Image display apparatus

Abstract

To provide an image display device having high efficiency (low power consumption) and capable of achieving both high luminance and uniformity.SOLUTION: The image display device includes an image generation element that generates an image, a light guide optical system that guides a light flux emitted from the image generation element to a pupil of an observer, and a unit that controls a light emission amount emitted from the image generation element for each partial region, has at least two or more display states having different luminance, and controls the light emission amount emitted from the image generation element to be different for each partial region when the display state transitions from one state to the other state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image display device that displays an image superimposed on a surrounding environment (external environment). [Background technology]

[0002] Conventionally, image display devices such as head mounted displays (HMDs) and head-up displays (HUDs) have been used that form an image displayed by a display means in space, allowing a user to visually recognize the image. Image display devices that form an image in space can display an image in front of a light guide plate, a combiner, a vehicle windshield (windshield), or the like as seen by an observer, making it possible to superimpose the image on the surrounding environment (external environment).

[0003] Head-mounted displays and head-up displays are generally used outdoors, and are required to display images with high visibility under various external lighting conditions.

[0004] Reference 1 describes that visibility can be improved by controlling the light source to be partially lit (local dimming) based on the arrangement of the display content. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-112668 Summary of the Invention [Problem to be solved by the invention]

[0006] Head-mounted displays and head-up displays are required to display images with high visibility under various external lighting conditions. In particular, in environments with very high levels of external light, such as outdoors during the day, it is desirable for image display devices to have high brightness. However, high brightness and high uniformity are in a contradictory relationship, and it is difficult to achieve both.

[0007] The technology of Patent Document 1 controls the turning on (or turning off) of light sources corresponding to areas where there is no display content, so it is not possible to achieve both high brightness and high uniformity.

[0008] An object of the present invention is to provide an image display device that takes advantage of the human visual characteristics, and is highly efficient (low power consumption) and can achieve both high brightness and uniformity. [Means for solving the problem]

[0009] In order to achieve the above object, the image display device of the present invention is an image display device comprising an image generating element that generates an image, a light guiding optical system that guides the light beam emitted from the image generating element to the observer's pupil, and a means for controlling the amount of emitted light emitted from the image generating element for each partial area, and is characterized in that it has at least two or more display states with different brightness, and when transitioning from one of the display states to the other, the amount of emitted light emitted from the image generating element is controlled to be different for each partial area. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an image display device that is highly efficient (low power consumption) and can achieve both high brightness and uniformity. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram showing an image display unit in the first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an image generating element in the first embodiment. [Figure 3] FIG. 2 is a diagram showing an image display unit in the first embodiment. [Figure 4] FIG. 1 is a diagram illustrating human visual characteristics. [Figure 5] FIG. 1 is a diagram illustrating human visual characteristics. [Figure 6] 10A and 10B are diagrams illustrating a luminance profile of an image display section with a high peripheral light amount ratio. [Figure 7] 10A and 10B are diagrams illustrating a luminance profile of an image display section with a low peripheral light ratio. [Figure 8] FIG. 4 is a diagram showing a luminance profile in the first embodiment. [Figure 9] FIG. 4 is a diagram showing a luminance profile in the first embodiment. [Figure 10] 1 is a diagram showing the configuration of a head-mounted display according to the present invention. [Figure 11] 1 is a diagram showing a configuration of a head-up display according to the present invention. [Figure 12] FIG. 10 is a diagram showing an image display unit in a second embodiment. [Figure 13] FIG. 10 is a diagram illustrating a light source device section in a second embodiment. [Figure 14] FIG. 10 is a diagram showing an image display unit in a third embodiment. [Figure 15] FIG. 10 is a diagram showing an illumination area in a third embodiment. [Figure 16] FIG. 10 is a diagram showing a collimator lens in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0012] Preferred embodiments of the present invention will be described below with reference to the drawings. For convenience, the drawings may be drawn at a scale different from the actual scale. The same reference numerals are used to designate the same components, and duplicated descriptions will be omitted.

[0013] An image display device 200 will be described with reference to Figs. 1 to 9. Fig. 1 shows the configuration of an image display unit 200 of the present invention. The image display device 200 includes an image generation element 10 for generating an image. In this embodiment, the image generation element 10 is a self-luminous device having a pixel structure 11 in two-dimensional directions, horizontally and vertically, as shown in Fig. 2, and may be, for example, an organic EL (organic electro-luminescence) device or a micro LED (micro light emitting diode) device.

[0014] Light emitted from the image generating element 10 is guided to the observer's pupil 100 via the light-guiding optical system 20. In FIG. 1, the light-guiding optical system 20 is composed of a lens optical system 20A. However, the light-guiding optical system 20 may alternatively be composed of a prism optical system (including a free-form surface) 20B that deflects the light path by transmission and reflection as shown in FIG. 3A, a light-guiding optical element 20C and a combiner 20D as shown in FIG. 3B, or a light-guiding plate 20E as shown in FIG. 3C. The prism optical system (including a free-form surface) 20B may be composed of multiple prisms as shown in FIG. 3A, or may be composed of a single prism. The light-guiding optical element 20C may be a prism, a lens, or a mirror. The combiner 20D may be a flat surface as shown in FIG. 3B, or a curved surface with a curvature.

[0015] Furthermore, the light deflection toward the observer's pupil 100 may be achieved by utilizing surface reflection of the combiner 20D, by providing a coating that reflects some or all of the light, or by providing a diffractive element or holographic element. The above-mentioned functions may be provided over the entire area of ​​the combiner 20D, or only over a portion through which the light beam passes. The light propagates through the light guide plate 20E by total internal reflection, and a diffractive optical element or holographic element is provided on the entrance and exit surfaces of the light guide plate 20E to deflect the light to an angle that causes total internal reflection or to deflect it so that it exits the light guide plate. A light guide optical system (not shown), including lenses, mirrors, etc., may be provided between the image generating element 10 and the light guide plate 20E.

[0016] The control means 80 is a means for controlling the image generating element 10, and is, for example, a processor such as a CPU (Central Processing Unit). The control means 80 can display an image to be displayed on the image generating element 10, and can control the lighting and light intensity of each pixel 11. The control means 80 may be provided outside the image display device 200.

[0017] As described above, a light beam from the image generating element 10 is guided to the observer's pupil 100 and is recognized as a display image superimposed on the surrounding environment (external environment). This display image may be a real image or a virtual image. When the display image is a virtual image, the virtual image is superimposed on the surrounding environment (external environment) light that passes through the prism optical system 20B, the combiner 20D, and the light guide plate 20E and actually reaches the observer's eye. When the display image is a real image, an image obtained by superimposing the display image on the surrounding environment (external environment) light acquired by a camera (not shown in the figure) or the like is displayed on the image generating element 10 by the control means 80, and the light is guided to the observer's pupil 100 via the lens optical system 20A, the prism optical system 20B, the combiner 20D, and the light guide plate 20E, and is recognized as a display image superimposed on the surrounding environment (external environment).

[0018] In order for the image display device 200 described above to display a highly visible image under any external light environment, it is necessary to guide light with high brightness and high uniformity to the observer's pupil 100. In particular, in environments with very high levels of external light, such as outdoors during the day, it is desirable for the image display device to have higher brightness. On the other hand, in environments with low levels of external light, such as at night, the brightness of the image display device is too bright and bothersome, so the brightness of the image display device must be adjusted according to the external light environment. In other words, achieving both high brightness and high uniformity is required under a wide range of external light environments. However, high brightness and high uniformity are mutually exclusive and difficult to achieve, so we focused on the characteristics of human vision. An explanation will be given based on the light distribution shown in Figures 4 and 5.

[0019] Fig. 4A shows a light emitting source 300 having a certain light distribution and a light receiving surface 310 onto which the light flux from the light emitting source 300 is incident, and Fig. 4B shows the light distribution on the light receiving surface 310. Fig. 4B shows an example of a light distribution with a full width at half maximum (FWHM) of 50 degrees. Note that although the scale of the vertical axis in Fig. 4B is linear, it is known that the amount of human perception is proportional to the logarithm of the amount of stimulus.

[0020] When the stimulus amount R changes, and the amount of human perception in response to this is E, the following relationship is obtained. Here, C is a constant, which indicates that the perceived amount E is proportional to the logarithm of the stimulus amount R. [Number 1] E = C log R

[0021] Figure 5 shows a graph of the luminous intensity distribution, similar to that of Figure 4B, but with different brightness levels. Figure 5A shows a graph of the luminous intensity distribution with a full width at half maximum (FWHM) of 50 degrees, at 100 cd / m 2 , 1000cd / m 2 , 10000cd / m 2 Figure 5C is a graph showing the profile of Figure 5A on a logarithmic vertical scale when the brightness is changed. Because the luminous intensity distribution is the same, when normalized by the maximum value, all the profiles overlap, as in the graph of Figure 5B. Figure 5C is a graph showing the profile of Figure 5A on a logarithmic vertical scale. Figure 5D is a graph of Figure 5C normalized by the maximum value. Like Figure 5A, the luminous intensity distribution is the same, but when scaled logarithmically, the profiles for each brightness do not match. This shows that the amount of perception by humans varies depending on the brightness (amount of stimulus). As shown in Figure 5D, humans are less sensitive to changes in brighter light and more sensitive to changes in darker light.

[0022] As shown in Fig. 6A, when the amount of peripheral light is high to begin with, even if the amount of light emitted from the image generation element 10 is uniformly changed to transition from a bright display state to a dark display state, a sufficient amount of peripheral light can be maintained even in the dark display state as shown in Fig. 6B. In other words, a light-guiding optical system 20 is required that can ensure a desired amount of peripheral light even in a dark display state.

[0023] On the other hand, if the light-guiding optical system 20 is designed to ensure a desired amount of peripheral light in a bright display state as shown in FIG. 7A, when the amount of light emitted from the image-generating element 10 is uniformly changed to transition from a bright display state to a dark display state, the viewer will perceive a decrease in peripheral light in the dark display state as shown in FIG. 7B, and will see an image with dark peripheries. However, to obtain the peripheral light intensity characteristics as shown in FIG. 6, a light-guiding optical system 20 with a large NA is required, which results in an increase in the size of the device. Furthermore, to improve the amount of peripheral light, it is necessary to increase the light distribution angle of the light emitted from the image-generating element 10, which makes it difficult to achieve both high brightness and high brightness.

[0024] Therefore, as shown in Fig. 8A, by designing a light-guiding optical system 20 that ensures a desired amount of peripheral light in a bright display state, and by varying the amount of light emitted from the image generation element 10 for each partial region rather than uniformly when transitioning to a dark display state, it is possible to ensure a desired amount of peripheral light even in a dark display state as shown in Fig. 8B. Furthermore, as shown in Fig. 9, the peripheral light distribution may be asymmetric with respect to the normal to the observer's pupil 100. Note that light adjustment for each partial region may be performed for each pixel 11 or for an area consisting of multiple pixels.

[0025] As described above, by designing the light-guiding optical system 20 so as to ensure the minimum necessary amount of peripheral light in a bright display state where human senses are insensitive to changes in brightness, and by controlling the amount of light emitted from the image generating element 10 to vary for each partial region when transitioning to a dark display state where human senses are sensitive to changes in brightness, it is possible to realize an image display device 200 that is small, highly efficient, and yet achieves both high brightness and peripheral light. Note that the peripheral light amount preferably satisfies the following conditions. [Number 2] log R ≧ 50% Assuming an environment where the amount of external light is darker than outdoors during the day, such as in the evening or indoors, the following conditions are desirable. [Number 3] log R ≧ 60% If we consider an environment with even lower ambient light, such as at night, the following conditions are desirable: [Number 4] log R ≧ 80%

[0026] FIG. 10 is a schematic diagram of a head-mounted display including an image display device 200 according to this embodiment. The image display device 200 is disposed within a frame 400, allowing the observer 100 to view a display image 1000. The control unit 80 may be disposed outside the frame 400, as shown in FIG. 10, or may be disposed within the frame 400. When disposed outside the frame 400, the connection to the frame may be wired or wireless. The image display device 200 may be disposed for each eye, as shown in FIG. 10, or for one eye. When the image display device 200 is disposed for each eye, it is possible to provide parallax to the displayed image, allowing the observer to view the display image 1000 in stereoscopic form. 410 denotes a first information acquisition unit, which is a unit for acquiring at least one of the observer's position information and viewpoint information, and is, for example, an imaging device such as a camera. The observer's position information is information regarding the position of at least a part of the user, such as information regarding the position of the observer's eye 100. The observer's viewpoint information is information about the observer's viewpoint and line of sight, for example, information about the movement of the user's eye 100 (pupil). 420 is a second information acquisition means, which is a means for acquiring outside world information (peripheral information), for example, an imaging device such as a camera.

[0027] The first acquisition means 410 acquires the position information of the user, thereby detecting the amount of deviation in the position of the observer's eye 100 relative to the image display device 200. The control means 80 can correct the deviation in relative position based on the information acquired by the first acquisition means 410.

[0028] The second acquisition means 420 can detect the brightness of the outside world by acquiring the outside world information. The control means 80 can display the display image 1000 with an appropriate brightness to the observer based on the information acquired by the second acquisition means 420. Note that the brightness of the display image can also be determined arbitrarily by the observer operating the control means 80, regardless of the information acquired by the second acquisition means 420.

[0029] 11 is a schematic diagram of a head-up display equipped with an image display device 200 of this embodiment. The image display device 200 is disposed in an in-vehicle system 600, and allows an observer 100 to view a display image 1000. 430 denotes a first information acquisition means, which is a means for acquiring at least one of the observer's position information and viewpoint information, and is, for example, an imaging device such as a camera. The observer's position information is information relating to the position of at least a part of the user, for example, information relating to the position of the observer's eye 100. The user's viewpoint information is information relating to the user's viewpoint or line of sight, for example, information relating to the movement of the observer's eye 100 (pupil).

[0030] The second acquisition means 440 is a means for acquiring external information (peripheral information) such as surrounding obstacles (pedestrians, other vehicles, etc.) and the surrounding environment (scenery), and is, for example, an imaging device such as a camera. The second acquisition means 440 according to this embodiment is arranged to acquire external information in front, but may also be arranged to acquire external information behind, to the sides, etc.

[0031] Next, the operation of the in-vehicle system 500 when a deviation occurs in the relative position between the observer's pupil 100 and the pupil of the image display device 200 will be described in detail.

[0032] The first acquisition means 430 acquires the position information of the user, thereby detecting the amount of deviation in the position of the observer's pupil 100. The control means 80 calculates the amount of adjustment of the reflecting surface 22 in the image display device 200 based on the information acquired by the first acquisition means 430, and moves the reflecting surface based on the amount of adjustment. This makes it possible to correct the deviation in the relative position between the observer's pupil 100 and the pupil of the image display device 200.

[0033] Furthermore, the control means 80 controls the display of an image by the image generating element 10 based on at least one of the user's viewpoint information acquired by the first acquisition means 430 and the external world information acquired by the second acquisition means 440. Then, it is possible to correct the deviation in the relative position between the surrounding environment and the display image 1000.

[0034] The second acquisition means 440 can detect the brightness of the outside world by acquiring the outside world information. The control means 80 can display the display image 1000 with an appropriate brightness to the observer based on the information acquired by the second acquisition means 440. Note that the brightness of the display image can also be determined arbitrarily by the observer operating the control means 80, regardless of the information acquired by the second acquisition means 440.

[0035] In the head-mounted display of FIG. 10 and the head-up display of FIG. 11, the image display device 200 of this embodiment may be replaced by an image display device of another embodiment described later. [Example]

[0036] FIG. 12 shows the configuration of an image display unit 200A according to a second embodiment of the present invention. The image display device 200A of this embodiment differs from the first embodiment in that the image generation element 10A is a non-self-luminous device, but is otherwise the same as the image display unit 200 of the first embodiment. Therefore, components common to the first embodiment are assigned the same reference numerals as the first embodiment and will not be described here. Because the image generation element 10A is a non-self-luminous device, it is illuminated by a light beam emitted from a light source device 12. The image generation element 10A in this embodiment is a so-called MEMS mirror whose tilt angle swings at high speed, and the light beam emitted from the light source device 12 is scanned two-dimensionally by changing the tilt angle of the mirror.

[0037] Although the image generating element 10A shown in FIG. 12 is a two-dimensional scanning MEMS mirror, two-dimensional scanning may also be achieved using multiple one-dimensional scanning MEMS mirrors. The control means 80 controls the time-division lighting of the light source device 12 in synchronization with the tilt angle of the image generating element 10A in response to an externally input image signal, thereby allowing the observer to perceive a two-dimensional image. The tilt angle of the MEMS mirror corresponds to the angle of view perceived by the observer, and the tilt angle of the MEMS mirror is determined according to the angle of view. By controlling the light emission intensity for each angle of view using the control means 80 in consideration of the characteristics of the light-guiding optical system 20, the peripheral light amount described in Example 1 can be achieved.

[0038] It is desirable that the light source device 12 used in the image display unit 200A use a light beam with high linearity (high parallelism). Figure 13 shows the configuration of the light source device 12. Reference numeral 13 denotes a light source, such as an LED (Light Emitting Diode) or a laser (Light Amplification by Stimulated Emission of Radiation). Light emitted from the light source 13 is incident on a collimator lens 14, which is arranged in a pair with the light source. The collimator lens 14 is a lens with positive power and has the function of collimating the light emitted from the light source. Using a laser that is close to a point source can provide light with higher parallelism. The beam width is shaped by a beam shaping means 15. The beam shaping means 15 may be an aperture stop made of an absorbing surface, or a compression means with a variable magnification effect, such as a lens or prism. Because the MEMS mirror used in the image generating element 200A is extremely small, it is desirable that the beam shaping means 15 shape the beam to match the shape of the MEMS mirror.

[0039] The configuration shown in this embodiment lights up the light source device only with the luminous flux of the required angle of view in a time-division manner, so that it is highly efficient and consumes less power, and can be driven for a long time using a battery or the like. [Example]

[0040] 14 shows the configuration of an image display unit 200B according to a third embodiment of the present invention. The image display device 200B of this embodiment is similar to the image display device 200A described in the second embodiment in that the image generation element 10B is a non-self-luminous device, but differs from the first embodiment in that the light source that illuminates the image generation element 10B is a plurality of light sources corresponding to partial regions, and other than that, it is the same as the image display unit 200 of the first embodiment. Therefore, the same reference numerals as those in the first embodiment will be used to designate the components that are common to the first embodiment, and a description thereof will be omitted.

[0041] A plurality of light sources 13 and collimator lenses 14, each paired with a corresponding light source 13, are arranged relative to the image generating element 10B. Light emitted from the plurality of light sources illuminates an area 16 corresponding to each partial area of ​​the image generating element 10B, as shown in FIG. 15. When a plurality of light sources are present, the collimator lens 14 may be a single lens (FIG. 14) or an array of integrated lenses (FIGS. 16A, 16B, and 16C). As shown in FIGS. 16B and 16C, the element lenses may be arranged to overlap each other or may be decentered. While the present embodiment uses a single collimator lens, it may be configured with two or three lenses as needed. The image generating element 10B in this embodiment is a transmissive liquid crystal element, and the control unit 80 drives the image generating element 10B in response to an externally input image signal. As a result, the light beam emitted from the light source 13 is converted into image light corresponding to the input image signal, and the light is guided to the observer's pupil 100 via the light-guiding optical system 20. In this case, by taking into consideration the characteristics of the light-guiding optical system 20 and controlling the light emission intensity of the light source 13 corresponding to each partial region by the control means 80, the amount of peripheral light described in the first embodiment can be realized.

[0042] By disposing a diffusion element 17 between the collimator lens 14 and the image generating element 10B, the boundaries between adjacent illumination areas 16 can be smoothed, enabling highly uniform illumination.

[0043] The configuration shown in this embodiment is an effective means when the image generating element 10B is large, and is suitable for head-up displays that are mainly mounted in cars.

[0044] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0045] 10 (10A, 10B) Image generating element 11. Elemental pixels of image generating element 12 Light source device 13 Light source 14 Collimator 15 Light beam shaping element 16 lighting area 17 Diffusion element 20(20A, 20B, 20C, 20D, 20E) Light guiding optical system 80 Control Means 100 Observer's Eye 200 Image display device 300 light sources 310 Photosensitive surface 400 frames 410, 420, 430, 440 Information acquisition means 500 In-Vehicle Systems 1000 display images

Claims

1. an image generating element for generating an image; a light guiding optical system that guides the light beam emitted from the image generating element to a pupil of an observer; a means for controlling an amount of light emitted from the image generating element for each partial region, An image display device having at least two or more display states with different brightnesses, and characterized in that when transitioning from one of the display states to another, the amount of light emitted from the image generating element is controlled so as to be different for each partial region.

2. 2. The image display device according to claim 1, wherein the distribution of brightness taken into the observer's pupil through the light-guiding optical system includes areas of relatively high brightness and areas of relatively low brightness, and when transitioning from one display state to the other, the amount of light emitted from the image generating element is controlled so that the brightness difference within the image display surface is reduced.

3. 3. The image display device according to claim 1, wherein one of said display states has a higher luminance than the other state.

4. The image display device according to any one of claims 1 to 3, characterized in that the image generating element is a non-self-luminous element, and has at least one light source and means for illuminating the image generating element for each partial region.

5. The image display device according to claim 4, wherein the image generating element is a scanning device that scans and emits a light beam from the light source to the light-guiding optical system, and the amount of light emitted from the light source is controlled in synchronization with the scanning device, thereby varying the amount of light emitted for each partial area.

6. The image display device according to any one of claims 1 to 3, characterized in that the image generating element is a non-self-luminous element, and has at least two or more light sources and a means for illuminating the image generating element for each partial region.

7. 7. The image display device according to claim 6, wherein a plurality of the light sources are arranged so as to illuminate the image generating element in partial regions.

8. 8. The image display device according to claim 6 or 7, wherein the image generating element is a light modulation element having a pixel structure that modulates the light beam from the light source into image light according to an input image signal and emits the image light to the light-guiding optical system, and the amount of light emitted for each partial region is varied by controlling the light amount of each light source corresponding to each partial region of the image generating element.

9. 9. A head-mounted display system, comprising: an image display device according to claim 1, held by a frame; and displaying a display image superimposed on external world information to an observer.

10. 10. The head mounted display system according to claim 9, further comprising a first acquisition means for acquiring at least one of position information and viewpoint information of the viewer.

11. 9. A head-up display system, comprising: an image display device according to claim 1, held by a mobile device, and displaying a display image superimposed on external world information to an observer.

12. 10. The head-up display system according to claim 9, further comprising a first acquisition means for acquiring at least one of position information and viewpoint information of an observer.

Images