brightness of the white color from Kw to Kw×(1+2Lb/255) to reduce black floating. The video display method according to [7].

According to the present invention, it is possible to reduce black floating due to external light from ceiling lights, which is most affected by reflective screens in bright environments, and all other external light. Furthermore, even if the color reproducibility of the image deteriorates due to black floating, it can be corrected, and furthermore, it is possible to prevent the deterioration of the color reproducibility, which is an excellent effect.

FIG. 1 is a schematic diagram showing an example of a surface shape diffusion sheet according to the present invention. FIG. 2 is a schematic diagram showing an example of a reflective screen equipped with the surface shape diffusion sheet of FIG. 1 and the arrangement of an image projection device. (a) is a schematic diagram showing the positional relationship between the reflective screen and the ceiling light, and (b) is a schematic diagram showing the positional relationship between the ceiling light, reflective screen, projector, and measurement device (luminance meter) in black floating measurement. . (a) is a schematic diagram showing an example of a reflective screen according to the present invention, and (b) is a sectional view in the thickness direction of the screen in (a). (a) is a schematic diagram showing another example of a reflective screen according to the present invention, and (b) is a sectional view in the thickness direction of the screen of (a). (a) is a schematic diagram showing yet another example of a reflective screen according to the present invention, and (b) is a sectional view in the thickness direction of the screen of (a). FIG. 2 is a schematic diagram showing ray tracing of incident light and reflected light of external light by the Fresnel lens of the spatial imaging iris surface type reflective screen according to the present invention. FIG. 2 is a schematic diagram showing an example of an internal optical system of an image projection device. FIG. 3 is a diagram showing a visual target display pattern for examining the relationship between black floating and color reproducibility. FIG. 4 is a diagram illustrating a visual target display pattern used for measuring the amount of reduction in brightness, where (a) is an example in which the brightness of the visual target = 230 and the amount of black floating = 215, and (b) is an example in which the brightness of the visual target = 230. , an example in which the amount of black floating = 115 is shown. FIG. 7 is a diagram showing the relationship between the amount of black floating and the amount of reduction in the brightness of the viewed object, using the brightness of the viewed object as a parameter. FIG. 3 is a diagram showing the relationship between the brightness of a visual object and the amount of brightness reduction using the amount of black floating as a parameter. When the amount of black float = 100, it is a diagram showing a visual target display pattern for checking the brightness range in which the brightness of the visual target does not decrease, and (a) shows the left side (black float amount = 0) and the right side ( (b) is a pattern in which the brightness of the visual target on the right side is increased so that the visual target on the left and right sides appear to have the same brightness. FIG. 7 is a diagram illustrating a display pattern of a visual target for confirming a decrease in brightness, with the amount of black floating being 255, and the visual target being white in (a) and green in (b). FIG. 7 is an explanatory diagram showing a method of correcting a decrease in brightness in a color non-reproducibility brightness range when the black floating amount is 78; FIG. 4 is an explanatory diagram showing that a change in brightness reduction amount with respect to the brightness of a visual object in a color non-reproducibility brightness range can be represented, for example, by a curve having the same shape as the graph line A in the figure. FIG. 3 is a flowchart showing a procedure for calculating a black floating amount value of an RGB color model. FIG. 7 is a diagram showing a black-filled brightness range, a color non-reproduction brightness range, and a color reproduction brightness range when the amount of black float is 78.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Surface shape diffusion sheet according to the present invention: [1] of the present invention)
First, the surface shape diffusion sheet according to the present invention will be explained.
FIG. 1 is a schematic diagram showing a surface shape diffusion sheet 1 according to the present invention. As shown in FIG. 2, the reflective screen 4 having the surface-shaped diffusion sheet 1 on its surface reflects the image light from the image projection device 5 and diffuses it out. As shown in FIG. 8, the image projection device 5 sequentially passes image light from a trichromatic light source 130 made of, for example, an LED chip through a diffusion film laminate 122, relay lenses 120a and 120b, and a digital mirror device 134, and then passes it through a plurality of The configuration is such that the light is sequentially reflected by a concave reflecting mirror 140 and a convex reflecting mirror 142 through a projection optical system 138 consisting of a lens and sent to the reflective screen 4. Note that light not directed toward the screen is blocked by a light blocking plate 136. The projection optical system 138 has a diaphragm, and the space inside the diaphragm is called an iris surface 18.

As shown in FIG. 1, the surface shape diffusion sheet 1 includes a surface shape anisotropic diffusion layer 2 and a flat substrate 3 underlying the surface shape anisotropic diffusion layer 2.

The surface shape anisotropic diffusion layer 2 is made of an ultraviolet curable resin such as urethane acrylate or epoxy acrylate, or other ionizing radiation curable resin such as an electron beam curable resin, and is flexible.

The surface shape anisotropic diffusion layer 2 has a surface shape in which a large number of irregular length protrusions extending in approximately one direction are arranged side by side at irregular intervals in a direction perpendicular to the extending direction. have The height of the protrusions is preferably greater than 0 μm and less than or equal to 10 μm. Here, the direction in which the protrusions extend is the vertical direction, and the direction in which the protrusions are arranged is the left-right direction. With such a surface shape, the horizontal diffusion angle is larger than the vertical diffusion angle. The vertical diffusion angle and the horizontal diffusion angle can be set to various values by changing manufacturing conditions.

The substrate 3 is made of, for example, a transparent resin material and has flexibility. The thickness of the substrate is preferably 50 μm or more and 250 μm or less from the viewpoint of ensuring strength and reducing weight.

A reflective screen 4 having a surface shape anisotropic diffusion layer 2 on its surface has a reflective layer 8 inside the screen, and a holding plate 10 for maintaining the flatness of the substrate 2 on the backmost side of the screen. In the reflective screen 4 shown in FIG. 2, as a preferable form, the reflective layer 8 has a surface that the incident light reaches in a Fresnel lens surface shape in order to deflect the incident image light in the normal direction of the screen surface. There is.

In the present invention, the diffusion angle in the in-plane vertical direction of the surface shape anisotropic diffusion layer 2 is within the range of ±14° (half width), and the visible light wavelength band is transmitted within or on the surface of the substrate. The ratio T was limited to be within the range of 0.5 or more and less than 1. Before describing the reasons for these limitations, black floating will be explained in more detail using FIG. 2.

As shown in FIG. 2, in the reflective screen 4 that reflects the image light from the image projection device 5 on the front side by the reflective layer 8 and diffuses it back to the front side, the ceiling light 11 and other lights other than the image light are reflected. Outside light from other places (floor, front wall and window) also enters the screen surface. These external lights are diffused on the screen surface (the surface of the surface shape diffusion layer 2), some of them are reflected on the screen surface toward the front, and the rest reaches the reflective layer 8 inside the screen and is reflected by the reflective layer 8. , emitted from the screen surface to the front side. These diffusely reflected light due to external light (hereinafter simply referred to as diffusely reflected light due to external light) is superimposed on the image light, causing black floating in the image. Note that in FIG. 2, only the principal rays of the emitted image light and external light are shown, and the diffused light is not shown.

(Diffusion angle of surface anisotropic diffusion layer)
In order to reduce black floating due to external light from the ceiling light 11, which is most affected, in the present invention, the vertical diffusion angle of the surface shape anisotropic diffusion layer 2 of the surface shape diffusion sheet 1 shown in FIG. 1 is set to ±14. ° (half width). The range of the diffusion angle is included in the vertical plane perpendicular to the reflective screen surface and the vertical direction, and the normal direction to the screen surface is 0°, and either the clockwise or counterclockwise angle is correct. , the other angle range is negative.

In the present invention, the reason why the vertical diffusion angle is set within the range of ±14° (half width) will be explained using FIG. 3(a). FIG. 3(a) shows a general positional relationship between the reflective screen 4A for studying the diffusion angle and the ceiling light 11. The reflective screen 4A is not shown except for the surface shape diffusion layer 2A provided on the screen surface. The surface shape diffusion layer 2A can take various diffusion angles θ in the vertical direction to examine the diffusion angle.

Assuming that the vertical size of the reflective screen 4A is 1H as shown in FIG. Assume that they are located 0.5H above and 0.5H, 1H, 1.5H, and 2H apart in the front direction. Note that the external light diffusely reflected by the ceiling light 11 tends to reach the observation position when it is incident on the top of the reflective screen 4A. Further, since the brightness of external light incident on the top is inversely proportional to the square of the distance r from the ceiling light, the position of 0.5H is the brightest. On the other hand, 1.5H and 2H are easier to reach the observation position. Therefore, the interaction between the brightness of the outside light and the reflection angle of the diffusely reflected light of the outside light determines the position of the ceiling light 11 where the influence of outside light is the worst, and in the case of FIG. 3, when the position of the ceiling light 11 is 1H , almost the worst condition. Under this worst-case condition, the diffusely reflected external light reaches observation positions 2H to 3H at an upward diffusion angle from the principal ray 61 of the diffusely reflected external light by the ceiling light 11 at position 1H, as shown in FIG. This is the case when θ is 14.6° or more (more than 14°). It is obvious that this point is the same even if the surface shape diffusion layer 2A is replaced with the surface shape anisotropic diffusion layer 2. Therefore, in the present invention, the vertical diffusion angle of the anisotropic surface shape diffusion layer 2 is within the range of ±14° (half width).

This prevents the diffusely reflected external light that is diffusely reflected on the screen surface from reaching the vicinity of the eyes of the viewer standing in front of the screen. Note that it is preferable that the diffusion angle in the left-right direction be as large as possible.

(Measurement of black float)
Next, in order to evaluate the effect of reducing black floating by setting the diffusion angle of the surface shape anisotropic diffusion layer within the range of ±14° (half width), the surface shape anisotropic diffusion layer 2 of FIG. Using this technology, we measured black floating caused by external light from ceiling lights. The measurement diffusion sheet used was one in which a surface anisotropic diffusion layer 2 having a surface shape as shown in FIG. 1 was formed on a transparent substrate. The diffusion angle of the measurement diffusion sheet is ±5° (half width) when measured as the diffusion angle of transmitted light that is vertically incident from the shape side (front side).An aluminum reflective layer is provided on the back of the substrate, and the transmitted light is When measured as the diffusion angle of the reflected light reflected by the reflective layer, it was ±10° (half width), so the value of surface shape diffusion (diffusion angle of the surface shape anisotropic diffusion layer of the measurement diffusion sheet) was ±10° (half width). It was considered to be within the range of 14° (half width). However, the external light diffusely reflected from the ceiling light also includes light that reaches the reflective layer inside the screen, is reflected by the reflective layer, and is emitted from the screen surface.

In FIG. 2, a reflective screen (referred to as SHL screen 82) was manufactured as the above-mentioned measurement diffusion sheet in place of the surface shape diffusion sheet 1, and measurements were performed in the arrangement shown in FIG. In addition, similar measurements were performed using a commercially available magnetic blackboard screen (referred to as White Matte Screen 81) for comparison.

FIG. 3(b) shows the positional relationship among the ceiling light 11, the SHL screen 82 (or white matte screen 81), the projector 5, and the measuring device (luminance meter 30). The positional relationship between the ceiling light 11 and the SHL screen 82 in FIG. 3(b) is almost the same as that between the ceiling light 11 and the reflective screen 4A in FIG. 3(a). The observation position was only 2H, which has stricter conditions than 3H.

The equipment shown in Table 1 was used for the measurement. Table 2 shows the illuminance at the center of each screen due to the ceiling light 11. In addition, Table 2 also shows the measured value of the illuminance of the table surface directly under the ceiling light as a reference value (the illuminance meter is not shown), but according to this, the lighting in the room used for the measurement was relatively bright. It turns out that there is something.

The black floating measurement results are shown in Table 3. From Table 3, it is confirmed that black floating (brightness in all black display) is reduced by approximately 60% (= (1-35/88) x 100) on the SHL screen compared to the white matte screen used for comparison. did it. Note that since the brightness is almost the same between all black display and when the projector is OFF, the black floating may be the brightness when the projector is OFF.

(Substrate transmittance T)
Next, in the present invention, the reason why it is decided that the transmittance T in the visible light wavelength band is within the range of 0.5 or more and less than 1 inside or on the surface of the substrate 3 will be explained. Here, the transmittance T is the rate at which incident light of a specific wavelength passes through the substrate, T = I/I ₀ , where I ₀ is the rate of incident light, and I is the rate of radiation of light that has passed through the substrate. It is the degree of divergence (unit: W/m ² ), and since I ₀ ≧I, T≦1.

This countermeasure is also essential because the diffusely reflected external light from the ceiling light includes light that reaches the reflective layer inside the screen, is reflected by the reflective layer, and is emitted from the screen surface. As a countermeasure against external light passing through the substrate 3 twice in this manner, in the present invention, the inside or surface of the substrate 3 is colored from transparent to black in order to lower the transmittance T in the visible wavelength band. Note that reducing the transmittance T in the visible light wavelength band inside or on the surface of the substrate 3 is called transparent blackening. As a result, the external light that has passed through the substrate 3 twice becomes darker, and black floating is reduced. Regardless of whether the portion where the transmittance T of the substrate 3 is lowered is inside or on the surface of the substrate 3, black floating is reduced.

In conventional diffusion sheets, it was common to increase the transmittance T in order to make the image light as bright as possible. Although the present invention has the disadvantage that the image light also becomes darker, priority is given to reducing the deterioration of image quality due to black floating. The reason behind this is that as the light source of projectors has evolved from lamps to LEDs and then to lasers, it has become possible to brighten the image light. However, even if the image light can be brightened in this way, if the transmittance T is less than 0.5, the image will be too dark, so the lower limit of the transmittance T was set at 0.5. The lower limit is preferably 0.7.

Here, a method for realizing the above transparent blackening will be explained. An example of this method is to uniformly mix an appropriate amount of a UV (ultraviolet light, hereinafter the same) transparent black dispersion into the resin that is the material of the substrate 3 (transparent blackening of the inside of the substrate). Since the surface shape anisotropic diffusion layer 2 of the surface shape diffusion sheet 4 is formed on the substrate 3 by UV polymerization, the substrate 3 used for UV polymerization allows UV light to pass through and has uniform visible light transmittance. It is necessary to have characteristics that lower The UV-transparent black dispersion liquid is a dispersion liquid that is made of fine particles of a pigment that is black (uniformly absorbs visible light) and UV-transparent, and is made of fine particles such as urethane resin, acrylic resin, ester resin, etc., which are the materials of the substrate 3. Since it is compatible with the resin, by uniformly mixing an appropriate amount of this dispersion liquid with the resin that is the material of the substrate, it is possible to make the inside of the substrate transparent and black.

In addition, as a transparent blackening method, in addition to the method of mixing the black dispersion liquid with the substrate material, there is also a method of applying the black dispersion liquid to a resin plate of the substrate material (transparent blackening of the substrate surface), or a method of applying the black dispersion liquid to the resin plate of the substrate material, or using an ND filter. It is also possible to adopt a method of vapor-depositing metal on the same resin plate (transparent blackening of the substrate surface) as shown in the figure below.

Note that the substrate 3 has flexibility, and the substrate thickness is preferably 50 μm or more and 250 μm or less from the viewpoint of ensuring strength and reducing weight.

(Confirmation of black floating reduction effect by surface shape diffusion sheet according to the present invention)
In the above-mentioned measurement of black floating, similar measurements were performed using a sample screen whose surface was provided with the surface shape diffusion sheet 1 according to the present invention. This sample screen was the same as the SHL screen 82 except that the transmittance T inside the substrate was lowered to 0.9 by the transparent blackening. As a result, on this sample screen, the black float (luminance in all black display) was approximately 30 cd/ ^m2 , which is approximately 66% (= (1-30/88) x 100) reduced compared to the white matte screen. This was confirmed. In this sample screen, by lowering the transmittance of the substrate, the black float is reduced compared to that of the SHL screen 82 (approximately 35 cd/m ² ).

(Reflective screen according to the present invention: [2] of the present invention)
Next, a reflective screen according to the present invention will be explained. This reflective screen is a reflective screen equipped with a surface shape diffusion sheet 1 according to the present invention. As an example, in the embodiment shown in FIG. 4, a reflective layer 8, A protective film 9 and a retaining plate 10 are provided.

The bonding surface between the reflective layer 8 and the substrate 3 becomes a surface that reflects the image light, the protective film 9 is a film that covers the reflective layer 8 from the back side, and the holding plate 10 maintains the flatness of the front substrate 3. It is a board that does.

(reflective layer)
The reflective layer 8 may be formed by, for example, depositing a thin layer of a metal with high reflectance (reflectance of 70% or more) such as aluminum, silver, or nickel so that it has flexibility, or thin small pieces of aluminum called aluminum flakes. It is preferable to form them by a method such as painting so that these surfaces are aligned parallel to each other. The thickness of the reflective layer 8 is about 0.5 to 0.9 μm in the case of vapor deposition, and about 10 to 50 μm in the case of painting, and is determined from the viewpoints of releasability, reflectance, bending strength, etc.

(Protective film)
The protective film 9 has flexibility and has the function of protecting the reflective layer 8 by suppressing deterioration and peeling of the reflective layer 8, damage to the reflective layer 8, and the like. Furthermore, the protective film 9 has a function of absorbing light. The material for the protective film 9 is a base material such as urethane resin, epoxy resin, acrylic resin, or a mixture of these resins, and a dark color paint such as black or a dark color paint such as black as the light absorbing material. Examples include materials to which dyes, pigments, etc., or beads containing these are added, and various additives having functions such as protecting the reflective layer 8 from deterioration such as oxidation. Further, the thickness of the protective film 9 is preferably 5 to 100 μm at the thinnest portion from the viewpoint of fully exhibiting the protective function and the light absorption function.

(retention plate)
The holding plate 10 is for maintaining the flatness of the substrate 3 (specifically, the flatness of the members from the surface shape diffusion sheet 1 to the protective film 9), and is preferably made of a plate, for example, from the viewpoint of ensuring rigidity and reducing weight. It is made of MDF made by compressing wood fibers with a thickness of 1.0 to 3.0 mm and hardening them with adhesive. The holding plate 10 is bonded to the protective film 9 via a bonding layer (not shown) made of an adhesive material such as double-sided tape. By having the holding plate 10, deformation during transportation can be prevented, and installation work such as hanging on a wall using a hook or the like is facilitated.

Note that instead of the holding plate 10, a structure in which a magnetic sheet (not shown) with a thickness of 300 to 400 μm is attached may be used.

In the example of FIG. 4, the thickness of the anisotropic surface shape diffusion layer 2 is 40 μm, and the thickness of the substrate 3 is 250 μm. In this embodiment, since there is no Fresnel lens for deflecting the image light, it becomes difficult for the image light from the left and right ends to reach the observation position, so the diffusion in the left and right direction in the anisotropic surface shape diffusion layer 2 appears to be complete diffusion. It is preferable to diffuse in all directions.

(Fresnel lens as a lens layer: [3] of the present invention)
Next, one embodiment using a Fresnel lens in the reflective screen according to the present invention will be described. In order to prevent the images at the left and right ends of the screen shown in FIG. 4 from becoming dark, it is preferable to use a Fresnel lens. One embodiment using a Fresnel lens has a lens layer 6 disposed and bonded between a substrate 3 and a reflective layer 8, as shown in FIG. 5, and the lens layer 6 has a reflective surface shape on the back side. This is a reflection type screen, which is made of a Fresnel lens having a Fresnel lens, and the joint surface between the reflection layer 8 and the lens layer 6 serves as a surface that reflects the image light.

The material of the lens layer 6 is an ultraviolet curable resin such as urethane acrylate or epoxy acrylate, or another ionizing radiation curable resin such as an electron beam curable resin, and is flexible and has a boundary in its thickness direction. The surface is a flat surface on the front side, and the surface on the back side is a Fresnel lens surface in which lens surfaces 6a and non-lens surfaces 6b are alternately arranged in a concentric arc shape. The layer thickness of the lens layer 6 is designed to be limited to about 50 μm at the maximum. The radial dimension of the Fresnel lens of the lens surface 6a is approximately 100 to 150 μm, and the dimension of the non-lens surface 6b is approximately 10 μm at maximum and 0 μm in an ideal Fresnel lens.

The Fresnel lens forming the lens layer 6 of the reflective screen 4 shown in FIG. f corresponds to the distance from the screen surface to the image projection device 5, more specifically, the distance a to the iris plane 18 (see FIG. 8), which is the space inside the aperture of the projection optical system 138 of the image projection device 5 (a = f). However, here, "coincidence" allows an error within ±10%.

Therefore, since the principal ray direction of the image light emitted from the left and right ends of the screen is also the normal direction of the screen surface, the image light is diffused twice by the surface-shaped anisotropic diffusion layer 2, and compared with FIG. This makes it easier to reach the observation position.

In FIG. 5(b), the lens layer 6 made of a Fresnel lens can be formed directly on the back surface of the substrate 3 of the surface shape diffusion sheet 1 by UV polymerization. may be pasted. In order to make the Fresnel lens a reflective type, it is covered with a reflective layer 8 in which thin pieces of aluminum called aluminum flakes are arranged parallel to the lens surface, and a protective film 9 is further coated on the surface for protection. The thickness of this reflective screen, excluding the holding plate 10, is approximately 400 μm, so in order to make the screen flat and without unevenness, it must be attached to the holding plate 10 with a thickness of 1.0 to 3.0 mm. is preferred. Further, instead of the holding plate 10, a screen to which a magnetic sheet (not shown) is attached may be directly attached to a board or wall to which a magnet is attached.

(Spatial imaging iris surface method: [4] of the present invention)
Next, another embodiment using a Fresnel lens in the reflective screen according to the present invention will be described.

In this embodiment, as shown in FIG. 6, the reflective screen 4 has an iris surface of the projection lens of the image projection device 4, which is located a distance a from the surface that reflects the image light with respect to the focal length f of the Fresnel lens. 18 (see FIG. 8) to create a spatial imaging iris surface 20 at a distance b that satisfies the relationship (1/a)+(1/b)=1/f. Note that an error within ±10% is allowed for the distances a and b with respect to the values that satisfy the above relationship.

The embodiment shown in FIG. 6 differs from the embodiment shown in FIG. 5 only in the Fresnel lens forming the lens layer 6. That is, the lens layer 6 (Fresnel lens) shown in FIG. 5 deflects the image light from the image projection device 5 in the normal direction of the screen, whereas in FIG. It has a condensing function of concentrating light. Optically, the focal lengths f are different from each other. The optical system shown in FIG. 6 is called a spatial imaging iris surface system. Therefore, the reflective screen of this embodiment is also referred to as a spatial imaging iris surface type reflective screen.

(Behavior of external light on spatial imaging iris surface method/reflective screen)
FIG. 7 is a ray tracing diagram of incident light and reflected light of external light through a Fresnel lens of a spatial imaging iris surface type reflective screen. Since the external light 51 from the floor surface 13 enters the lens surface 6a of the Fresnel lens of the reflective screen 4 from the same direction as the image light 50 from the image projection device 5, it causes black floating.

Outside light 52 other than this outside light 51 that enters the lens surface 6a from the ceiling light 11 or the front window 12 is deflected by the lens surface 6a so as not to reach the spatial imaging iris surface 20, so that the outside light 52 does not appear black. It won't be the cause. On the other hand, a portion of the external light 53 and 54 that enters the non-lens surface 6b from the ceiling light 11 and the front window 12, respectively, reaches the spatial imaging iris surface 20, causing black floating.

According to the surface shape diffusion sheet 1 according to the present invention, it is possible to reduce black floating caused by external light 51 to 54, but in order to further reduce black floating caused by external light 53 and 54, the inclination of the non-lens surface 6b of the Fresnel lens is is perpendicular to the screen surface as well as the screen normal direction, or the non-lens surface 6b is excluded from being coated with the reflective layer (for example, a metal film) so that the non-lens surface 6b does not become a reflective surface. Alternatively, it is preferable to cover with an absorbing film that absorbs light in place of the reflective layer.

(Video display system according to the present invention: [5] and [6] of the present invention)
Next, a video display system according to the present invention will be explained. This image display system is premised on being equipped with the above-described reflective screen 4 according to the present invention and an image projection device 5 (illustrated in FIG. 8) that projects image light. Note that the image projection device 5 is not limited to the one illustrated in FIG. 8, and may include various commercially available projectors.

Based on the above premise, in a bright environment affected by external light, there is a problem that as the brightness of black due to black floating increases, the image becomes grayish and the vividness of colors is lost, making it impossible to reproduce the original colors. In order to solve this problem, the inventors of the present invention have repeatedly studied the relationship between black floating and color reproducibility. As a result, it was found that the deterioration in color reproducibility can be quantified by expressing the luminance of black that is floating as the amount of black that is floating using RGB color model values. The process of the above consideration will be explained below.

(Black floating amount)
In the RGB color model, each RGB element is expressed as R=0 to 255, G=0 to 255, and B=0 to 255. The numerical value 0 to 255 is an integer, called lightness (brightness), and indicates the relative intensity of brightness. The minimum value is 0 and the maximum value is 255. Therefore, absolute black is R=0, G=0, B=0, and the brightest white is R=255, G=255, B=255.

On the other hand, the brightness (cd/m ² ) of floating black measured with a brightness meter is measured on the screen surface when absolute black (R=0, G=0, B=0) is projected under external light. Since this is the minimum brightness, black floating is expressed as a ratio to the maximum brightness (cd/m ² ) when white (R = 255, G = 255, B = 255) is projected, that is, relative brightness (0 to 1). be able to.

However, the color of the image observed under the black floating state is also expressed by the brightness (0 to 255) of each element of the RGB color model, similar to the color of the projection light from the image projection device 5. Therefore, in quantifying the effect of black floating on the color reproducibility of images observed on the screen, the condition of black floating is determined by the brightness of each element of black floating, rather than the relative luminance of the black. = 255 x (relative brightness of black) It is thought that it is easier to organize the relationship between the color of the image and the black floating state. Therefore, hereinafter, the black floating state is expressed by the brightness of each black floating element, and the value of the brightness (assuming that the brightness of each black element is the same) is referred to as the "black floating amount". Lb is used as the sign of the amount of black floating. That is, the definition formula for the amount of black floating Lb is Lb=255×(relative brightness of black).

However, since brightness is an integer as mentioned above, the integer part of the value of this formula is used. Here, the integer part may be a value obtained by rounding off, rounding down, or rounding up the decimal point of the calculated value, but in the following, the rounded value is used.

For example, in the case of the SHL screen shown in Table 3, the luminance of the black with floating black is 35.59 cd/m ² of all black, and the luminance of white is 994.3 cd/m ² of all white, so the amount of black floating is Lb= 255×35.59/994.3=9.

Therefore, in the above study, red (R), green (G), blue (B) in the RGB color model that constitutes the color of the image, and white, which is a mixture of these, are selected as viewing objects. Then, the visual object was observed while varying the brightness of the object and varying the amount of black floating against a background of black, which corresponds to a black floating black. Then, in a range where the brightness of the viewed object is greater than or equal to Lb and less than 2Lb, a "brightness reduction" occurs in which the brightness of the viewed object apparently decreases with respect to the reference value. Note that the reference value here is the brightness of the object to be viewed when the background is black with no black float (both RGB are 0, that is, the black float amount is 0). Note that when the brightness of the viewing object is less than Lb, there is a so-called crushed black state in which black gradation cannot be expressed.

(Visual test of brightness reduction)
A visual experiment of brightness reduction for determining the relationship between the amount of black floating and the amount of brightness reduction of a visual object will be described below. In this visual experiment, as shown in Figure 9, using the brightness (0 to 255) of each element of the RGB color model on the screen of the liquid crystal display, a black color with no black float (black float amount = 0) on the right side was used. , a black rectangle with an arbitrary black floating amount (in FIG. 9, black floating amount = 215, that is, 215 for both RGB) is displayed adjacent to the left side. Next, each color to be viewed is displayed in a circle within each rectangle, and the diameter of the circle is 1.2 cm, and the observation distance is approximately 30 cm, and the left and right colors are viewed from the front to see if there is a difference in brightness between each color. was visually observed. As a result, it was found that each color of the visual object appears darker when the amount of black float = 215 than the basic color when the amount of black float = 0. When black float occurs, the image becomes grayish and the vividness of the colors is impaired.The reason for this is that due to black float, the brightness of each color is apparently lower than the standard value (brightness when black float amount = 0), and color reproducibility is affected. This is thought to be because it is damaged.

In FIG. 9, the image displayed on the liquid crystal screen (the viewing object and background) was visually observed, and when the brightness of this image was measured, the brightness of black (R=0, G=0, B=0) was 1.5 cd. /m ² and white (R=255, G=255, B=255) was 85 cd/m ² .

Furthermore, even if the same image as the image shown in FIG. 9 on the liquid crystal screen is projected from the image projection device 5 shown in FIG. The phenomenon in which each color (basic color) with a black float amount of 0 appeared darker was observed in the same way as when displayed on a liquid crystal display screen.

Next, in order to quantitatively measure the decrease in brightness from the reference value of each color to be viewed, in the rectangle on the right side, write the brightness of each color to the right of the circle to be viewed, as shown in Figure 10(a). In the rectangle on the left, a circle with brightness correction added to the top of each visual target to compensate for the decrease in brightness at the bottom and look the same as each color on the right (colors whose brightness is the reference value) is added. to add. The brightness is written on the left side of each visual object in the same way as on the right side. FIG. 10A shows that when the amount of black float is set to 215, the brightness of each color decreases by about 18 from the reference value. This value was determined by observation by five people, considering that it depends on the individual's visual sense. FIG. 10(b) shows the amount of black floating that is the same brightness on the right and left sides by varying the amount of black floating. From this, it has been found that when the brightness of the viewed object is 230, if the amount of black float is set to 115 or less, the brightness of the viewed object will not decrease. Using the same method as in FIG. 10, using the brightness of the viewed object (brightness of the viewed object = 230 in FIG. 10) as a parameter, the amount of decrease in brightness of the viewed object relative to the amount of black floating was determined, and the result was as shown in FIG. 11. From this figure, it was found that the amount of black floating at which the brightness of the viewed object begins to decrease is equal to the brightness of the viewed object/2.

Next, FIG. 12 shows the relationship between the brightness of the visual object and the amount of brightness reduction using the amount of black floating as a parameter. From this figure, when the brightness of the viewed object becomes twice or more the amount of black floating, the brightness of the viewed object does not decrease. White colors of various brightnesses (R = L, G = L, B = L, L = 255, 230, 200, 170, 135, 115, where the brightness is L) were viewed, and the amount of black in the background = 100. 13(a) and 13(b) show prepared viewing target patterns in order to confirm the brightness range of the viewing object in which the brightness of the viewing object does not decrease. It was confirmed that no reduction in brightness occurs when the brightness of the visual object is 200 or more, which is more than twice the black floating amount = 100. Further, in FIG. 13(b), the amount of brightness reduction of the visual object is calculated, and it can be seen that if the brightness is increased by the brightness reduction, the brightness of the left and right visual objects becomes the same.

From the above study, it is concluded that the color reproducibility of the viewed object does not deteriorate in the brightness range where the brightness of the viewed object is twice or more the amount of black floating. In conventional reflective screens, under a bright environment with ceiling lights on, as in the case of the white matte screen shown in Table 3, the brightness of black floating (minimum brightness) is as large as approximately 88 cd/ ^m2 , and the brightness of all white (maximum brightness) is as high as approximately 88 cd/m2. is 289 cd/m ² , so the amount of black floating is 255×88/289=78.

Therefore, in the case of black float amount = 78, the brightness of the visual object does not decrease when the brightness is between black float amount x 2 (= 156) to 255, but as shown in the graph of black float amount = 78 in Fig. 12, The brightness of the visual object decreases in a wide range of brightness of the object from black floating amount (=78) to 2× black floating amount (=155).

(Color reproduction brightness range, color non-reproduction brightness range, and black crushed brightness range)
In this way, by determining the amount of black float, it is possible to identify the brightness range in which the brightness of the viewed object decreases (referred to as the color reproduction brightness range) and the brightness range in which the brightness of the viewed object does not decrease (referred to as the color reproduction brightness range). . If Lb is the amount of black floating, 2Lb is 2×the amount of black floating, and L is the brightness of each element of the viewing object, the color non-reproduction brightness range is Lb≦L<2Lb, and the color reproduction brightness range is 2Lb≦L≦255. It is expressed as

Note that the brightness range of 0≦L<Lb is the brightness range in which crushed black occurs as described above (black gradation cannot be expressed due to floating black), and is referred to as the brightness range with crushed black.

(Expansion of color reproduction brightness range by adjusting transmittance T and white brightness)
In the SHL screen shown in Table 3, the black floating amount is 9 (=255×36/994), and the color reproduction lightness range is 18 (=2×9) to 255. In such a color reproduction brightness range, the minimum value of the brightness range is determined by the minimum brightness that is the source of the amount of black floating, and the maximum value can be expanded by increasing the brightness of full white (white), which is the maximum brightness. Therefore, by adjusting the transmittance T of the substrate 3 of the surface shape diffusion sheet 1 and the white brightness Kw, which is the maximum brightness of the image light from the image projection device 5, the color reproduction brightness range can be widened. For example, the relationship between the amount of black floating Lb and Lmax (maximum value of brightness ≦255) is defined as Lb≦Lmax/4, and the transmittance T of the substrate 3 of the surface shape diffusion sheet 1 is set so as to satisfy this relationship. Through the above-mentioned transparent blackening, the image light output from the image projection device 5 is increased by 1/T2 to reduce the black floating amount Lb to a range of 0.25≦T2<1 and to compensate for the decrease in Lmax. increase to Here, T2 is used because the image light passes through the substrate 3 twice in the reflective screen 4. This makes it possible to lower only Lb without lowering Lmax, and expand the color reproduction brightness range to 2Lb×T2≦color reproduction brightness range≦Lmax. However, the external light reflected on the screen surface was sufficiently smaller than the external light reflected on the reflective layer 8 inside the screen.

For example, if the transmittance T of the substrate 3 of the reflective screen 4 is about 0.9 and the output of the image light from the image projection device 5 is increased by 1.24 times (1/T2 times), the color reproduction brightness range is The lower limit of is 2Lb×0.81, and the color reproduction brightness range can be expanded by 2Lb×(1-0.81) toward the lower brightness side.

Furthermore, when the black floating amount Lb becomes the brightness of white (R=255, G=255, B=255) at the maximum brightness, 255, the lower limit 2Lb of the color reproduction brightness range becomes 510, which exceeds the upper limit 255, so the color There is no reproduction brightness range, and a decrease in brightness occurs throughout the brightness range (0 to 255) of the viewing object. FIG. 14(a) shows the decrease in brightness of the visual target when the black float amount is 255 and white is used as the visual target. FIG. 14(b) shows a case where green (G) is used instead of white. From these, it means that when the black float reaches its maximum brightness, that is, the white background, the brightness decreases from the brightness (reference value) of the visual target on a black background without black float across the entire brightness range of the visual target. . It turns out that it makes sense to use a black background instead of white in order to see objects in bright, vivid colors.

(Correction of brightness reduction: [5] of the present invention)
Based on the above study results, the video display system according to [5] of the present invention is configured to correct the decrease in brightness in the brightness range Lb≦L<2Lb (which is the color non-reproducibility brightness range). That is, this video display system includes the reflective screen and video display device based on the above premise, and further includes a luminance meter, black floating amount calculation means, and brightness adjustment means.

(Luminance meter)
The luminance meter measures black (R=0, G=0, B=0) and white (R=255, G=0) in an RGB color model, which are projected from the image projection device onto the reflective screen under external light. 255, B=255) to obtain respective measured values Kmin and Kw.

The black color in the video image and the black color under external light correspond to the visual object and the black background (background) in the visual test of brightness reduction described above, respectively.
The luminance meter can be constructed from ordinary commercially available products.

(Black floating amount calculation means)
The black floating amount calculation means calculates the black floating amount Lb as the integer part of the value of the formula: 255×Kmin/Kw. This equation corresponds to the above-mentioned definition equation for the amount of black floating, "Lb=255×(relative brightness of black color)".

(Brightness adjustment means)
The brightness adjustment means corrects a decrease in brightness observed within a brightness range Lb≦L<2Lb of the brightness L of the image.

As described in the above discussion, the brightness range Lb≦L<2Lb is the color non-reproducibility brightness range in which a decrease in the brightness of the viewing object is observed. Therefore, the brightness adjustment means corrects this brightness reduction. For this correction, the results of the aforementioned visual experiment of brightness reduction (for example, FIG. 12) are used.

FIG. 15 shows the color non-reproduction lightness range and the color reproduction lightness range when the amount of black floating in FIG. 12 is 78. A method for correcting a decrease in brightness will be explained using this figure as an example. As shown in the figure, in the color reproduction lightness range (156 to 255), the amount of reduction in brightness of the viewing object is 0, so no reduction in brightness occurs, so each RGB color having the brightness on the horizontal axis is output as image light. On the other hand, in the color non-reproducibility brightness range (78 to 155), the brightness reduction of the viewing object is taken as a negative value, so that when each RGB color having the brightness on the horizontal axis is output as image light, the brightness decreases. In order to prevent this reduction in brightness, if the brightness of each RGB color to be output as image light falls within the color non-reproducibility brightness range, the brightness value on the horizontal axis is adjusted as shown in the figure. Correction is performed by adding the absolute value of the brightness reduction amount on the corresponding vertical axis, and each RGB color having the corrected brightness is output as image light.

As a result, it is possible to project an image with no reduction in brightness not only in the color reproduction brightness range of the viewing object but also in the color non-reproduction brightness range.

A method for correcting the above-mentioned reduction in brightness will be described in more detail below.
As shown in FIG. 16, the relationship between the brightness of the visual object represented by the RGB color model and the amount of brightness reduction changes as shown in the graph of A in the figure. In addition, the graph A in this figure shows a curve obtained by extrapolating the relationship curve between the brightness of the visual object and the amount of brightness reduction when the amount of black floating = 50 to the range of brightness less than 50, and color unreproducibility. The range is 50 or more and less than 100. The change in the graph of A (curve shape) is that RGB is not only a primary color (red is only R, green is only G, blue is only B is a non-zero value, and the others are 0), but also white (both RGB are non-zero). This also applies to colors that are a mixture of primary colors such as (the same numerical value of) (the curve shape is almost the same as that of graph A). Therefore, even for the general colors of the RGB color model (R=Lr, G=Lg, B=Lbl), Lb≦Lr, Lg, Lbl<2Lb, that is, the color non-reproducibility lightness range is greater than or equal to Lb and less than 2Lb. Become.

Next, FIG. 17 shows the procedure for determining the value of the amount of black floating. Since the amount of black floating changes depending on the external light in the installation environment of the video display system, the amount of black floating must be determined for each installation environment. The brightness and the amount of brightness reduction of the viewing object, whether it is the RGB primary colors or a general color that is a mixture of these, changes along a relational curve that has almost the same shape as the graph A in Figure 16, so the amount of black floating for each installation environment changes. Once understood, correction is easy.

As shown in Figure 17, black (RGB both 0) and white (RGB both 255) are projected in a bright environment with the influence of external light, the brightness of each image is measured, and the measured values Kmin and Kw are calculated. From this, the black floating amount Lb is determined by the formula: Lb=255×Kmin/Kw. Once the black floating amount Lb is determined, A is translated in the horizontal axis direction so that A fits the change in brightness reduction in the brightness range Lb to 2Lb in FIG. Find the amount of brightness reduction in . General colors of the RGB color model (R=Lr, G=Lg, B=Lbl) are corrected separately for each primary color.

If Lr, Lg, and Lbl are within the color nonreproducibility lightness range of Lb or more and less than 2Lb, correct Lr, Lg, and Lbl individually from the graph of A.

A brightness adjustment means that performs such correction can be achieved by installing software in which the procedure for the correction is described in the image projection device.

(Adjustment of image light output: [6] of the present invention)
By correcting the brightness reduction described above, the color non-reproducible brightness range can be converted into the color reproducible brightness range. However, a black-filled brightness range where the brightness is less than Lb remains, and in this range black is displayed with the same brightness, making it impossible to express black in detailed gradations. Therefore, the video display system according to [6] of the present invention eliminates the black-out brightness range, further eliminates the color non-reproduction brightness range, and makes the entire brightness range of the viewing object the color reproduction brightness range. This reduces black floating.

Therefore, in [6] of the present invention, in [5] of the present invention, instead of or in addition to the brightness adjusting means, an image light output adjusting means is provided, and this image light output adjusting means is configured to adjust the brightness of the white color. It is characterized by increasing the Kw from Kw to Kw×(1+2Lb/255) to reduce black floating.

When the brightness of the white color is increased from Kw to Kw x (1+2Lb/255), the color reproduction lightness range that was 2Lb or more and 255 or less changes to a value that exceeds 255 and 255+2Lb, which is outside the range of brightness (0 to 255) of the RGB color model. The following is newly added to obtain an expanded color reproduction brightness range of 2Lb to 255+2Lb. An image having a brightness within this color reproduction brightness range will not suffer from crushed shadows or a decrease in brightness.

By converting the expanded color reproduction brightness range from 2Lb to 255 + 2Lb to a brightness range from 0 to 255, images can be observed without crushed blacks or brightness reduction over the entire brightness range (0 to 255) of the RGB color model. is possible.

Embodiment [6] of the present invention will be described using the example of FIG. 18. FIG. 18 shows the brightness range of crushed blacks (0 or more and less than 78), the color reproduction brightness range (78 or more and less than 156), and the color reproduction brightness range (156 or more) and 255 or less) and the color reproduction brightness range (0 or more and 255 or less) after reducing black floating.

The image light output adjusting means increases the white luminance by (1+156(=2×78)/255) times. As a result, the color reproduction lightness range becomes 156 or more and 411 (=255+156) or less. Therefore, the brightness (0 to 255) of each element of the visual object represented by the RGB color model is shifted by 156 (brightness + 156 (=2×78)) and then projected by the image projection device.

Note that the function of deriving the expanded color reproduction brightness range and converting the colors of the RGB color model can be realized by installing software that describes the procedure of such derivation and conversion in the video light output adjustment means. Further, the image light output adjusting means may be built into the image projection device.

Therefore, after reducing black floating, the entire brightness range of the RGB color model (0 to 255) becomes the color reproduction brightness range, and an image without crushed black and brightness can be observed.

Various black expressions using absolute black (both RGB are 0, image brightness = 0 cd/m ² ) cannot be achieved unless the room is in a dark room with no external light. Therefore, the present invention is useful as a method for expressing various blacks by gradation expression from the minimum luminance black under external light as absolute black. In [6] of the present invention, black (2Lb) obtained by multiplying the brightness of white by (1+2Lb/255) is defined as the absolute black.

(Video display method according to the present invention: [7] of the present invention)
Next, the video display method according to [7] of the present invention will be explained. This method is based on the premise that the reflective screen according to any one of [2] to [4] of the present invention and an image projection device that projects image light are used.

In [7] of the present invention, first, black (R=0, G=0, B=0) and white (R=255, G=255, B=255).

Next, the luminance of the black and white colors is measured under external light to obtain the respective measured values Kmin and Kw. To measure the brightness, various commercially available brightness meters can be used.

Next, the black floating amount Lb is calculated as the integer part of the value of the formula: 255×Kmin/Kw. A commercially available personal computer or scientific calculator can be used for this calculation.

Finally, the reduction in brightness observed within the brightness range Lb≦L<2Lb of the brightness L of the image is corrected. This is called the brightness adjustment process. The brightness adjustment means described above can be used to carry out this step.

(Video display method according to the present invention: [8] of the present invention)
Next, the video display method according to [8] of the present invention will be explained. In this method, in [7] of the present invention, instead of or in addition to the brightness adjustment step, the brightness of the white color is increased from Kw to Kw×(1+2Lb/255) to reduce black floating. It has an adjustment process. The above-mentioned image light output adjusting means can be used to carry out this step.

1 Surface shape diffusion sheet (present invention)
2 Surface shape anisotropic diffusion layer 2A Surface shape diffusion layer (for examining diffusion angle)
3 Substrate 4 Reflective screen (present invention)
4A Reflective screen (for examining diffusion angle)
5 Image projection device (projector)
6 Lens layer 6a Lens surface 6b Non-lens surface 8 Reflective layer 9 Protective film 10 Holding plate 11 Ceiling light 12 Front window (window in front of the screen)
13 Floor surface 18 Iris surface 20 Spatial imaging iris surface 30 Luminance meter 50 Image light 51 External light from floor surface to lens surface 52 External light from other than floor surface to lens surface 53 External light from ceiling light to non-lens surface 54 External light from the front window to the non-lens surface 60 Observation position 61 Principal ray of diffusely reflected external light from the ceiling light 81 White matte screen 82 SHL screen 120a Relay lens 120b Relay lens 122 Diffusion film laminate 130 Three primary color light source 134 Digital mirror Device 136 Light shielding plate 138 Projection optical system 140 Concave reflecting mirror 142 Convex reflecting mirror

Claims (8)

1. A surface shape diffusion sheet provided on the surface of a reflective screen that diffuses and emits image light from an image projection device,
   surface shape anisotropic diffusion layer,
   A flat substrate is provided as a base of the surface shape anisotropic diffusion layer,
   The diffusion angle of the surface of the anisotropic surface shape diffusion layer in the in-plane vertical direction is within the range of ±14° (half width),
   A surface shape diffusion sheet for reducing black floating, characterized in that the transmittance T in the visible light wavelength band is within a range of 0.5 or more and less than 1 on the inside or on the surface of the substrate.
2. A reflective screen equipped with a diffusion sheet on the surface,
   The diffusion sheet is the surface shape diffusion sheet according to claim 1,
   A reflective layer, a protective film, and a retaining plate are sequentially arranged and bonded from the substrate to the back side,
   a bonding surface between the reflective layer and the substrate serves as a surface that reflects the image light;
   The protective film is a film that covers the reflective layer,
   A reflective screen characterized in that the holding plate is a plate that maintains flatness of the substrate.
3. further comprising a lens layer disposed and bonded between the substrate and the reflective layer;
   The lens layer is made of a Fresnel lens having a reflective surface shape on the back side,
   3. The reflective screen according to claim 2, wherein a joint surface between the reflective layer and the lens layer serves as a surface that reflects the image light.
4. With respect to the focal length f of the Fresnel lens, reflecting the image light from the iris surface of the projection lens of the image projecting device that is a distance a from the surface that reflects the image light, (1/a) + ( 4. The reflective screen according to claim 3, wherein the spatial imaging iris surface is formed at a distance b that satisfies the relationship: 1/b)=1/f.
5. An image display system comprising the reflective screen according to any one of claims 2 to 4, an image projection device, a luminance meter, a black floating amount calculation means, and a brightness adjustment means,
   The image projection device projects image light,
   The luminance meter measures black (R=0, G=0, B=0) and white (R=255, G=0) in an RGB color model, which are projected from the image projection device onto the reflective screen under external light. 255, B=255) to obtain the respective measured values Kmin and Kw,
   The black floating amount calculation means calculates the black floating amount Lb as an integer part of the value of the formula: 255×Kmin/Kw,
   The brightness adjustment means corrects a decrease in brightness observed within a brightness range Lb≦L<2Lb of the brightness L of each element in the black-to-black image (R=Lb, G=Lb, B=Lb). A video display system characterized by:
6. In place of or in addition to the brightness adjustment means, an image light output adjustment means is provided,
   6. The video display system according to claim 5, wherein the video light output adjusting means increases the brightness of the white color from Kw to Kw×(1+2Lb/255) to reduce black floating.
7. An image display method using the reflective screen according to any one of claims 2 to 4 and an image projection device that projects image light,
   Projecting black (R=0, G=0, B=0) and white (R=255, G=255, B=255) in an RGB color model from the image projection device onto the reflective screen;
   a step of measuring the luminance of the black and white colors under external light to obtain respective measured values Kmin and Kw;
   Calculating the black floating amount Lb as the integer part of the value of the formula: 255 × Kmin / Kw,
   A brightness adjustment step of correcting a decrease in brightness observed within the brightness range Lb≦L<2Lb of the brightness L of each element in the image where the black becomes black (R=Lb, G=Lb, B=Lb). A video display method characterized by comprising:
8. 7. Instead of or in addition to the brightness adjustment step, the image light output adjustment step is performed to increase the brightness of the white color from Kw to Kw×(1+2Lb/255) to reduce black floating. The video display method described in .

Images