JP2024156502A - Display device - Google Patents

Abstract

A display device is provided that is capable of displaying images that do not cause a plurality of users to feel uncomfortable due to the viewing angle characteristics and light reflection characteristics of the display, while suppressing an increase in power consumption.
[Solution] The display device includes a solar radiation estimation unit 12c that estimates solar radiation areas and non-sun radiation areas on the display surface of a display 20, a position information acquisition unit 12e that acquires position information of at least two users relative to the display 20, and a brightness control unit 12f. The brightness control unit 12f executes a first brightness control that makes the brightness of a solar radiation pixel group located in the solar radiation area higher than the brightness of a non-sun radiation pixel group located in the non-sun radiation area based on the estimation result by the solar radiation estimation unit 12c. The brightness control unit 12f also executes a second brightness control that makes the difference in contrast ratio as seen by the two users at least in the non-sun radiation area equal to or less than a predetermined value based on the position information of the at least two users and the viewing angle characteristics and reflection characteristics of the display 20.
[Selected Figure] Figure 1

Description

The present invention relates to a display device that can control the brightness of the display on a pixel-by-pixel basis or on a pixel-group basis up to a certain number of pixels.

Display devices have been proposed that improve the visibility of the screen by controlling the brightness of the display when the display surface is exposed to sunlight (for example, Patent Document 1). The device described in Patent Document 1 is a vehicle display device mounted on a moving object such as an automobile, and is configured to automatically control the brightness level of the entire display screen based on conditions such as the time of use and the vehicle's traveling position. As a result, the brightness corresponds to the brightness of the surrounding environment in which the display device is mounted, even without providing a sensor to detect brightness, improving the visibility of the display screen.

Japanese Patent Application Publication No. 11-184446

However, because this display device automatically controls the brightness level of the entire display screen in response to certain conditions, it is not possible to adjust the brightness level of only a portion of the screen. For example, this display device will raise the brightness level of the entire screen even in a situation where only a portion of the display screen is exposed to sunlight, resulting in an unnecessary increase in power consumption.

One possible solution is to place multiple illuminance sensors around the display, estimate the sunlit area, which is the area of the display that receives sunlight, based on the illuminance signal from the illuminance sensors, and perform brightness control to make the estimated sunlit area relatively brighter than other areas. This makes it possible to perform partial brightness control on the pixel group located in the sunlit area among the constituent pixels of the display, i.e., the sunlit pixel group, and improves the visibility of the sunlit area of the displayed image while suppressing increases in power consumption.

However, the above brightness control does not take into account changes in brightness based on the viewing angle characteristics of the display itself, and the effects of the light reflection characteristics of the display screen. Specifically, due to the viewing angle characteristics of the display itself, the brightness perceived by the user changes depending on the user's position relative to the display screen, even if the same set brightness is used. In addition, due to the light reflection characteristics of the display screen, even if a constant amount of external light is reflected, the brightness of the reflected light perceived by the user changes depending on the user's position relative to the display screen. For this reason, a display image after brightness control based only on illuminance information obtained by multiple illuminance sensors may cause the user to feel uncomfortable. Furthermore, when there are multiple users, the viewing angle characteristics and reflection characteristics of the display change depending on the position of each user, making it difficult to create an image that is easy for each user to see.

In view of the above, the present invention aims to provide a display device that can perform brightness control that takes into account the viewing angle characteristics and light reflection characteristics of the display while suppressing increases in power consumption, and is capable of displaying images that do not cause discomfort to multiple users.

In order to achieve the above object, the display device according to claim 1 is a display device for controlling image display on a display (20) having a plurality of pixels, and includes a solar radiation estimation unit (12c) for estimating a solar radiation area, which is an area of the display surface (20a) of the display that is irradiated by sunlight, and a non-sun radiation area, which is the remaining part of the display surface, based on position information of the sun and the display, an illuminance acquisition unit (12d) for acquiring illuminance information of the environment in which the display is installed, a position information acquisition unit (12e) for acquiring position information of a user relative to the display from an imaging device (34) that images a user of the display, and a position information acquisition unit (12f) for acquiring the luminance of a solar radiation pixel group, which is a pixel group located in the solar radiation area among the plurality of pixels, based on the estimation result of the solar radiation estimation unit, and an image information acquisition unit (12g) for acquiring the luminance of a pixel group located in the non-sun radiation area. and a brightness control unit (12f) that executes a first brightness control to make the brightness higher than that of the non-sunlight pixel group, which is a group of pixels. The position information acquisition unit acquires position information of at least two users, and the brightness control unit executes a second brightness control to make the difference in contrast ratio as seen by the two users less than a predetermined value for at least a portion of the area (R3, R4, R5) located between the two users on the display surface based on the user's position information relative to the display, the viewing angle characteristics of the display, and the light reflection characteristics on the display surface. The portion of the display image that includes at least one of characters, figures, and symbols is defined as an information portion, and the remaining portion is defined as a background portion, and the contrast ratio is the ratio of the brightness of the information portion to the brightness of the background portion.

According to this, the solar radiation estimation unit estimates solar radiation areas and non-sun radiation areas on the display surface of the display, the position information acquisition unit acquires position information of multiple users relative to the display surface, and the luminance control unit performs a first luminance control that makes the luminance of the solar radiation pixel group higher than the luminance of the non-sun radiation pixel group. The luminance control unit performs a second luminance control that makes the difference in contrast ratio of at least a portion of the area of the display surface located between the two users less than a predetermined value based on the position information of at least two users, the viewing angle characteristics of the display, and the light reflection characteristics of the display surface. This allows the display device to perform luminance control that takes into account the viewing angle characteristics and light reflection characteristics of the display without increasing the luminance of the entire pixel group more than necessary, and to display images that do not cause discomfort to multiple users.

The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below.

1 is a block diagram showing a display system according to an embodiment; 1 is an explanatory diagram of the line of sight angle and its distribution on the display surface of a display. FIG. 11 is a diagram illustrating an example of solar radiation region data. 4 is a flowchart showing brightness control in the display system. FIG. 13 is a diagram illustrating an example of determining a luminance control coefficient based on an estimation result of a solar radiation area. 1 is a diagram illustrating an example of a relationship between a user's line of sight angle with respect to a display surface of a display and a surface luminance ratio. 1 is a diagram illustrating an example of a relationship between a user's line of sight angle with respect to a display surface of a display and a surface reflectance ratio. 13 is an explanatory diagram of correction of the brightness control coefficient in the second brightness control executed when there is only one user. FIG. 11 is an explanatory diagram of the distribution of gaze angles when there are two users; FIG. FIG. 13 is an explanatory diagram of a comparative example of adjustment of the brightness control coefficient in the second brightness control calculated when there are two users. FIG. 11 is an explanatory diagram of a first adjustment example of a luminance control coefficient in the second luminance control calculated when there are two users. FIG. 11 is an explanatory diagram of a second adjustment example of the brightness control coefficient in the second brightness control calculated when there are two users. FIG. 13 is an explanatory diagram of a third adjustment example of the brightness control coefficient in the second brightness control calculated when there are two users. FIG. 11 is an explanatory diagram of a second brightness control when there are three or more users.

The following describes embodiments of the present invention with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are denoted by the same reference numerals.

(Embodiment)
An OLED display system to which a display device according to an embodiment is applied will be described. In this embodiment, a case where the OLED display system is an in-vehicle display system for use in a vehicle such as an automobile will be described as a representative example, but the OLED display system may of course be applied to other uses. The OLED display system may also be called an "organic EL display system" or an "EL display system." OLED and EL are abbreviations for Organic Light Emitting Diode and Electro-Luminescence, respectively.

[Basic configuration]
The OLED display system of this embodiment includes a drawing controller 10, a display 20, and an in-vehicle device 30, as shown in FIG.

The drawing controller 10 corresponds to a display control device that controls image display by the display 20, and controls image display on the display 20 based on various signals transmitted from the in-vehicle device 30. For example, the drawing controller 10 is directly connected to the display 20 via a connection wire, and is connected to the in-vehicle device 30 via an in-vehicle LAN 40, which is an in-vehicle communication bus. LAN is an abbreviation for Local Area Network. Therefore, various signals from the in-vehicle device 30 are input to the drawing controller 10 directly or through the in-vehicle LAN 40. The detailed configuration of the drawing controller 10 will be described later.

The display 20 is a self-luminous display having a plurality of pixels composed of self-luminous elements such as OLEDs. The display 20 displays an image corresponding to a video output signal from the drawing controller 10. The display 20 is configured to be capable of adjusting the brightness level by applying a variable driving voltage to each of the self-luminous elements constituting the display area for displaying an image, i.e., to each of the pixels. As shown in FIG. 2, the display 20 has a horizontally long rectangular shape when viewed from the front of the display surface 20a, but is not limited to this and may have other shapes such as a square, a vertically long rectangle, or a curved shape.

In this specification, the display 20 will be described as an OLED display as a representative example, but since self-luminous displays such as OLED displays are well known, a detailed description of the display itself will be omitted. In addition, although OLEDs will be described as a representative example of self-luminous elements, this is not limited to this, and other self-luminous elements such as inorganic EL and micro LEDs may also be used.

Display 20 may also be a liquid crystal display that uses, for example, multiple micrometer-sized micro LEDs as a backlight and can control the brightness for each small area by local dimming, i.e., partial driving. In other words, display 20 may be any display device that can control the brightness for each individual pixel or for each pixel group occupying an area of a predetermined size or less. An example of an area of a predetermined size or less is, but is not limited to, a 1 mm square size. When the above-mentioned liquid crystal display is used as display 20, the first and second brightness controls described below are performed for each pixel group to which one of the multiple backlights is assigned.

The in-vehicle device 30 is composed of, for example, various devices for inputting video signals and vehicle information to the drawing controller 10, and various sensors for outputting detection signals corresponding to physical quantities such as illuminance and angular velocity to the drawing controller 10. Here, the in-vehicle device 30 is composed of a navigation device 31, a gyro sensor 32, an illuminance sensor 33, an occupant imaging device 34, a communication device 35, and a vehicle ECU 36. However, the above configuration of the in-vehicle device 30 is merely an example, and in addition to the above devices and sensors, the in-vehicle device 30 may also include various devices such as multimedia and air conditioning devices, and may be modified as appropriate.

The navigation device 31 inputs video signals showing the vehicle's current position and map images to the drawing controller 10 based on map information stored in a map database. The navigation device 31 also inputs video signals showing, for example, images for setting a destination and images related to facilities and store information around the vehicle or the destination to the drawing controller 10 based on user operations. Furthermore, the navigation device 31 obtains information related to the vehicle's latitude, longitude, current time, and the direction the vehicle is facing, for example, using a well-known GPS, and inputs this information to the drawing controller 10. GPS is an abbreviation for Global Positioning System.

The gyro sensor 32 is a sensor that detects the angular velocity corresponding to the change in the attitude of the vehicle as a voltage value. The gyro sensor 32 is fixed to the vehicle and measures the angular velocity occurring around each of three mutually orthogonal axes that are predefined for the vehicle. For example, the gyro sensor 32 measures the angular velocity associated with the yawing, pitching, and rolling of the vehicle, and sequentially outputs the measurement data to the drawing controller 10 or the like. For example, the measurement data of the angular velocity corresponding to the yawing of the vehicle output by the gyro sensor 32 is used to estimate the direction in which the vehicle is traveling, i.e., the orientation in which the vehicle is facing when viewed from above.

The illuminance sensor 33 is arranged, for example, near the display 20, and outputs a signal corresponding to the amount of sunlight on the display 20, i.e., the ambient illuminance. For example, one or more illuminance sensors 33 are arranged near the display 20, and detect the ambient illuminance of the entire display surface of the display 20 or each of the divided regions obtained by dividing the display surface into multiple regions. For example, when the number of illuminance sensors 33 is three, the region of the display 20 that displays the image is set as the display region, and the display region is divided into three regions, and each of the three illuminance sensors 33 is associated with one of the first region to the third region. When there are multiple illuminance sensors 33, their arrangement and the corresponding regions of the display region are arbitrary and are not limited to the above-mentioned example, and can be changed as appropriate. In this way, the illuminance sensor 33 detects the illuminance of the associated region, and outputs a detection signal corresponding to the illuminance to the drawing controller 10.

The occupant imaging device 34 is, for example, any imaging device that captures an image of a user of the display 20 among the occupants of the vehicle. The user to be imaged is, for example, the driver sitting in the driver's seat of the vehicle or the occupant sitting in the passenger seat. The occupant imaging device 34 is, for example, a Driver Status Monitor (registered trademark) manufactured by Denso Corporation, but is not limited to this. The occupant imaging device 34 estimates the position coordinates of the user's eyes within the vehicle from image data including the captured user's eyes based on, for example, known image recognition technology. For example, multiple occupant imaging devices 34 are arranged in the passenger compartment of the vehicle, and each captures an image of a different user's face.

For ease of explanation, the user who is the subject of imaging by the occupant imaging device 34 will be referred to as the "target user" below. Also, as shown in Fig. 2, the direction along the virtual line VL connecting a point on the display surface of the display 20 that is located in the line of sight of the target user and the eye position _PE of the target user, and that is directed from the target user side to the display surface side, will be referred to as the "gaze direction."

Below, we will explain an example of capturing an image of one target user and calculating the distribution of gaze angles as seen from the target user, which will be described later. Note that, for example, when there are multiple users, a process of calculating the distribution of gaze angles as seen from each user is performed based on the image capture results of each user.

The passenger image pickup device 34 outputs, for example, the estimated eye position coordinates of the target user to the drawing controller 10 as eye position information. The above-mentioned eye position information, together with, for example, preset position information of the display 20 in the vehicle, is used to calculate the angular distribution of the gaze direction of the target user on the display surface of the display 20, which is the surface on which various images are displayed. The "angle of the gaze direction" means, for example, as shown in FIG. 2, the gaze direction of the target user, that is, the angle θ between the virtual straight line VL and the normal direction D1 to the display surface of the display 20, and is 0° at a point P1 on the display surface 20a located in front of the target user. Hereinafter, the angle θ of the gaze direction is referred to as the "gaze angle θ". The distribution of the gaze angle θ is calculated, for example, for each of a plurality of divided regions obtained by dividing the display surface 20a of the display 20 by a predetermined area, but is not limited thereto. For example, as shown in FIG. 2, the gaze angle θ increases as the points P2, P3, and P4 on the display surface 20a are positioned in that order from the user's eye position _PE . In other words, the display surface 20a has a distribution of gaze angles θ. The distribution of the gaze angles θ may be calculated by the drawing controller 10 or may be calculated by the occupant imaging device 34. Note that the occupant imaging device 34 may be mounted at a position where it can capture an image of the eyes of a user who uses the display 20, and may be disposed at any position within the cabin of the host vehicle.

The position P _E of the user's eyes may be estimated as separate position coordinates for the right eye and the left eye, or may be estimated as position coordinates corresponding to the center position of both eyes. In the former case, for example, the position P _E is estimated for each of the right eye and the left eye, the line of sight angle corresponding to the position of the right eye and the line of sight angle corresponding to the position of the left eye are calculated, and a luminance control coefficient (to be described later) is calculated for each of the eyes. In the latter case, for example, the center position of both eyes is estimated as the position P _E , and the line of sight angle and the luminance control coefficient (to be described later) are calculated using the center position as a representative value.

The communication device 35 acquires various information such as weather information via the Internet, for example, via a wireless LAN, and outputs the weather information to the drawing controller 10 via the in-vehicle LAN 40. The weather information acquired by the communication device 35 may be input, for example, to the illuminance acquisition unit 12d described below, and used to estimate the environmental illuminance of the display 20. Note that the communication device 35 may also be used to acquire various information other than weather information, exchange data with the outside, etc.

The vehicle ECU 36 is connected to, for example, the above-mentioned navigation device 31 or communication device 35 via the in-vehicle LAN 40, and outputs signals and information from these various devices to the drawing controller 10. ECU is an abbreviation for Electronic Control Unit.

For example, the navigation device 31 is configured to directly input a video signal to the drawing controller 10 as shown in FIG. 1. The gyro sensor 32, illuminance sensor 33, occupant image capture device 34, and communication device 35 may be configured to input various signals to the drawing controller 10 via the in-vehicle LAN 40, not via the vehicle ECU 36, as in the case of the navigation device 31.

The above is the basic configuration of an OLED display system.

[Drawing Controller]
Next, the detailed configuration of the drawing controller 10 will be described.

As described above, the drawing controller 10 is an electronic control unit that controls the image display on the display 20, and is configured to have, as functional units for realizing this, for example, a communication unit 11, a control unit 12, and an external storage device 13.

The communication unit 11 is a part that acquires information from the in-vehicle device 30 through the in-vehicle LAN 40. Signals and information transmitted from the in-vehicle device 30 to the in-vehicle LAN 40 are acquired by the communication unit 11. For example, FIG. 1 shows an acquisition path for the navigation device 31 that allows information and video signals to be input directly to the drawing controller 10, and an acquisition path that allows input via the communication unit 11. In this way, the acquisition path for information and video signals from the in-vehicle device 30 is arbitrary, and the information and video signals may be input directly to the drawing controller 10, or may be input from the in-vehicle LAN 40 via the communication unit 11.

The control unit 12 is configured by, for example, a microcomputer equipped with a CPU, ROM, RAM, I/O, etc. The CPU, ROM, RAM, and I/O are abbreviations for Central Processing Unit, Read Only Memory, Random Access Memory, and Input/Output, respectively. The control unit 12 reads and executes various programs stored in the external storage device 13, thereby outputting a display image on the display 20 based on a video signal and information transmitted from the in-vehicle device 30. In addition, the control unit 12 receives, for example, a detection signal from an illuminance sensor 33, and adjusts the brightness level of the display 20 based on the detection signal. Specifically, the control unit 12 is configured to include a video input/combination unit 12a, a drawing unit 12b, a solar radiation estimation unit 12c, an illuminance acquisition unit 12d, a position information acquisition unit 12e, a brightness control unit 12f, and a video output unit 12g.

The video input/combining unit 12a receives a video signal directly from the in-vehicle device 30 or via the in-vehicle LAN 40, and outputs image data indicated by the video signal to the brightness control unit 12f. In addition, if there is image data drawn by the drawing unit 12b, the video input/combining unit 12a inputs it and combines it with the image data indicated by the video signal, and outputs the combined image data to the brightness control unit 12f.

The drawing unit 12b receives various information about the vehicle transmitted from the in-vehicle device 30 and acquired by the communication unit 11, and generates image data for drawing the information on the display 20.

The solar radiation estimation unit 12c estimates the solar radiation area of the display 20 that is the area exposed to sunlight based on the position information of the sun, the installation state of the display 20, and the attitude information of the vehicle, and outputs the estimation result to the brightness control unit 12f. Specifically, the solar radiation estimation unit 12c acquires, for example, from the navigation device 31, angle information of the altitude and azimuth of the sun relative to the vehicle, i.e., solar information. In addition, for example, the external storage device 13 stores information on the panel mounting angle, which is the direction in which the normal direction to the display surface 20a of the display 20 on the vehicle points and corresponds to the altitude and azimuth angle of the sun. The solar radiation estimation unit 12c estimates the panel incidence angle, which is the angle of the altitude and azimuth of sunlight relative to the display surface 20a of the display 20, based on the solar information, the panel mounting angle, and the traveling direction of the vehicle acquired from the gyro sensor 32. Also, for example, the external storage device 13 stores in advance three-dimensional shape data of the vehicle and a plurality of solar radiation area data, which is distribution data of solar radiation areas and non-sun radiation areas that occur on the display surface of the display 20 according to the panel incidence angle of sunlight. The solar radiation estimation unit 12c estimates the solar radiation areas and non-sun radiation areas on the display surface 20a of the display 20 based on one or more solar radiation area data corresponding to the estimated panel incidence angle among the plurality of solar radiation area data.

The non-sunlight area refers to the remaining area of the display surface 20a of the display 20 that is different from the sunlight area, that is, the area where sunlight does not directly enter. The sunlight area data is, for example, as shown in FIG. 3, binarized image format data in which white corresponds to the sunlight area and black corresponds to the non-sunlight area, and is associated with coordinates on the display surface 20a of the display 20. The sunlight area data is created in advance one by one corresponding to different panel incidence angles by appropriately setting the panel incidence angle based on the three-dimensional shape data of the vehicle and the arrangement of the display 20 using optical simulation software, for example.

The solar radiation estimation unit 12c may also be configured to calculate an optical flow (OF), which is a vector indicating the direction and amount of change in the solar radiation area relative to the amount of change in the panel incidence angle, and estimate the solar radiation area using the OF, as described in JP 2022-187806 A, for example. The solar radiation estimation unit 12c may also be configured to estimate the solar radiation area based on output signals from multiple illuminance sensors 33 arranged near the display surface of the display 20, as described in JP 2021-92626 A. In this way, the solar radiation estimation unit 12c may also be configured to estimate the solar radiation area and the non-sun radiation area by other known methods.

The illuminance acquisition unit 12d, for example, receives a detection signal from the illuminance sensor 33 and acquires the environmental illuminance in which the display 20 is installed. The illuminance acquisition unit 12d outputs, for example, an electrical signal corresponding to the environmental illuminance as illuminance information to the brightness control unit 12f. The illuminance acquisition unit 12d may also be configured to estimate the environmental illuminance based on, for example, weather information input from the communication device 35, time information, and data on the reference illuminance corresponding to the time stored in the external storage device 13, etc. For example, the ratio to the reference illuminance corresponding to the weather information is set in advance, such as 100% when the weather information is sunny, 70% when it is cloudy, and 30% when it is rainy, and stored in the external storage device 13, etc. Then, for example, the illuminance acquisition unit 12d estimates the value obtained by multiplying the ratio corresponding to the acquired weather information by the reference illuminance as the environmental illuminance. In this way, the illuminance acquisition unit 12d is configured to acquire illuminance information from the illuminance sensor 33, or estimate the illuminance based on time information and weather information from the communication device 35, for example.

In addition, this display system may be configured so that the in-vehicle device 30 has at least one of an illuminance sensor 33 and a communication device 35 for acquiring weather information, and the illuminance acquisition unit 12d can acquire or estimate the environmental illuminance of the display 20.

The position information acquisition unit 12e acquires, for example, eye position information of the user of the display 20 from the occupant imaging device 34. The user's eye position information is, for example, the eye position coordinates of the target user in the vehicle, and is calculated by a known image authentication technology using an image of the user captured by the occupant imaging device 34. For example, when there are multiple users, the position information acquisition unit 12e acquires or calculates eye position information for the multiple users individually. For example, the position information acquisition unit 12e estimates the distribution of the gaze angle θ on the display surface 20a of the display 20 based on the position information of the display 20 and the eye position information of the target user. This will be described in detail later.

For ease of explanation, the pixel groups that make up the display 20 and are located in the sunlight area will be referred to as the "sunlight pixel group," and the pixel groups that are located in the non-sunlight area, which is an area not exposed to sunlight, will be referred to as the "non-sunlight pixel group."

The brightness control unit 12f adjusts the brightness of each of the sunlight-irradiated pixel group and the non-sun-irradiated pixel group of the display 20 for the image data input from the image input/combination unit 12a, and outputs the data to the image output unit 12g. The brightness control unit 12f determines the sunlight-irradiated pixel group and the non-sun-irradiated pixel group, for example, based on the sunlight area estimated by the sunlight estimation unit 12c. The brightness control unit 12f sets the brightness of the sunlight-irradiated pixel group and the non-sun-irradiated pixel group, for example, based on the environmental illuminance from the illuminance acquisition unit 12d and the estimation result of the sunlight-irradiated area/non-sun-irradiated area from the sunlight estimation unit 12c. The brightness control unit 12f acquires, for example, angular distribution data of the line of sight angle θ on the display surface 20a of the display 20 from the position information acquisition unit 12e, and reads the viewing angle characteristic data of the display 20 and the light reflection characteristic data on the display surface 20a from the external storage device 13. The luminance control unit 12f then corrects the set luminance of the sunlight pixel group and the non-sunlight pixel group based on, for example, the angle distribution data of the line of sight angle θ, the viewing angle characteristic data, and the reflection characteristic data described above. The luminance control unit 12f generates image data corresponding to the corrected set luminance for each of the sunlight pixel group and the non-sunlight pixel group. The luminance control unit 12f then outputs, for example, the image data with the adjusted set luminance to the video output unit 12g. Details of this luminance control will be described later.

The video output unit 12g outputs a video output signal to display the brightness-adjusted image data transmitted from the brightness control unit 12f on the display 20.

The external storage device 13 stores various programs executed by the control unit 12 and various data transmitted from the control unit 12, and allows the control unit 12 to read programs and write data. Note that the external storage device 13 is given here as a non-transient tangible recording medium and is configured separately from the control unit 12, but it may also be a ROM or RAM within the control unit 12.

The above is the basic configuration of the drawing controller 10. Note that the drawing controller 10 is, for example, an electronic control unit independent of the in-vehicle device 30, but is not limited to this and may be configured as part of the vehicle ECU 36.

[Brightness control overview]
Next, brightness control in an OLED display system will be described.

For ease of explanation, the luminance resulting from the energization of the image display of the pixel group of the display 20 will be referred to as the "set luminance", the light of sunlight or other light reflected by the display surface 20a of the display 20 will be referred to simply as the "reflected light", and the luminance resulting from the reflected light will be referred to as the "reflected luminance". The reflected luminance means the luminance resulting only from the reflected light, assuming that sunlight or other light is reflected by the display surface 20a in a black display or non-display state. In addition, the luminance perceived by a user who sees the light of the display image of the display 20 displayed at a predetermined set luminance superimposed with the reflected light of sunlight or other light on the display surface 20a will be referred to as the "visible luminance".

As shown in FIG. 2, when the display surface 20a of the display 20 is substantially rectangular in a front view, the direction along the longitudinal direction, i.e., the width direction, is referred to as the "X direction", and the direction along the lateral direction, i.e., the direction perpendicular to the X direction, is referred to as the "Y direction". For example, in the case of an in-vehicle application, the display 20 is mounted on the vehicle so that the X direction is along the vehicle width direction.

When a predetermined start condition is met, such as when the display 20 is turned on, the OLED display system executes the control flow shown in FIG. 4.

In step S100, for example, the control unit 12 acquires the vehicle's position information and date and time information from the in-vehicle device 30, specifies the latitude of the vehicle, and calculates the altitude angle and azimuth angle of the sun relative to the vehicle using a known method such as spherical trigonometry using the sun's declination and hour angle.

In step S110, for example, the control unit 12 obtains the traveling direction of the vehicle from the gyro sensor 32, and calculates the panel incidence angle based on the traveling direction, the panel mounting angle, and the altitude angle and azimuth angle of the sun. This allows the incident direction of sunlight on the display surface 20a of the display 20, i.e., the solar radiation direction, to be estimated.

In step S120, for example, the solar radiation estimation unit 12c estimates the solar radiation area and the non-sun radiation area on the display 20 based on one or more solar radiation area data corresponding to the solar radiation direction estimated in step S110 from among the above-mentioned multiple solar radiation area data. The data of the estimated solar radiation area and the non-sun radiation area is output to, for example, the brightness control unit 12f.

In step S130, for example, the position information acquisition unit 12e acquires the eye position coordinates of the target user from the occupant imaging device 34. For example, when the occupant imaging device 34 detects one user, the position information acquisition unit 12e acquires the eye position coordinates of the one user, and when the occupant imaging device 34 detects two users, the position information acquisition unit 12e acquires the eye position coordinates of both users.

In the next step S140, for example, the position information acquisition unit 12e calculates the distribution of the gaze angle θ as shown in Fig. 2 by geometric calculation based on the information of the user's eye position _PE and the position coordinates of the display surface 20a of the display 20. Here, a case where only the distribution of the gaze angle θ in the X direction of the display surface 20a is calculated will be described as a representative example, but the distribution of the gaze angle in the Y direction may also be calculated. The calculated gaze angle distribution data is output to, for example, the brightness control unit 12f.

In step S150, the brightness control unit 12f executes a first brightness control to make the brightness of the sunlight irradiated pixel group higher than the brightness of the non-sun irradiated pixel group based on the estimation result of the sunlight irradiated area/non-sun irradiated area and the ambient illuminance. As a result, the brightness of the sunlight irradiated pixel group is higher than the brightness of the non-sun irradiated pixel group and is set to a brightness corresponding to the illuminance value of the sunlight irradiated area, so that the display 20 displays an image with a brightness setting that is easy to see for both the sunlight irradiated area and the non-sun irradiated area. In addition, because the brightness of the non-sun irradiated area does not need to be higher than necessary, an increase in power consumption can be suppressed.

Here, when viewed from the front, the display 20 has a viewing angle characteristic in which, even if the set luminance is constant, the area where the line of sight angle θ is 0° has the highest visible luminance, while the visible luminance decreases toward areas where the line of sight angle θ is larger. For this reason, even if an image with a uniform set luminance is displayed on the display 20, the visible luminance changes from area to area depending on the line of sight angle θ on the display surface 20a.

The display 20 has a reflection characteristic in which the reflected luminance increases in proportion to the reflectance on the display surface 20a, with the display surface 20a reflecting external light such as sunlight and other light. The reflectance on the display surface 20a increases, for example, as the line of sight angle θ increases in an area. For this reason, the reflected luminance on the display surface 20a is smallest in the front area located directly in front of the user's eyes, and a luminance distribution is generated in which the reflected luminance increases toward areas further away from the front area.

The first brightness control described above does not take into account the change in perceived brightness due to the viewing angle characteristics and the change in reflected brightness due to the reflection characteristics. Therefore, the displayed image after only the first brightness control is performed may have a deviation between the set brightness and the perceived brightness, resulting in an unintended contrast ratio, which may cause the user to feel uncomfortable. The "contrast ratio" here means the ratio of the brightness of the information part of an image to the brightness of the background part of the image. Note that, for example, the information part is the part that displays information for the user and is the part of the image that includes at least one of characters, figures, and symbols, and the background part is the remaining part other than the information part.

Therefore, in step S150, the luminance control unit 12f executes a second luminance control to correct the luminance control coefficient described below based on the viewing angle characteristics and reflection characteristics of the display 20 and the distribution of the line of sight angle θ of the display surface 20a in accordance with the first luminance control. As a result, the set luminance is corrected to a luminance value that takes into account the distribution of the reflected luminance and the change in the visible luminance based on the viewing angle characteristics, and the difference in contrast ratio between regions in the displayed image is less than a predetermined value, making it possible to display an image that does not cause the user to feel uncomfortable. Finally, the video output unit 12g outputs the video signal after the second luminance control to the display 20 based on the output signal from the luminance control unit 12f. The control unit 12 then returns the process to step S100.

Second Brightness Control: Single User
Next, the second brightness control in the case where there is only one user will be described in detail.

Although Figures 5 and 8 do not show cross sections, the non-sunlight irradiated area R2 is hatched to make it easier to see the sunlight irradiated area R1 and the non-sunlight irradiated area R2 on the display surface 20a of the display 20.

First, let us explain the first brightness control.

For example, as shown in FIG. 5, the brightness control unit 12f determines the brightness control coefficient α for each predetermined divided region of the display surface 20a based on the estimation results of the sunlit region R1 and the non-sunlit region R2 by the sunlit estimation unit 12c and the information on the ambient illuminance from the illuminance acquisition unit 12d.

Note that FIG. 5 shows an example in which one brightness control coefficient α is set for each divided region obtained by equally dividing the display surface 20a, but this is not limited to this. For example, for a divided region in which both a sunlit region R1 and a non-sunlit region R2 exist, the brightness control unit 12f may set different brightness control coefficients α for regions R1 and R2.

The brightness control coefficient α is determined, for example, by the following formula (1):

α=(C×L _R )/L _max ...(1)
In formula (1), C is a target contrast value, L _R is a reflected luminance, and L _max is a maximum value of the set luminance. The target contrast value is a contrast ratio at which the image is perceived as easy to see in terms of human visual characteristics. The reflected luminance L _R varies depending on the amount of light on the display surface 20a of the display 20, and is calculated, for example, by the following formula (2).

L _R =a×E...(2)
In formula (2), a is a conversion coefficient for converting an illuminance value into luminance, and E is an illuminance value. The conversion coefficient a is, for example, when the display surface 20a of the display 20 is in a black display or non-luminous state. The luminance of the display surface 20a is calculated in advance by illuminating the display surface 20a with an arbitrary light source to obtain a predetermined illuminance value and measuring the luminance of the display surface 20a. Note that the display surface 20a of the display 20 is covered with another transparent cover glass or the like when used. In this case, it is preferable to calculate the conversion coefficient a with the display 20 covered with a cover glass or the like. The illuminance value E is the environmental illuminance, and is determined based on, for example, an output signal from the illuminance sensor 33. .

The set luminance is, for example, a luminance value that is uniquely determined by a relational expression based on the gradation value in the video signal of the display image and the gamma characteristic of the display 20. For example, when a display 20 capable of adjusting the gamma characteristic is used, the set luminance is adjusted to a value corresponding to the environmental luminance by correcting the gamma characteristic according to the illuminance value. For example, when a self-emitting display 20 such as an OLED is used, the maximum value of the set luminance is determined, and the set luminance is adjusted to be lowered according to the illuminance value, thereby performing relative luminance adjustment on the display surface. For example, a data table of correction values of the gamma characteristic corresponding to the illuminance value classification is created in advance, and the data table is stored in the external storage device 13 or a recording medium (not shown) of the control unit 12. Then, for example, the above data table is read as necessary, and the gamma characteristic is adjusted, so that a set luminance that is easy to see according to the environmental illuminance can be determined. Note that the gradation value of the display image is set so that the information part and the background part have different set luminances so that the contrast ratio is easy to see for the human visual characteristics.

For example, in the first brightness control, the brightness control unit 12f determines the brightness control coefficient α for each divided region, as shown in FIG. 5, based on the estimation results of the sunlight region R1/non-sunlight region R2, the data table of the ambient illuminance and the set brightness, and the above formulas (1) and (2). As a result, the brightness is set to an easy-to-view setting for each of the sunlight region R1/non-sunlight region R2, and the display 20 displays an image according to the ambient illuminance.

However, in the first brightness control, the set brightness is determined on the assumption that the entire display surface 20a of the display 20 is viewed from the front. In addition, when an image with a predetermined set brightness is displayed on the display surface 20a with a certain illuminance, the perceived brightness is the sum of the set brightness and the reflected brightness. Therefore, when a user views the display surface 20a from an oblique angle, a deviation may occur between the brightness assumed in the set brightness and the perceived brightness due to changes in the perceived brightness caused by the viewing angle characteristics of the display 20 and changes in the reflected brightness caused by the reflection characteristics. In this case, the contrast ratio in the image becomes an unintended value, and the contrast ratio of the image perceived by the user is outside the range that is easy to see with human visual characteristics, which may cause the user to feel uncomfortable. In order to prevent such a situation, the display system of this embodiment executes the second brightness control.

Next, we will explain the second brightness control.

In the second brightness control, the brightness control unit 12f corrects the brightness control coefficient α based on the angular distribution of the line of sight angle θ on the display surface 20a, the viewing angle characteristic data and the reflection characteristic data of the display 20.

The viewing angle characteristic data is defined, for example, as the maintenance rate of luminance when an image with a predetermined luminance value is viewed by changing the line of sight angle θ, and is prepared in advance as a data table consisting of the line of sight angle θ and the corresponding surface luminance ratio as shown in FIG. 6. The surface luminance ratio is, for example, the maintenance rate of luminance described above, and is a value obtained by dividing the luminance when the line of sight angle θ is changed by the reference value (=1) where the line of sight angle θ=0°, i.e., the luminance in frontal view, is set as the reference value. For example, as shown in FIG. 6, the surface luminance ratio is 1.00, 0.95, 0.85, 0.70, and 0.50 at the points where the line of sight angle θ=0°, 15°, 30°, 45°, and 60°, respectively, but is not limited to this and varies depending on the configuration of the display 20, etc.

The reflection characteristic data is defined as the reflection luminance ratio before and after changing the line of sight angle θ when viewing the display surface 20a at a predetermined illuminance value, and is prepared in advance as a data table consisting of the line of sight angle θ and the corresponding surface reflection ratio as shown in FIG. 7. The surface reflection ratio is, for example, a value obtained by dividing the reflection luminance when the line of sight angle θ is changed by a reference value (=1) where the line of sight angle θ=0°, i.e., the reflection luminance in frontal view, by the reference value. For example, as shown in FIG. 7, the surface reflection ratios are 1.00, 1.00, 1.00, 1.20, and 2.50 at the points where the line of sight angles θ=0°, 15°, 30°, 45°, and 60°, respectively, but are not limited thereto, and vary depending on the configuration of the display surface 20a and the transparent cover covering it.

The viewing angle characteristic data and reflection characteristic data are stored, for example, in the external storage device 13 or a recording medium (not shown) of the control unit 12, and are read in the second brightness control. The viewing angle characteristic data and reflection characteristic data can be created, for example, by using the display 20 and an arbitrary light source and performing brightness measurements with different line-of-sight angles θ.

Here, we consider the contrast ratio when the display 20 is viewed from the front, the maximum luminance of the information part of the image is 500 cd/ ^m2 , the maximum luminance of the background part is 0 cd/ ^m2 (=black display), the reflected luminance is 6 cd/ ^m2 , and the contrast target value C=3.

In this case, the brightness control coefficient α is 3 x 6/500 = 0.036 according to formula (1). The contrast ratio is the value obtained by dividing the visible luminance of the information part by the visible luminance of the background part. If the visible luminance of the information part is "information luminance L1", the visible luminance of the background part is "background luminance L2", and the contrast ratio is C1, then information luminance L1, background luminance L2, and contrast ratio C1 are expressed by the following formulas (3), (4), and (5).

L1=L ₀₁ ×α×β+L _R1 ×γ...(3)
L2=L ₀₂ ×α×β+L _R2 ×γ...(4)
C1=L1/L2...(5)
In formula (3), _L01 is the set luminance of the information part, and _L02 is the set luminance of the background part, and _L03 is the reflective luminance of _the background part. In the formulas (3) and (4), β is the surface luminance ratio, and γ is the surface reflectance ratio.

In the portion where the line of sight angle θ=0°, as shown in Figures 6 and 7, the surface luminance ratio is 1 and the surface reflectance ratio is 1, so the contrast ratio C1 is (500 x 0.036 x 1 + 6 x 1)/(0 x 0.036 x 1 + 6 x 1) = 4. In the portion where the line of sight angle θ=0°, the contrast ratio C1 exceeds the contrast target value C=3, making it easy to see.

On the other hand, in the portion where the line of sight angle θ = 60°, for example, the surface luminance ratio is 0.5 and the surface reflection ratio is 2.5, so the luminance of the information portion is 0.5 times and the reflected luminance is 2.5 times. Therefore, the contrast ratio C1 in the portion where the line of sight angle θ = 60° is (500 x 0.5 x 0.036 + 6 x 2.5) / (0 x 0.5 x 0.036 + 6 x 2.5) = 1.6. In the portion where the line of sight angle θ = 60°, the contrast ratio C1 does not satisfy the contrast target value C = 3, and the portion is not easy to see.

In the above example, the contrast ratio C1 of the part where the line of sight angle θ = 15° is (500 x 0.95 x 0.036 + 6 x 1) / (0 x 0.95 x 0.036 + 6 x 1) = 3.85. The contrast ratio C1 of the part where the line of sight angle θ = 30° is (500 x 0.85 x 0.036 + 6 x 1) / (0 x 0.85 x 0.036 + 6 x 1) = 3.55. The contrast ratio C1 of the part where the line of sight angle θ = 45° is (500 x 0.7 x 0.036 + 6 x 1.2) / (0 x 0.7 x 0.036 + 6 x 1.2) = 2.75. In this case, the contrast ratio C1 of the parts where the line of sight angles θ = 15° and 30° exceeds the target value of 3, and is easy to see. In contrast, in the area where the line of sight angle θ is 45°, the contrast ratio C1 does not meet the target value of 3, and the image is not easy to see.

As described above, with only the first brightness control, the image may contain a mixture of easily visible contrast ratio C1 parts and unviewable contrast ratio C1 parts, which may cause the user to feel uncomfortable. In particular, for the non-sunlight region R2, the set brightness of the non-sunlight pixel group is lower than that of the sunlight pixel group, so depending on the line of sight angle θ, an area may appear very dark to the user.

Therefore, the brightness control unit 12f performs a second brightness control to correct the brightness control coefficient α based on the viewing angle characteristic data and the reflection characteristic data.

For example, in the above example, for the portion where the line of sight angle θ=60°, the luminance control coefficient is calculated by using the reflected luminance L _R in formula (1) corrected based on the reflection characteristic data, and the maximum value L _max of the set luminance corrected based on the viewing angle characteristic data. In other words, the luminance control coefficient after correction in the second luminance control is set to α _C1 , and α _C1 is calculated by the following formula (6).

α _C1 = (C×L _{R_C} )/L _{max_C} (6)
In the formula (6), L _{R_C} is the reflected luminance after correction based on the reflection characteristic data, and L _{max_C} is the maximum value of the set luminance after correction based on the viewing angle characteristic data. The reflected luminance L _{R_C} of the light source is calculated by multiplying the luminance converted by the ambient illuminance by the surface reflection ratio, that is, 6×2.5=15 cd/m ^2. The maximum value L _max of the set luminance is set The value obtained by multiplying the luminance by the surface luminance ratio is 500×0.5=250 cd/ ^m2 . The corrected luminance control coefficient α _C at the line of sight angle θ=60° is expressed as follows: (3) According to the formula, (3×15)/250=0.18. Then, by the second luminance control, the contrast ratio C1 at the portion where the line of sight angle θ=60° is (500×0.5×0.18+6×2.5)/(0×0.5×0.18+6× 2.5)=4, which exceeds the contrast target value C=3, resulting in an easy-to-see state.

In the portion where the line of sight angle θ=0°, the surface luminance ratio is 1 and the surface reflection ratio is 1, and there is no change in the maximum values of the reflected luminance and the set luminance, so the luminance control coefficient α _C1 =α, and the contrast ratio C1 remains the same as above at 4. In addition, for example, in the portions where the line of sight angles θ=15°, 30°, and 45°, the corrected luminance control coefficient α _C is approximately 0.038, approximately 0.042, and approximately 0.062, and the contrast ratio C1 is 4 in all cases.

As described above, in the second luminance control, the luminance control unit 12f corrects each of the luminance control coefficients α calculated for each divided region based on the angular distribution of the line of sight angle θ, the viewing angle characteristic data, and the reflection characteristic data, and calculates the corrected luminance control coefficient α _C1 . For example, as shown in FIG. 8, the luminance control coefficient α of the divided region corresponding to the sunlight region R1 is set to 1, and the luminance control coefficient α of the divided region corresponding to the non-sunlight region R2 is set to 0.4 by the first luminance control based on the estimation result of the sunlight region. In this case, for example, the luminance control unit 12f calculates the corrected luminance control coefficient α C1 of each divided region based on the angular distribution of the line of sight angle θ and the surface luminance ratio (i.e., viewing angle characteristic) and surface reflection ratio (i.e., reflection characteristic) corresponding to the line of sight angle θ, and replaces α with α _C1 . As a result, the luminance control is performed taking into account the viewing angle characteristic and reflection characteristic of _the display 20, and the contrast ratio C1 perceived by the user is a value that is easy to see, and the difference in the contrast ratio C1 is less than a predetermined value in the image, so that an image that the user does not feel uncomfortable is displayed.

Note that while Figures 5 to 8 show examples in which various values of the line of sight angle θ are set in increments of 15°, this is not limiting and may be changed as appropriate, for example, to increments of 5° or 10°, depending on fluctuations in the surface luminance ratio and surface reflectance ratio. Also, the luminance control coefficients, surface luminance ratios, and surface reflectance ratios shown in Figures 5 to 8 are merely examples, and may be changed as appropriate depending on the configuration of the display 20, the surface treatment of the display surface 20a, or the transparent member covering it, etc.

In addition, in the above, an example was described in which the brightness control coefficient α is corrected in the second brightness control so that the difference in contrast ratio within the screen becomes zero, but this is not limited to this, and it is acceptable for a difference in contrast ratio to occur that is not noticeable to the human eye. Furthermore, in the above, an example was described in which the second brightness control is performed on the non-sunlight pixel group, but of course the second brightness control may also be performed on the sunlight pixel group.

Although the above description has been given as a representative example in which the contrast target value C is a constant, this is not limiting. For example, if the set luminance required to provide an easily viewable display for a certain reflected luminance can be expressed by a predetermined relational expression such as the following expression (7), the contrast target value C may be calculated as a value corresponding to the reflected luminance as in expression (8) and set as required. Note that x and y in expression (7) are arbitrary constants determined by the relationship between the set luminance and the reflected luminance.

Set luminance = x × reflected luminance + y (7)
C = (x + 1) + y / reflected luminance (8)
Second Brightness Control: Issues with Two Users
Next, a second brightness control problem when there are two users will be described.

For example, if two occupant imaging devices 34 detect the faces of different users, the position information acquisition unit 12e calculates the distribution of the two gaze angles θ based on the eye position information of each user. Note that detection of multiple users may be performed based on an in-vehicle device 30 other than the occupant imaging device 34, such as an occupant sensor (not shown) mounted on each seat or seat belt, or may be performed by any other known method.

For convenience of explanation, hereinafter, as shown in Fig. 9, the line-of-sight angle θ based on the viewpoint of the first user is referred to as "line-of-sight angle θ1", and the line-of-sight angle θ based on the viewpoint of the second user is referred to as "line-of-sight angle θ2". The line-of-sight angle θ1 is an angle between a virtual line VL1 connecting the eye position P _E1 of the first user and a point on the display surface 20a in the line-of-sight direction of the first user, and a normal direction D1 of the display surface 20a. The line-of-sight angle θ2 is an angle between a virtual line VL2 connecting the eye position P _E2 of the second user and a point on the display surface 20a in the line-of-sight direction of the second user, and a normal direction D1 of the display surface 20a.

The position information acquisition unit 12e, for example, calculates the distribution of the gaze angles θ1 and θ2 in the same manner as described above, and outputs the angle distribution data of the gaze angles θ1 and θ2 to the luminance control unit 12f. Then, the luminance control unit 12f calculates a luminance control coefficient α C1 corresponding to each user for each divided region of the display 20, for example, as shown in FIG. 10, based on the angle distribution data of the gaze angles θ1 and _θ2 , the viewing angle characteristic data, and the reflection characteristic data in the same manner as described above.

Hereinafter, as shown in Fig. 10, some consecutive regions among the multiple divided regions will be referred to as "first region Z1", "second region Z2", "third region Z3", "fourth region Z4", and "fifth region Z5" from the left in the X direction for the sake of distinction. Also, in Fig. 10, for ease of viewing, the brightness control coefficient _αC1 is shown only for some of the multiple divided regions, and although it does not show a cross section, regions with a larger contrast ratio are hatched whiter and regions with a smaller contrast ratio are hatched blacker.

Here, as shown in Fig. 10, one position in the Y direction among the divided regions of the display 20, and one row along the X direction will be described as a representative example, but the same process as described below is performed for the other rows. For convenience, the brightness control coefficient α C1 calculated based on the distribution of the line-of-sight angle θ1 of the first user, the viewing angle characteristic data, and the reflection characteristic data will be referred to as the "brightness control coefficient α _C1-1 ". Also, the brightness control coefficient α _C1 calculated based on the distribution of the line-of-sight angle _θ2 of the second user, the viewing angle characteristic data, and the reflection characteristic data will be referred to as the "brightness control coefficient α _C1-2 ".

If only one of the brightness control coefficients α _C1-1 and α _C1-2 is reflected, the displayed image will be easy to view for one of the two users, but will not be easy to view for the other. Therefore, the brightness control unit 12f calculates a new brightness control coefficient α _C2 corresponding to both users for some of the multiple divided regions, based on the brightness control coefficient α _C1-1 corresponding to the first user and the brightness control coefficient α _C1-2 corresponding to the second user.

Hereinafter, the region where the new brightness control coefficient α _C2 is calculated is referred to as the "adjustment region R3". The adjustment region R3 is a part or all of the region located between at least two users on the display 20, or a region gazed upon by both of the two users. For example, in a case where the positions of the two users and the arrangement of the display 20 are determined in advance, such as in an in-vehicle application, the adjustment region R3 may be set as a region located between a region located in front of the driver's seat and a region located in front of the passenger seat on the display 20. The adjustment region R3 may be calculated as a region located between a front region of the first user and a front region of the second user on the display 20 based on the position information of the display 20 and the position information of the eyes or heads of the two users from the passenger imaging device 34. Also, for example, the gaze regions located in the central visual field and the effective visual field of each of the two users on the display 20 may be calculated based on the line-of-sight directions of the two users from the passenger imaging device 34, and the overlapping regions of these gaze fields may be set as the adjustment region R3. The gaze area is calculated, for example, by calculating the coordinates of the intersection between a virtual line formed by the gaze directions of the two users and the display surface 20a of the display 20, and is calculated as an area located within a predetermined range of viewing angles (for example, within 10 degrees) centered on the intersection. In this way, the adjustment area R3 is determined by any method.

A method of calculating the brightness control coefficient α _C2 is to compare the brightness control coefficients α _C1-1 and α _C1-2 in the same divided region of the adjustment region R3 and select a larger value from the viewpoint of safety, as in the comparative example shown in Fig. 10. However, if the brightness control coefficient is determined by such a simple combination, there will be regions in which the contrast ratio C1 in the first to fifth regions Z1 to Z5 changes suddenly when viewed by either of the two users, resulting in a display that feels unnatural.

Specifically, for example, the line-of-sight angle θ1 is 60° in the second region Z2, 45° in the third region Z3, 30° in the fourth region Z4, and 15° in the fifth region Z5. The line-of-sight angle θ2 is 15° in the first region, 30° in the second region Z2, 45° in the third region Z3, and 60° in the fourth region Z4. In addition, when the display 20 is viewed from the front, the maximum luminance of the information portion of the image is 500 cd/m ² , the maximum luminance of the background portion is 0 cd/m ² (=black display), the reflected luminance is 6 cd/m ² , and the contrast target value C is 3. In this case, the luminance control coefficients α _C1-1 of the second to fifth regions Z2 to Z5 are 0.18, approximately 0.062, approximately 0.042, and approximately 0.037, respectively, according to formula (6). Moreover, the brightness control coefficient α _C1-2 of the first through fourth regions Z1 through Z4 is approximately 0.037, approximately 0.042, approximately 0.062, and 0.18, respectively, according to formula (6). If the second region Z2, the third region Z3, and the fourth region Z4 are the adjustment region R3 and a larger brightness control coefficient is selected by a simple combination, the brightness control coefficients of the second through fourth regions Z2 through Z4 are 0.18, 0.062, and 0.18, respectively.

In addition, in Fig. 10, for the sake of space, the brightness control coefficients α _C1-1 and α _C1-2 that have values below the fourth decimal place are shown as values rounded off to the nearest whole number. Specifically, in Fig. 10, 0.037 is 0.037895..., 0.042 is 0.042353..., 0.062 is 0.061714..., and each of these values is obtained by rounding off to the nearest whole number. The same applies to the brightness control coefficients shown in Figs. 11 to 13 that are written to the third decimal place.

Here, the contrast ratios of the second to fourth regions Z2 to Z4 as viewed from the first user are calculated. The second region Z2 has a surface luminance ratio of 0.5, a surface reflection ratio of 2.5, and a corrected reflected luminance L _R-C of 6×2.5=15 cd/m ² , and the contrast ratio C1 is (500×0.5×0.18+6×2.5)/(0×0.5×0.18+6×2.5)=4. The third region Z3 has a surface luminance ratio of 0.7, a surface reflection ratio of 1.2, and a corrected reflected luminance L _R-C of 6×1.2=7.2 cd/m ² , and the contrast ratio C1 is (500×0.7×approx. 0.062+6×1.2)/(0×0.7×approx. 0.062+6×1.2)≒4. The fourth region Z4 has a surface luminance ratio of 0.85, a surface reflection ratio of 1, a corrected reflection luminance L _R-C of 6×1=6 cd/m ² , and a contrast ratio C1 of (500×0.85×0.18+6×1)/(0×0.85×0.18+6×1)=13.75. In other words, the display image seen by the first user has contrast ratios of 3 or more in the third region Z3 and the fourth region Z4, and the difference between these is 3 times or more, resulting in a rapid change in contrast ratio.

In addition, the contrast ratios of the second to fourth regions Z2 to Z4 as viewed by the second user are calculated. The second region Z2 has a surface luminance ratio of 0.85, a surface reflection ratio of 1, and a corrected reflected luminance L _R-C of 6×1=6 cd/m ² , and the contrast ratio C1 is (500×0.85×0.18+6×1)/(0×0.85×0.18+6×1)=13.75. The third region Z3 has a surface luminance ratio of 0.7, a surface reflection ratio of 1.2, and a corrected reflected luminance L _R-C of 6×1.2=7.2 cd/m ² , and the contrast ratio C1 is (500×0.7×approx. 0.062+6×1.2)/(0×0.7×approx. 0.062+6×1.2)≒4. The fourth region Z4 has a surface luminance ratio of 0.5, a surface reflection ratio of 2.5, a corrected reflection luminance L _R-C of 6×2.5=15 cd/ ^m2 , and a contrast ratio C1 of (500×0.5×0.18+6×2.5)/(0×0.5×0.18+6×2.5)=4. In other words, the display image seen by the second user has contrast ratios of the second region Z2 and the third region Z3 of 3 or more, and the difference between these is three times or more, resulting in a rapid change in contrast ratio.

As described above, if the larger of the brightness control coefficients α _C1-1 and α _C1-2 is set as the brightness control coefficient for adjustment region R3, the contrast ratio in adjustment region R3 will change suddenly when viewed by either of the two users, resulting in an image that feels unnatural. In order to prevent such a sudden change in contrast ratio, the brightness control unit 12f performs adjustment of the brightness control coefficient, which will be described next.

[Second Brightness Control: First Adjustment for Two Users]
The luminance control unit 12f may execute an adjustment to set the average value of the luminance control coefficients α _C1-1 and α _C1-2 for the adjustment region R3 as a new luminance control coefficient α _C2 , as shown in Fig. 11. Note that the luminance control coefficients α _C1-1 and α _C1-2 shown in Fig. 11 are calculated under the same conditions as the distribution of the line-of-sight angles θ1 and θ2, the maximum luminance, reflected luminance, surface luminance ratio, surface reflection ratio, and contrast target value of the information portion and background portion described in Fig. 10.

For example, the luminance control unit 12f adjusts the α _C1-1 and α _C1-2 of the second region Z2, the third region Z3, and the fourth region Z4 to approximately 0.111, approximately 0.062, and approximately 0.111, respectively, which are the average values of the α C1-1 and α C1-2, and sets these values as the new luminance control coefficient α _C2 . Note that the luminance control coefficient 0.111 in FIG. 11 is a value obtained by rounding off 0.11117... to three decimal places.

In this case, the second to fourth regions Z2 to Z4 seen from the first user have a reduced change in contrast ratio between adjacent regions. Specifically, the second region Z2 has a surface luminance ratio of 0.5, a surface reflection ratio of 2.5, and a corrected reflection luminance L _R-C of 6×2.5=15 cd/m ^2. Therefore, the contrast ratio C1 of the second region Z2 seen from the first user is (500×0.5×approximately 0.111+6×2.5)/(0×0.5×approximately 0.111+6×2.5)≈2.85. The third region Z3 has a new luminance control coefficient α _C2 that is the same as above, so it is about 4. The fourth region Z4 has a surface luminance ratio of 0.85, a surface reflection ratio of 1, and a corrected reflection luminance L _R-C of 6×1=6 cd/m ² , and a contrast ratio C1 of (500×0.85×approximately 0.111+6×1)/(0×0.85×approximately 0.111+6×1)≈8.88. The display image seen by the first user has contrast ratios of approximately 2.85, approximately 4, and approximately 8.88 for the second to fourth regions Z2 to Z4, respectively, and the change in contrast ratio in the adjustment region R3 is suppressed, reducing the sense of incongruity compared to when the regions are simply combined.

The contrast ratios in the second to fourth regions Z2 to Z4 as viewed by the second user are as follows: The second region Z2 has a surface luminance ratio of 0.85, a surface reflection ratio of 1, and a corrected reflection luminance L _R-C of 6×1=6 cd/ ^m2 , resulting in a contrast ratio C1 of (500×0.85×approximately 0.111+6×1)/(0×0.85×approximately 0.111+6×1)≈8.88. The third region Z3 has a new luminance control coefficient α _C2 that is the same as above, resulting in a contrast ratio of approximately 4. The fourth region Z4 has a surface luminance ratio of 0.5, a surface reflection ratio of 2.5, and a corrected reflection luminance L _R-C of 6×2.5=15 cd/m ² , and a contrast ratio C1 of (500×0.5×approximately 0.111+6×2.5)/(0×0.5×approximately 0.111+6×2.5)≈2.85. In other words, the display image seen by the second user has contrast ratios of approximately 8.88, approximately 4, and approximately 2.85 in the second to fourth regions Z2 to Z4, and the change in contrast ratio is reduced compared to before adjustment, similar to the case seen by the first user.

As a result, even when there are two users, the displayed image reflects the viewing angle characteristics and reflection characteristics as seen by each user, while reducing the change in contrast ratio for each user, thereby reducing the sense of discomfort.

In addition, for the regions other than the adjustment region R3 among the divided regions, the brightness control coefficient α _C1-1 is selected in the region on the first user side, and the brightness control coefficient α _C1-2 is selected in the region on the second user side. For example, the region on the first user side is a region closer to the eye position P _E1 of the first user than the adjustment region R3, and the region on the second user side is a region closer to the eye position P _E2 of the second user than the adjustment region R3. This is because it is assumed that the first user mainly views the region on the first user side, and the second user mainly views the region on the second user side. As a result, the display image displayed on the display 20 has a reduced difference in contrast ratio between the parts mainly viewed by each user, even in the parts other than the adjustment region R3.

[Second Brightness Control: Second Adjustment in the Case of Two Users]
For example, as shown in FIG. 12, the brightness control unit 12f may perform an adjustment in which, when there is an area in the adjustment area R3 where the change in contrast ratio is large, the number of areas is increased and a new brightness control coefficient α _C2 is set for the increased area.

Specifically, the brightness control unit 12f first selects the larger of the brightness control coefficients α _C1-1 and α _C1-2 for the adjustment region R3, as in the comparative example. Then, for example, the brightness control unit 12f calculates the contrast ratios as seen by the first user and the second user for the regions Z2 to Z4 in the adjustment region R3, and compares the contrast ratios for the two adjacent regions. At this time, if a predetermined condition is satisfied, such as "the contrast ratio of at least one of the adjacent regions is 3 or more, and the contrast ratio of one region is twice or more the contrast ratio of the other region," the brightness control unit 12f sets a new region in the adjacent region.

The above-mentioned predetermined conditions for determining whether to add an area are conditions that the user recognizes as causing a sudden change in contrast ratio between areas, and may be changed as appropriate depending on the user's attributes, such as age and eyesight. In addition, the above-mentioned predetermined conditions may be set by the user himself, since different users have different perceptions of differences in contrast ratio.

For example, the luminance control unit 12f sets new regions by setting parts of the second region Z2 and the third region Z3 as the sixth region Z6, and parts of the third region Z3 and the fourth region Z4 as the seventh region Z7. For example, the luminance control unit 12f sets the average value of the two luminance control coefficients in the original adjacent regions as the new luminance control coefficient α _C2 for the newly set region. Specifically, since the sixth region Z6 is located between the second region Z2 with a luminance control coefficient of 0.18 and the third region Z3 with a luminance control coefficient of approximately 0.062, the luminance control coefficient α _C2 is set to approximately 0.12, which is the average value of these values. Since the seventh region Z7 is located between the third region Z3 with a luminance control coefficient of 0.062 and the fourth region Z4 with a luminance control coefficient of 0.18, the luminance control coefficient α _C2 is set to approximately 0.12, which is the average value of these values. The brightness control coefficient of approximately 0.12 referred to here is a value obtained by rounding off 0.120857... to two decimal places.

The surface luminance ratio and surface reflection ratio in the sixth region Z6 and the seventh region Z7 are determined according to the positions of the two users, but for convenience, they are assumed to be the intermediate value of the surface reflection ratios of the regions located on both sides. For example, from the first user's viewpoint, the sixth region Z6 is between the second region Z2 with a surface luminance ratio of 0.5 and a surface reflection ratio of 2.5 and the third region Z3 with a surface luminance ratio of 0.7 and a surface reflection ratio of 1.2, so that the surface luminance ratio is 0.6 and the surface reflection ratio is about 1.8. From the second user's viewpoint, the sixth region Z6 is between the second region Z2 with a surface luminance ratio of 0.85 and a surface reflection ratio of 1 and the third region Z3 with a surface luminance ratio of 0.7 and a surface reflection ratio of 1.2, so that the surface luminance ratio is about 0.8 and the surface reflection ratio is 1.1. Similarly, the seventh region Z7 has a surface luminance ratio of approximately 0.8 and a surface reflectance ratio of 1.1 from the first user's viewpoint, and a surface luminance ratio of 0.6 and a surface reflectance ratio of approximately 1.8 from the second user's viewpoint.

That is, the luminance control unit 12f resets, for example, a region obtained by combining parts of adjacent regions whose contrast ratio difference satisfies a predetermined condition as at least one new region. Then, for the reset new region, i.e., the added region, the luminance control unit 12f sets a value between the luminance control coefficients set in the two regions on both sides of the added region, for example, an average value, as a new luminance control coefficient α _C2 . As a result, the difference in contrast ratio is reduced compared to before the adjustment, making it possible to create a display image that is less likely to cause discomfort when viewed by either of the two users.

The second to fourth regions Z2 to Z4 as viewed from the first user have contrast ratios of 4, 4, and 13.75, respectively, because the brightness control coefficient does not change before and after the adjustment. The sixth region Z6 has a surface brightness ratio of 0.6, a surface reflection ratio of approximately 1.8, and a corrected reflected brightness L _R-C of 6×1.8≒10.8cd/m ^2. Therefore, the sixth region Z6 has a contrast ratio C1 of (500×0.6×approximately 0.12+6×1.8)/(0×0.6×approximately 0.12+6×1.8)≒4.3. The seventh region Z7 has a surface brightness ratio of approximately 0.8, a surface reflection ratio of 1.1, and a corrected reflected brightness L _R-C of 6×1.1=6.6cd/m ² . Therefore, in the seventh region Z7, the contrast ratio C1 is (500×approximately 0.8×approximately 0.12+6×1.1)/(0×approximately 0.8×approximately 0.12+6×1.1)≈8.27. Therefore, in the adjustment region R3, the contrast ratios as seen by the first user are 4, approximately 4.3, 4, approximately 8.27, and 13.75, respectively, from the second region Z2 side to the right in the X direction, and the change in the contrast ratio is suppressed, reducing the sense of discomfort.

The second to fourth regions Z2 to Z4 as viewed from the second user have contrast ratios of 13.75, 4, and 4, respectively, because the brightness control coefficient does not change before and after the adjustment. The sixth region Z6 has a surface brightness ratio of about 0.8, a surface reflection ratio of 1.1, and a corrected reflected brightness L _R-C of 6×1.1=6.6 cd/m ^2. Therefore, the sixth region Z6 has a contrast ratio C1 as viewed from the second user of (500×about 0.8×about 0.12+6×1.1)/(0×about 0.8×about 0.12+6×1.1)≒8.27. The seventh region Z7 has a surface brightness ratio of 0.6, a surface reflection ratio of about 1.8, and a corrected reflected brightness L _R-C of 6×about 1.8≒10.8 cd/m ² , so the contrast ratio C1 is about 8.27, similar to when viewed from the first user. Therefore, in adjustment region R3, the contrast ratio when viewed by the second user is 13.75, approximately 8.27, 4, approximately 4.3, and 4, respectively, from the second region Z2 side to the right in the X direction, thereby suppressing changes in the contrast ratio and reducing the sense of discomfort.

The second adjustment described above also provides the same effect as the first adjustment.

In the above, an example was described in which one new region was added between the second region Z2 and the third region Z3, and one new region was added between the third region Z3 and the fourth region Z4, but the number of regions added may be two or more, and may be changed as appropriate according to the difference in contrast ratio. For example, when adding two or more regions, the new brightness control coefficients can be set so that the adjusted brightness control coefficients approach each other in stages, i.e., form a gradation, from one of the two original adjacent divided regions to the other.

[Second Brightness Control: Third Adjustment for Two Users]
For example, as shown in FIG. 13, the brightness control unit 12f may select a brightness control coefficient α _C1-1 for the frontal region of the first user, select a brightness control coefficient α _C1-2 for the frontal region of the second user, and perform adjustment to set a new brightness control coefficient α _C2 .

For ease of explanation, the area of the display surface 20a of the display 20 located in front of the first user will be referred to as the "first front area R4," and the area located in front of the second user will be referred to as the "second front area R5." In FIG. 13, a representative example will be described in which the first front area R4 is the area to the right of the fourth area Z4 in the X direction and the area to the left of the second area Z2 in the X direction, but this is not limited thereto, and areas R4 and R5 can be changed as appropriate depending on the positions of the first and second users.

In the third adjustment, the luminance control unit 12f sets, for example, the luminance control coefficient α _C1-1 as the new luminance control coefficient α _C2 for the first front region R4. This is because, for example, in the case of in-vehicle use, the first front region R4 is a region where images for the driver, such as meters and a navigation screen, are mainly displayed, and it is preferable to prioritize visibility for the first user.

Furthermore, the brightness control unit 12f sets, for example, the brightness control coefficient α _C1-1 as the new brightness control coefficient α _C2 for the second front region R5. This is because, for example, in the case of in-vehicle use, the second front region R5 is a region where images for passengers, such as audio and multimedia compatible screens, are mainly displayed, and it is preferable to prioritize visibility for the second user.

For other regions other than the front regions R4 and R5 such as the third region Z3, the new brightness control coefficient α _C2 may be set to one of the brightness control coefficients α _C1-1 and α _C1-2 or their average value in the same manner as in the first adjustment, depending on the content of the image to be displayed. For example, for the other regions, the brightness control coefficient α _C1-1 is set as the new brightness control coefficient α C2 when the content for the first user is mainly displayed, and the brightness control coefficient α _C1-2 is set as the new brightness control coefficient α _C2 when the content for the second user is mainly displayed. For the other regions, the new brightness control coefficient α _C2 may be set in the same manner as in the first adjustment or the second adjustment when the content for the first and second users is displayed. In this manner, the new brightness control coefficient α _C2 may be appropriately set for the other regions.

According to the third adjustment, an area of the display 20 displaying content for a first user can display an image that is easy for the first user to see, and an area of the display 20 displaying content for a second user can display an image that is easy for the second user to see. In other words, according to the third adjustment, the change in contrast ratio seen by each user is reduced for the portion of the image displayed in the area viewed by one user and the portion displayed in the area viewed by the other user, so that neither user feels uncomfortable.

[Second Brightness Control: When There are Three or More Users]
For example, as shown in FIG. 14(a), when three users, a first user U1, a second user U2, and a third user U3, are detected in that order from the left side in the X direction of the display 20, the brightness control unit 12f adjusts the brightness control coefficient as follows.

For example, the brightness control unit 12f groups the first user U1 and the second user U2 into a first group G1, and the second user U2 and the third user U3 into a second group G2, and performs one of the first to third adjustments described above for each of the two groups G1 and G2.

For example, the luminance control unit 12f determines the adjustment region R3 located between the first user U1 and the second user U2 on the display surface 20a of the display 20, that is, the adjustment region R3 of the first group G1. Also, for example, the luminance control unit 12f calculates the luminance control coefficient α _c1-1 corresponding to the first user U1 and the luminance control coefficient α _c1-2 corresponding to the second user U2. Then, for the adjustment region R3 of the first group G1, the luminance control unit 12f calculates the luminance control coefficient α c2-1 of the first group G1 by the above-mentioned first or second adjustment based on the luminance control coefficients α _c1-1 and α _c1-2 . Alternatively, for example, the luminance control unit 12f may determine the luminance control coefficient α _c1-1 for the region located in front of the first user U1 on the display surface _20a and the luminance control coefficient α _c1-2 for the region located in front of the second user U2 by the third adjustment.

Also, for example, the luminance control unit 12f determines the adjustment region R3 located between the second user U2 and the third user U3 on the display surface 20a of the display 20, that is, the adjustment region R3 of the second group G2. For example, the luminance control unit 12f calculates the luminance control coefficient α _c1-2 corresponding to the second user U2 and the luminance control coefficient α _c1-3 corresponding to the third user U3. Then, for the adjustment region R3 of the second group G2, the luminance control unit 12f calculates the luminance control coefficient α c2-2 of the second group G2 by the above-mentioned first or second adjustment based on the luminance control coefficients α _c1-2 and α _c1-3 . Alternatively, for example, the luminance control unit 12f may determine the luminance control coefficient α _c1-2 for the region located in front of the second user U2 on the display surface _20a and the luminance control coefficient α _c1-3 for the region located in front of the third user U3 by the third adjustment.

As a result, the area between adjacent users is set to an appropriate brightness control coefficient, or the area in front of each user is set to the brightness control coefficient of the corresponding user, making it possible to display images that reduce the sense of discomfort felt by each user even when there are three users.

The brightness control unit 12f also performs basically the same adjustment as above when, for example, as shown in FIG. 14(b), four users are detected, in order from the left side in the X direction of the display 20: a first user U1, a second user U2, a third user U3, and a fourth user U4.

For example, the brightness control unit 12f groups the first user U1 and the second user U2 into a first group G1, the second user U2 and the third user U3 into a second group G2, and the third user U3 and the fourth user U4 into a third group G3. The brightness control unit 12f then determines the brightness control coefficient for each of the groups G1, G2, and G3 by performing one of the first to third adjustments in the same manner as described above.

As a result, even when there are four users, the area between adjacent users is set to an appropriate brightness control coefficient, or the area in front of each user is set to the brightness control coefficient of the corresponding user, resulting in an image that reduces the sense of incongruity felt by each user. Although not shown, when there are five or more users, the first to third adjustments can be performed on the areas between adjacent users for four groups, each group consisting of two adjacent users. In other words, when the number of users is n (n: an integer of 3 or more), two adjacent users can be treated as one group, and the first to third adjustments can be performed on each of the (n-1) groups.

In addition, as shown in FIG. 14(c), when three users are detected and the distance between some adjacent users is less than a predetermined distance, the brightness control unit 12f regards the adjacent users whose distance is less than a predetermined distance as one user and performs the adjustment of the brightness control coefficient. Here, "less than a predetermined distance" refers to, for example, but not limited to, a case where the distance between the eyes of the two detected users is less than 50 cm. For example, suppose that a first user U1, a second user U2, and a third user U3 are present from the left side in the X direction of the display 20, the distance between the users U1 and U2 is less than a predetermined distance, and the second user U2 and the third user U3 are far apart. In this case, for example, the brightness control unit 12f regards the first group G1 consisting of the users U1 and U2 who are close to each other as one user, and performs the first to third adjustments based on the brightness control coefficient corresponding to the first group G1 and the brightness control coefficient corresponding to the third user U3.

As a result, the area between the first group G1 and the third user U3 is set to an appropriate brightness control coefficient, or the area in front of each user is set to the brightness control coefficient of the corresponding user, resulting in an image that reduces the sense of discomfort felt by each user. Note that for the brightness control coefficient corresponding to the first group G1, for example, the brightness control coefficient corresponding to either the first user U1 or the second user U2 is adopted. Although the above describes a case where there are three users, the brightness control coefficient can also be adjusted in a similar manner when there are four or more users and the distance between some of the users is less than a predetermined value.

According to this embodiment, the luminance control unit 12f performs a first luminance control to make the luminance of the sunlight pixel group higher than that of the non-sunlight pixel group based on the estimation result of the sunlight estimating unit 12c on the sunlight region R1/non-sunlight region R2 on the display surface 20a and the environmental illuminance acquired by the illuminance acquiring unit 12d. In addition, the luminance control unit 12f performs a second luminance control to make the difference in contrast ratio for at least the non-sunlight region R2 less than a predetermined value based on the distribution of the line of sight angle θ on the display surface 20a based on the user's position information, the viewing angle characteristic data and the reflection characteristic data of the display 20. As a result, by performing luminance control that takes into account the viewing angle characteristics and light reflection characteristics of the display 20 without increasing the luminance of the entire pixel group more than necessary, a display system is achieved that can display images that do not cause a user to feel uncomfortable.

Also, when there are two users, the line-of-sight angles θ1, θ2 and the brightness control coefficients α _c1-1 , α _c1-2 of each user are calculated, and a new brightness control coefficient α _c2 is set for the adjustment region R3 located in the region between the users, i.e., the gap region, of the display 20. The brightness control coefficient α _c2 is, for example, set to the average value of the brightness control coefficients α _c1-1 , α _c1-2 , or a new region is added to the adjacent region in which the difference in contrast ratio satisfies a predetermined condition, and a value between the brightness control coefficients α _c1-1 , α _c1-2 is set for the new region. As a result, the difference in contrast ratio in the gap region is reduced compared to before the adjustment, and a display system is obtained that can display an image in which the sense of incongruity caused by the difference in contrast ratio is reduced when viewed from either of the users.

Furthermore, when there are two users, the brightness control coefficient α _c1-1 may be set for the front region of the first user on the display 20, and the brightness control coefficient α _c1-2 may be set for the front region of the second user as a new brightness control coefficient α _c2 . This reduces the difference in contrast ratio as seen by the first user in the region primarily gazed upon by the first user, and reduces the difference in contrast ratio as seen by the second user in the region primarily gazed upon by the second user, resulting in a display that reduces the sense of discomfort for both users.

In addition, when there are three or more users, two adjacent users are regarded as one group, and a new brightness control coefficient is determined for each group by one of the first to third adjustments described above. As a result, an appropriate brightness control coefficient is determined for the area between adjacent users, or the brightness control coefficient of the corresponding user is determined for the front area of each user, resulting in a display with reduced contrast ratio differences for each user. In addition, when there are three or more users, if the distance between some adjacent users is less than a predetermined value, the adjacent users are regarded as one user, and one of the first to third adjustments described above is performed between adjacent users who are far away. This also allows a display with reduced contrast ratio differences for each user.

Other Embodiments
Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one, or less than one, are also within the scope and concept of the present disclosure.

The control unit 12 and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit 12 and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit 12 and the method described in the present disclosure may be realized by one or more dedicated computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transient tangible recording medium as instructions executed by the computer.

It goes without saying that in each of the above embodiments, the elements constituting the embodiment are not necessarily essential, except when expressly stated as essential or when it is clearly considered essential in principle. Furthermore, in each of the above embodiments, when the numbers, values, amounts, ranges, etc. of the components of the embodiment are mentioned, they are not limited to the specific numbers, except when expressly stated as essential or when it is clearly limited to a specific number in principle. Furthermore, in each of the above embodiments, when the shapes, positional relationships, etc. of the components are mentioned, they are not limited to the shapes, positional relationships, etc., except when expressly stated as essential or when it is clearly limited to a specific shape, positional relationship, etc. in principle.

12c Solar radiation estimation unit 12d Illuminance acquisition unit 12e Position information acquisition unit 12f Brightness control unit 20 Display 20a Display surface 34 Imaging device

Claims (4)

A display device for controlling image display on a display (20) having a plurality of pixels, comprising:
a solar radiation estimation unit (12c) that estimates a solar irradiated area, which is an area of a display surface (20a) of the display that is irradiated by the sun, and a non-sun irradiated area, which is the remaining part of the display surface, based on position information of the sun and the display;
an illuminance acquisition unit (12d) for acquiring illuminance information of an environment in which the display is installed;
a position information acquisition unit (12e) that acquires position information of the user relative to the display from an imaging device (34) that images the user of the display;
a luminance control unit (12f) that executes a first luminance control to make a luminance of a solar radiation pixel group, which is a pixel group located in the solar radiation region among the plurality of pixels, higher than a luminance of a non-sun radiation pixel group, which is a pixel group located in the non-sun radiation region, based on an estimation result of the solar radiation estimating unit;
The location information acquisition unit acquires location information of at least two of the users,
the luminance control unit executes a second luminance control for making a difference in contrast ratio as seen by the two users equal to or less than a predetermined value for at least a part of an area (R3, R4, R5) located between the two users on the display surface based on position information of the user with respect to the display, a viewing angle characteristic of the display, and a light reflection characteristic on the display surface;
A display device in which a portion of a display image on the display that includes at least one of characters, figures, and symbols is defined as an information portion, and the remaining portion is defined as a background portion, and the contrast ratio is the ratio of the luminance of the information portion to the luminance of the background portion. The display device of claim 1, wherein, in the second brightness control, the brightness control unit sets an area of the display surface located between the two users as an adjustment area (R3), calculates two brightness control coefficients (α _c1-1 , α _c1-2 ) corresponding to each of the two users for the adjustment area, and sets the average value of the two brightness control coefficients as a new brightness control coefficient (α _c2 ) for the adjustment area. The luminance control unit is
In the second brightness control,
a region of the display surface located between the two users and composed of a plurality of regions (Z2 to Z4) is defined as an adjustment region (R3), two luminance control coefficients (α _c1-1 , α _c1-2 ) corresponding to each of the two users are calculated for the adjustment region, and the larger of the two luminance control coefficients is selected as the luminance control coefficient for the plurality of regions in the adjustment region;
The display device of claim 1, wherein when the difference in the contrast ratio between two adjacent regions among the plurality of regions after the brightness control coefficients have been selected for the two users is greater than or equal to a predetermined value, at least one new region (Z6, Z7) is added between the two regions, and a value between the brightness control coefficients selected for the two regions is set as a new brightness control coefficient (α _c2 ) for the new region. The luminance control unit is
In the second brightness control,
calculating two brightness control coefficients (α _c1-1 , α _c1-2 ) for the display surface corresponding to each of the two users;
For a first front region (R4) located in front of one of the users on the display surface, the brightness control coefficient corresponding to the one of the users is set as a new brightness control coefficient (α _c2 );
The display device according to claim 1 , wherein for a second front region (R5) of the display surface located in front of the other user, the brightness control coefficient corresponding to the other user is set as a new brightness control coefficient (α _c2 ).

Images