Display System

Abstract

To provide a display system which can improve the visibility between a plurality of display devices.SOLUTION: A display system according to an embodiment comprises: a first display device which emits first display light related to a first image that is visually recognized by a viewer by being superimposed on an actual scene; a second display device which emits second display light related to a second image that is visually recognized by the viewer without being superimposed on the actual scene; an illuminance acquisition unit which acquires illuminance of external light; and a display control unit which controls the first display device and the second display device so as to reduce luminance of the first display light and the second display light as the illuminance decreases. The display control unit executes first luminance control of controlling the first display device and the second display device such that an inter-display unit luminance difference being a difference between the luminance of the first display light and the luminance of the second display light changes at a first change rate when the illuminance is higher than prescribed illuminance, and executes second luminance control of controlling the first display device and the second display device such that the inter-display unit luminance difference changes at a second change rate smaller than the first change rate when the illuminance is equal to or less than the prescribed illuminance.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a display system for a vehicle or the like having a plurality of display devices. [Background technology]

[0002] 2. Description of the Related Art Conventionally, it is known that a plurality of display devices are arranged at a plurality of locations within a vehicle and are controlled in an interlocking manner. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2011-230625 Summary of the Invention [Problem to be solved by the invention]

[0004] Vehicles are equipped with head-up displays that can display information in various display modes, as well as large display panels that can display a large amount of information. Furthermore, in order to emphasize and convey information that is particularly important to the viewer, the same image may be displayed simultaneously on multiple display devices. However, if the display devices have different modes, even if the intention is to display images in the same hue, they may be displayed in the hue specific to each display device, potentially resulting in hue differences between images. The present disclosure has been made in consideration of the above circumstances, and aims to provide a display system that can improve visibility among a plurality of display devices. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the display system of the present disclosure includes a first display device that emits first display light relating to a first image that is superimposed on an actual scene and that is visually recognized by a viewer, and a second display light that emits second display light relating to a second image that is visually recognized by the viewer without being superimposed on the actual scene. The firsta display control unit that controls the first display device and the second display device so as to reduce the luminance of the first display light and the second display light as the illuminance decreases, and when the illuminance is higher than a predetermined illuminance, executes a first luminance control that controls the first display device and the second display device so that an inter-display luminance difference, which is a difference between the luminance of the first display light and the luminance of the second display light, changes at a first rate of change; and when the illuminance is lower than the predetermined illuminance, executes a first luminance control that controls the first display device and the second display device so that an inter-display luminance difference, which is a difference between the luminance of the first display light and the luminance of the second display light, changes at a first rate of change. In a range where the luminance difference between the displays is not zero, The display control unit executes second brightness control to control the first display device and the second display device so that the brightness difference between the display devices changes at a second change rate that is smaller than the first change rate. [Effects of the Invention]

[0006] In the display system of the present disclosure, visibility among a plurality of display devices can be improved. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing an example of the system configuration of a display system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing an example of a display by two display devices. [Figure 3] 6 is a graph showing the relationship between the upper HUD luminance and the lower HUD luminance and the illuminance in the first luminance control and the third luminance control. [Figure 4] 6 is a graph showing the relationship between the luminance difference between the display units and the illuminance in the first luminance control and the third luminance control. [Figure 5] 6 is a flowchart illustrating a brightness control process executed by a main control unit. [Figure 6] FIG. 10 is an explanatory diagram showing a display example in which the upper HUD image and the lower HUD image are images of the same format. [Figure 7] 10 is a graph showing the relationship between the luminance difference between the display devices and the illuminance in the first luminance control and the second luminance control. [Figure 8] 10 is a graph illustrating the relationship between the upper HUD luminance and the lower HUD luminance and the illuminance, explaining a second luminance control as a first example. [Figure 9] 10 is a graph showing the relationship between the upper HUD luminance and the lower HUD luminance and the illuminance, illustrating a second luminance control as a second example executed by the main control unit. [Figure 10] 10 is a graph showing the relationship between the upper HUD luminance and the lower HUD luminance and the illuminance, illustrating a second luminance control as a third example executed by the main control unit. [Figure 11] 10 is a graph showing the relationship between the upper HUD luminance and the lower HUD luminance and the illuminance, illustrating a second luminance control as a fourth example executed by the main control unit. [Figure 12] 8 is a graph showing the relationship between the luminance difference between the displays and the illuminance as another example corresponding to FIG. 7. [Figure 13] 10 is a graph showing another example of control of the upper HUD luminance and the lower HUD luminance. [Figure 14] 10 is a graph showing yet another example of control of the upper HUD luminance and the lower HUD luminance. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of a display system according to the present disclosure will be described with reference to the accompanying drawings. The display system according to the present disclosure can be applied to display systems mounted on vehicles such as automobiles and motorcycles, as well as on ships, agricultural machinery, and construction machinery. In this embodiment, the display system according to the present disclosure will be described using an example in which the display system is mounted on a vehicle and has two head-up displays (HUDs) that display required information based on various information acquired from the vehicle.

[0009] FIG. 1 is a diagram showing an example of the system configuration of a display system 10 according to this embodiment. FIG. 2 is a diagram showing an example of a display by two display devices.

[0010] In the following description, "front," "rear," "upper," "lower," "right," and "left" follow the definitions of "Fr.", "Re.", "To.", "Bo.", "R," and "L" in Figures 1 and 2.

[0011] The display system 10 is mounted within the instrument panel 2 of the vehicle 1. The display system 10 includes an upper HUD 20, a lower HUD 30, and a main control unit 40.

[0012] The upper HUD 20 (first display device) is disposed forward of the steering wheel 5, and irradiates the windshield 3 with display light L1 (first display light). The display light L1 is reflected by the windshield 3 toward the driver 4 (viewer), allowing the driver 4 to view an image (first image, hereinafter referred to as "upper HUD image 28") based on a virtual image V1 in front of the vehicle 1. The upper HUD image 28 is displayed, for example, within the virtual upper HUD display area 8 in FIG. 2, and is viewed superimposed on the actual scenery ahead, such as the road surface.

[0013] The lower HUD 30 (second display device) is positioned further forward (away from the driver 4) than the upper HUD 20 and irradiates a light-shielding portion 3a formed around the windshield 3 with display light L2 (second display light). The light-shielding portion 3a is a portion made of a light-shielding color such as black, made of black ceramics or the like. The light-shielding portion 3a is formed for the purposes of preventing deterioration of the adhesive that secures the windshield 3 to the vehicle 1 due to sunlight, concealing the adhesive, and improving the design. The display light L2 is reflected by the light-shielding portion 3a toward the driver 4, allowing the driver 4 to view an image (second image, hereinafter referred to as a "lower HUD image 39") formed by a virtual image V2 in front of the vehicle 1. The lower HUD image 39 is displayed, for example, in a virtual lower HUD display area 9 different from the upper HUD display area 8 in FIG. 2 and is viewed forward of the light-shielding portion 3a. Unlike the upper HUD image 28, the lower HUD image 39 is not superimposed on the actual scene, but is superimposed on the light-shielding area 3a for visibility.

[0014] The upper HUD 20 displays an image such that the upper HUD image 28, represented by the virtual image V1, is visible at a distance d1 vertically relative to the driver's (driver's) line of sight 4a. The lower HUD 30 displays an image such that the lower HUD image 39, represented by the virtual image V2, is visible at a distance d2, which is greater than the distance d1 relative to the driver's (driver's) line of sight 4a. In other words, the distance the driver 4 needs to move to shift their line of sight 4a to the lower HUD image 39 is greater than the distance the driver 4 needs to move to shift their line of sight 4a to the upper HUD image 28. To put it another way, the angle θ2 formed by the direction of the line of sight 4a and the direction of the line of sight to view the lower HUD image 39 is greater than the angle θ1 formed by the direction of the line of sight 4a and the direction of the line of sight to view the upper HUD image 28. Therefore, driver 4 views the lower HUD image 39 from a position further from the line of sight 4a than the upper HUD image 28, and below the upper HUD image 28.

[0015] In this embodiment, the upper HUD 20 forms the upper HUD image 28 in front of the lower HUD image 39. That is, the upper HUD image 28 is viewed from a position farther from the driver 4 in the front-to-rear direction, and the lower HUD image 39 is viewed from a position closer to the driver 4 in the front-to-rear direction.

[0016] The display surface of the upper HUD display area 8 and the lower HUD display area 9 is a surface having four sides: top, bottom, left, and right. For example, the bottom sides 8a, 9a and the top sides 8b, 9b are sides that are approximately parallel to the left-right direction. The left sides 8c, 9c and the right sides 8d, 9d are surfaces that are set at any angle with respect to the up-down direction. For example, the display surface is formed so that the left sides 8c, 9c and the right sides 8d, 9d are surfaces that are aligned along the up-down direction (surfaces perpendicular to the road surface), inclined at a predetermined angle with respect to the up-down direction (surfaces inclined with respect to the road surface), or surfaces that are aligned along the front-to-rear direction (surfaces that are superimposed (approximately parallel) to the road surface). Alternatively, the display surface may be a surface that is formed so that the left sides 8c, 9c and the right sides 8d, 9d are curved so that the side closer to the driver 4 is aligned along the up-down direction and curves along the front-to-rear direction as they become farther away. A display surface formed on a surface other than perpendicular to the road surface can display an image that expresses a sense of depth, with the display distance between the driver 4 and the virtual image varying depending on the display position on the display surface. For example, if the display surface is a surface that is inclined so that the left sides 8c, 9c and the right sides 8d, 9d are positioned forward of the upper sides 8b, 9b relative to the lower sides 8a, 9a, the driver 4 can perceive depth on the display surface.

[0017] Furthermore, information regarding the driver's line of sight 4a (viewpoint) for calculating the display distance of the image may be pre-set and held by the main control unit 40, etc., or if the vehicle 1 or the display system 10 has a sensor for detecting the driver's line of sight, it may be detected by this sensor.

[0018] The upper HUD 20 includes a display 21, a concave mirror 22, a housing 24, and an upper HUD display control unit 25.

[0019] The display unit 21 emits display light L1 toward the concave mirror 22. The display unit 21 is, for example, a TFT (Thin Film Transistor) type liquid crystal display or an organic EL (Electroluminescence) display. The display unit 21 may also have a projector and a screen that constitutes the display surface.

[0020] The concave mirror 22 reflects the display light L1 emitted by the display device 21 toward the windshield 3. The concave mirror 22 functions as a magnifying glass, and enlarges the image displayed on the display device 21 and reflects it toward the windshield 3. In other words, the driver 4 sees an enlarged version of the image displayed on the display device 21.

[0021] The housing 24 supports therein the concave mirror 22, the display 21, and a control board on which the upper HUD display control unit 25 is mounted.

[0022] The upper HUD display control unit 25 has a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., and executes predetermined arithmetic processing according to a program written in the ROM. Specifically, the upper HUD display control unit 25 controls the display 21 to display a required image based on instructions from the main control unit 40.

[0023] The lower HUD 30 includes a display 31, a housing 34, and a lower HUD display control unit 35.

[0024] The display 31 directly emits display light L2 to the light-shielding portion 3a outside the housing 34. The display 31 has a configuration similar to that of, for example, the upper HUD 20. This allows the driver 4 to view an image displayed on the display 31 and reflected by the light-shielding portion 3a.

[0025] The housing 34 supports a control board on which the display 31 and the lower HUD display control unit 35 are mounted inside the housing 34.

[0026] The lower HUD display control unit 35 has a CPU, ROM, RAM, etc., and executes predetermined arithmetic processing in accordance with a program written in the ROM. Specifically, the lower HUD display control unit 35 controls the display 31 to display a required image based on instructions from the main control unit 40.

[0027] The main control unit 40 (display control unit) controls the upper HUD 20 and the lower HUD 30, particularly based on information acquired from each unit of the vehicle 1, which will be described later. The main control unit 40 has a CPU, a ROM, a RAM, etc., and executes predetermined calculation processing and brightness control processing, which will be described later, according to a program written in the ROM.

[0028] In addition to the display system 10, the vehicle 1 has an ambient light sensor 51, a surrounding information acquisition unit 52, an outside-vehicle information acquisition unit 53, a car navigation system 54, and a vehicle ECU (Electronic Control Unit) 55. Each unit and the main control unit 40 are connected via, for example, a CAN (Controller Area Network) bus 50. The main control unit 40 determines information (images) to be displayed in the upper HUD display area 8 and the lower HUD display area 9 based on information acquired from, for example, the surrounding information acquisition unit 52, the outside-vehicle information acquisition unit 53, the car navigation system 54, and the vehicle ECU 55.

[0029] The external light sensor 51 is, for example, a photodiode, and detects the brightness (external light) inside or outside the vehicle 1 to obtain information about the external light illuminance (illuminance). The information about the illuminance can be used by the upper HUD 20 to determine the brightness of the display light L1. For this reason, it is preferable that the external light sensor 51 detects the illuminance of the upper HUD display area 8, for example. Note that the external light sensor 51 may be provided on the display system 10 side rather than on the vehicle 1 side, such as by being disposed in the housing 24 of the upper HUD 20, for example.

[0030] The surrounding information acquisition unit 52 acquires information about the surroundings (external) of the vehicle 1. The surrounding information acquisition unit 52 performs communication between the vehicle 1 and a wireless network, between the vehicle 1 and other vehicles, between the vehicle 1 and pedestrians, and between the vehicle 1 and roadside infrastructure. For example, the surrounding information acquisition unit 52 has a communication module that can directly access a wide area network (WAN), a communication module for communicating with an external device (such as a mobile router) that can access the WAN, or an access point of a public wireless local area network (LAN), and performs Internet communication. The surrounding information acquisition unit 52 also has a wireless communication module that complies with a predetermined wireless communication standard. Furthermore, the surrounding information acquisition unit 52 has a communication device that wirelessly communicates with roadside infrastructure, and acquires object information and traffic information from a base station of a driving safety support system (DSSS) via a roadside wireless device installed as infrastructure, for example.

[0031] The outside-vehicle information acquisition unit 53 detects the contents and positions of objects such as people, structures, and other vehicles that exist in the external environment, which is above, below, behind, on the left, and on the right (surroundings of the vehicle 1) of the vehicle 1. The outside-vehicle information acquisition unit 53 is, for example, a stereo camera that captures images of the scenery around the vehicle 1, a distance measurement sensor such as a LIDAR (Laser Imaging Detection And Ranging) that measures the distance from the vehicle 1 to an object, a sonar, an ultrasonic sensor, a millimeter-wave radar, or the like that detects objects located around the vehicle 1.

[0032] The car navigation system 54 has a GPS controller that calculates the position of the vehicle 1 based on GPS (Global Positioning System) signals received from artificial satellites, etc. The car navigation system 54 has a memory unit that stores map data, and based on the position information from the GPS controller, reads map data for the area around the current position from the memory unit and determines a guide route to the destination set by the user. The car navigation system 54 outputs information about the current position of the vehicle 1 and the determined guide route to the main control unit 40.

[0033] Furthermore, the car navigation system 54, by referring to map data, outputs information to the main control unit 40 indicating the name and type of facilities in front of the vehicle 1, the distance between the facilities and the vehicle 1, etc. The map data associates various types of information with location data, such as road shape information (lanes, road width, number of lanes, intersections, curves, junctions, etc.), traffic information such as road signs including speed limits, road closures, alternating one-way traffic, speed restrictions, etc., and information about each lane when there are multiple lanes. The car navigation system 54 outputs these various types of information to the main control unit 40. Note that the car navigation system 54 is not limited to being installed in the vehicle 1, but may also be implemented by a portable terminal with car navigation functionality (e.g., a smartphone or tablet PC (Personal Computer)) that communicates with the main control unit 40 by wire or wireless connection.

[0034] The vehicle ECU 55 acquires vehicle information necessary for the operation of vehicle 1, such as vehicle speed and engine speed, from various sensors installed on vehicle 1, and controls the operation of vehicle 1. The vehicle ECU 55 outputs necessary vehicle information, such as vehicle speed and warning information for vehicle 1 itself (e.g., low fuel, abnormal engine oil pressure), to the main control unit 40.

[0035] Next, the brightness control process performed by the display system 10 will be described in detail. The display system 10 controls the brightness of the display light L1 emitted from the display unit 21 of the upper HUD 20 (hereinafter referred to as "upper HUD brightness") and the brightness of the display light L2 emitted from the display unit 31 of the lower HUD 30 (hereinafter referred to as "lower HUD brightness") according to the illuminance obtained from the ambient light sensor 51.

[0036] Figure 3 is a graph showing the relationship between the upper HUD brightness B1 and lower HUD brightness B2 and illuminance in the first brightness control C1 and third brightness control C3 (described later) executed by the main control unit 40. Figure 4 is a graph showing the relationship between the difference between the upper HUD brightness B1 and the lower HUD brightness B2 (hereinafter referred to as the "dual-display brightness difference") and illuminance.

[0037] As shown in FIG. 3, the main control unit 40 controls the upper HUD 20 and the lower HUD 30 to reduce the upper HUD luminance B1 and the lower HUD luminance B2 as the illuminance decreases. At this time, the upper HUD 20 displays the upper HUD image 28 superimposed on the actual scene, which may result in reduced visibility due to the influence of external light. For this reason, the upper HUD luminance B1 is set higher than the lower HUD luminance B2. Furthermore, as the illuminance decreases (becomes darker), the viewer's eyes become more sensitive. Therefore, to avoid abrupt changes in luminance, the rate of change of the upper HUD luminance B1 and the lower HUD luminance B2 is set smaller when the illuminance is below a predetermined illuminance that is set arbitrarily than when the illuminance is higher than the predetermined illuminance.

[0038] The upper HUD 20 emits display light L1 from the display 21, passes through a concave mirror 22, which is a relay optical system, and is reflected by the windshield 3, thereby allowing the driver 4 to view the display light L1. The lower HUD 30 emits display light L2 from the display 31 and reflects it off the shading portion 3a, allowing the driver 4 to view the display light L2. That is, the lower HUD 30 emits the display light L2 directly to the shading portion 3a, which is a projection member. Due to these differences, it is more difficult for the driver 4 to view the upper HUD image 28 in the same hue as the display light L1 output from the display 21 than the lower HUD image 39. In other words, the upper HUD image 28 has poor hue expression. The upper HUD image 28 is superimposed on the actual scene, while the lower HUD image 39 is superimposed on the black shading portion 3a. For this reason, the upper HUD image 28 is more susceptible to the influence of the actual scene than the lower HUD image 39, resulting in lower contrast.

[0039] For this reason, when the main control unit 40 attempts to display the upper HUD image 28 and the lower HUD image 39 as images of the same form, the upper HUD image 28 has lower contrast and poorer hue expression than the lower HUD image 39, resulting in a difference in hue between the two images. As a result, the driver 4 may perceive the upper HUD image 28 and the lower HUD image 39, which are images of the same form, as images conveying different information, which may result in the information not being conveyed accurately. Note that images of the same form refer to images that are expressed in the same color (hue) and have the same shape (including similar shapes).

[0040] Therefore, the display system 10 in this embodiment solves the above problem by controlling the display system to intentionally increase the difference in brightness between displays when certain conditions are met in a region below a predetermined illuminance where the difference in brightness between displays is small. A detailed explanation follows below.

[0041] Figure 5 is a flowchart illustrating the brightness control process performed by the main control unit 40. The brightness control process is performed continuously while the display system 10 is running.

[0042] In step S1, the main control unit 40 (illuminance acquisition unit) acquires the illuminance from the external light sensor 51. The main control unit 40 determines whether the acquired illuminance is equal to or less than a predetermined illuminance that has been set in advance. If the main control unit 40 determines that the illuminance is not equal to or less than the predetermined illuminance (higher than the predetermined illuminance) (NO in step S1), the main control unit 40 executes first luminance control in step S2, which controls the upper HUD luminance B1 and the lower HUD luminance B2 so that they change at a first rate of change.

[0043] The first rate of change is a predetermined rate of change that is set and stored in advance, for example, as defined in Figure 4, which is the rate of change in the luminance difference between displays when the illuminance is higher than a predetermined illuminance. The first luminance control C1 controls the upper HUD luminance B1 and the lower HUD luminance B2 by the first rate of change when the illuminance is higher than a predetermined illuminance.

[0044] On the other hand, if the main control unit 40 determines that the illuminance is equal to or lower than the predetermined illuminance (YES in step S1), it determines in step S3 whether the displayed upper HUD image 28 and lower HUD image 39 are images of the same type (whether the predetermined condition is satisfied). FIG. 6 is an explanatory diagram showing a display example in which the upper HUD image 28 and the lower HUD image 39 are images of the same type. As shown in FIG. 6, the main control unit 40 displays, for example, an image showing a warning mark (warning) on ​​the upper HUD 20 and the lower HUD 30 as the upper HUD image 28 and the lower HUD image 39 to notify the driver 4 of a warning. The main control unit 40 displays the warning mark in, for example, a red warning color.

[0045] If the main control unit 40 determines that the upper HUD image 28 and the lower HUD image 39 are not images of the same form (NO in step S3), in step S4, it executes a third brightness control C3 to control the upper HUD brightness B1 and the lower HUD brightness B2 so that they change at a third rate of change.

[0046] Here, the third rate of change is a predetermined rate of change that is less than or equal to the first rate of change and greater than the second rate of change, which will be described later. The third rate of change is, for example, the rate of change of the luminance difference between displays when the illuminance is below a predetermined illuminance, as defined in Figure 4. The third luminance control C3 controls the upper HUD luminance B1 and the lower HUD luminance B2 by the third rate of change when the illuminance is below a predetermined illuminance.

[0047] On the other hand, if the main control unit 40 determines that the upper HUD image 28 and the lower HUD image 39 are images of the same form as shown in Figure 6 (YES in step S3), in step S5, it executes a second brightness control C2 to control the upper HUD brightness B1 and lower HUD brightness B2 so that the brightness difference between the displays changes at a second rate of change that is smaller than the first rate of change. Here, Figure 7 is a graph showing the relationship between the brightness difference between the displays and illuminance in the first brightness control C1 and the second brightness control C2. Note that the brightness difference between the displays in the first brightness control C1 in Figure 7 is the same as that in the first brightness control C1 in Figure 4.

[0048] The second rate of change is a predetermined rate of change that is set and stored in advance so as to be smaller than the first and third rates of change. For example, it is the rate of change in the luminance difference between displays when the illuminance is below a predetermined illuminance, as defined in Figure 7. The second luminance control C2 controls the upper HUD luminance B1 and lower HUD luminance B2 by the second rate of change when the illuminance is below a predetermined illuminance.

[0049] By controlling the luminance at the second change rate, the main control unit 40 increases the luminance difference between the display devices compared to when controlling at the third change rate. That is, when the upper HUD image 28 and the lower HUD image 39 are images of the same format, the main control unit 40 executes the second luminance control C2 to reduce the sense of incongruity caused by the hue difference (correct the hue difference). On the other hand, when the upper HUD image 28 and the lower HUD image 39 are images of different formats, the main control unit 40 determines that the sense of incongruity caused by the hue difference will not be given to the driver 4, and executes the third luminance control C3.

[0050] Here, Fig. 8 is a graph illustrating the relationship between the upper HUD luminance B1 and the lower HUD luminance B2 and illuminance, explaining the second luminance control C2 as a first example. Fig. 9 is a graph illustrating the relationship between the upper HUD luminance B1 and the lower HUD luminance B2 and illuminance, explaining the second luminance control C2 as a second example. Fig. 10 is a graph illustrating the relationship between the upper HUD luminance B1 and the lower HUD luminance B2 and illuminance, explaining the second luminance control C2 as a third example. Fig. 11 is a graph illustrating the relationship between the upper HUD luminance B1 and the lower HUD luminance B2 and illuminance, explaining the second luminance control C2 as a fourth example.

[0051] Furthermore, in Figures 8 to 11, and Figures 12 to 14 described later, the upper HUD brightness B1, lower HUD brightness B2, and the brightness difference between displays in the case of the third brightness control C3 are shown by dotted lines for explanatory purposes.

[0052] To reduce the second change rate, i.e., to increase the luminance difference between the display devices compared to when the third luminance control C3 is executed, the main control unit 40 may increase the upper HUD luminance B1 compared to the upper HUD luminance B1 when the third change rate is used and may increase the lower HUD luminance B2 to the same as the lower HUD luminance B2 when the third change rate is used, as shown in Fig. 8. Alternatively, the main control unit 40 may decrease the lower HUD luminance B2 compared to the lower HUD luminance B2 when the third change rate is used and may increase the upper HUD luminance B1 compared to the upper HUD luminance B1 when the third change rate is used, as shown in Fig. 9. As a result, the main control unit 40 can increase the luminance difference between the display devices when the second luminance control C2 is executed compared to when the third luminance control C3 is executed.

[0053] Furthermore, the main control unit 40 may discontinuously change the upper HUD brightness B1 and lower HUD brightness B2 when switching between the first brightness control C1 and the second brightness control C2 at a predetermined illuminance. Specifically, as shown in Figure 10, the main control unit 40 may increase (decrease) the upper HUD brightness B1 by a predetermined value when the illuminance decreases (increases) and reaches a predetermined illuminance. Also, as shown in Figure 11, the main control unit 40 may decrease (increase) the lower HUD brightness B2 by a predetermined value when the illuminance decreases (increases) and reaches a predetermined illuminance. As a result, the main control unit 40 can increase the brightness difference between displays when executing the second brightness control C2 compared to when executing the third brightness control C3.

[0054] If the change in the upper HUD luminance B1 and the lower HUD luminance B2 at a predetermined illuminance is discontinuous, a sudden change in the luminance occurs in the upper HUD luminance B1 and the lower HUD luminance B2. In this case, it is preferable that the main control unit 40 gradually increases or decreases (changes) the luminance at the time of switching to the luminance after switching.

[0055] After the brightness control execution steps S2, S4, and S5, the main control unit 40 returns to the illuminance determination step S1 and repeats the subsequent processing. However, if the upper HUD image 28 and the lower HUD image 39 are no longer images of the same form (the predetermined conditions are no longer met) during the execution of the second brightness control C2, or if the upper HUD image 28 and the lower HUD image 39 become images of the same form (the predetermined conditions are met) during the execution of the third brightness control C3, the upper HUD brightness B1 and the lower HUD brightness B2 may change discontinuously, potentially causing a rapid change in brightness. Therefore, if the main control unit 40 is executing the second brightness control C2, it may gradually change the brightness to the brightness applicable to the upper HUD 20 and the lower HUD 30 in the third brightness control C3 before executing the third brightness control C3. Alternatively, if the main control unit 40 is executing the third brightness control C3, it may gradually change the brightness to the brightness applicable to the upper HUD 20 or the lower HUD 30 in the second brightness control C2 before executing the second brightness control C2.

[0056] In this embodiment, the display system 10 performs a second brightness control C2 in a range below a predetermined illuminance where a hue difference occurs between the upper HUD image 28 and the lower HUD image 39, which may cause discomfort to the driver 4. This reduces the discomfort caused by the hue difference between the upper HUD image 28 and the lower HUD image 39. In other words, the display system 10 makes the second rate of change, which is the rate of change of the brightness difference between the displays when the illuminance is below a predetermined level, smaller than the first rate of change, which is the rate of change of the brightness difference between the displays when the illuminance is higher than a predetermined level. As a result, the display system 10 maintains the required brightness difference without making the brightness difference between the displays too small when the illuminance is low. Therefore, the display system 10 can relatively improve the visibility of the upper HUD image 28 and reduce discomfort caused by unintentionally occurring hue differences.

[0057] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0058] For example, in the above example, the luminance difference between the display devices changes linearly and the first to third change rates are constant. However, as shown in Fig. 12, the luminance difference between the display devices may change in a curved manner as long as the relationship of first change rate > third change rate > second change rate holds.

[0059] Furthermore, the control of the upper HUD luminance B1 and the lower HUD luminance B2 in FIGS. 3 and 8 to 11 is merely an example, and various controls can be applied, for example, as shown in FIGS.

[0060] In the display system 10, the predetermined condition is that the upper HUD image 28 and the lower HUD image 39 are images of the same form. However, the predetermined condition is not limited to this, and other conditions may be used, such as the upper HUD image 28 and the lower HUD image 39 being images with similar hues, even if they are of different forms. Furthermore, the display system may perform second brightness control below a predetermined illuminance without determining whether the predetermined condition is met.

[0061] The predetermined illuminance does not need to be constant and may be variable. For example, if the display system 10 allows the driver 4 to arbitrarily adjust the upper HUD brightness B1 and lower HUD brightness B2, and the brightness is set higher than normal, the predetermined illuminance may be set to a value lower than the reference value. In this case, the display system 10 may set the amount of change in the predetermined illuminance according to the amount of change in brightness by the driver 4. Furthermore, if the display system 10 allows the driver 4 to arbitrarily adjust the amount of hue correction by the second brightness control C2 or the illuminance at which the second brightness control C2 is started, the predetermined illuminance may also be variable. For example, if the driver 4 sets the illuminance at which the second brightness control C2 is started to be small (i.e., if the driver 4 is set to have difficulty perceiving hue differences), the predetermined illuminance may be set to a value lower than the reference value. These settings from the driver 4 are made, for example, via an input device (not shown).

[0062] Furthermore, although an example was described in which both the first and second display devices are HUDs, the second display device may also be one that displays a real image on a display panel such as a TFT (Thin Film Transistor) type liquid crystal display or an organic EL (Electroluminescence) display. Also, although an example was described in which the projection member of the upper HUD 20 is a windshield 3, a combiner may be used instead. [Explanation of symbols]

[0063] 1 vehicle 2. Instrument panel 3 Windshield 3a Light shielding part 4 Driver (visitor) 4a line of sight 5 Steering wheel 8 Upper HUD display area 8a bottom edge 8b Top 8c Left side 8d Right hand side 9 Lower HUD display area 9a bottom edge 9b Top edge 9c left side 9d Right side 10 Display System 20 Upper HUD (first display device) 21 Display 22 concave mirror 24 cabinets 25 Upper HUD display control unit 28. Upper HUD image (first image) 30 Lower HUD (second display) 31 Display 34 cabinets 35 Lower HUD display control unit 39 Lower HUD image (second image) 40 Main control unit (display control unit) 50 CAN bus 51 Ambient light sensor 52 Peripheral Information Acquisition Unit 53 External vehicle information acquisition unit 54 Car Navigation System 55 Vehicle ECU C1 First Brightness Control C2 Second Brightness Control C3 Third brightness control L1 display light (first display light) L2 display light (second display light) V1, V2 virtual images d1, d2 distance θ1, θ2 angle

Claims

1. a first display device that emits first display light relating to a first image that is superimposed on an actual scene and that is viewed by a viewer; a second display device that emits second display light related to a second image that is to be viewed by the viewer without being superimposed on the actual scene; an illuminance acquisition unit that acquires the illuminance of external light; a display control unit that controls the first display device and the second display device to reduce the luminance of the first display light and the second display light as the illuminance decreases, and when the illuminance is higher than a predetermined illuminance, executes first luminance control to control the first display device and the second display device so that a luminance difference between the display devices, which is the difference between the luminance of the first display light and the luminance of the second display light, changes at a first change rate; and when the illuminance is equal to or lower than the predetermined illuminance, executes second luminance control to control the first display device and the second display device so that the luminance difference between the display devices changes at a second change rate that is smaller than the first change rate, within a range where the luminance difference between the display devices does not become zero.

2. 2. The display system of claim 1, wherein the display control unit executes the second brightness control when a predetermined condition is satisfied and the illuminance is equal to or lower than the predetermined illuminance, and executes a third brightness control to control the first display device and the second display device so that the luminance difference between the display devices changes at a third change rate that is equal to or lower than the first change rate and greater than the second change rate when the predetermined condition is not satisfied and the illuminance is equal to or lower than the predetermined illuminance.

3. The display system according to claim 2 , wherein the predetermined condition is that the first image and the second image are images of the same format.

4. 3. The display system of claim 2, wherein if the predetermined condition is no longer satisfied during execution of the second brightness control, the display control unit gradually changes the brightness to the brightness applied to the first display light and the second display light in the third brightness control and then executes the third brightness control, and if the predetermined condition is satisfied during execution of the third brightness control, the display control unit gradually changes the brightness to the brightness applied to the first display light or the second display light in the second brightness control and then executes the second brightness control.

5. 3. The display system of claim 2, wherein the display control unit, when using the second change rate, makes the brightness of the first display light greater than the brightness of the first display light when using the third change rate, and makes the brightness of the second display light equal to the brightness of the second display light when using the third change rate.

6. 3. The display system of claim 2, wherein the display control unit, when using the second change rate, makes the brightness of the second display light smaller than the brightness of the second display light when using the third change rate, and makes the brightness of the first display light equal to the brightness of the first display light when using the third change rate.

Images