Virtual image display device

Abstract

This virtual image display device is provided with: a backlight that causes a light-emitting element in a selected one of illumination segments to emit light and directs the light toward a display panel, each illumination segment being provided with a light-emitting element, the selected illumination segment corresponding to an image in the display panel; and a control unit that performs local dimming control of the backlight to turn on light-emitting elements in image-corresponding illumination segments corresponding to the image, and turn off light-emitting elements in non-image-corresponding illumination segments not corresponding to the image. The image is composed of image information having a vanishing point and created by a perspective projection method, and the control unit reduces a drive current input to a light-emitting element as the image information corresponding thereto is closer to the vanishing point, and turns on the light-emitting elements in the image-corresponding illumination segments.

Description

Virtual image display device

[0001] The present disclosure relates to a virtual image display device that can be implemented as a Head Up Display (HUD) device.

[0002] Prior art virtual image display devices are described in, for example, Patent Documents 1 to 3.

[0003] JP 2021-39205 A JP 2022-65806 A JP 2012-35784 A

[0004] The virtual image display device disclosed herein is a virtual image display device that displays a virtual image superimposed on an external scene on a reflective member by irradiating the reflective member with light from an image displayed on a display panel, and includes a backlight having light-emitting elements provided in each of a plurality of lighting segments, which illuminates the light-emitting elements of a selected lighting segment from the plurality of lighting segments that corresponds to the image, and emitting the light from the illuminated light-emitting elements toward the display panel, and a control unit that performs local dimming control on the backlight to turn on the light-emitting elements in the image-corresponding lighting segment that corresponds to the image and to turn off the light-emitting elements in the image-non-corresponding lighting segment that does not correspond to the image, wherein the image is composed of image information having a vanishing point created by perspective projection, and the control unit reduces the drive current input to the light-emitting elements as the image information approaches the vanishing point, thereby turning on the light-emitting elements in the image-corresponding lighting segment.

[0005] The objectives, features, and advantages of the present disclosure will become clearer from the detailed description and drawings below. 1 is a cross-sectional view schematically illustrating a virtual image display device according to an embodiment of the present disclosure. 2 is a front view showing an enlarged view of a portion of a backlight. 3 is a cross-sectional view of a backlight and a liquid crystal panel taken along the section line III-III in FIG. 2. 4 is a front view showing an example in which an image on a display panel created using a perspective projection method is displayed as a HUD (Head Up Display) display image (virtual image). 5 is a side view showing the optical path of a virtual image visually recognized by a user. 6 is a front view showing Example 1 in which an image on a display panel created using a perspective projection method is displayed as a HUD display image. 7 is a front view showing Example 2 in which an image on a display panel created using a perspective projection method is displayed as a HUD display image. 8 is a front view showing Comparative Example 1 in which a two-dimensional image on a display panel without using a perspective projection method is displayed as a HUD display image. 9 is a front view showing Comparative Example 2 in which a two-dimensional image on a display panel without using a perspective projection method is displayed as a HUD display image. 1A and 1B are diagrams illustrating display examples of a HUD display image created by one-point perspective projection according to an embodiment of the present disclosure, a two-point perspective projection according to another embodiment of the present disclosure, and a three-point perspective projection according to another embodiment of the present disclosure.

[0006] Various prior art virtual image display devices have been proposed that allow a user to view image light emitted from a display device as a virtual image. When the display device is a liquid crystal display device including a backlight and a liquid crystal panel, local dimming control of the backlight allows the user to view a virtual image with improved contrast. Such virtual image display devices are described in, for example, Patent Documents 1 to 3.

[0007] The prior art technologies of Patent Documents 1 to 3 described above aim to improve the visibility of the virtual image viewed by the user by eliminating the sense of discomfort in the perspective of the virtual image, but there is a demand for a virtual image display device that can display virtual images with perspective and three-dimensionality and with higher visibility.

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the drawings used in the following description are schematic. The dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones. In this specification, for convenience, a Cartesian coordinate system xyz is defined in some drawings, and the positive direction of the z-axis is defined as upward, and terms such as upper surface and lower surface are used. The x-axis direction, y-axis direction, and z-axis direction are also referred to as the first direction, second direction, and third direction, respectively. The first direction is also referred to as the horizontal direction, and the second direction is also referred to as the vertical direction.

[0009] FIG. 1 is a cross-sectional view schematically illustrating a virtual image display device according to an embodiment of the present disclosure. As shown in FIG. 1 , the virtual image display device 1 of this embodiment includes a display unit 2, an optical system 3, and a control unit 4. The virtual image display device 1 allows a user (also referred to as a viewer) 5 to view a virtual image. The virtual image display device 1 is also referred to as a head-up display (HUD). In the following description, the head-up display may be abbreviated as HUD. The virtual image display device 1 may be mounted on a mobile object such as a vehicle, a ship, or an aircraft. When the virtual image display device 1 is mounted on a mobile object, the user 5 may be a driver, an operator, or a passenger of the mobile object. The virtual image display device 1 can display a virtual image by reflecting display light of the image using the optical system 3.

[0010] FIG. 2 is a front view showing an enlarged portion of the backlight, and FIG. 3 is a cross-sectional view of the backlight and the liquid crystal panel as seen from the section line III-III in FIG. 2. The virtual image display device 1 includes a display panel 7 having a display surface 7a (shown in FIG. 1) for displaying an image. The virtual image display device 1 also includes a backlight 6 that divides a light source surface on which a plurality of light-emitting elements 61 are provided, has a plurality of illumination segments 63 arranged in a matrix, and is switchable between an on state and an off state, and emits light from the light-emitting elements 61 of selected illumination segments 63 that are on toward the display panel 7. The virtual image display device 1 also includes a control unit 4 that performs local dimming control on the backlight 6 to turn on the light-emitting elements 61 of illumination segments 63 located directly below the image display (also referred to as image-corresponding segments 63) and turn off the light-emitting elements 61 of illumination segments 63 not located directly below the image display (also referred to as image-non-corresponding segments 63).

[0011] In local dimming control, typically, multiple light-emitting elements 61, such as light-emitting diodes, arranged on the light source surface of the backlight 6 are individually controlled according to the image. This allows the light-emitting elements 61 to be relatively bright in relatively bright areas (e.g., image areas) of the display unit (also referred to as the display surface) 7a, and relatively dark in relatively dark areas (e.g., non-image areas) of the display surface 7a, thereby increasing the contrast ratio between the image and non-image areas. In this embodiment, the control unit 4 may control the drive current (or drive voltage) of the light-emitting elements 61 provided in the illumination segments 63 according to the gradation value of the image. Furthermore, local dimming control can prevent the occurrence of a postcard phenomenon, in which the light source surface of the backlight 6 is faintly reflected as a background image (also referred to as a postcard image) of a virtual image. The virtual image is, for example, 20Q shown in FIG. 1 , and the postcard image is, for example, 10Q shown in FIG. 1 .

[0012] The control unit 4 controls the lighting / extinguishing of the image for each of the plurality of divided images corresponding to the plurality of illumination segments 63. That is, if the number of low-gradation pixels, whose gradation values ​​are equal to or less than a predetermined threshold (for example, gradation values ​​equal to or less than 5 when the maximum gradation value is 255), of each divided image corresponding to each illumination segment 63 is a predetermined percentage (for example, 90% or more) of the total number of pixels in the divided image, the illumination segment 63 may be determined to be a non-image corresponding segment 63, and the light-emitting element 61 of the illumination segment 63 may be turned off. Conversely, if the number of low-gradation pixels is less than a predetermined percentage of the total number of pixels in the divided image, the illumination segment 63 may be determined to be an image corresponding segment 63, and the light-emitting element 61 of the illumination segment 63 may be turned on.

[0013] The display unit 2 displays an image to be projected into the field of view of the user 5. The display unit 2 may be configured as a transmissive display device. The transmissive display device may be, for example, a liquid crystal display (LCD) including a backlight 6 and a display panel 7. The backlight 6 and the display panel 7 are arranged in this order from the side farthest from the user 5 along the optical path of image light of the image displayed to the user 5.

[0014] The backlight 6 may be a direct-type backlight. ２ SiF ６ : Mn ４＋ The KSF type backlight 6 includes a plurality of light emitting elements 61 having KSF and an emission surface 6a capable of emitting light from the plurality of light emitting elements 61. The KSF type backlight 6 can suppress a decrease in the color purity of a virtual image. ４+This is because KSF (Korean Fluorescent Phosphor) is a type of line-emitting phosphor with a wide color gamut and a narrow wavelength spectrum width of the three primary colors RGB (highly sharp wavelength spectrum). The backlight 6 may include a base 62 and a diffuser 65. The base 62 may have a main surface (also referred to as a light source surface) 62a facing the display panel 7, and a plurality of light-emitting elements 61 may be two-dimensionally arranged on the main surface 62a. The diffuser 65 may be located in front of the base 62 (on the left side in FIG. 1 ) and cover the plurality of light-emitting elements 61. The diffuser 65 diffuses light emitted from the plurality of light-emitting elements 61, thereby allowing the backlight 6 to irradiate the display panel 7 with light in a planar manner. The exit surface 6a may be the surface of the diffuser 65 facing the display panel 7.

[0015] Each of the light-emitting elements 61 includes at least one light source. The light source may be a point light source such as a light-emitting diode (LED). The LED includes a mini-LED and a micro-LED.

[0016] The display panel 7 has a display surface 7 a. The display surface 7 a is a surface that displays images based on an image display signal, and can output images to the optical system 3 side by light emitted from the emission surface 6 a of the backlight 6.

[0017] The display panel 7 may be a known liquid crystal panel, such as an IPS (In-Plane Switching) liquid crystal panel, an FFS (Fringe Field Switching) liquid crystal panel, a VA (Vertical Alignment) liquid crystal panel, or an ECB (Electrically Controlled Birefringence) liquid crystal panel. The display panel 7 includes two glass substrates (an array substrate and a color filter substrate) arranged to sandwich a liquid crystal layer, and the color filter substrate has a color filter CF on its surface facing the liquid crystal layer.

[0018] The control unit 4 controls the backlight 6. The control unit 4 switches each of the plurality of light-emitting elements 61 between an emitting state and a non-emitting state. The control unit 4 may control the light emission brightness of the light-emitting elements 61 that are in the emitting state based on image data of an image to be displayed on the display surface 7 a. The control unit 4 may control the light emission brightness of the light-emitting elements 61 that are in the emitting state based on the background brightness in the field of view of the user 5.

[0019] The image information includes predetermined image information and other standard image information. The control unit 4 may control the drive current of the light-emitting element 61 driven by the predetermined image information to be different from the drive current of the light-emitting element 61 driven by the standard image information. In this case, the brightness of the light-emitting element 61 in the image-corresponding segment 63 located directly below the image is changed, for example, by decreasing the brightness as it approaches the vanishing point VP, thereby displaying a virtual image with perspective and three-dimensionality and high visibility. For example, the standard image information may be image information of the area with the highest brightness in the image and virtual image (e.g., the area displayed closest to the user 5 in the image and virtual image), and the predetermined image information may be image information of the area with gradually decreasing brightness in the image and virtual image. Furthermore, the standard image information may be image information of the area with the lowest brightness in the image and virtual image (e.g., the area displayed farthest from the user 5 in the image and virtual image), and the predetermined image information may be image information of the area with gradually increasing brightness in the image and virtual image. In addition, the standard image information may be image information of an area in the image and virtual image where the brightness is the median or average value (for example, an area that is displayed as an area in an intermediate position as seen by the user 5 in the image and virtual image), and the specified image information may be image information of an area in the image and virtual image where the brightness changes.

[0020] The control unit 4 controls the drive current (I ＬＥＤ The brightness of the virtual image portion (referred to as Bi) may be controlled as follows: When the distance at which the user 5 is expected to look at an arbitrary portion of the virtual image (also referred to as a virtual image portion) is L, the brightness of the virtual image portion (referred to as Bi) may be controlled as I so that it is inversely proportional to L. ＬＥＤThat is, I may be controlled so that Bi=B1 / L (where B1 may be the initial brightness or the maximum brightness). ＬＥＤ may be controlled.

[0021] The control unit 4 calculates Bi=B1 / e L (where e is Napier's constant) ＬＥＤ That is, Bi may be controlled to decrease nonlinearly and exponentially with respect to L.

[0022] The control unit 4 also adjusts the brightness of each part of the virtual image in inverse proportion to the distance L that is assumed when the user 5 looks at each part of the virtual image, to obtain I ＬＥＤ than when lowering I ＬＥＤ The control unit 4 may perform control to reduce the rate of decrease in I so that Bi=B1 / (L / n) (where n is a constant consisting of a real number from 2 to 10) holds. ＬＥＤ may be controlled so that the slope of the inverse proportionality of Bi to L becomes gentle. ＬＥＤ may be controlled. In this case, it is possible to prevent the virtual image portion (also referred to as the virtual image far portion) that is displayed as being far from the user 5 from being extremely difficult to see when viewed from the user 5. That is, since the virtual image far portion is smaller in size than the virtual image portion (also referred to as the virtual image near portion) that is displayed as being close to the user 5, if the luminance of the virtual image far portion is reduced in proportion to L, the virtual image far portion tends to become extremely difficult to see. Therefore, it is possible to prevent the virtual image far portion from becoming extremely difficult to see as L increases. Note that n is not limited to a real number from 2 to 10.

[0023] In order to prevent the far part of the virtual image from becoming extremely difficult to see as L increases, Bi = B1 / e L / n So that I ＬＥＤ It is also possible to control I so that the degree to which Bi decreases nonlinearly and exponentially with respect to L becomes gentle. ＬＥＤ Similarly, Bi=B1 / L 1 / n So that I ＬＥＤ may be controlled.

[0024] As described above, since the size of the virtual image far portion decreases, reducing the luminance of the virtual image far portion tends to make the virtual image far portion extremely difficult to see. Therefore, the luminance of the vanishing point and / or its surroundings (also referred to as vanishing point luminance) may be increased. If the luminance of the virtual image far portion decreases as L approaches the vanishing point, the vanishing point and its surroundings may become almost invisible to the user 5. In this case, if the vanishing point luminance is, for example, inversely proportional to L or higher than the luminance of the surroundings of the vanishing point (in this case, the luminance is a portion farther from the vanishing point than the surroundings near the vanishing point), the user 5 can easily recognize the location of the vanishing point. As a result, the user 5 can view the virtual image with a greater sense of perspective and three-dimensionality. Note that if the vanishing point luminance is higher than the maximum luminance of the virtual image, the perspective and three-dimensionality of the virtual image are likely to be impaired. Therefore, the vanishing point luminance may be lower than the maximum luminance of the virtual image, or may be 50% or less, or 30% or less, of the maximum luminance of the virtual image. The vanishing point luminance may be 5% or more, or 10% or more of the maximum luminance of the virtual image.

[0025] When increasing the brightness of the area around the vanishing point, the area around the vanishing point may be in a range of more than 1 to about 10 times the area of ​​the vanishing point, or more than 2 to about 5 times the area of ​​the vanishing point, but is not limited to these ranges.

[0026] The control unit 4 may control not only the backlight 6 but also each component of the virtual image display device 1. The control unit 4 is configured as, for example, a processor. The control unit 4 may include one or more processors. The processor may include a general-purpose processor that loads a specific program to execute a specific function, and a dedicated processor specialized for a specific process. The dedicated processor may include an application-specific integrated circuit (ASIC). The processor may include a programmable logic device (PLD). The PLD may include a field-programmable gate array (FPGA). The control unit 4 may be either a system-on-a-chip (SoC) or a system-in-a-package (SiP) in which one or more processors work together. The control unit 4 may include a memory unit that stores various information or programs for operating each component of the virtual image display device 1. The memory unit may be configured as, for example, a semiconductor memory. The memory unit may function as a work memory for the control unit 4.

[0027] The optical system 3 is located in the optical path of image light emitted from the display unit 2 and reaching the eyes of the user 5. The optical system 3 projects the image light emitted from the display unit 2 onto the eyes of the user 5, forming a virtual display image in the eyes of the user 5. The optical system 3 may enlarge or reduce the image displayed on the display unit 2 to form a virtual display image in the eyes of the user 5. The optical system 3 includes a first optical member (also referred to as a first reflecting member) 3a and a second optical member (also referred to as a second reflecting member) 3b. The second optical member 3b is a reflecting member (e.g., a windshield of a moving body such as an automobile) having a transmissive / reflective function. The light of the image displayed on the display surface 7a of the display panel 7 is irradiated onto the reflecting member, thereby displaying a virtual image superimposed on the external scene viewed by the user 5 through the reflecting member.

[0028] As shown in FIG. 1 , the second reflecting member 3b, which is a reflecting member, may have a transflective concave surface. The second reflecting member 3b may have a concave surface that reflects the image light (also referred to as first image light) from the output surface 6a and the image light (also referred to as second image light) from the display surface 7a, which are reflected by the first reflecting member 3a, toward the eyes of the user 5. In this case, the first image light and the second image light converge toward the user 5, thereby suppressing a decrease in the brightness and resolution of the virtual image 10Q generated by the first image light and suppressing a decrease in the brightness and resolution of the virtual image 20Q generated by the second image light. The concave surface of the second reflecting member 3b may be a spherical surface, an elliptical surface, a hyperbolic surface, a free-form surface, or the like. Furthermore, since the windshield of a moving object such as an automobile has a concave surface on the side facing the user 5, the second reflecting member 3b may be a windshield.

[0029] As shown in FIG. 1 , a first reflecting member 3a made of a concave mirror may be disposed between the display panel 7 and the second reflecting member 3b. The first reflecting member 3a reflects the image on the exit surface 6a of the backlight 6 and the image on the display surface 7a of the display panel 7 toward the second reflecting member 3b. The first reflecting member 3a may be a plane mirror, a convex mirror, or a concave mirror. If the first reflecting member 3a is a concave mirror, it may be a spherical mirror, an elliptical mirror, a hyperbolic mirror, a free-form mirror, or the like. If the first reflecting member 3a is a concave mirror, the first image light and the second image light converge toward the second optical member 3b, thereby suppressing a decrease in the brightness and resolution of the virtual image 10Q generated by the first image light and suppressing a decrease in the brightness and resolution of the virtual image 20Q generated by the second image light. The second reflecting member 3b reflects the image on the exit surface 6a and the image on the display surface 7a reflected by the first reflecting member 3a toward the eyes of the user 5. The number of optical elements constituting the optical system 3 is not limited to two, and may be three or more, or may be four or more. The optical elements may include reflective elements including convex or concave mirrors. The optical elements may include reflective elements including free-form mirrors. The optical elements may include refractive elements including convex or concave lenses. Convex lenses include biconvex lenses, plano-convex lenses, and convex meniscus lenses. Concave lenses include biconcave lenses, plano-concave lenses, and concave meniscus lenses. The optical elements are not limited to reflective elements or refractive elements, and may include various other optical elements such as hologram elements.

[0030] The curvature of the first reflecting member 3a may be greater than the curvature of the second reflecting member 3b. The curvature may be a curvature, or if the concave surface is aspherical, may be an average curvature of the entire concave surface. The first reflecting member 3a may have a relatively large curvature to converge the second image light that has a field angle and is divergent. The second reflecting member 3b, which forms a defocused virtual image formed by reflected light (divergent light) of the first image light and the second image light, may have a relatively small curvature. The curvature of the first reflecting member 3a may be more than 1 time and approximately 3 times or less the curvature of the second reflecting member 3b, but is not limited to this range.

[0031] The incident surface 7b of the display panel 7 (shown in FIG. 1) is disposed so as to be inclined at a predetermined angle θ with respect to the exit surface 6a of the backlight 6. Since the display surface 7a and the incident surface 7b of the display panel 7 are generally parallel to each other, the predetermined angle θ may be the inclination angle between the display surface 7a of the display panel 7 and the exit surface 6a of the backlight 6. The predetermined angle θ may be, for example, 10° or more and 45° or less. Depending on the predetermined angle θ, it is possible to adjust the birefringence retardation, which depends on the thickness of the liquid crystal layer of the display panel 7, and set an appropriate chromaticity.

[0032] As shown in FIGS. 1 and 3 , the backlight 6 may include a diffuser 65 that condenses light emitted from the multiple light-emitting elements 61. The diffuser 65 is located above the first surface 64a of the base 64, and the distance between the diffuser 65 and the base 64 may be, for example, approximately 1 to 10 mm, or approximately 5 mm. The diffuser 65 may be a microlens array in which multiple microlenses are arranged two-dimensionally. Each microlens may be, for example, a biconvex lens, a plano-convex lens, or a convex meniscus lens. The diffuser 65 may also be composed of a combination of cylindrical lenses. The thickness of the diffuser 65 may be approximately 0.1 to 3 mm, or approximately 1 mm. The diffuser 65 may also be a brightness enhancement film, such as the BEF series of prism films manufactured by Sumitomo 3M Limited. A prism sheet is an optical component that condenses light by utilizing double reflection as light passes through the film and the refractive index of light. Prism sheets may also be stacked. In the case of a stacked arrangement, the prisms may be arranged so that their ridgelines are perpendicular to each other.

[0033] As shown in FIG. 2 , the backlight 6 may include a reflector 66 positioned on the first surface 64 a of the base 64. As shown in FIG. 2 , the reflector 66 has a lattice pattern, with one light-emitting element 61 positioned in each of the regions partitioned by the reflector 66. The reflector 66 may have an exit surface 6 a that is farthest from the first surface 64 a in the third direction (z-axis direction) in contact with the diffuser 65. This prevents light emitted from the light-emitting elements 61 in an emitting state from entering regions of the liquid crystal panel corresponding to the light-emitting elements 61 in a non-emitting state during local dimming control, thereby reducing the risk of a decrease in the effectiveness of local dimming control. The reflector 66 may have a side surface 66 b facing the light-emitting elements 61 that is reflective. The side surface 66 b of the reflector 66 may be made of a metal material such as aluminum (Al) or silver (Ag). The top portion 66 a of the reflector 66 may be in contact with the diffuser 65.

[0034] The diffuser 65 anisotropically diffuses light emitted from the backlight 6. The diffuser 65 has a diffusing power in a first direction (x-axis direction) that is different from that in a second direction (y-axis direction), and thus anisotropically diffuses and emits incident light. When the backlight 6 includes the diffuser 65, the diffuser 65 can diffuse incident light at a designed diffusion angle (also referred to as a light distribution angle). The diffusing power of the diffuser 65 in the first direction and the second direction can be determined according to the aspect ratio of the virtual image 10Q (shown in FIG. 1 ) formed by the virtual image display device 1. For example, if the virtual image 10Q is displayed horizontally, the diffusing power in the first direction can be high and the diffusing power in the second direction can be lower than the diffusing power in the first direction. In particular, in the virtual image display device 1 used in a HUD, the luminance uniformity in the first direction may be higher than the luminance uniformity in the second direction, so the diffusing power in the first direction is specified within a specific range.

[0035] The diffuser 65 may be a plate- or sheet-shaped member made of transparent resin with numerous microlenses regularly arranged on the light incident surface. The diffuser 65 may also be a microlens array in which multiple microlenses are two-dimensionally arranged. The microlenses may be configured to have a peak of diffusion in a specific direction, such as the first direction. That is, the shape of the microlenses may be configured so that the diffusion ability is strong in the x-axis direction and the diffusion ability in the y-axis direction is smaller than the diffusion ability in the x-axis direction. Each microlens may be, for example, a biconcave lens, a plano-concave lens, a concave meniscus lens, or the like. The diffuser 65 may be in contact with the base 64 in the third direction or may be spaced apart from the base 64. The thickness of the diffuser 65 may be approximately 0.5 to 2 mm, or may be approximately 1 mm. The diffusion and anisotropy of the diffuser 65 are controlled by the microlens' microstructure. That is, the desired anisotropic diffusion ability can be obtained by adjusting the concave-convex pitch and height of the microlenses. For example, if the anisotropic diffusivity is expressed as a numerical value of H20V13, the diffusivity in the horizontal direction (in this embodiment, the x-axis direction) is 20, and the diffusivity in the vertical direction (in this embodiment, the y-axis direction) is 13, indicating that the diffusivity in the x-axis direction and the y-axis direction is different and that it is more likely to diffuse in the x-axis direction.

[0036] The diffuser plate 65 diffuses the incident light. The diffuser plate 65 may be composed of, for example, a substrate made of transparent resin, glass, or the like, and light-diffusing particles made of silicone resin, polystyrene resin, silica, calcium carbonate, or the like dispersed in the substrate.

[0037] The array substrate 7ar and the color filter substrate 7cf constituting the liquid crystal panel 7 may be glass substrates, plastic substrates, etc. The thickness of each of the array substrate 7ar and the color filter substrate 7cf may be about 0.05 to 0.3 mm, or may be about 0.1 mm.

[0038] The diffusion plate 65 is configured to have a predetermined haze value H (%). The haze value H is obtained by multiplying the value Td / Tt, which is obtained by dividing the diffuse transmittance Td by the total light transmittance Tt, by 100. The diffuse transmittance Td and the total light transmittance Tt are measured by known measurement methods.

[0039] As shown in FIG. 3 , the display panel 7, which is a liquid crystal panel, is located above the diffuser plate 65. The liquid crystal panel 7 includes an array substrate 7ar and a color filter substrate 7cf that sandwich a liquid crystal layer 7lc. The thickness L of the liquid crystal layer 7lc defines the birefringence phase difference. The liquid crystal panel 7 has a display surface 7a and a polarizing plate 9 on the display surface 7a side. Another polarizing plate 9 may be located on the incident surface 7b side of the liquid crystal panel 7. The display surface 7a is the surface of the display panel 7 opposite the surface facing the backlight 6. The display panel 7 displays an image based on an externally input image signal on the display surface 7a. In other words, the display panel 7 emits image light from the display surface 7a based on the externally input image signal. The display surface 7a of the display panel 7 is also the display surface of the virtual image display device 1.

[0040] The control unit 4 may perform control to increase the brightness of the backlight 6 compared to when the display panel 7 is parallel to the backlight 6 (θ = 0°). When the display panel 7 is tilted with respect to the backlight 6 (θ > 0°), the optical path length through which light emitted from the backlight 6 passes through the display panel 7 increases, making the light transmittance of the display panel 7 more likely to decrease. As a result, the brightness of the image displayed on the display panel 7 decreases, and the brightness of the virtual image also tends to decrease. The above control can prevent this problem from occurring.

[0041] When the display panel 7 is tilted with respect to the backlight 6, the length of the optical path passing through the display panel 7 increases by (1 / cos θ) times. Therefore, the luminance of the backlight 6 may be increased by (1 / cos θ) times compared to when the display panel 7 is parallel to the backlight 6. In this case, the control unit 4 increases the luminance of the backlight 6 as the tilt angle of the display panel 7 with respect to the backlight 6 increases.

[0042] Furthermore, when the display panel 7 is tilted with respect to the backlight 6, light emitted from the backlight 6 may be reflected by Fresnel reflection on the incident surface 7b of the display panel 7. In this case, the transmittance Tf (Tf = 1 - Rf) of the transmitted light decreases by the amount of light reflected at the reflectance Rf (0 < Rf < 1) due to Fresnel reflection. Therefore, the luminance of the backlight 6 may be increased by (1 / Tf) times compared to when the display panel 7 is parallel to the backlight 6. Furthermore, the luminance of the backlight 6 may be increased by (1 / Tf cos θ) times compared to when the display panel 7 is parallel to the backlight 6.

[0043] FIG. 4 is a front view showing an example of a display in which an image on the display panel 7 created using perspective projection is displayed as a HUD display image (virtual image) 20Q, and FIG. 5 is a side view showing the optical path of light that forms the virtual image 20Q viewed by the user 5. An image created using perspective projection is displayed on the display surface 7a of the display panel 7. This image has a vanishing point VP on the horizon EL and is an oblique image centered on this vanishing point VP. The display panel 7 is disposed at an angle θ with respect to the backlight 6, so that the lower side of the virtual image 20Q is displayed closer to the user 5 and the upper side is displayed farther from the user 5. This allows the user 5 to view the virtual image 20Q with a sense of perspective and three-dimensionality.

[0044] The virtual image 20Q displayed by perspective projection may be formed by tilting the display panel 7 with respect to the backlight 6, as shown in FIGS. 1 and 5 . Alternatively, when the display panel 7 is not tilted with respect to the backlight 6, the virtual image 20Q displayed by perspective projection may be formed by performing a conversion process in advance by an image processing unit that converts a two-dimensional image into an image displayed by perspective projection. Alternatively, in order to form the virtual image 20Q displayed by perspective projection, the display panel 7 may be tilted with respect to the backlight 6 and the conversion process may be performed simultaneously. The conversion process may also be performed by the control unit 4. In this case, the conversion process software may be stored in a storage unit such as a RAM or ROM of the control unit 4, and the conversion process may be performed by calling the conversion process software from the storage unit when the control unit 4 performs the conversion process.

[0045] FIG. 6 is a front view showing Example 1 in which an image on the display panel 7 created using perspective projection is displayed as a HUD display image, and FIG. 7 is a front view showing a similar Example 2. FIG. 8 is a front view showing Comparative Example 1 in which a two-dimensional image on the display panel 7 without using perspective projection is displayed as a HUD display image, and FIG. 9 is a front view showing a similar Comparative Example 2. The virtual image shown in FIG. 6 is created using perspective projection, so the user 5 can view a virtual image with a sense of perspective. On the other hand, the virtual image shown in FIG. 8 is created by displaying the image on the display panel 7 without using perspective projection as a two-dimensional image, so the user 5 cannot view it as a virtual image with a sense of perspective or three-dimensionality.

[0046] 10 is a diagram illustrating an example of a HUD display image created using one-point perspective according to an embodiment of the present disclosure. It is a schematic diagram of an image created using one-point perspective, with a vanishing point VP1 being a point on the horizon EL. The controller 4 reduces the drive current applied to the light-emitting elements 61 as the image information approaches the vanishing point VP1, allowing the user 5 to view the image as a virtual image with perspective and three-dimensionality.

[0047] 11 is a diagram illustrating an example of a HUD display image created using two-point perspective according to another embodiment of the present disclosure. It is a schematic diagram of an image created using two-point perspective, with two points on the horizon EL as vanishing points VP1 and VP2. The controller 4 reduces the drive current applied to the light-emitting elements 61 as the image information approaches the vanishing points VP1 and VP2. This allows the user 5 to view a virtual image with perspective and three-dimensionality, as a more realistic oblique image.

[0048] 12 is a diagram illustrating an example of a HUD display image created using three-point perspective according to another embodiment of the present disclosure. This image is created using three-point perspective, with two vanishing points VP1 and VP2 on the horizon EL and a third vanishing point VP3 below the horizon EL. The control unit 4 reduces the drive current applied to the light-emitting elements 61 as the image information approaches the vanishing points VP1, VP2, and VP3. This allows the user 5 to view a virtual image with perspective and three-dimensionality, as well as a more realistic oblique image.

[0049] According to the virtual image display device of the present disclosure, the image displayed on the display unit of the display panel is composed of image information having a vanishing point created by perspective projection. The control unit 4 drives the light-emitting elements 61 by reducing the drive current applied to the light-emitting elements 61 as the image information approaches the vanishing point. Therefore, the image displayed on the display unit 2 of the display panel 7 has lower brightness for areas of the image that are displayed as being farther away from the user 5. As a result, it is possible to display a virtual image with excellent perspective and three-dimensionality, thereby improving visibility.

[0050] The present disclosure can implement the following configurations (1) to (15).

[0051] (1) A virtual image display device that displays a virtual image superimposed on an external scene on a reflective member by irradiating the reflective member with light from an image displayed on a display panel, the virtual image display device comprising: a backlight in which light-emitting elements are provided in each of a plurality of lighting segments, and that causes the light-emitting elements of a selected lighting segment from the plurality of lighting segments that corresponds to the image to emit light from the emitted light-emitting elements toward the display panel; and a control unit that performs local dimming control on the backlight to turn on the light-emitting elements in the image-corresponding lighting segment that corresponds to the image and to turn off the light-emitting elements in the image-non-corresponding lighting segment that does not correspond to the image, the image being composed of image information having a vanishing point created by perspective projection, and the control unit reduces the drive current input to the light-emitting elements as the image information approaches the vanishing point, thereby turning on the light-emitting elements in the image-corresponding lighting segment.

[0052] (2) The control unit reduces the driving current by adjusting the brightness of each part of the virtual image in inverse proportion to the estimated distance when the user views each part of the virtual image.

[0053] (3) The control unit of the virtual image display device described in (1) reduces the rate at which the drive current is reduced by making the brightness of each part of the virtual image inversely proportional to the estimated distance when the user views each part of the virtual image.

[0054] (4) The control unit reduces the driving current so that Bi = B1 / (L / n) (where Bi is the brightness of each part of the virtual image, B1 is the maximum brightness of the virtual image, L is the estimated distance when the user views each part of the virtual image, and n is a real number between 2 and 10).

[0055] (5) A virtual image display device described in any one of (1) to (4) above, wherein the image information includes predetermined image information and other standard image information, and the control unit controls the driving current of the light-emitting element driven by the predetermined image information among the image information so that it is different from the driving current of the light-emitting element driven by the standard image information.

[0056] (6) The virtual image display device according to (5) above, wherein the standard image information is the image information of a portion of the virtual image that has the highest brightness.

[0057] (7) The virtual image display device according to (5) above, wherein the standard image information is the image information of a portion of the virtual image with the lowest brightness.

[0058] (8) The virtual image display device according to any one of (1) to (7) above, wherein the image is configured by the image information having a plurality of the vanishing points.

[0059] (9) The virtual image display device according to any one of (1) to (8) above, wherein the display panel is disposed at a predetermined angle with respect to the backlight.

[0060] (10) The virtual image display device according to (9), wherein the predetermined angle is equal to or greater than 10° and equal to or less than 45°.

[0061] (11) The virtual image display device according to (9) or (10), wherein the control unit increases the luminance of the backlight compared to when the display panel is parallel to the backlight.

[0062] (12) The virtual image display device according to (11), wherein the control unit increases the luminance of the backlight as the tilt angle of the display panel with respect to the backlight increases.

[0063] (13) The virtual image display device according to any one of (1) to (12) above, wherein the backlight has the light-emitting element containing a fluoride red phosphor.

[0064] (14) The virtual image display device according to any one of (1) to (13), wherein the reflecting member has a transmissive-reflective concave surface.

[0065] (15) The virtual image display device according to any one of (1) to (14) above, wherein another reflecting member made of a concave mirror is provided between the display panel and the reflecting member.

[0066] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible within the scope of the gist of the present disclosure. It goes without saying that all or part of the components constituting each of the above-described embodiments can be combined as appropriate within the scope of not contradicting each other.

[0067] REFERENCE SIGNS LIST 1 Virtual image display device 2 Display unit 3 Optical system 4 Control unit 5 User 7 Display panel 7a Display surface 61 Light-emitting element 62 Light source surface 63 Illumination segment 6 Backlight 6a Emission surface 64 Base 65 Diffusion plate 62a Main surface 62 Base 3a First optical member (first reflecting member) 3b Second optical member (second reflecting member) 6a Display surface 7b Incident surface θ Predetermined angle

Claims

1. A virtual image display device that displays a virtual image superimposed on an external scene on a reflective member by irradiating the reflective member with light of an image displayed on a display panel, the virtual image display device comprising: a backlight having a plurality of lighting segments each provided with a light-emitting element, which illuminates the light-emitting elements of a selected lighting segment from the plurality of lighting segments that corresponds to the image, and emits the light of the illuminated light-emitting elements toward the display panel; and a control unit that performs local dimming control of the backlight to turn on the light-emitting elements in the image-corresponding lighting segment that corresponds to the image, and to turn off the light-emitting elements in the image-non-corresponding lighting segment that does not correspond to the image, the image being composed of image information having a vanishing point created by a perspective projection method, and the control unit reduces the drive current input to the light-emitting elements the closer the image information is to the vanishing point, thereby turning on the light-emitting elements in the image-corresponding lighting segment.

2. A virtual image display device as described in claim 1, wherein the control unit reduces the drive current by making the brightness of each part of the virtual image in inverse proportion to the distance at which a user is expected to view each part of the virtual image.

3. A virtual image display device as described in claim 1, wherein the control unit reduces the rate at which the drive current is reduced by making the brightness of each part of the virtual image smaller than when the drive current is reduced by making it inversely proportional to the distance at which a user is expected to view each part of the virtual image.

4. The virtual image display device according to claim 3, wherein the control unit reduces the drive current so that Bi = B1 / (L / n) (where Bi is the luminance of each part of the virtual image, B1 is the maximum luminance of the virtual image, L is the estimated distance when the user views each part of the virtual image, and n is a real number from 2 to 10).

5. A virtual image display device as described in any one of claims 1 to 4, wherein the image information includes predetermined image information and other standard image information, and the control unit controls the drive current of the light-emitting element driven by the predetermined image information among the image information to be different from the drive current of the light-emitting element driven by the standard image information.

6. The virtual image display device according to claim 5, wherein the standard image information is the image information of a portion of the virtual image that has the highest brightness.

7. The virtual image display device according to claim 5, wherein the standard image information is the image information of a portion of the virtual image that has the lowest brightness.

8. The virtual image display device according to any one of claims 1 to 7, wherein the image is constituted by the image information having a plurality of the vanishing points.

9. The virtual image display device according to any one of claims 1 to 8, wherein the display panel is disposed at a predetermined angle with respect to the backlight.

10. The virtual image display device according to claim 9, wherein the predetermined angle is equal to or greater than 10° and equal to or less than 45°.

11. The virtual image display device according to claim 9 or 10, wherein the control unit increases the luminance of the backlight compared to when the display panel is parallel to the backlight.

12. The virtual image display device according to claim 11, wherein the control unit increases the luminance of the backlight as the tilt angle of the display panel with respect to the backlight increases.

13. The virtual image display device according to any one of claims 1 to 12, wherein the backlight has the light-emitting elements containing a fluoride red phosphor.

14. The virtual image display device according to any one of claims 1 to 13, wherein the reflective member has a transmissive-reflective concave surface.

15. The virtual image display device according to any one of claims 1 to 14, wherein another reflecting member made of a concave mirror is disposed between the display panel and the reflecting member.

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