Surface shape diffusion sheet with reduced blackening, reflective screen, image display system and image display method

Abstract

Provided are a surface shape diffusion sheet, a reflective screen, an image display system, and an image display method for reducing blackening. The surface shape diffusion sheet (1) comprises a surface shape anisotropic diffusion layer (2) and a substrate (3) serving as its base. The diffusion angle of the surface shape anisotropic diffusion layer (3) in the vertical direction within the plane is within the range of ±14° (half-value width), and the transmittance (T) of the visible light wavelength band within or on the surface of the substrate (3) is within the range of 0.5 or more and less than 1. The image display system calculates the blackening amount (Lb) of the image (=255×black brightness / white brightness) and corrects the brightness reduction observed within the brightness range of Lb≤L<2Lb of the brightness (L) of each element of the image.

Description

Technical Field

[0001] The present invention relates to a surface shape diffusion sheet for reducing blackening applied to a reflective screen, a reflective screen having the diffusion sheet, an image display system having the reflective screen, and an image display method using the reflective screen (hereinafter also referred to as the screen) and an image projection device.

[0002] The reflective screen mentioned here is a screen that diffuses / reflects the image light from the image projection device (also called a projector) on the front side (observer side) of the screen toward the front side and emits it. It refers to a type that diffuses / reflects the image light incident from the surface of the screen on the surface of the screen, and a type that diffuses the image light incident from the surface of the screen on the surface of the screen and reflects it from the internal reflective layer. Background Art

[0003] Reflective screens have a phenomenon called hot spots, in which incident image light appears as bright spots on the screen surface. Another phenomenon called reflection occurs in which the brightness of overhead lights and windows near the screen is reflected on the screen surface and is visible.

[0004] To prevent these phenomena, a conventional method is to provide a surface-shaped diffusion layer with a concave-convex surface with a pitch of several μm to several tens of μm on the screen surface. This diffuses the hot spots and incident light on the screen surface, making them less noticeable (see Patent Document 1). The combination of this surface-shaped diffusion layer and a substrate serving as its base is referred to as a surface-shaped diffusion sheet.

[0005] However, when the surface of the surface-shaped diffusion layer serves as the screen surface, not only the image light from the projector but also external light (unnecessary light other than the image light) from the ceiling light, the floor, and the walls and windows in front of the screen also diffuses on the screen surface. Furthermore, some of this light is reflected toward the front side of the screen, while the remainder reaches the reflective layer inside the screen, where it is reflected and emitted toward the front side. This so-called diffused and reflected external light is superimposed on the image light, generating so-called noise light, which degrades the image quality of the object being observed.

[0006] This phenomenon particularly increases the brightness of black in an image, and is therefore called "blooming".

[0007] If blackening is caused by external light, the contrast, grayscale expression and color reproduction of the image will be greatly damaged. The image will not look three-dimensional, the black will not be tight but gray, and the image as a whole will not be bright in color. It will look thin and blurry, making it difficult to reproduce the image clearly.

[0008] This darkening depends on the intensity of external light, so it can be prevented by turning off overhead lights and using curtains to block external light from reaching the screen. However, in classrooms and corporate meeting rooms, activities such as viewing large displays, checking each other's expressions, reviewing documents, and taking notes are also important. If these activities are impeded by darkening the room, the efficiency of lectures and meetings will be significantly reduced.

[0009] On the other hand, there are also methods of using liquid crystals, OLEDs, or micro LEDs with less black coverage as large displays for use in lectures and meetings, but these require large displays of 80 inches or more. In order to mass-produce these displays, large-scale manufacturing equipment and manufacturing processes consume a large amount of medicines, water, electricity, etc., which is too heavy an environmental burden from the perspective of SDGs (Sustainable Development Goals). In addition, due to the large size, weight, and power consumption of the display body, it is difficult to transport and install, and the price is also expensive, making it difficult to widely popularize. Due to the above situation, there is an increasing need to develop an image display system that uses a reflective screen that can reproduce high-quality images even in a bright environment affected by external light.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent No. 5971742 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] As mentioned above, when blackout occurs due to external light, the contrast, grayscale representation, and color reproducibility of the image projected on the reflective screen are significantly affected. Since contrast is expressed as the ratio of the brightness of white to the brightness of black, contrast deteriorates by the amount that the brightness of black increases due to blackout. Similarly, grayscale representation is determined by the difference between the brightness of white and black, so the brightness range of grayscale representation narrows by the amount that the brightness of black increases.

[0015] The conventional approach to addressing the aforementioned contrast and grayscale issues is to increase the brightness of white on the projector side by an amount corresponding to the amount of black cast. Currently, the image light output of commercially available projectors for schools and offices is high, with a maximum output of around 4,000 lumens.

[0016] On the other hand, there are currently few measures to address the deterioration in color reproducibility caused by black cast. Even in reflective projection displays using high-output projectors, the following problem persists: in bright environments affected by external light, original colors cannot be reproduced, and color reproducibility deteriorates proportionally to the brightness of the black cast.

[0017] Therefore, the present invention provides a surface-shaped diffusion sheet that reduces image quality degradation caused by external light from overhead lighting, which has the greatest impact on blackout, and further, by all external light, in bright environments of a reflective screen, and a reflective screen equipped with the surface-shaped diffusion sheet. Furthermore, the present invention provides an image display system and an image display method that can reduce degradation in the color reproducibility of images on the reflective screen and correct any degraded image color reproducibility.

[0018] Solutions for solving problems

[0019] To address the above-mentioned problem, the present inventors conducted intensive research and found that an effective solution is to use a surface shape diffusion layer of the surface shape diffusion sheet as a surface shape anisotropic diffusion layer that restricts the diffusion angle in the vertical direction, and to reduce the transmittance of a substrate serving as a base for the surface shape anisotropic diffusion layer in the visible light wavelength band. Furthermore, the present inventors found that the deterioration of image color reproducibility can be quantified by expressing black cast using numerical values ​​in the RGB color model.

[0020] The present inventors have further studied based on the above findings and have completed the present invention.

[0021] [1] A surface-shaped diffusion sheet provided on the surface of a reflective screen for diffusing image light emitted from an image projection device, wherein the surface-shaped diffusion sheet reduces blackening and is characterized by:

[0022] a surface anisotropic diffusion layer; and

[0023] a flat substrate, which is the base of the surface anisotropic diffusion layer,

[0024] wherein the diffusion angle in the vertical direction of the surface of the surface anisotropic diffusion layer is within the range of ±14° (half-value width),

[0025] The transmittance T of the visible light wavelength band inside or on the surface of the substrate is within a range of 0.5 or more and less than 1.

[0026] [2] A reflective screen having a diffusion sheet on its surface, wherein:

[0027] The diffusion sheet is a diffusion sheet having a surface shape according to [1],

[0028] The reflective screen includes a reflective layer, a protective film, and a retaining plate that are sequentially arranged and bonded from the substrate toward the back side.

[0029] The bonding surface between the reflective layer and the substrate becomes a surface for reflecting the image light.

[0030] The protective film is a film covering the reflective layer,

[0031] The holding plate is a plate for maintaining the flatness of the substrate.

[0032] [3] The reflective screen according to [2], characterized in that:

[0033] It also includes a lens layer, which is arranged and bonded between the substrate and the reflective layer.

[0034] The lens layer is composed of a Fresnel lens having a reflective surface shape on the back side.

[0035] The bonding surface between the reflective layer and the lens layer serves as a surface for reflecting the image light.

[0036] [4] The reflective screen according to [3], characterized in that:

[0037] The image light is reflected from the aperture surface of the projection lens of the image projection device, which is separated from the surface reflecting the image light by a distance a with respect to the focal length f of the Fresnel lens, thereby forming a spatial imaging aperture surface at a position separated by a distance b, where b satisfies the relationship (1 / a)+(1 / b)=1 / f.

[0038] [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 flooding calculation unit, and a brightness adjustment unit, wherein:

[0039] The image projection device projects image light,

[0040] The luminance meter measures the luminance of black (R=0, G=0, B=0) and white (R=255, G=255, B=255) in an RGB color model projected from the image projection device onto the reflective screen under external light to obtain respective measurement values ​​Kmin and Kw.

[0041] The black flooding amount calculation unit calculates the black flooding amount Lb as the integer part of the value of the formula: 255×Kmin / Kw,

[0042] The brightness adjustment unit corrects the brightness reduction observed within the brightness range Lb≤L<2Lb of the brightness L of each element in the image that is washed out from black (R=Lb, G=Lb, B=Lb).

[0043] [6] The image display system according to [5], characterized in that:

[0044] An image light output adjustment unit is provided in place of the brightness adjustment unit or in addition to the brightness adjustment unit.

[0045] The image light output adjustment unit increases the brightness of the white light from Kw to Kw×(1+2Lb / 255) to reduce black cast.

[0046] [7] An image display method using the reflective screen according to any one of [2] to [4] and an image projection device for projecting image light, the image display method comprising the following steps:

[0047] 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;

[0048] Measuring the brightness of the black and white colors under external light to obtain respective measurement values ​​Kmin and Kw;

[0049] The blackening amount Lb is calculated as the integer part of the value of the formula: 255×Kmin / Kw; and

[0050] The brightness adjustment step corrects the brightness reduction observed within the brightness range Lb≤L<2Lb of the brightness L of each element in the image that has been blackened (R=Lb, G=Lb, B=Lb).

[0051] [8] The image display method according to [7] is characterized in that it has an image light output adjustment process instead of or in addition to the brightness adjustment process, and in the image light output adjustment process, the brightness of the white is increased from Kw to Kw×(1+2Lb / 255) to reduce blackening.

[0052] Effects of the Invention

[0053] According to the present invention, it is possible to reduce the blackening caused by external light, most notably overhead lighting, on reflective screens in bright environments. Furthermore, even if the blackening causes deterioration in image color reproducibility, this deterioration can be corrected, and further, the deterioration in color reproducibility can be prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a schematic diagram showing an example of the surface shape diffusion sheet according to the present invention.

[0055] Figure 2 It shows that Figure 1 An example of a reflective screen with a surface shape diffusion sheet and a schematic diagram of the configuration of an image projection device.

[0056] Figure 3 (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, the reflective screen, the projector, and the measuring device (luminance meter) in the blackout measurement.

[0057] Figure 4 (a) is a schematic diagram showing an example of a reflective screen according to the present invention, and (b) is a cross-sectional view of (a) in the screen thickness direction.

[0058] Figure 5 (a) is a schematic diagram showing another example of the reflective screen according to the present invention, and (b) is a cross-sectional view of (a) in the screen thickness direction.

[0059] Figure 6 (a) is a schematic diagram showing another example of the reflective screen according to the present invention, and (b) is a cross-sectional view of (a) in the screen thickness direction.

[0060] Figure 7 This is a schematic diagram showing ray tracing of incident light and reflected light of external light by the Fresnel lens of the spatial imaging aperture surface system / reflective screen according to the present invention.

[0061] Figure 8 It is a schematic diagram showing an example of an internal optical system of the image projection device.

[0062] Figure 9 : is a diagram showing a visual object display pattern used to study the relationship between black cast and color reproducibility.

[0063] Figure 10 The figures show the visual object display patterns used in the measurement of the brightness reduction amount. (a) shows an example of the case where the brightness of the visual object = 230 and the black cast amount = 215, and (b) shows an example of the case where the brightness of the visual object = 230 and the black cast amount = 115.

[0064] Figure 11 This is a line graph showing the relationship between the amount of black cast and the amount of reduction in brightness of the visual object, using the brightness of the visual object as a parameter.

[0065] Figure 12This is a line graph showing the relationship between the brightness of a visual object and the amount of brightness reduction, using the amount of black cast as a parameter.

[0066] Figure 13 The figures show visual object display patterns for confirming the brightness range that does not cause a decrease in the brightness of the visual object when the black level is set to 100. (a) is a pattern in which the brightness of the visual object is set to be the same on the left side (black level = 0) and the right side (black level = 100), and (b) is a pattern in which the brightness of the visual object on the right side is increased so that the visual object appears to have the same brightness on the left and right sides.

[0067] Figure 14 The figures show display patterns of visual objects for confirming reduced brightness, with the black level set to 255, the visual object set to white in (a), and the visual object set to green in (b).

[0068] Figure 15 This is an explanatory diagram showing a correction method for brightness reduction in a color non-reproducible brightness range when the black cast amount = 78.

[0069] Figure 16 This is an explanatory diagram showing that the change in the brightness reduction amount relative to the brightness of the visual object in the color non-reproducible brightness range can be represented by, for example, a curve having the same shape as the curve A in the figure.

[0070] Figure 17 This is a flowchart showing a procedure for obtaining a value of the black cast amount in the RGB color model.

[0071] Figure 18 Graph showing the blackening lightness range, the color non-reproducible lightness range, and the color reproducible lightness range when the blackening amount is 78. DETAILED DESCRIPTION

[0072] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0073] (Surface shape diffusion sheet according to the present invention: [1] of the present invention)

[0074] First, the surface shape diffusion sheet according to the present invention will be described.

[0075] Figure 1 This is a schematic diagram showing the surface shape diffusion sheet 1 involved in the present invention. Figure 2 As shown in FIG. 5 , the image light from the image projection device 5 is reflected and diffused. Figure 8As shown, the image light from a three-primary-color light source 130, for example, composed of LED chips, passes sequentially through a diffusion film laminate 122, relay lenses 120a and 120b, and a digital mirror device 134. It then passes through a projection optical system 138 composed of multiple lenses, is sequentially reflected by a concave reflector 140 and a convex reflector 142, and is then transmitted to a reflective screen 4. Furthermore, light that does not reach the screen is shielded by a light shielding plate 136. The projection optical system 138 has an aperture, and the space inside this aperture is referred to as an aperture surface 18.

[0076] like Figure 1 As shown, the surface shape diffusion sheet 1 includes a surface shape anisotropic diffusion layer 2 and a flat substrate 3 located as a base of the surface shape anisotropic diffusion layer 2 .

[0077] The anisotropic surface shape diffusion layer 2 is made of ultraviolet curable resin such as urethane acrylate and epoxy acrylate, or other ionizing radiation curable resin such as electron beam curable resin, and has flexibility.

[0078] The anisotropic surface diffusion layer 2 has a surface configuration in which numerous ridges of irregular length extending in a generally uniform direction are arranged laterally at irregular intervals in a direction perpendicular to the direction of extension. The height of the ridges is preferably greater than 0 μm and less than 10 μm. Here, the ridges extend in the vertical direction, and are arranged in the horizontal direction. This surface configuration results in a greater diffusion angle in the horizontal direction than in the vertical direction. The vertical and horizontal diffusion angles can be set to various values ​​by varying the manufacturing conditions.

[0079] The substrate 3 is made of, for example, a transparent resin material and has flexibility. From the perspective of achieving both strength and weight reduction, the substrate thickness is preferably 50 μm or more and 250 μm or less.

[0080] The reflective screen 4 having the anisotropic diffusion layer 2 on the surface has a reflective layer 8 inside the screen and a retaining plate 10 for maintaining the flatness of the substrate 3 on the back side of the screen. Figure 2 In the reflective screen 4 , as a preferred embodiment, the reflective layer 8 has a Fresnel lens surface shape as the surface on which the incident light arrives in order to deflect the incident image light in the normal direction of the screen surface.

[0081] In the present invention, it is defined that the diffusion angle in the vertical direction of the surface of the surface anisotropic diffusion layer 2 is within the range of ±14° (half-value width), and the transmittance T of the visible light wavelength band inside or on the surface of the substrate is within the range of 0.5 or more and less than 1. Before explaining the reasons for these limitations, Figure 2Let's explain blackening in more detail.

[0082] like Figure 2 In that way, in the reflective screen 4 that makes the image light from the image projection device 5 on the front side reflected by the reflective layer 8 and diffused and emitted again to the front side, in addition to the image light, external light from the ceiling light 11 and other places (floor, front wall, window) also enters the screen surface. These external lights are diffused on the screen surface (the surface of the anisotropic diffusion layer 2), part of which is reflected on the screen surface toward the front side, and the rest reaches the reflective layer 8 inside the screen and is reflected by the reflective layer 8, and is emitted from the screen surface toward the front side. The diffuse reflected light caused by these external lights (hereinafter referred to as the diffuse reflected light caused by external light) is superimposed on the image light, causing the image to be blackened. In addition, in Figure 2 In the figure, only the incident image light and the principal rays of external light are shown, and the diffuse light is not shown.

[0083] (Diffusion angle of surface anisotropic diffusion layer)

[0084] In order to reduce the blackening caused by the external light from the top light 11, which has the greatest impact, in the present invention, Figure 1 The diffusion angle of the anisotropic diffusion layer 2 of the surface profile diffusion sheet 1 shown in the figure is set within a range of ±14° (full width at half maximum) in the vertical direction. The diffusion angle range is an angle range within which either a clockwise or counterclockwise angle is considered positive and the other is considered negative, with the normal direction being 0° relative to the screen surface, in a vertical plane perpendicular to the reflective screen surface in the vertical direction.

[0085] In the present invention, the use Figure 3 (a) of FIG. 1 illustrates the reason for setting the vertical diffusion angle to be within the range of ±14° (half-value width). Figure 3 (a) shows the general positional relationship between a reflective screen 4A and a ceiling light 11 for studying diffusion angles. The reflective screen 4A is not shown except for the surface-shaped diffusion layer 2A provided on its surface. The surface-shaped diffusion layer 2A is designed to achieve various diffusion angles θ in the vertical direction for studying diffusion angles.

[0086] When Figure 3When the longitudinal dimension of the reflective screen 4A is set to 1H, it is assumed that the observation position 60 of the reflective screen 4A is 2H to 3H away from the center of the screen, and the ceiling light 11 is located approximately 0.5H above the reflective screen 4A and at positions 0.5H, 1H, 1.5H, and 2H away in the front direction. In addition, the diffuse reflected light of the external light caused by the ceiling light 11 is likely to reach the observation position when it is incident on the uppermost part of the reflective screen 4A. In addition, the brightness of the external light incident on the uppermost part is inversely proportional to the square of the distance r from the ceiling light, so the position of 0.5H is the brightest. On the other hand, the observation position is easily reached at 1.5H and 2H. Therefore, the position of the ceiling light 11 where the influence of external light is the worst is determined by the interaction between the brightness of the external light and the reflection angle of the diffuse reflected light of the external light. Figure 3 In the case of the top light 11 at the position of 1H, it is almost the worst condition. Under this worst condition, the diffuse reflected light of the external light reaches the observation position 2H ~ 3H as follows Figure 3 As shown in FIG. 1 , the upward diffusion angle θ of the principal ray 61 of diffusely reflected light from the ceiling light 11 at position 1H is 14.6° or greater (greater than 14°). This is of course the same even when 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 surface shape anisotropic diffusion layer 2 is set within the range of ±14° (full width at half maximum).

[0087] Thus, the diffusely reflected light of the external light diffusely reflected on the screen surface does not reach the vicinity of the eyes of the observer located in the front. In addition, it is preferable that the diffusion angle in the left-right direction is as large as possible.

[0088] (Determination of blackening)

[0089] Next, in order to evaluate the blackening reduction effect of setting the diffusion angle of the surface anisotropic diffusion layer to a range of ±14° (half-value width), the Figure 1 The blackening caused by external light from the ceiling light was measured by using a surface anisotropic diffusion layer 2. As a diffusion sheet for measurement, a sheet having a surface anisotropic diffusion layer formed on a transparent substrate was used. Figure 1The diffusion sheet has a surface anisotropic diffusion layer 2 with a surface shape like that. The diffusion angle of the measurement diffusion sheet, when measured as the diffusion angle of transmitted light incident perpendicularly from the shape side (front side), is ±5° (full width at half maximum). Since an aluminum reflective layer is provided on the back side of the substrate, the diffusion angle of the measurement diffusion sheet, when measured as the diffusion angle of reflected light after the transmitted light is reflected by the reflective layer, is ±10° (full width at half maximum). Therefore, the surface shape diffusion value (the diffusion angle of the surface anisotropic diffusion layer of the measurement diffusion sheet) is considered to be within the range of ±14° (full width at half maximum). However, the diffusely reflected light from the overhead light also includes light that reaches the reflective layer inside the screen, is reflected by the reflective layer, and then exits the screen surface.

[0090] replace Figure 2 The surface shape of the diffuse sheet 1 is prepared as the reflective screen (called SHL screen 82) of the diffuse sheet for measurement, and the reflective screen 82 is prepared as the reflective screen 82 of the diffuse sheet for measurement. Figure 2 The measurement was performed using the arrangement shown in the figure. In addition, for comparison, the same measurement was performed using a commercially available magnetic blackboard screen (referred to as white matte screen 81).

[0091] exist Figure 3 (b) shows the positional relationship between the ceiling light 11, the SHL screen 82 (or the white matte screen 81), the projector 5, and the measuring device (luminance meter 30). Figure 3 (b) The positional relationship between the top light 11 and the SHL screen 82 and Figure 3 The positional relationship between the top light 11 and the reflective screen 4A in (a) is substantially the same. Measurements were performed only when the observation position was set to 2H, which is a more stringent condition than 3H.

[0092] The equipment types shown in Table 1 were used for the measurements. Table 2 shows the illuminance of the ceiling light 11 at the center of each screen. Table 2 also shows the measured illuminance of the table directly below the ceiling light (illuminometer not shown) as a reference value, but this indicates that the room used for the measurements was relatively brightly lit.

[0093] Table 3 shows the results of the blackout measurement. Table 3 confirms that the blackout (brightness during a completely black display) on the SHL screen was reduced by approximately 60% (= (1-35 / 88) × 100) compared to the white matte screen used for comparison. Furthermore, since the brightness during a completely black display and when the projector is off are roughly the same, the blackout can also be measured as the brightness when the projector is off.

[0094] [Table 1]

[0095] Measurement conditions

[0096] projector EH-LS500 Projector configuration Figure 3 (b) Displaying images Media player HDMI output (full white, full black image) indoor lighting Full brightness Luminance meter LS-110

[0097] [Table 2]

[0098] Ceiling light illumination measurement results (unit: lx)

[0099] Center of the screen The tabletop directly below the ceiling light Illumination 410 750

[0100] [Table 3]

[0101] Blackening test results (unit: cd / m 2 )

[0102]

[0103] (Transmittance T of substrate)

[0104] Next, the reason why the transmittance T of the visible light wavelength band inside or on the surface of the substrate 3 is set to be within the range of 0.5 or more and less than 1 in the present invention will be explained. Here, the transmittance T refers to the ratio of incident light of a specific wavelength that passes through the substrate, T = I / I0, I0 is the radiant divergence of the incident light, I is the radiant divergence of the light that has passed through the substrate (unit: W / m 2 ), since I0≥I, so T≤1.

[0105] This measure is also necessary because the diffusely reflected light from the overhead light includes light that reaches the reflective layer inside the screen, is reflected by the reflective layer, and then exits the screen surface. As a measure against external light that passes through substrate 3 twice, the present invention imparts a transparent to black hue to the interior or surface of substrate 3 in order to reduce the transmittance T of the visible light wavelength band. Furthermore, reducing the transmittance T of the visible light wavelength band inside or on the surface of substrate 3 is called transparent blackening. Thus, blackening reduces the amount of darkening caused by external light that passes through substrate 3 twice. Regardless of whether the area of ​​substrate 3 where the transmittance T is reduced is inside or on the surface of substrate 3, blackening is reduced.

[0106] In previous diffuser sheets, the transmittance T was typically increased to make image light as bright as possible. In the present invention, while this also presents the drawback of darkening the image light, the priority is to minimize the deterioration of image quality caused by blackening. This is because, against this backdrop, the evolution of projector light sources from lamps to LEDs, and further to lasers, has made it possible to brighten image light. However, even if this brightens the image light, if the transmittance T is less than 0.5, the image becomes too dark. Therefore, 0.5 is set as the lower limit for the transmittance T. Preferably, 0.7 is set as the lower limit.

[0107] Here, a method for achieving the above-mentioned transparent blackening is described. As one of the methods, a method of uniformly mixing an appropriate amount of UV (ultraviolet rays, the same below) black transparent dispersion into the resin serving as the material of the substrate 3 is cited (transparent blackening inside the substrate). Since the surface shape anisotropic diffusion layer 2 of the surface shape diffusion sheet 1 is formed on the substrate 3 by UV polymerization, the substrate 3 used in the UV polymerization needs to have the characteristics of allowing UV light to pass through and uniformly reducing the transmittance of visible light. The UV black transparent dispersion is a dispersion obtained by finely granulating a pigment having the characteristics of being black (uniformly absorbing visible light) and allowing UV to pass through. It is compatible with resins such as polyurethane resin, acrylic resin, ester resin, etc. serving as the material of the substrate 3. Therefore, the inside of the substrate can be transparently blackened by uniformly mixing an appropriate amount of the dispersion into the resin serving as the material of the substrate.

[0108] In addition, as a method of transparent blackening, in addition to the method of mixing the black dispersion into the substrate material, a method of applying the black dispersion to the resin plate of the substrate material (transparent blackening of the substrate surface) or a method of vapor-depositing metal onto the resin plate like an ND filter (transparent blackening of the substrate surface) can also be adopted.

[0109] Furthermore, the substrate 3 has flexibility, and in order to achieve a balance between strength and weight reduction, the substrate thickness is preferably 50 μm or more and 250 μm or less.

[0110] (Confirmation of the Blackening Reduction Effect of the Surface Shape Diffusing Sheet According to the Invention)

[0111] In the above-mentioned blackening measurement, the same measurement was conducted using a sample screen having the surface-shaped diffusion sheet 1 according to the present invention on its surface. This sample screen was identical to the SHL screen 82, except that the transmittance T inside the substrate was reduced to 0.9 by the transparent blackening described above. The results confirmed that the blackening (brightness when displaying a completely black display) of this sample screen was approximately 30 cd / m². 2 , which is reduced by about 66% (= (1-30 / 88) × 100) compared to the white matte screen. In this sample screen, by reducing the transmittance of the substrate, the blackening is better than that of the SHL screen 82 (about 35 cd / m 2 ) has decreased.

[0112] (Reflective screen according to the present invention: [2] of the present invention)

[0113] Next, the reflective screen according to the present invention will be described. This reflective screen is a reflective screen having a surface-shaped diffusion sheet 1 according to the present invention. Figure 4In the illustrated embodiment, a reflective layer 8 , a protective film 9 , and a holding plate 10 are provided, which are sequentially arranged and bonded from the substrate 3 toward the back surface side.

[0114] The bonding surface between the reflective layer 8 and the substrate 3 reflects image light. The protective film 9 covers the reflective layer 8 from the back side. The holding plate 10 maintains the flatness of the substrate 3 .

[0115] (Reflective layer)

[0116] The reflective layer 8 is preferably formed by vapor-depositing a thin layer of a metal with high reflectivity (reflectivity of 70% or more), such as aluminum, silver, or nickel, to provide flexibility, or by applying thin aluminum flakes, called aluminum flakes, with their surfaces aligned parallel to each other. The thickness of the reflective layer 8 is 0.5 to 0.9 μm for vapor deposition and 10 to 50 μm for coating, depending on factors such as peelability, reflectivity, and bending strength.

[0117] (Protective film)

[0118] The protective film 9 is flexible and protects the reflective layer 8 by suppressing degradation, peeling, and damage to the reflective layer 8. Furthermore, the protective film 9 absorbs light. Examples of materials for the protective film 9 include a base material made from a blend of polyurethane resins, epoxy resins, acrylic resins, or other resins, to which a dark-colored paint, dye, or pigment, or beads containing such materials, such as black, are added as a light-absorbing material, along with various additives that protect the reflective layer 8 from degradation, such as oxidation. To fully demonstrate both the protective and light-absorbing functions, the protective film 9 preferably has a thickness of 5 to 100 μm at its thinnest point.

[0119] (Retaining plate)

[0120] The retaining plate 10 maintains the flatness of the substrate 3 (specifically, the flatness of the entire structure from the surface shape diffusion sheet 1 to the protective film 9). To achieve a balance between rigidity and lightweight, it is preferably constructed from, for example, MDF, which is made by compressing wood fibers with a thickness of 1.0 mm to 3.0 mm and affixing them with an adhesive. The retaining plate 10 is attached to the protective film 9 via a bonding layer (not shown) made of an adhesive such as double-sided tape. The retaining plate 10 prevents deformation during transport and facilitates installation, such as hanging on a wall using a hook or the like.

[0121] Alternatively, a structure in which a magnet sheet (not shown) having a thickness of 300 μm to 400 μm is adhered may be employed instead of the holding plate 10 .

[0122] exist Figure 4In the example shown in FIG. 1 , the thickness of the anisotropic surface 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 image light, image light from the left and right ends is unlikely to reach the observation position. Therefore, the left-right diffusion of the anisotropic surface diffusion layer 2 is preferably completely diffused in all directions.

[0123] (Fresnel lens as lens layer: [3] of the present invention)

[0124] Next, one embodiment of the invention using a Fresnel lens in a reflective screen is described. Figure 4 The images on the left and right sides of the screen are darkened, so it is best to use a Fresnel lens. Figure 5 As shown, in one embodiment using a Fresnel lens, there is a reflective screen as follows: it has a lens layer 6 arranged and bonded between a substrate 3 and a reflective layer 8, the lens layer 6 is composed of a Fresnel lens having a reflective surface shape on the back side, and the bonding surface between the reflective layer 8 and the lens layer 6 becomes a surface that reflects the image light.

[0125] The lens layer 6 is made of a UV-curable resin such as urethane acrylate or epoxy acrylate, or another ionizing radiation-curable resin such as an electron beam-curable resin. It is flexible and has a thickness-direction boundary consisting of a Fresnel lens surface, with a flat surface on the front side and lens surfaces 6a and non-lens surfaces 6b alternating in a concentric arc arrangement on the back side. The thickness of the lens layer 6 is designed to be minimized to a maximum of approximately 50 μm. Furthermore, the radial dimension of the Fresnel lens on the lens surface 6a is approximately 100 to 150 μm, while the radial dimension of the Fresnel lens on the non-lens surface 6b is approximately 10 μm at most. An ideal Fresnel lens is one with a radial dimension of 0 μm.

[0126] form Figure 5 The Fresnel lens of the lens layer 6 of the reflective screen 4 shown in the figure has a focal length f, and deflects the image light from the image projection device 5 in the normal direction of the screen surface. Therefore, the focal length f is related to the distance from the screen surface to the image projection device 5, and more specifically, to the space inside the aperture of the projection optical system 138 of the image projection device 5, that is, the aperture surface 18 (see Figure 8 However, the “consistent” here allows an error within ±10%.

[0127] Therefore, since the main light 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 anisotropic diffusion layer 2 and is Figure 4 Easier to reach the observation position.

[0128] exist Figure 5In (b), the lens layer 6 composed of Fresnel lenses can be formed directly on the back of the substrate 3 of the surface-shaped diffuser sheet 1 by UV polymerization, but the sheet-like Fresnel lens can also be adhered to the back of the substrate 3. In order to make the Fresnel lens reflective, it is covered with a reflective layer 8 made of thin small pieces of aluminum called aluminum sheets aligned parallel to the transparent surface, and a protective film 9 is applied to its surface for protection. Since the thickness of this reflective screen is about 400 μm excluding the retaining plate 10, in order to make it a flat screen without bumps, it is preferably adhered to the retaining plate 10 with a thickness of 1.0 mm to 3.0 mm. In addition, instead of the retaining plate 10, a screen with a magnetic sheet (not shown) attached thereto can be directly adhered to a plate or wall with a magnet.

[0129] (Spatial imaging aperture surface method: [4] of the present invention)

[0130] Next, another embodiment in which a Fresnel lens is used in the reflective screen according to the present invention will be described.

[0131] In this embodiment, if Figure 6 As shown, the reflective screen 4 reflects the image light from the projection lens of the image projection device 5 separated by a distance a from the surface reflecting the image light with respect to the focal length f of the Fresnel lens (see Figure 8 ) of the image light, thereby forming a spatial imaging aperture surface 20 at a position separated by a distance b, where b satisfies the relationship (1 / a)+(1 / b)=1 / f. In addition, the distances a and b are allowed to have an error within ±10% relative to the values ​​satisfying the above relationship.

[0132] Should Figure 6 The implementation method and Figure 5 The embodiment of the invention is different from the Fresnel lens in that only the lens layer 6 is formed. Figure 5 The lens layer 6 (Fresnel lens) shown in FIG. 5 deflects the image light from the image projection device 5 toward the normal direction of the screen. Figure 6 In the embodiment, the image light is focused to a position separated from the front of the screen by a distance b. Optically, the focal lengths f are different from each other. Figure 6 Such an optical system is called a spatial imaging aperture surface system. Therefore, the reflective screen of this embodiment is also called a spatial imaging aperture surface system reflective screen.

[0133] (Behavior of external light on a spatial imaging aperture-type reflective screen)

[0134] Figure 7This is a ray tracing diagram of incident and reflected external light from the Fresnel lens of a reflective screen using a spatial imaging aperture surface. External light 51 from floor 13 enters lens surface 6a of the Fresnel lens of reflective screen 4 from the same direction as image light 50 from image projection device 5, causing blackening.

[0135] In addition to this external light 51, external light 52 incident on lens surface 6a from ceiling light 11 and front window 12 is deflected by lens surface 6a so as not to reach spatial imaging aperture surface 20, thus not causing blackout. On the other hand, portions of external light 53 and 54 incident on non-lens surface 6b from ceiling light 11 and front window 12, respectively, reach spatial imaging aperture surface 20, thus causing blackout.

[0136] According to the surface shape diffusion sheet 1 involved in the present invention, it is possible to reduce the blackening caused by external light 51 to 54. However, in order to further reduce the blackening caused by external light 53 and 54, it is preferred to make the inclination of the non-lens surface 6b of the Fresnel lens perpendicular to the screen surface in the same direction as the screen normal, or exclude the non-lens surface 6b from the coverage of the reflective layer (for example, a metal film) so that the non-lens surface 6b does not become a reflective surface, or cover it with an absorption film that absorbs light instead of the reflective layer.

[0137] (Image display system according to the present invention: [5] and [6] of the present invention)

[0138] Next, the image display system according to the present invention will be described. The image display system comprises the reflective screen 4 according to the present invention and an image projection device 5 for projecting image light (in Figure 8 In addition, as the image projection device 5, it is not limited to Figure 8 The image projection apparatus exemplified in FIG. 1 may include various projectors available on the market.

[0139] Under the above premise, there is a problem: in bright environments affected by external light, the brightness of black increases due to blackout, which casts the image gray, impairing color vividness and rendering the original color impossible. To address this issue, the inventors have repeatedly studied the relationship between blackout and color reproducibility. As a result, they have discovered that by expressing the brightness of blackout as the amount of blackout using numerical values ​​from the RGB color model, it is possible to quantify the deterioration in color reproducibility. The following describes the process of this research.

[0140] (Amount of blackening)

[0141] In the RGB color model, the elements of RGB are represented by R = 0-255, G = 0-255, and B = 0-255. The values ​​0-255 are integers called value (brightness), indicating 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.

[0142] On the other hand, the brightness of the black color measured by the luminance meter (cd / m 2 ) is the minimum brightness measured on the screen when projecting absolute black (R=0, G=0, B=0) under external light. Therefore, it can be expressed relative to the maximum brightness (cd / m2) when projecting white (R=255, G=255, B=255). 2 ) ratio, that is, relative brightness (0 to 1), to express blackness.

[0143] However, the color of the image observed in the blackout state is also represented by the brightness of each element of the RGB color model (0 to 255), just like the color of the projection light from the image projection device 5. Therefore, when quantifying the influence of blackout on the color reproducibility of the color of the image observed on the screen, it is considered easier to organize the relationship between the color of the image and the blackout state by expressing the blackout state with the brightness of each element of the blackout = 255×(relative brightness of black) than by expressing it with the relative brightness of black. Therefore, hereinafter, the blackout state is represented by the brightness of each element of the blackout, and the value of this brightness (assuming the brightness of each element of black is the same) is called the "blackout amount". The symbol for the blackout amount is Lb. That is, the definition of the blackout amount Lb is Lb=255×(relative brightness of black).

[0144] However, since lightness is an integer as described above, the integer part of the value of this formula is used. Here, although the integer part can be the value obtained by rounding off, discarding, or carrying up the decimal point of the calculated value, the rounded value is used below.

[0145] For example, in the case of the SHL screen in Table 3, the brightness of the black is 35.59 cd / m 2 The white brightness is 994.3cd / m 2 , so the blackening amount is Lb = 255 × 35.59 / 994.3 = 9.

[0146] Therefore, in the above study, red (R), green (G), blue (B) and the white obtained by mixing them in the RGB color model of the colors that constitute the image were selected as visual objects. Then, the brightness of the visual object was changed in various ways, and the amount of blackening was changed in various ways with a black background equivalent to black that has been blackened, and the visual object was observed. As a result, in the range where the brightness of the visual object is greater than Lb and less than 2Lb, a "brightness reduction" occurs, in which the brightness of the visual object decreases relative to the reference value in appearance. In addition, the reference value here refers to the brightness of the visual object when the background is black without blackening (RGB is all 0, that is, the amount of blackening = 0). In addition, when the brightness of the visual object is less than Lb, it is a so-called blackened state in which the grayscale representation of black cannot be performed.

[0147] (Visual experiment of brightness reduction)

[0148] The following describes a visual experiment of brightness reduction for determining the relationship between the amount of blackening and the amount of brightness reduction of a visual object. Figure 9 As shown, in the screen of the liquid crystal display, the brightness (0 to 255) of each element of the RGB color model is used to compare the black rectangle with no blackening (blackening amount = 0) on the right with the arbitrary blackening amount (in the range of 0 to 255) on the left. Figure 9 In the image, black rectangles (with a black cast amount of 215, i.e., RGB values ​​of 215) are connected and displayed. Next, circles representing the colors of the visual object are placed within each rectangle. The diameter of the circles is 1.2 cm, and the viewing distance is set to approximately 30 cm. The left and right colors are viewed from the front, and the presence or absence of differences in brightness between the colors is visually observed. The results show that when the black cast amount is 215, the colors of the visual object appear darker than the basic colors when the black cast amount is 0. When black cast occurs, the image becomes gray, and the vividness of the colors is impaired. This is believed to be because the apparent brightness of each color is lower than the baseline value (brightness when the black cast amount is 0) due to black cast, resulting in impaired color reproducibility.

[0149] exist Figure 9 In the experiment, the image (the visual object and the background) displayed on the liquid crystal screen was visually observed. However, when the brightness of the image was measured, the brightness of black (R=0, G=0, B=0) was 1.5 cd / m 2 , white (R=255, G=255, B=255) is 85 cd / m 2 .

[0150] And, even with Figure 9 The image on the LCD screen is the same as the image from Figure 3The image projection device 5 of (b) is projected onto the SHL screen 82 and the aforementioned sample screen, and it can be seen that the colors with a blackout amount of 215 are darker than the colors with a blackout amount of 0 (basic colors), which is also observed in the same way as the situation displayed on the screen of the LCD display.

[0151] Next, in order to quantitatively measure the brightness reduction of each color as a visual object relative to the reference value, as shown in FIG. Figure 10 As shown in (a), in the right rectangle, the brightness of each color is written on the right side of the circle of the visual object. Figure 9 The same is true for the rectangle on the left. A circle is added to the upper part of each visual object to compensate for the brightness reduction of the lower part so that it looks the same as the colors on the right (colors with the same brightness as the reference value). On the left side of each visual object, the brightness is recorded in the same way as on the right. Figure 10 In (a), it is shown that the lightness of each color is reduced by about 18 from the reference value when the blackening amount is set to 215. This value is considered to depend on individual vision and was determined by observation by 5 people. Figure 10 (b) is a graph in which the amount of blackening is varied and the amount of blackening that makes the brightness on the right and left sides the same is obtained. It can be seen from this that when the brightness of the visual object is 230, if the amount of blackening is set to 115 or less, the brightness of the visual object will not be reduced. Figure 10 The same method is used to measure the brightness of the visual object (in Figure 10 In the example, the brightness of the visual object = 230) is used as a parameter to determine the brightness reduction amount of the visual object corresponding to the amount of blackening. Figure 11 As can be seen from the figure, the amount of blackening that begins when the brightness of the visual object decreases is equal to the brightness of the visual object / 2.

[0152] then, Figure 12 This is a graph that examines the relationship between the brightness of a visual object and the amount of brightness reduction using the amount of blackening as a parameter. According to this graph, when the brightness of a visual object becomes more than twice the amount of blackening, the brightness of the visual object will not be reduced. Figure 13 (a) and (b) show visual object patterns prepared to confirm the range of visual object brightness that does not cause a decrease in the brightness of the visual object when white of various brightnesses (brightness is set to L, R=L, G=L, B=L, L=255, 230, 200, 170, 135, 115) is used as the visual object and the black level is set to 100 as the background. It can be confirmed that the brightness does not decrease when the brightness of the visual object is 200 or more, which is more than twice the black level of 100. In addition, Figure 13 As can be seen from (b), the amount of brightness reduction of the visual object is calculated. When the brightness is increased by the amount of brightness reduction, the brightness of the visual objects on the left and right becomes the same.

[0153] Based on the above research, the color reproducibility of a visual object does not deteriorate within the brightness range where the brightness of the visual object is more than twice the amount of blackening. In conventional reflective screens, such as the white matte screen in Table 3, in a bright environment with the ceiling light on, the brightness of blackening (minimum brightness) is approximately 88 cd / m 2 as large as that, and the brightness of all white (maximum brightness) is 289 cd / m 2 , so the amount of blackening is 255×88 / 289 = 78.

[0154] Therefore, when the amount of blackening = 78, within the brightness range of the amount of blackening × 2 (= 156) to 255 of the visual object, the brightness reduction of the visual object is not caused. However, as shown in the curve graph of the amount of blackening = 78 as Figure 12 , the brightness of the visual object causes the brightness reduction of the visual object within a wide range of the amount of blackening (= 78) to 2 × the amount of blackening (= 155).

[0155] (Color reproduction brightness range, color non-reproduction brightness range, and blackening brightness range)

[0156] By finding the amount of blackening in this way, it is possible to determine the brightness range (referred to as the color non-reproduction brightness range) that causes the brightness reduction of the visual object and the brightness range (referred to as the color reproduction brightness range) that does not cause the brightness reduction of the visual object. When Lb is set as the amount of blackening, 2Lb is set as 2 × the amount of blackening, and L is set as the brightness of each element of the visual object, the color non-reproduction brightness range is expressed as Lb ≤ L < 2Lb, and the color reproduction brightness range is expressed as 2Lb ≤ L ≤ 255.

[0157] In addition, the brightness range of 0 ≤ L < Lb is the brightness range that causes blackening (unable to perform black gray scale display due to blackening) as described above, and is referred to as the blackening brightness range.

[0158] (Expanding the color reproduction brightness range by adjusting the transmittance T and the brightness of white)

[0159] In the SHL screen shown in Table 3, the blackout amount is 9 (= 255 × 36 / 994), and the color reproduction brightness range is 18 (= 2 × 9) to 255. Within this color reproduction brightness range, the minimum value of the brightness range is determined by the minimum brightness, which is the basis for the blackout amount, and the maximum value is 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 brightness Kw of white, which is the maximum brightness of the image light from the image projection device 5, the color reproduction brightness range can be expanded. For example, the relationship between the blackout amount Lb and Lmax (maximum brightness ≤ 255) is set to Lb ≤ Lmax / 4. To satisfy this relationship, the transmittance T of the substrate 3 of the surface shape diffusion sheet 1 is reduced to the range of 0.25 ≤ T2 < 1 through the aforementioned transparent blackening. This reduces the blackout amount Lb while increasing the output of the image light from the image projection device 5 by 1 / T2 to compensate for the reduction in Lmax. Here, T2 is used because image light passes through substrate 3 twice in reflective screen 4. This allows Lb to be reduced without reducing Lmax, and the color reproduction brightness range can be expanded to 2Lb × T2 ≤ Color reproduction brightness range ≤ Lmax. This assumes that the amount of external light reflected on the screen surface is sufficiently small compared to the amount of external light reflected by reflective layer 8 within the screen.

[0160] For example, if the transmittance T of the substrate 3 of the reflective screen 4 is set to approximately 0.9 and the output of the image light from the image projection device 5 is set to 1.24 times (1 / T2 times), the lower limit of the color reproduction brightness range becomes 2Lb×0.81, and the color reproduction brightness range can be expanded to the low brightness side by 2Lb×(1-0.81).

[0161] Furthermore, when the black cast amount Lb reaches the brightness of 255, which is the maximum brightness of white (R=255, G=255, B=255), the lower limit 2Lb of the color reproduction brightness range becomes 510, which exceeds the upper limit 255. Therefore, there is no color reproduction brightness range, and the brightness is reduced in the entire brightness range (0 to 255) of the visual object. Figure 14 (a) shows a decrease in the brightness of the visual object when the blackening amount is set to 255 and white is used as the visual object. Figure 14 (b) shows the case where green (G) is used instead of white. Therefore, when the background becomes white, with the maximum brightness, the brightness of the visual object decreases across the entire brightness range of the visual object relative to the brightness (baseline value) of a black background without blackening. To make the visual object appear bright and vivid, it is reasonable to use a black background instead of a white one.

[0162] (Correction of brightness reduction: [5] of the present invention)

[0163] Based on the above research results, the image display system according to the present invention [5] is configured to correct the brightness reduction in the brightness range Lb≤L<2Lb (the color non-reproducible brightness range). Specifically, the image display system includes the reflective screen and image display device as the aforementioned premise, as well as a luminance meter, a black flooding calculation unit, and a brightness adjustment unit.

[0164] (Brightness meter)

[0165] The luminance meter measures the luminance of black (R=0, G=0, B=0) and white (R=255, G=255, B=255) in the RGB color model projected from the image projection device onto the reflective screen under external light, and obtains respective measurement values ​​Kmin and Kw.

[0166] The image and the black under external light correspond to the visual object and the darkened black (background) in the aforementioned visual experiment with reduced brightness, respectively.

[0167] The luminance meter can be formed of a common commercially available product.

[0168] (Black level calculation unit)

[0169] The blackening amount calculation unit calculates the blackening amount Lb as the integer part of the value of the formula: 255×Kmin / Kw. This formula corresponds to the above-mentioned definition formula of the blackening amount "Lb=255×(relative brightness of black)".

[0170] (Brightness adjustment unit)

[0171] The brightness adjustment unit corrects brightness reduction observed within a brightness range of Lb≤L<2Lb of the brightness L of the image.

[0172] As described in the above study, the brightness range Lb≤L<2Lb is a color non-reproducible brightness range in which the brightness reduction of the visual object is observed. Therefore, it is assumed that the brightness adjustment unit corrects this brightness reduction. The results of the aforementioned visual experiment of brightness reduction (e.g. Figure 12 ).

[0173] Figure 15 Shown Figure 12The color non-reproduced brightness range and the color reproduction brightness range when the blackening amount in the image is 78. This figure is used as an example to illustrate the method of correcting the brightness reduction. As shown in the figure, in the color reproduction brightness range (156 to 255), the brightness reduction of the visual object is 0, so no brightness reduction occurs, and therefore each RGB color with the brightness of the horizontal axis is output as image light. On the other hand, in the color non-reproduced brightness range (78 to 155), the brightness reduction of the visual object is set to a negative value, so when each RGB color with the brightness of the horizontal axis is output as image light, brightness reduction occurs. In order to prevent this brightness reduction, when the brightness of each RGB color to be output as image light enters the color non-reproduced brightness range, as shown in the figure, the brightness is corrected by adding the absolute value of the brightness reduction amount of the vertical axis corresponding to the value of the brightness of the horizontal axis, and each RGB color with the corrected brightness is output as image light.

[0174] As a result, it is possible to project an image without brightness reduction not only in the color reproduction brightness range of the visual object but also in the color non-reproduction brightness range.

[0175] Next, the above-mentioned method of correcting the brightness reduction will be described in more detail.

[0176] like Figure 16 As shown, the relationship between the lightness and the amount of lightness reduction of a visual object represented by the RGB color model changes as shown by Curve A in the figure. Curve A in the figure shows, as an example, the curve obtained by extrapolating the lightness-reduction curve for a visual object with a black cast amount of 50 to a lightness range less than 50. The color-unreproducible lightness range is 50 or greater and less than 100. The change in Curve A (curve shape) holds true not only for RGB primary colors (only red (R), only green (G), and only blue (B) are non-zero values, with the others being 0), but also for colors resulting from a mixture of primary colors, such as white (all RGB have the same non-zero value) (forming a curve shape substantially similar to Curve A). Therefore, even for general colors in the RGB color model (R = Lr, G = Lg, B = Lbl), Lb ≤ Lr, Lg, and Lbl < 2Lb holds true, meaning that the color-unreproducible lightness range is between Lb and less than 2Lb.

[0177] Then, in Figure 17 The process of calculating the value of the black cast is shown in FIG. The black cast varies depending on the external light in the installation environment of the image display system, so the black cast must be calculated for each installation environment. The brightness and brightness reduction of the visual object are calculated in accordance with the same principle whether in the RGB primary colors or in the general colors obtained by mixing them. Figure 16 Since the relationship curve changes in roughly the same shape as curve A in , correction can be easily performed if the amount of black cast in each setting environment is known.

[0178] like Figure 17 As shown in the figure, in a bright environment with external light, black (RGB is 0) and white (RGB is 255), the brightness of each image is measured, and the black level Lb is calculated based on the measured values ​​Kmin and Kw using the formula: Lb = 255 × Kmin / Kw. When calculating the black level Lb, Figure 16 In the example, A is shifted parallel to the horizontal axis to match the change in brightness reduction within the brightness range Lb to 2Lb. The brightness reduction within the color non-reproducible brightness range (Lb and less than 2Lb) is then calculated. General colors in the RGB color model (R = Lr, G = Lg, B = Lbl) are corrected separately for each primary color.

[0179] When Lr, Lg, and Lbl enter a color non-reproducible brightness range that is greater than or equal to Lb and less than 2Lb, Lr, Lg, and Lbl are individually corrected using Curve A.

[0180] The brightness adjustment unit that performs such correction can be realized by installing software describing the correction procedure in the image projection device.

[0181] (Adjustment of image light output: [6] of the present invention)

[0182] By correcting the brightness reduction described above, the color non-reproducible brightness range can be converted to the color reproducible brightness range. However, the residual brightness is less than the blackening brightness range of Lb, and in this range, the black display becomes black with the same brightness, making it impossible to perform detailed grayscale representation of black. Therefore, the image display system involved in [6] of the present invention eliminates the blackening brightness range and the color non-reproducible brightness range, and sets the entire area of ​​the brightness range of the visual object to the color reproducible brightness range, thereby reducing blackening.

[0183] Therefore, the present invention [6] is characterized in that, in the present invention [5], an image light output adjustment unit is provided instead of the brightness adjustment unit, or in addition to the brightness adjustment unit, the image light output adjustment unit increases the brightness of the white from Kw to Kw×(1+2Lb / 255) to reduce blackening.

[0184] When the brightness of white is increased from Kw to Kw×(1+2Lb / 255), brightness values ​​exceeding 255 and below 255+2Lb, which are outside the brightness range (0-255) of the RGB color model, are newly added to the color reproduction brightness range of 2Lb to 255, thereby obtaining an expanded color reproduction brightness range of 2Lb to 255+2Lb. Images with brightness within this color reproduction brightness range do not cause blackening or a decrease in brightness.

[0185] Then, by converting the extended color reproduction brightness range of more than 2Lb and less than 255+2Lb into a brightness range of more than 0 and less than 255, an image without blackening and brightness reduction can be observed in the entire brightness range (0 to 255) of the RGB color model.

[0186] use Figure 18 The example of [6] is used to illustrate the implementation method of the present invention. Figure 18 The diagram shows the blackening brightness range (0 to less than 78) before reducing the blackening, the color non-reproduction brightness range (78 to less than 156), the color reproduction brightness range (156 to 255) and the color reproduction brightness range (0 to 255) after reducing the blackening when the blackening amount Lb = 78.

[0187] The image light output adjustment unit increases the brightness of white by a factor of (1 + 156 (= 2 × 78) / 255). This results in a color reproduction brightness range of 156 or more and 411 (= 255 + 156) or less. Therefore, the following transformation is performed: the brightness (0 to 255) of each element of the visual object represented by the RGB color model is shifted by (brightness + 156 (= 2 × 78)) and 156, and then projected using the image projection device.

[0188] Furthermore, the function of deriving the expanded color reproduction brightness range and converting the color of the RGB color model can be realized by installing software describing the derivation and conversion process in the image light output adjustment unit. Alternatively, the image light output adjustment unit can be built into the image projection device.

[0189] Therefore, after the black cast is reduced, the entire brightness range of the RGB color model (0 or more and 255 or less) becomes the color reproduction brightness range, and an image without black cast and brightness reduction can be observed.

[0190] Absolute black (RGB are all 0, image brightness = 0cd / m 2 ) can only be achieved in a dark room without external light. Therefore, the present invention is useful as a method of expressing various blacks by grayscale expression, using the black with the minimum brightness under external light as absolute black. In [6] of the present invention, the black (2Lb) obtained by multiplying the brightness of white by (1+2Lb / 255) is set as the absolute black.

[0191] (Image display method according to the present invention: [7] of the present invention)

[0192] Next, the image display method of the present invention [7] is described. This method is based on the use of the reflective screen according to any one of the present invention [2] to [4] and an image projection device for projecting image light.

[0193] In [7] of the present invention, first, black (R=0, G=0, B=0) and white (R=255, G=255, B=255) in the RGB color model are projected from the image projection device onto the reflective screen.

[0194] Next, the brightness of the black and white colors is measured under external light to obtain respective measurement values ​​Kmin and Kw. Various commercially available brightness meters can be used for the brightness measurement.

[0195] Next, the blackening amount Lb is calculated as the integer part of the value of the formula: 255×Kmin / Kw. For this calculation, a commercially available personal computer or a computer can be used.

[0196] Finally, the brightness reduction observed within the brightness range Lb≤L<2Lb of the image is corrected. This is referred to as a brightness adjustment step. The brightness adjustment unit can be used in the implementation of this step.

[0197] (Image display method according to the present invention: [8] of the present invention)

[0198] Next, the image display method of the present invention [8] is described. In this method, the image light output adjustment step is included in place of, or in addition to, the brightness adjustment step in the present invention [7]. In the image light output adjustment step, the brightness of the white color is increased from Kw to Kw×(1+2Lb / 255) to reduce black cast. The image light output adjustment unit can be used in the implementation of this step.

[0199] Explanation of symbols

[0200] 1: Surface shape diffusion sheet (present invention); 2: Surface shape anisotropic diffusion layer; 2A: Surface shape diffusion layer (for diffusion angle research); 3: Substrate; 4: Reflective screen (present invention); 4A: Reflective screen (for diffusion angle research); 5: Image projection device (projector); 6: Lens layer; 6a: Lens surface; 6b: Non-lens surface; 8: Reflective layer; 9: Protective film; 10: Retaining plate; 11: Ceiling light; 12: Front window (window on the front of the screen); 13: Floor; 18: Aperture surface; 20: Spatial imaging aperture surface; 30: Luminance meter; 50: Image light; 51 : External light from the floor to the lens surface; 52: External light from outside the floor to the lens surface; 53: External light from the ceiling light to the non-lens surface; 54: External light from the front window to the non-lens surface; 60: Observation position; 61: Main light of the diffused reflected light of external light caused by the ceiling light; 81: White matte screen; 82: SHL screen; 120a: Relay lens; 120b: Relay lens; 122: Diffusing film laminate; 130: Three primary color light source; 134: Digital mirror device; 136: Sunshade; 138: Projection optical system; 140: Concave reflector; 142: Convex reflector.

Claims

1. An image display system for reducing blackout caused by external light and the deterioration of color reproducibility caused by the blackout, the image display system comprising a reflective screen, an image projection device, a luminance meter, a blackout amount calculation unit, and a brightness adjustment unit. The reflective screen is a reflective screen that diffuses the image light from the image projection device, reduces blackening caused by external light, and includes: Surface anisotropic diffusion layer; a flat substrate, which is located at the base of the surface anisotropic diffusion layer; and A reflective layer, a protective film, and a retaining plate are sequentially arranged and bonded from the substrate toward the back side. The bonding surface between the reflective layer and the substrate becomes a surface for reflecting the image light. The protective film is a film covering the reflective layer, The holding plate is a plate for maintaining the flatness of the substrate. It also includes a lens layer, which is arranged and bonded between the substrate and the reflective layer. The lens layer is composed of a Fresnel lens having a reflective surface shape on the back side. The bonding surface between the reflective layer and the lens layer serves as a surface for reflecting the image light. The image light from the aperture surface of the projection lens of the image projection device is separated from the surface reflecting the image light by a distance a with respect to the focal length f of the Fresnel lens, thereby forming a spatial imaging aperture surface at a position separated by a distance b, where b satisfies the relationship (1 / a)+(1 / b)=1 / f. The diffusion angle of the surface of the anisotropic diffusion layer in the vertical direction is set to be within the range of ±14°, and the transmittance T of the visible light wavelength band inside or on the surface of the substrate is set to be within the range of 0.5 or more and less than 1. The luminance meter is a unit that measures the luminance of black (R=0, G=0, B=0) and white (R=255, G=255, B=255) in the RGB color model projected from the image projection device onto the reflective screen forming the spatial imaging aperture surface under external light, and obtains respective measurement values ​​Kmin and Kw. The black flooding amount calculation unit is a unit that calculates the black flooding amount Lb as the integer part of the value of the formula: 255×Kmin / Kw. The brightness adjustment unit is a unit that corrects the brightness reduction observed in the brightness range Lb≤L<2Lb of the brightness L of each element in the image that is washed out from the black (R=Lb, G=Lb, B=Lb).

2. The image display system according to claim 1, wherein: An image light output adjustment unit is provided in place of the brightness adjustment unit or in addition to the brightness adjustment unit. The image light output adjustment unit is a unit that increases the brightness of the white color from Kw to Kw×(1+2Lb / 255) to reduce black cast.

3. An image display method for reducing blackout caused by external light and the deterioration of color reproducibility caused by the blackout, the method using the image display system according to claim 1, the image display method comprising the following steps: Projecting black (R=0, G=0, B=0) and white (R=255, G=255, B=255) in the RGB color model from the image projection device onto the reflective screen forming the spatial imaging aperture surface; Measuring the brightness of the black and white colors under external light to obtain respective measurement values ​​Kmin and Kw; The blackening amount Lb is calculated as the integer part of the value of the formula: 255×Kmin / Kw; and The brightness adjustment step corrects the brightness reduction observed within the brightness range Lb≤L<2Lb of the brightness L of each element in the image that has been blackened (R=Lb, G=Lb, B=Lb).

4. The image display method according to claim 3, wherein: Instead of or in addition to the brightness adjustment step, an image light output adjustment step is provided, in which the brightness of the white light is increased from Kw to Kw×(1+2Lb / 255) to reduce black cast.

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