Electronic display device for vehicle

Abstract

An electronic display device (1) for a vehicle comprises: an imaging section (2) for capturing an image at least to the rear of a vehicle; a control unit (4) for acquiring the image captured by the imaging section 2, and changing a luminance histogram included in the information of the image to execute image processing for generating a display image having a diopter value smaller than that of the image captured by the imaging section (2); and a display section (5) for displaying the display image generated by the control unit (4).

Description

Vehicle electronic display device

[0001] The present disclosure relates to an electronic display device for a vehicle, for example, mounted on an automobile or the like.

[0002] For example, as disclosed in Patent Documents 1 to 3, electronic display devices are sometimes used as rearview mirrors installed in the passenger compartment of automobiles. This type of electronic display device includes an imaging unit that captures images of the rear and sides of the vehicle, and a display unit that displays the images captured by the imaging unit. The display unit is installed diagonally above and in front of the driver, similar to conventional rearview mirrors.

[0003] Furthermore, Patent Documents 4 and 5 disclose a display device mounted on a vehicle that uses a projection unit to project a virtual image onto a screen in front of the vehicle.

[0004] JP 2023-176131 A JP 2021-136463 A JP 2020-79025 A JP 2005-329768 A JP 2021-35807 A

[0005] Conventional vehicle inner mirrors consist of mirrors. When a driver uses a mirror to check an object behind or to the side, he or she looks at the object reflected in the mirror and focuses his or her eyes on the object reflected in the mirror.

[0006] In contrast, when an electronic display device is used as an inner mirror, the image captured by the imaging unit is displayed on a display unit such as a liquid crystal display (LCD) or an organic light-emitting diode (OLED).In this case, the driver recognizes objects by focusing their eyes on the image displayed on the display unit (display surface).

[0007] On the other hand, when driving a vehicle, the driver typically looks several tens of meters ahead of the vehicle. When a driver needs to check the rearview mirror, they shift their gaze from the forward position to the rearview mirror installed diagonally above. As mentioned above, in the case of a mirror, the driver focuses on the object reflected in the mirror itself, whereas in the case of an electronic display device, the driver must focus on the display surface. In particular, in the case of a rearview mirror, the driver is installed at the top center of the front windshield, so the distance between the driver and the rearview mirror is short. Given such a short distance, the driver can quickly and easily focus on the object reflected in the mirror itself, but in the case of an electronic display device, the driver must shift their focus from several tens of meters ahead to the display surface directly in front of them, which takes time. This time is particularly significant when the driver's ability to shift focus when viewing objects declines with age. As a result, the driver's ability to see the rearview mirror is delayed.

[0008] To facilitate such focusing, methods have been proposed in which a projection unit is used instead of a display to project a virtual image onto a screen in front of the vehicle, as disclosed in, for example, Patent Documents 4 and 5. By projecting a virtual image, it is possible to eliminate the delay in focusing by adjusting the focus to the virtual image. However, it may be difficult to install such a projection device and a screen for displaying the virtual image in the interior space of a vehicle.

[0009] The present disclosure has been made in consideration of the above points, and its purpose is to enable a driver to quickly check behind him / her without using a large display device such as a projection unit and a screen.

[0010] To achieve the above object, one aspect of the present disclosure can be based on a vehicle electronic display device mounted on a vehicle, the vehicle electronic display device including: an imaging unit that captures an image of at least a rear area of ​​the vehicle; an image processing unit that acquires the image captured by the imaging unit and performs image processing to generate a display image having a smaller diopter value than the image captured by the imaging unit by changing a luminance histogram included in information about the image; and a display unit that displays the display image generated by the image processing unit.

[0011] According to this configuration, when the display unit is installed at the upper center of the front of the windshield in a manner similar to a conventional rearview mirror, the distance between the display unit and the driver of the vehicle will be closer. The image displayed on the display unit has a smaller diopter value than the image captured by the imaging unit, due to image processing performed by the image processing unit on the image captured by the imaging unit. The diopter value is a numerical value defined as the reciprocal of the visual distance. When focusing from a distant object to a near object, the diopter value decreases as the depth of focus increases. Therefore, an image with a smaller diopter value is easier to focus on than an image with a larger diopter value. Therefore, when the driver is looking several tens of meters ahead of the vehicle and then focuses their gaze on the display unit to check the rear, the display image displayed on the display unit is more easily focused, allowing for quick rearward check.

[0012] The vehicle electronic display device may further include an illuminance acquisition unit that acquires environmental illuminance around the vehicle. In this case, the image processing unit can generate the display image by changing a luminance histogram based on the environmental illuminance acquired by the illuminance acquisition unit.

[0013] The image processing unit can generate the display image by performing contrast conversion, gamma value conversion, and sharpness conversion as the image processing. The image processing unit can generate a display image with good color reproducibility and a natural appearance by not performing local flattening processing in the image processing.

[0014] The image processing unit determines whether the vehicle is in a bright place or a dark place based on the ambient illuminance acquired by the illuminance acquisition unit, and can change parameters of the image processing depending on whether the vehicle is in a bright place or a dark place. A dark place is a place with low ambient illuminance, such as when driving at night or in a tunnel. A bright place is a place with high ambient illuminance, such as when driving at night or in a tunnel.

[0015] When the vehicle is in a bright place, the image processing unit can set the contrast conversion parameter to 0.80 or more and 0.93 or less, the gamma value conversion parameter to 0.70 or more and 0.90 or less, and the sharpness conversion parameter to 0.66 or more and 1.00 or less.

[0016] When the vehicle is in a dark place, the image processing unit can set the contrast conversion parameter to 0.80 or more and 1.06 or less, the gamma value conversion parameter to 0.50 or more and 0.90 or less, and the sharpness conversion parameter to 0.33 or more and 1.00 or less.

[0017] The image processing unit may execute, as the image processing, a process of multiplying the luminance histogram of the image captured by the imaging unit by a parameter of the contrast conversion, and a process of raising the luminance histogram of the image captured by the imaging unit to the power of a parameter of the gamma value conversion.

[0018] As described above, it is possible to display on the display unit an image for display that has a smaller diopter value than the image captured by the imaging unit, which makes it easier for the driver to focus when checking behind the vehicle and enables the driver to check behind the vehicle quickly without using a large-scale display device such as a projection unit and screen.

[0019] FIG. 1 is a schematic diagram showing a portion of a vehicle equipped with a vehicle electronic display device according to an embodiment of the present invention. FIG. 2 is a diagram illustrating the configuration of the vehicle electronic display device. FIG. 3 is a functional block diagram of a control unit. FIG. 4 is a diagram illustrating an example of an image and a brightness histogram. FIG. 5 is a schematic plan view of a test device for verifying the focusing effect of each image processing parameter. FIG. 6 is a side view of the test device. FIG. 7 is a graph showing the distribution of diopter values ​​when the brightness, gamma value, and contrast are changed. FIG. 8 is a graph showing shaded areas where the diopter value decreases when the gamma value, contrast, and brightness are changed. FIG. 9 is a graph showing shaded areas where the diopter value decreases when the gamma value, contrast, and local flattening are changed. FIG. 10 is a graph showing shaded areas where the diopter value decreases when the gamma value, sharpness, and brightness are changed. FIG. 11 is a graph showing the distribution of diopter values ​​when the contrast, sharpness, and local flattening are changed. Fig. 12 is a graph showing the distribution of diopter values ​​when contrast, sharpness, and brightness are changed. Fig. 13 is a graph showing the relationship between the gamma value, sharpness, local flattening, and diopter values. Fig. 14 is a graph showing the relationship between the gamma value, sharpness, contrast, and diopter values. Fig. 15 is a graph showing the relationship between the gamma value, contrast, local flattening, and diopter values. Fig. 16 is a graph showing the relationship between the distance from the display unit and focusing time.

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses.

[0021] FIG. 1 is a schematic diagram showing a portion of a vehicle 100 equipped with a vehicle electronic display device 1 according to an embodiment of the present invention. The type of vehicle 100 is not particularly limited, and may be, for example, a passenger car or a freight vehicle (such as a truck). The vehicle 100 includes a front windshield 101, a roof 102, a rear windshield 103, a dashboard 104, and a driver's seat 105. A driver 200 is seated in the driver's seat 105. In this embodiment, the vehicle electronic display device 1 is described as being used as an electronic display device for an inner mirror. However, the present invention is not limited to this, and the vehicle electronic display device 1 can also be used as an electronic display device for an outer mirror disposed on the outside of the vehicle 100.

[0022] 2 , the vehicle electronic display device 1 mounted on the vehicle 100 includes an imaging unit 2, an ambient light sensor 3, a control unit 4, and a display unit 5. The power supply 6 is for supplying power to the vehicle electronic display device 1 and is configured, for example, by an on-board battery. The power supply 6 may or may not be included in the vehicle electronic display device 1.

[0023] The imaging unit 2 is configured with a camera for capturing images of at least the rear of the vehicle 100 and is capable of capturing video. Although not shown, the imaging unit 2 includes an imaging element such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS). The imaging element generates an image based on the intensity of light received via an optical system (not shown) possessed by the imaging unit 2. The image is generated at a predetermined frame rate (e.g., 30 fps or higher) and output from the imaging unit 2. The image output from the imaging unit 2 is input to the control unit 4. The image output from the imaging unit 2 may be input to a vehicle control device (not shown) and then input to the control unit 4. Power is supplied to the imaging unit 2 via the control unit 4.

[0024] As shown in FIG. 1 , the imaging unit 2 is installed inside the rear windshield 103 of the vehicle 100. This allows the imaging unit 2 to continuously capture images of at least the area behind the vehicle 100 through the rear windshield 103. The field of view of the imaging unit 2 may include not only the area behind the vehicle 100 but also the sides. The imaging unit 2 may be installed outside the passenger compartment. The imaging unit 2 can continue capturing images not only while the vehicle 100 is moving, but also when the vehicle 100 is stopped. The imaging unit 2 may be configured, for example, as a camera for a drive recorder or a camera for a backup monitor.

[0025] The ambient light sensor 3 is an illuminance acquisition unit that acquires the ambient illuminance around the vehicle 100 and includes a light-receiving element such as a photodiode. In this embodiment, the ambient light sensor 3 is mounted on the top surface of the dashboard 104 and receives light that has passed through the windshield 101 and reached the vehicle interior. The ambient illuminance around the vehicle 100 can be acquired based on the intensity of the received light. When acquiring the ambient illuminance around the vehicle 100, the ambient illuminance can be calculated taking into account the light transmittance of the windshield 101. If the vehicle 100 is equipped with an automatic light system, the illuminance sensor of the automatic light system may be used as the ambient light sensor 3. Furthermore, since the image sensor 2 is a component that can receive external light and acquire the intensity of the external light (corresponding to the ambient illuminance), the image sensor 2 may also be used as the ambient light sensor 3. The ambient light sensor 3 acquires the ambient illuminance in approximately real time. The signal output from the ambient light sensor 3 is input to the control unit 4. The ambient light sensor 3 may be installed outside the vehicle interior.

[0026] The display unit 5 is a display device configured, for example, by a liquid crystal display (LCD) or an organic light emitting diode (OLED). The display unit 5 is configured by a high-brightness display, and the brightness of the display unit 5 is 500 Cd / m ２The above is the case. The shape of the display unit 5 is not particularly limited, but may be elongated in the vehicle width direction and have a shape similar to that of a conventional inner mirror. The front portion of the display unit 5 is attached to the upper center front of the windshield 101 via a stay 5a so that the angle can be adjusted. The display unit 5 may be attached to the interior surface of the roof 102. In addition, the surface of the display unit 5 has a half-mirror structure so that it can be used as an inner mirror when not displaying an image. Power is supplied to the display unit 5 via the control unit 4.

[0027] 3 is a functional block diagram of the control unit 4. As shown in this diagram, the control unit 4 includes an input unit 4a, an image processing unit 4b, a display panel control unit 4c, and a storage unit 4d. The input unit 4a, the image processing unit 4b, and the display panel control unit 4c may be configured as hardware of the control unit 4, or may be configured as a combination of hardware and software.

[0028] A typical example of the configuration of the control unit 4 is a configuration including a microcomputer having a central processing unit, ROM, RAM, etc. For example, a storage section 4d can be configured by ROM, and in addition to the operation program, various data, control parameters, image processing parameters (described later), etc. are stored in advance in this storage section 4d.

[0029] The control unit 4 may be provided with a processing device such as an FPGA (Field Programmable Gate Array) or an ISP (Image Signal Processor). The control unit 4 may also be provided with a processor that integrates processing devices such as an FPGA or a DSP. Some of the input unit 4a, image processing unit 4b, and display panel control unit 4c may be configured with a first processing device, and the rest may be configured with a second processing device.

[0030] The input unit 4a includes a connection interface to which the imaging unit 2 and the ambient light sensor 3 are connected, for example, and accepts input of image data captured by the imaging unit 2, as well as input of a signal related to ambient illuminance output from the ambient light sensor 3. The image data and the signal related to ambient illuminance received by the input unit 4a are output to the image processing unit 4b.

[0031] The image processing unit 4b acquires an image captured by the imaging unit 2 and performs image processing to generate a display image having a smaller diopter value than the image captured by the imaging unit 2 by changing a luminance histogram included in the information of the image captured by the imaging unit 2. When performing image processing, the image processing unit 4b also acquires a signal related to the ambient illuminance output from the ambient light sensor 3. The image processing unit 4b then changes the luminance histogram based on the ambient illuminance acquired by the ambient light sensor 3, thereby generating a display image to be displayed on the display unit 5.

[0032] 4 is a diagram showing an example of an image acquired by the image processing unit 4b and an example of a luminance histogram of the image acquired by the image processing unit 4b. In the case of a color image, the luminance histogram is shown for each of R, G, and B. The characteristics of the image acquired by the image processing unit 4b can be shown by the luminance histogram.

[0033] The display panel control unit 4c is a unit that controls the display unit 5. The display image data generated by the image processing unit 4b is output to the display panel control unit 4c. The display panel control unit 4c generates a signal for controlling the display unit 5 based on the acquired display image data and transmits it to the display unit 5. As a result, the display image generated by the image processing unit 4b is displayed on the display unit 5.

[0034] The diopter value is a numerical value defined as the reciprocal of the visual distance, and when focusing from a distant object to a near object, the diopter value decreases as the depth of focus increases. The depth of focus is an index indicating the range in which an object can be seen in focus, and a larger depth of focus indicates easier focusing (a wider range in which an object can be seen in focus). Easy focusing means that the eye movement places less strain on the eyes. Therefore, by generating a display image with a smaller diopter value than the image captured by the imaging unit 2 and displaying it on the display unit 5, the driver can easily focus and quickly check behind the vehicle without using a large display device such as a projection unit and screen.

[0035] Examples of parameters that affect the focal depth include brightness, contrast, γ value (gamma value), sharpness, local flattening, etc. of the image for display, but in this embodiment, the image processing unit 4b generates the image for display by performing contrast conversion, γ value conversion, and sharpness conversion on the image captured by the imaging unit 2 as image processing for generating the image for display on the display unit 5. The image processing unit 4b may perform all of the contrast conversion, γ value conversion, and sharpness conversion, or may perform any one or any two of the contrast conversion, γ value conversion, and sharpness conversion as necessary.

[0036] Here, we will explain how to convert the brightness histogram, which shows the characteristics of an image, using the above parameters and consider the parameters related to the depth of focus. First, we will explain how to apply each parameter to change the brightness histogram.

[0037] For brightness conversion, we use the sliding method (average brightness change), which adds a constant brightness to the brightness histogram of the original image.

[0038] (Output) = (Input) + (brightness value)

[0039] The contrast conversion is performed by multiplying the brightness histogram of the original image by a certain constant value. That is, the image processing unit 4b performs image processing by multiplying the brightness histogram of the image captured by the imaging unit 2 by a contrast conversion parameter.

[0040] (Output) = (Input) × (Scale value)

[0041] The gamma conversion is a method of raising the brightness histogram of the original image by a certain constant value. That is, the image processing unit 4b executes, as image processing, a process of raising the brightness histogram of the image captured by the imaging unit 2 by a gamma value conversion parameter.

[0042] (Output) = (Input)^γ

[0043] Sharpness transformation converts the pixel value of a pixel of interest by performing convolution processing using the pixel values ​​of the central pixel and eight surrounding pixels. Convolution processing involves using the output value of a product-sum operation between each pixel of an image and a filter as the pixel value of the central pixel. The filter consists of nine coefficient values ​​that are set for the central pixel and the eight adjacent pixels. The filter used for sharpness transformation is expressed as follows:

[0044]

[0045] The multiply-and-accumulate operation involves calculating the product of each coefficient value of the filter and the corresponding pixel value of the original image, and then adding them up.

[0046] Local flattening is a process of dividing an image into small tiles and flattening the histogram in each area. In this embodiment, since performing local flattening reduces color reproducibility and creates an unnatural image, the image processing unit 4b does not perform local flattening in the image processing for generating a display image to be displayed on the display unit 5.

[0047] Before performing the image processing, the image processing unit 4b performs a determination process to determine whether the vehicle 100 is in a bright place or a dark place based on the ambient illuminance acquired by the ambient light sensor 3. For example, when the vehicle 100 is traveling at night or in a tunnel, the ambient illuminance around the vehicle 100 is, for example, approximately 50 lx. When the ambient illuminance acquired by the ambient light sensor 3 is input to the image processing unit 4b, if the input ambient illuminance is 50 lx or less, the image processing unit 4b determines that the vehicle 100 is in a dark place. On the other hand, if the ambient illuminance input from the ambient light sensor 3 exceeds 50 lx, the image processing unit 4b determines that the vehicle 100 is in a bright place. The determination threshold of "50 lx" used in the determination process by the image processing unit 4b is an example, and the determination threshold is not limited to 50 lx. Any determination threshold that is generally recognized as a dark place when the vehicle 100 is traveling can be used. The determination threshold can be set, for example, in the range of 40 to 100 lx. Furthermore, for example, the environmental illuminance when the headlights of the vehicle 100 are turned on in an automatic light system may be used as the determination threshold value.

[0048] The image processing unit 4b changes the image processing parameters depending on whether the vehicle 100 is determined to be in a bright place or a dark place in the determination process. Specifically, when the image processing unit 4b determines that the vehicle 100 is in a bright place in the determination process, the image processing unit 4b sets the contrast conversion parameter to 0.80 or more and 0.93 or less, the gamma value conversion parameter to 0.70 or more and 0.90 or less, and the sharpness conversion parameter to 0.66 or more and 1.00 or less. On the other hand, when the image processing unit 4b determines that the vehicle 100 is in a dark place in the determination process, the image processing unit 4b sets the contrast conversion parameter to 0.80 or more and 1.06 or less, the gamma value conversion parameter to 0.50 or more and 0.90 or less, and the sharpness conversion parameter to 0.33 or more and 1.00 or less. Each parameter is pre-stored in, for example, the storage unit 4d, and the image processing unit 4b determines which parameter to apply based on the determination process.

[0049] (Test Example) Next, a test to verify the focusing effect of each parameter applied during image processing by the image processing unit 4b will be described. Figures 5 and 6 are diagrams that schematically show a test device 300 for verifying the focusing effect of each parameter related to image processing by the image processing unit 4b. This test device 300 simulates a situation in which a model driver 200A shifts his or her gaze from a forward-viewing state to an inner mirror while driving on a highway.

[0050] The main display 301 is placed 6 m ahead of the simulated driver 200A to simulate a forward field of view. The sub-display 302 is placed 450 mm ahead of the simulated driver 200A and diagonally above it to simulate an inner mirror. The relationship between the installation position of the sub-display 302 and the simulated driver 200A is approximately the same as the positional relationship between the driver 200 and the display unit 5 in the actual vehicle 100, as shown in FIG. 1. As shown in FIG. 6, the height of the eyes of the simulated driver 200A is 1,150 mm. The display surface of the sub-display 302 is inclined 5° with respect to a vertical line 303. Furthermore, assuming a horizontal plane 304 passing through the eyes of the simulated driver 200A, a line 305 connecting the eyes of the simulated driver 200A and the vertical center of the sub-display 302 is at an angle of 10° with respect to the horizontal plane 304. 5, the horizontal center of the main display 301 is located directly in front of the eyes of the simulated driver 200A. A line 306 connecting the eyes of the simulated driver 200A and the horizontal center of the sub-display 302 is at an angle of 20° with a line 307 connecting the eyes of the simulated driver 200A and the horizontal center of the main display 301.

[0051] Alphabetical characters or numbers were displayed alternately every 2.5 seconds on the main display 301 and the sub-display 302. Numbers were displayed approximately once every 6 to 8 times (15 to 20 seconds). The head of the simulated driver 200A was fixed by the chin rest 310.

[0052] The simulated driver 200A visually recognizes the symbols displayed on the main display 301 and determines, depending on the type of symbol, whether to continue looking at the main display 301 or to move his / her gaze to the sub-display 302. If the symbols displayed on the main display 301 are alphabetic characters, the simulated driver 200A is made to continue gazing at the main display 301. If the symbols displayed on the main display 301 are numbers, the gaze is moved from the main display 301 to the sub-display 302.

[0053] When the simulated driver 200A moved his / her viewpoint to the sub-display 302, the simulated driver 200A was made to determine whether the numbers displayed on the main display 301 and the sub-display 302 were the same and to operate a button. If the numbers displayed on the main display 301 and the sub-display 302 were the same, the simulated driver 200A was made to press the button with his / her right hand, and if the numbers on the main display 301 and the sub-display 302 were different, the simulated driver 200A was made to press the button with his / her left hand.

[0054] In the above test, the diopter change of the viewpoint of the simulated driver 200A was measured. The diopter value was calculated from the depth coordinate of the focus using an eye tracking device. The diopter value and reaction time, which are related to the depth of focus, were evaluated, and the conditions under which the diopter value becomes smaller were analyzed.

[0055] The image displayed on the sub-display 302 was processed by the image processing unit 4b, and the change in the diopter value related to the focal depth and the time required for the simulated driver 200A to press the button after the image was displayed on the sub-display 302 (the reaction time of the simulated driver 200A) were evaluated.

[0056] The parameters used in image processing by the image processing unit 4b were brightness between 0 and 60, contrast between 0.8 and 1.2, gamma value between 0.5 and 1.1, sharpness between 0 and 1.3, and local flattening between 4 and 32. The image processing unit 4b randomly changed two or three of these parameters to perform image processing and generate the image to be displayed on the sub-display 302.

[0057] The reaction time of the simulated driver 200A was plotted in three dimensions for each combination of the changed parameters, and the conditions for reducing the diopter value were examined. That is, for each parameter, the diopter value was classified into three ranges: a 10% range with a high diopter value, a 10% range with a low diopter value, and the remaining range with a median value. The three-dimensional plot was then performed to verify what image transformation conditions affect the diopter value. To facilitate focusing, the conditions for reducing the diopter value are preferable.

[0058] The graph shown in Figure 7 shows the distribution of diopter values ​​when the brightness, gamma value, and contrast, which are parameters used in image processing by the image processing unit 4b, are changed. The diopter values ​​were classified into three types as described above. The diopter values ​​were classified into the large 10% range (indicated by black squares), the small 10% range (indicated by black circles), and the remaining median value (indicated by black triangles), and plotted on the graph.

[0059] To make it easier to understand the correlation between each of the changed parameters, the processing shown in FIG. 8 was performed. The points in FIG. 8 indicate the parameters resulting from the experiment. All of the experimental points are plotted on the graph in FIG. 8. Of the three types of classification based on diopter value described above, the parameters that indicate the area where the depth of focus is large, i.e., the area where the diopter value is small, are indicated by diagonal lines to make it easier to understand. As a result, it was found that the area with small diopter values ​​is distributed (indicated by diagonal lines in FIG. 8) in the area where the gamma value is between 0.5 and 0.9, and the contrast is between 0.8 and 1.066.

[0060] Figure 9 shows the distribution of diopter values ​​when the gamma value, contrast, and local flattening are changed. The same analysis as above was performed, and the areas with low diopter values ​​are indicated by diagonal lines. The areas with low diopter values ​​are distributed near the midpoint between contrasts of 0.933 and 1.066. On the other hand, it can be seen that local flattening has almost no effect. The results of Figures 8 and 9 show that contrast has a large effect as a parameter that reduces the diopter value, i.e., increases the depth of focus.

[0061] Figure 10 shows the distribution of diopter values ​​when the gamma value, sharpness, and brightness are changed. A region with small diopter values ​​is distributed in the sharpness range of 0 to 0.33. On the other hand, this graph shows that the gamma value and brightness have almost no effect on the diopter value.

[0062] Figures 11 and 12 show the distribution of diopter values ​​when contrast, sharpness, and local flattening are changed, and contrast, sharpness, and brightness are changed, respectively. The large 10% range of diopter values ​​(shown as black squares), the small 10% range (shown as black circles), and the remaining median value (shown as black triangles) are classified and plotted on a graph. With this parameter conversion, it was found that the "black circles" plotted with small diopter values ​​are uniformly distributed and no correlation is observed.

[0063] To examine the optimum parameters in more detail, the scatter plots showing trends in the small diopter value range were divided into grids and analyzed.

[0064] Fig. 13 shows the relationship between sharpness, γ value, local flattening and diopter value. Fig. 14 shows the relationship between γ value, contrast, sharpness and diopter value. Fig. 15 shows the relationship between γ value, contrast, local flattening and diopter value.

[0065] In Figures 13 to 15, the areas where the diopter value decreases are indicated by black areas. From Figures 13 to 15, we derived that the optimal image transformation parameters for decreasing the diopter value are a contrast transformation parameter of 0.80 to 0.93, a gamma value transformation parameter of 0.70 to 0.90, and a sharpness transformation parameter of 0.66 to 1.00. By setting the image transformation parameters within these ranges, the diopter value becomes 2.02 to 2.93. Test results have shown that luminance has almost no effect on the diopter value. By applying parameters within this range to image processing by the image processing unit 4b, a display image with a reduced diopter value, i.e., a greater depth of focus, can be obtained. As a result, a display image that is easy to focus on can be provided as close as 450 mm from the driver 200.

[0066] Note that an image that has undergone local flattening has poor color reproducibility compared to an actual image, resulting in an unnatural-looking image. Therefore, the image processing unit 4b does not perform local flattening, and generates a display image under the conditions for a natural-looking image, in which the contrast conversion parameter is 0.80 to 0.93, the gamma value conversion parameter is 0.70 to 0.90, and the sharpness conversion parameter is 0.66 to 1.00, and the display image is displayed on the display unit 5.

[0067] Twelve subjects (four in their 60s, two in their 50s, two in their 40s, two in their 30s, and two in their 20s) were asked to actually drive a vehicle 100 equipped with a display unit 5 on which a display image according to an embodiment of the present invention is displayed. After that, a questionnaire was conducted regarding the visibility of the display unit 5. The vehicle 100 was driven in the daytime under clear skies with an ambient illuminance of 10,000 lx. The results are shown below.

[0068] Easy to focus and see 5 people Less fatigue 3 people Nothing in particular 3 people Unable to focus and blurry 1 person

[0069] As described above, when the display image processed according to the embodiment of the present invention was displayed on the display unit 5, three people felt nothing in particular, and five people said that it was easy to focus. Three people also said that the display image processed according to the embodiment of the present invention was not glaring and did not cause fatigue. Younger generations have a high ability to focus and are less likely to experience focusing delays. However, as people age, this ability declines, resulting in focusing delays. The results of this survey show that optimizing image processing parameters can make it easier to focus, making it appear as if the object was in focus, a phenomenon that occurs when the ability to change focus declines with age.

[0070] A similar experiment was conducted under a dark condition of 40 lx. A similar analysis was conducted, and the following image conversion parameters were derived to reduce the diopter value: a contrast conversion parameter of 0.80 to 1.06, a gamma value conversion parameter of 0.50 to 0.90, and a sharpness conversion parameter of 0.33 to 1.00.

[0071] As in the results of the study under bright conditions, the image with local flattening had poor color reproducibility, so the image processing unit 4b did not perform local flattening. When the subject performed a test drive at night (ambient illuminance: 50 lx), the results showed that focusing was easy, similar to the results under bright conditions.

[0072] FIG. 16 shows the relationship between the distance from the display unit 5 and the time required to focus. The time is shown as a relative time. It can be seen that the time required to focus decreases as the distance from the display unit 5 increases. This indicates that focusing becomes easier as the distance between the display unit 5 and the eye increases. Focusing at close distances requires greater changes in the crystalline lens, which increases the time required to focus. In this test, the ease of focusing at a relatively short distance of 450 mm from the sub-display 302 (corresponding to the display unit 5) was verified. This effect is effective regardless of the distance from the display unit 5, and the effect of this embodiment remains unchanged regardless of the distance. However, the effect of image processing by the image processing unit 4b is particularly pronounced when the distance from the sub-display 302 is between 400 mm and 550 mm, which is a relatively short range.

[0073] From the above test results, when the vehicle 100 is in a bright place, the diopter value of the driver 200 can be reduced by setting the contrast conversion parameter to 0.80 or more and 0.93 or less, the gamma value conversion parameter to 0.70 or more and 0.90 or less, and the sharpness conversion parameter to 0.66 or more and 1.00 or less. Also, when the vehicle 100 is in a dark place, the diopter value of the driver 200 can be reduced by setting the contrast conversion parameter to 0.80 or more and 1.06 or less, the gamma value conversion parameter to 0.50 or more and 0.90 or less, and the sharpness conversion parameter to 0.33 or more and 1.00 or less.

[0074] The above-described embodiments are merely examples in all respects and should not be construed as limiting. Furthermore, all modifications and variations within the scope of the claims are within the scope of the present invention.

[0075] As described above, the electronic display device for a vehicle according to the present disclosure can be used as, for example, an inner mirror of a vehicle, and can also be applied to an electronic display device for an outer mirror.

[0076] REFERENCE SIGNS LIST 1 Vehicle electronic display device 2 Imaging unit 3 Ambient light sensor (illuminance acquisition unit) 4 Control unit 4b Image processing unit 100 Vehicle

Claims

1. An electronic display device for a vehicle that is mounted on a vehicle, comprising: an imaging unit that captures an image of at least the rear of the vehicle; an image processing unit that acquires the image captured by the imaging unit and performs image processing to generate an image for display that has a smaller diopter value than the image captured by the imaging unit by changing a luminance histogram included in the image information; and a display unit that displays the image for display generated by the image processing unit.

2. An electronic display device for a vehicle according to claim 1, further comprising an illuminance acquisition unit that acquires the environmental illuminance around the vehicle, wherein the image processing unit generates the display image by changing a brightness histogram based on the environmental illuminance acquired by the illuminance acquisition unit.

3. An electronic display device for a vehicle according to claim 2, wherein the image processing unit generates the display image by performing contrast conversion, gamma value conversion, and sharpness conversion as the image processing.

4. The electronic display device for a vehicle according to claim 2, wherein the image processing unit does not execute local flattening processing in the image processing.

5. An electronic display device for a vehicle as described in claim 3, wherein the image processing unit determines whether the vehicle is in a bright place or a dark place based on the ambient illuminance acquired by the illuminance acquisition unit, and changes the image processing parameters depending on whether the vehicle is in a bright place or a dark place.

6. An electronic display device for a vehicle according to claim 5, wherein the image processing unit, when the vehicle is in a bright place, sets the contrast conversion parameter to 0.80 or more and 0.93 or less, the gamma value conversion parameter to 0.70 or more and 0.90 or less, and the sharpness conversion parameter to 0.66 or more and 1.00 or less.

7. An electronic display device for a vehicle according to claim 5, wherein the image processing unit, when the vehicle is in a dark place, sets the contrast conversion parameter to 0.80 or more and 1.06 or less, the gamma value conversion parameter to 0.50 or more and 0.90 or less, and the sharpness conversion parameter to 0.33 or more and 1.00 or less.

8. An electronic display device for a vehicle according to claim 3, wherein the image processing unit executes, as the image processing, a process of multiplying the brightness histogram of the image captured by the imaging unit by a parameter of the contrast conversion.

9. An electronic display device for a vehicle according to claim 3, wherein the image processing unit executes, as the image processing, a process of raising the brightness histogram of the image captured by the imaging unit by a parameter for the gamma value conversion.

10. In the electronic display device for a vehicle according to claim 1, the luminance of the display unit is 500 Cd / m ２ That is all for the vehicle electronic display device.

Images