Display control method and display control device

Abstract

In the present invention, a controller: detects the inter-vehicle distance between a host vehicle (V1) and a following vehicle (V2); calculates the relative speed of the host vehicle (V1) and the following vehicle (V2); determines rapid approaching of the following vehicle (V2) to the host vehicle (V1) on the basis of the inter-vehicle distance and the relative speed; and displays the size of the following vehicle (V2) in a captured image of behind the host vehicle (V1) on a display (13) without adjusting said size if the following vehicle (V2) is rapidly approaching, and displays the size of the following vehicle (V2) in the captured image of behind the host vehicle (V1) on the display (13) while adjusting said size according to the inter-vehicle distance if the following vehicle (V2) is not rapidly approaching.

Description

Display control method and display control device

[0001] The present invention relates to a display control method and a display control device for a display provided in a vehicle.

[0002] In recent years, so-called digital inner mirrors have become known that display an image of the area behind the vehicle on a display screen instead of a rearview mirror that displays the area behind the vehicle (see, for example, Patent Document 1). Patent Document 1 describes a method for generating a cropped image based on a field of view value from a rearview image of the area behind the vehicle captured by a camera, and then generating a display image from the cropped image that matches the size of the display area. The field of view value indicates the size of the cropped image relative to the size of the rearview image, and is set based on the distance between the vehicle and the following vehicle so that the size of the following vehicle in the display image is equal to the size of the following vehicle reflected in the mirror surface that reflects the area behind the vehicle (the vehicle when the rearview is viewed using a conventional rearview mirror).

[0003] Japanese Patent Application Laid-Open No. 2018-129668

[0004] However, the technology of Patent Document 1 has the problem that even when a following vehicle approaches the vehicle suddenly, the angle of view of the display image is adjusted, making it difficult for the vehicle occupants to notice the following vehicle's sudden approach.

[0005] An object of the present invention is to provide a display control method and a display control device that allow a vehicle occupant to easily notice the sudden approach of a following vehicle.

[0006] A display control method according to one aspect of the present disclosure detects a distance between a vehicle and a following vehicle, calculates a relative speed of the following vehicle with respect to the vehicle, and determines whether the following vehicle is rapidly approaching the vehicle based on the distance between the vehicles and the relative distance. When displaying an image of the rear of the vehicle captured by a camera on a display, if it is determined that the following vehicle is rapidly approaching, the size of the following vehicle included in the captured image is displayed on the display without being adjusted, and if it is determined that the following vehicle is not rapidly approaching, the size of the following vehicle included in the captured image is adjusted based on the distance between the vehicles and then displayed on the display.

[0007] As a result, when a following vehicle approaches suddenly, the angle of view value is not adjusted, so that the vehicle occupants can easily notice the following vehicle approaching suddenly from the image displayed on the display.

[0008] 1 is a block diagram showing an example of a display control device according to an embodiment of the present invention. FIG. 3 is a diagram showing an example of mapping data for determining a sudden approach of a following vehicle in the present embodiment. FIG. 4 is a plan view showing an example of a driving scene for controlling the display of a display in the present embodiment. FIG. 4 is a diagram showing an example of an image acquired by a camera of the host vehicle of FIG. 3. FIG. 5 is a diagram showing an example of an image displayed on the display of the host vehicle of FIG. 3. FIG. 5 is a diagram showing an example of an image reflected in a rearview mirror attached in the same position as the digital inner mirror in the host vehicle of FIG. 3. FIG. 6 is a diagram showing another example of an image acquired by a camera of the host vehicle of FIG. 3. FIG. 6 is a diagram showing another example of an image displayed on the display of the host vehicle of FIG. 3. FIG. 7 is a diagram showing another example of an image reflected in a rearview mirror attached in the same position as the digital inner mirror in the host vehicle of FIG. 3. A flowchart showing an example of a display control method in the present embodiment.

[0009] An embodiment of the present disclosure will be described below. Fig. 1 is a block diagram showing an example of a display control device 1 according to this embodiment. The display control device 1 is a group of devices that control the display of a display 13 provided in a vehicle. As shown in Fig. 1, the display control device 1 includes a camera 11, a distance sensor 12, a display 13, a speaker 14, and a controller 20. These devices are connected via a controller area network (CAN) or other in-vehicle LAN, and can exchange information with each other.

[0010] The camera 11 is a device that captures images of objects around the vehicle. Examples of the camera 11 include a general color image camera equipped with an imaging element such as a charge coupled device (CCD) and a color filter such as an RGB filter. Other examples of the camera 11 include an infrared camera capable of capturing infrared images and a multispectral camera capable of capturing image light of multiple wavelengths.

[0011] The distance sensor 12 is a device that detects the relative distance and relative speed between the vehicle and an object. Examples of the distance sensor 12 include a laser radar, a millimeter-wave radar, and a LiDAR (light detection and ranging) unit. In order to reduce blind spots where an object cannot be detected, it is preferable to provide a plurality of cameras 11 and distance sensors 12 at the front, rear, sides, etc. of the vehicle.

[0012] The objects detected by the camera 11 and distance sensor 12 are objects that exist on the road and its surroundings, including lane boundaries, center lines, road markings, medians, guardrails, curbs, road signs, traffic lights, etc. The objects also include obstacles that may affect the travel of the vehicle, such as other vehicles, motorcycles, bicycles, and pedestrians.

[0013] The detection results of the camera 11 and the distance sensor 12 are acquired by the controller 20 at predetermined time intervals (for example, every 0.1 to 1 millisecond) as needed. The controller 20 recognizes objects around the vehicle and the vehicle's driving environment from the acquired detection results. The controller 20 may also integrate or synthesize the detection results of the camera 11 and the distance sensor 12 (so-called sensor fusion).

[0014] The display 13 is a device that provides information to vehicle occupants. An example of the display 13 is a digital inner mirror that is installed in the vehicle cabin and displays an image of the rear of the vehicle acquired by the camera 11. Such a digital inner mirror is installed, for example, at the upper center of the vehicle windshield instead of a conventional rearview mirror. Alternatively, the display 13 may be a liquid crystal display or the like provided on the instrument panel. In this case, the display 13 may be equipped with an input device that allows the vehicle occupant to input instructions to the controller 20. Examples of the input device include a touch panel and a switch.

[0015] The speaker 14 is a device that provides information to the vehicle occupants by voice. The location where the speaker 14 is installed is not particularly limited, and the speaker 14 may be installed, for example, on the instrument panel, on the interior side of the door, or on the ceiling of the vehicle.

[0016] The controller 20 controls the display on the display 13 and the audio output from the speaker 14 by cooperating with each device constituting the display control device 1. The controller 20 is, for example, a computer, and includes a storage unit 21 in which programs and various data are stored, and a processor 22 that implements predetermined functions by reading and executing the programs stored in the storage unit 21. The controller 20 may be provided outside the vehicle.

[0017] The storage unit 21 is configured with a storage device such as a semiconductor memory, and stores various programs for controlling the display 13 and the audio output of the speaker 14. The storage unit 21 also stores mapping data for determining whether a following vehicle traveling behind the host vehicle is rapidly approaching the host vehicle. Details of the mapping data will be described later.

[0018] The processor 22 is configured with an arithmetic circuit such as a CPU (Central Processing Unit), and realizes various functions by reading and executing programs stored in the storage unit 21. Specifically, as shown in FIG. 1 , the processor 22 functions as an acquisition unit 221, an inter-vehicle distance detection unit 222, a relative speed calculation unit 223, a sudden approach determination unit 224, an output control unit 225, and the like. Note that, although an example is shown in which the processor 22 executes a program to realize the respective functional configurations of the acquisition unit 221, the inter-vehicle distance detection unit 222, the relative speed calculation unit 223, the sudden approach determination unit 224, and the output control unit 225, some or all of these may be realized by individual hardware configurations.

[0019] The acquisition unit 221 acquires image information (captured image) from the camera 11. As described above, the captured image is an image of objects around the vehicle, and includes at least an image of the rear of the vehicle. The inter-vehicle distance detection unit 222 detects the distance to the following vehicle (inter-vehicle distance) measured by the distance sensor 12.

[0020] The relative speed calculation unit 223 calculates the relative speed between the host vehicle and the following vehicle based on a change over time in the inter-vehicle distance to the following vehicle. Note that, although an example in which the relative speed calculation unit 223 calculates the relative speed based on a change over time in the inter-vehicle distance is used here, this is not limiting. For example, the relative speed may be calculated by calculating the difference between the speed of the host vehicle and the speed of the following vehicle.

[0021] The sudden approach determination unit 224 determines whether the following vehicle is rapidly approaching the host vehicle. To do this, the sudden approach determination unit 224 determines that the following vehicle is rapidly approaching the host vehicle when the relative speed of the following vehicle with respect to the host vehicle is equal to or greater than a predetermined threshold, and determines that the following vehicle is not rapidly approaching the host vehicle when the relative speed is less than the threshold. This threshold is set based on mapping data stored in the storage unit 21. FIG. 2 is a diagram showing an example of the mapping data. In FIG. 2, the horizontal axis represents the inter-vehicle distance between the host vehicle and the following vehicle, and the vertical axis represents the relative speed of the following vehicle with respect to the host vehicle. In FIG. 2, line A represents the threshold for detecting the sudden approach of the following vehicle. For example, in FIG. 2, when the inter-vehicle distance is L1, the threshold for the relative speed is S1. If the following vehicle approaches the host vehicle at a relative speed equal to or greater than S1, the sudden approach determination unit 224 determines that the following vehicle is rapidly approaching the host vehicle.

[0022] The output control unit 225 generates a display image to be displayed on the display 13 based on the information of the captured image acquired by the acquisition unit 221, and outputs and displays the image on the display 13. At this time, the output control unit 225 causes the image to be displayed on the display 13 to differ depending on whether the following vehicle is rapidly approaching the host vehicle or not.

[0023] First, a case where a following vehicle is not rapidly approaching the host vehicle will be described. Fig. 3 is a plan view showing an example of a driving scene in which display control is performed by the display control device 1. The road shown in Fig. 3 has a left lane L1 defined by lane boundary lines C1 and C2, a center lane L2 defined by lane boundary lines C2 and C3, and a right lane L3 defined by lane boundary lines C3 and C4. Vehicles traveling on the road shown in Fig. 3 are assumed to travel from left to right in the drawing.

[0024] In the scene shown in FIG. 3 , a host vehicle V1 is traveling at position P1 in the center lane L2, and a following vehicle V2 is traveling at position P2 behind the host vehicle V1 in the center lane L2, behind position P1. The host vehicle V1 shown in FIG. 3 is equipped with a controller 20 and a digital inner mirror (display 13) installed inside the vehicle. The digital inner mirror, which is the display 13, is installed at the upper center of the windshield of the host vehicle V1. In addition, a camera 11 (wide-angle camera) that captures an image behind the host vehicle V1 is installed at the upper center of the rear window of the host vehicle V1. In the following description, the host vehicle V1 may also be simply referred to as a vehicle.

[0025] The angle of view α shown in FIG. 3 indicates the imaging range (so-called horizontal angle of view) of the camera 11 when the host vehicle V1 is viewed from the top. In other words, the camera 11 captures an image of an object within the range defined by the boundaries A1 and A2 (specifically, the range corresponding to the minor angle formed by the direction of the boundary A1 and the direction of the boundary A2). The camera 11 has an angle of view α within a predetermined range (e.g., 40° to 120°) corresponding to the horizontal size of the imaging element, and the controller 20 controls the angle of view α within the range from the minimum angle of view to the maximum angle of view of the camera 11. Note that the imaging range (so-called vertical angle of view) of the camera 11 when the host vehicle V1 is viewed from the side is an angle of view corresponding to the vertical size of the imaging element of the camera 11.

[0026] 3 , the acquisition unit 221 acquires information about a captured image from the camera 11. The output control unit 225 crops a portion of the captured image acquired from the camera 11 to fit the size of the display area of ​​the display 13, generates a display image to be displayed on the display 13, and outputs the generated display image to the display 13 for display. This allows the occupants of the vehicle V1 to check what is behind the vehicle V1 from the image displayed on the display 13.

[0027] In this embodiment, when the following vehicle V2 is not rapidly approaching the host vehicle V1, the output control unit 225 cuts out a portion of the captured image acquired from the camera 11 so as to generate an image similar to the image (mirror image) that would be displayed in a rearview mirror if a rearview mirror were installed in the same position as the digital inner mirror. The cut-out range of the image acquired from the camera 11 that is cut out by the output control unit 225 is set in advance based on the installation position of the digital inner mirror, the installation position of the camera 11, the angle of view α of the camera 11, etc.

[0028] If a rearview mirror were attached to the upper center of the windshield of the host vehicle V1, the image in the rearview mirror would include objects within the range defined by boundaries B1 and B2, which corresponds to the angle of view β shown in Figure 3. As shown in Figure 3, the angle of view α of camera 11 is larger than the angle of view β of the rearview mirror, and the position of camera 11 is behind the position of the digital inner mirror, so there is a discrepancy between the imaging range of camera 11 and the range included in the image in the rearview mirror. As a result, the size of objects present in the same position appears different in the image captured by camera 11 and the image in the rearview mirror.

[0029] As an example, an object at position P3 appears larger in the image acquired by camera 11 than in the image in the rearview mirror. The image acquired by camera 11 includes an image of range W1 of the object at position P3. On the other hand, the image in the rearview mirror includes an image of range W2 of the object at position P3. Because range W1 is narrower than range W2, if the image acquired by camera 11 and the image in the rearview mirror are made the same size, the object at position P3 will appear larger in comparison.

[0030] For example, in the driving scene shown in Fig. 3, when a following vehicle V2 is traveling at position P3, an image G1 shown in Fig. 4A is acquired by the wide-angle camera. The output control unit 225 cuts out a predetermined cut-out range Ma from the image G1 shown in Fig. 4A. If the cut-out range Ma is used as the display image, the image shown in Fig. 4B will be displayed on the display 13 (digital inner mirror) of the host vehicle V1. On the other hand, if a rearview mirror were attached in the same position as the display 13, the image shown in Fig. 4C would be displayed. At position P3, the range captured by the camera 11 (range W1) is narrower than the range captured in the rearview mirror M (range W2). Therefore, the following vehicle V2 traveling at position P3 will be displayed larger on the display 13.

[0031] As another example, an object at position P4 in Figure 3 appears smaller in the image acquired by camera 11 than in the image in the rearview mirror. In the image acquired by camera 11, objects within range W3 of the objects at position P4 are displayed. On the other hand, in the image in the rearview mirror, objects within range W4 of the objects at position P4 are included. Because range W3 is wider than range W4, if the image acquired by camera 11 and the image in the rearview mirror are made the same size, the object at position P4 will appear relatively small.

[0032] For example, in the driving scene shown in Fig. 3, when a following vehicle V2 is traveling at position P4, the camera 11 acquires an image G2 shown in Fig. 5A. The output control unit 225 extracts a predetermined extraction range Ma from the image G2 shown in Fig. 5A. If the extraction range Ma is used as the display image, the image shown in Fig. 5B will be displayed on the display 13 (digital inner mirror) of the host vehicle V1. On the other hand, if a rearview mirror were attached in the same position as the display 13, the image shown in Fig. 5C would be displayed. At position P4, the range captured by the camera 11 (range W3) is wider than the range captured in the rearview mirror M (range W4). Therefore, the following vehicle V2 traveling at position P4 will appear smaller on the display 13.

[0033] Therefore, in order to prevent the occupants of the host vehicle V1 from feeling uncomfortable due to the size of an object appearing different on the display 13 from that in the rearview mirror, the output control unit 225 adjusts the size of the following vehicle V2 displayed in the display image according to the inter-vehicle distance between the host vehicle V1 and the following vehicle V2. Note that the following vehicle V2 does not necessarily have to be traveling in the same lane as the host vehicle V1. For example, in the driving scene shown in FIG. 2, the following vehicle V2 is traveling in the center lane L2, just like the host vehicle V1, but it may also be traveling in the left lane L1 or the right lane L3.

[0034] When the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 is less than a first predetermined distance, the output control unit 225 executes a first process of reducing the size of the following vehicle V2 displayed in the display image. On the other hand, when the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 is equal to or greater than a second predetermined distance that is longer than the first predetermined distance, the output control unit 225 executes a second process of increasing the size of the following vehicle V2 displayed in the display image. Furthermore, when the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 is equal to or greater than the first predetermined distance and less than the second predetermined distance, the output control unit 225 does not execute the first process or the second process.

[0035] The first predetermined distance is set based on the position where the range in which the object is displayed in the image captured by camera 11 coincides with the range in which the object is included in the image in the rearview mirror, and is, for example, 2 to 4 meters. In the driving scene shown in FIG. 3 , at position Px, the range in which the object is displayed in the image captured by camera 11 coincides with the range in which the object is included in the image in the rearview mirror, so the distance D1 from position Pa corresponding to the rear end of vehicle V1 to position Px is set as the first predetermined distance. Meanwhile, the second predetermined distance can be set to an appropriate value within a range that can suppress the discomfort felt by the occupants of vehicle V1, and is, for example, 10 to 20 meters. In the driving scene shown in FIG. 3 , the distance D2 from position Pa to position Pb is set as the second predetermined distance.

[0036] The first process for reducing the size of the following vehicle V2 is not particularly limited. Examples of the first process include increasing the angle of view α of the wide-angle camera, reducing and cropping the image acquired from the wide-angle camera, and interpolating the difference between the range W1 and the range W2 shown in FIG. 3 through image processing. Similarly, the second process for increasing the size of the following vehicle V2 is not particularly limited. Examples of the second process include reducing the angle of view α of the wide-angle camera, and enlarging and cropping the image acquired from the wide-angle camera.

[0037] In the scene shown in Figure 3, since the distance D3 from position Pa to position Pc corresponding to the front end of the following vehicle V2 is shorter than the distance D1, the output control unit 225 executes the first process to reduce the size of the following vehicle V2 in the display image.

[0038] Next, a case where a following vehicle is rapidly approaching the host vehicle will be described. When the rapid approach determination unit 224 determines that the following vehicle V2 is rapidly approaching the host vehicle V1, it is preferable that the output control unit 225 not executes the first process and instead displays the following vehicle V2 large on the display 13 so that the occupants (particularly the driver) of the host vehicle V1 can easily recognize the rapid approach of the following vehicle V2. Therefore, when the output control unit 225 of this embodiment determines that the following vehicle V2 is rapidly approaching the host vehicle V1, it does not adjust the size of the following vehicle V2 displayed in the image.

[0039] Specifically, the output control unit 225 executes the first process when the sudden approach determination unit 224 determines that the following vehicle V2 is not rapidly approaching the host vehicle V1. In contrast, when the sudden approach determination unit 224 determines that the following vehicle V2 is rapidly approaching the host vehicle V1, the output control unit 225 does not execute the first process. In this case, the output control unit 225 outputs a predetermined range (cropping range Ma) of the image acquired from the camera 11 to the output unit 23 as a display image as is.

[0040] Therefore, when the following vehicle V2 approaches the host vehicle V1 so rapidly that the inter-vehicle distance becomes less than the first predetermined distance, the following vehicle V2 is displayed larger on the display 13 than when the following vehicle V2 does not approach the host vehicle V1 so rapidly. This makes it easier for the occupants of the host vehicle V1 to recognize the following vehicle V2 approaching rapidly.

[0041] Furthermore, when the following vehicle V2 is traveling at a distance greater than the second predetermined distance, the size of the following vehicle V2 appears smaller than when its mirror image is captured in a rearview mirror. However, as shown in FIG. 3 , the change in size of the image of the following vehicle V2 as the following vehicle V2 approaches the vehicle itself is greater than the change in size of the rearview mirror image. For example, in FIG. 3 , when the following vehicle V2 approaches from position P4 to position P5, the background area other than the following vehicle V2 in the rearview mirror image is reduced by a proportion equivalent to 2×W5, and the proportion of the mirror image occupied by the following vehicle V2 increases accordingly. On the other hand, when the image captured by the camera 11 is displayed on the display 13 without performing the second process, the background area other than the following vehicle V2 is reduced by a proportion equivalent to 2×W6, and the proportion of the captured image occupied by the following vehicle V2 increases accordingly. Here, because the angle of view α of camera 11 is larger than the angle of view β of the rearview mirror, W6 > W5. Therefore, when the following vehicle V2 moves from position P4 to position P5, the change over time in the size of the following vehicle V2 included in the captured image by camera 11 is larger than the change over time in the size of the following vehicle V2 included in the mirror image captured by the rearview mirror. In other words, by displaying the captured image on display 13 without performing the second process, the image of the rapidly approaching following vehicle V2 becomes suddenly larger, emphasizing the approach of the following vehicle V2 and making it possible to attract the attention of the occupants of the host vehicle V1.

[0042] In addition, when the output control unit 225 detects that the following vehicle V2 is approaching suddenly, it warns the occupants of danger. For example, the output control unit 225 may output an alert sound or voice guidance from the speaker 14, or may display an alert image on the display 13. Furthermore, an approach warning light that notifies the driver of the approach of the following vehicle V2 may be provided in the vehicle, for example, in a position that is easily visible to the driver, and the output control unit 225 may alert the occupants of the sudden approach of the following vehicle V2 by turning on the approach warning light.

[0043] [Display Control Method in Display Control Device] Next, a description will be given of a display control method by the controller 20. Fig. 6 is a flowchart showing an example of a display control method executed in the display control device 1. In this embodiment, each process described below is executed by the processor 22 of the controller 20 at predetermined time intervals (for example, every 0.1 to 1 millisecond).

[0044] First, the acquisition unit 221 determines whether or not a following vehicle V2 is present based on the detection results of the camera 11 and the distance sensor 12 (step S1). If the determination in step S1 is NO (determined that a following vehicle V2 is not present), the acquisition unit 221 repeats step S1.

[0045] If step S1 returns YES (i.e., if the following vehicle V2 is present), the inter-vehicle distance detection unit 222 detects the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 using the distance sensor 12 (step S2: inter-vehicle distance detection step). Furthermore, the relative speed calculation unit 223 calculates the relative speed of the following vehicle V2 with respect to the host vehicle V1 (step S3: relative speed calculation step). For example, the relative speed calculation unit 223 calculates the relative speed of the following vehicle V2 with respect to the host vehicle V1 based on a change in the inter-vehicle distance over time.

[0046] The sudden approach determination unit 224 then determines whether the following vehicle V2 is rapidly approaching the host vehicle V1 based on the inter-vehicle distance and the relative speed (step S4: sudden approach determination step). Specifically, the sudden approach determination unit 224 refers to mapping data previously stored in the storage unit 21 and reads a threshold value corresponding to the inter-vehicle distance detected in step S2. The sudden approach determination unit 224 then determines whether the relative speed calculated in step S3 exceeds the threshold value, and if the relative speed exceeds the threshold value and the following vehicle V2 approaches the host vehicle V1, it determines that the following vehicle V2 is rapidly approaching.

[0047] If step S4 returns NO (determined not to be a rapid approach), the output control unit 225 generates a display image in which the size of the following vehicle V2 in the captured image is adjusted according to the inter-vehicle distance (step S5). That is, if the inter-vehicle distance to the following vehicle V2 is less than a first predetermined distance, the output control unit 225 executes a first process. That is, the output control unit 225 generates a display image in which the image of the following vehicle V2 is reduced so that the image is the same or substantially the same as if the following vehicle V2 were projected in a mirror using a rearview mirror positioned at the display 13. On the other hand, if the inter-vehicle distance to the following vehicle V2 is equal to or greater than a second predetermined distance, the output control unit 225 executes a second process. That is, the output control unit 225 generates a display image in which the image of the following vehicle V2 is enlarged so that the image is the same or substantially the same as if the following vehicle V2 were projected in a mirror using a rearview mirror positioned at the display 13. In addition, if the distance between the following vehicle V2 is equal to or greater than a first predetermined distance and less than a second predetermined distance, the output control unit 225 does not change the size of the following vehicle V2, and generates a display image by cutting out a cut-out range Ma from the captured image according to the display area of ​​the display 13.

[0048] Thereafter, the output control unit 225 outputs the display image to the display 13 for display (step S6). Then, execution of the routine ends. As a result, if the determination in step S4 is NO, for example, if the following vehicle V2 is traveling at position P3 in Fig. 3, a display image as shown in Fig. 4C, in which an image of the following vehicle V2 is reflected by a rearview mirror, is displayed on the display 13. Also, if the following vehicle V2 is traveling at position P4 in Fig. 3, a display image as shown in Fig. 5C, in which an image of the following vehicle V2 is reflected by a rearview mirror, is displayed on the display 13.

[0049] On the other hand, if step S4 returns YES (i.e., if the following vehicle V2 is rapidly approaching), the output control unit 225 maintains the angle of view α of the camera 11 (step S7). The output control unit 225 also outputs an alert notifying the following vehicle V2 of its rapid approach (step S8: warning step). For example, the output control unit 225 may output an alert sound or a voice message from the speaker 14 notifying the following vehicle V2 of its rapid approach, or may display an alert image on the display 13 notifying the following vehicle V2 of its rapid approach. Alternatively, the output control unit 225 may perform processing such as turning on an approach warning light (not shown). The output control unit 225 then generates a display image by cropping a crop area Ma from the captured image in accordance with the display area of ​​the display 13 without changing the size of the following vehicle V2 in the captured image (step S9). Then, the process proceeds to step S6, where the generated display image is displayed on the display 13, thereby terminating the routine. As a result, if the determination in step S4 is YES, for example, if the following vehicle V2 is traveling at position P3 in Fig. 3, a display image in which the image of the following vehicle V2 is larger than when the image of the following vehicle V2 is reflected in a rearview mirror, as shown in Fig. 4B, is displayed on the display 13. Also, if the following vehicle V2 is traveling at position P4 in Fig. 3, a display image in which the image of the following vehicle V2 is smaller than when the image of the following vehicle V2 is reflected in a rearview mirror, as shown in Fig. 5B, is displayed on the display 13.

[0050] [Effects of the Present Embodiment] The display control device mounted on a vehicle according to the present embodiment includes a camera 11, a display 13, and a controller 20 configured by a computer. The camera 11 captures an image of the area behind the host vehicle V1 to acquire the captured image. The display 13 is provided inside the host vehicle V1 and displays the captured image. The controller 20 includes a memory unit 21 that stores various programs and a processor 22. The processor 22 loads and executes the programs stored in the memory unit 21 to function as an acquisition unit 221, an inter-vehicle distance detection unit 222, a relative speed calculation unit 223, a sudden approach determination unit 224, and an output control unit 225. The controller 20 then performs an inter-vehicle distance detection step (step S2), a relative speed calculation step (step S3), a sudden approach determination step (step S4), and a display control step (steps S5 to S9). In step S2, the inter-vehicle distance detection unit 222 detects the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 based on the detection result from the distance sensor 12. In step S3, the relative speed calculation unit 223 calculates the relative speed of the following vehicle V2 with respect to the host vehicle V1. In step S4, the sudden approach determination unit 224 determines whether the following vehicle V2 is rapidly approaching the host vehicle V1 based on the inter-vehicle distance and the relative speed. In steps S5 to S9, if it is determined that the following vehicle V2 is rapidly approaching, the output control unit 225 causes the display 13 to display the size of the following vehicle V2 included in the captured image without adjusting it, and if it is determined that the following vehicle V2 is not rapidly approaching, the output control unit 225 causes the display 13 to display the size of the following vehicle V2 included in the captured image after adjusting it based on the inter-vehicle distance. As a result, in a scene where the following vehicle V2 is rapidly approaching, if the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 is less than the first predetermined distance, the image of the following vehicle V2 displayed on the display 13 is displayed larger than when a mirror image of the following vehicle V2 is displayed using a rearview mirror. Therefore, an occupant (e.g., the driver) of the host vehicle V1 can easily notice the rapidly approaching following vehicle V2. Also, even when the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 is equal to or greater than the second predetermined distance, the size of the image of the following vehicle V2 displayed on the display 13 changes more significantly over time than when a mirror image of the following vehicle V2 is displayed using a rearview mirror.Therefore, the approach of the following vehicle V2 appears to be emphasized to the occupants (for example, the driver) of the vehicle V1, making it easier for them to notice the rapidly approaching following vehicle V2.

[0051] In this embodiment, in step S4, the sudden approach determination unit 224 determines whether the following vehicle V2 is suddenly approaching the host vehicle V1 using mapping data indicating the relationship between the relative speed, the inter-vehicle distance, and a threshold value for identifying whether a following vehicle is suddenly approaching. This allows the sudden approach determination unit 224 to appropriately determine whether a sudden approach is occurring based on the inter-vehicle distance. In other words, when the inter-vehicle distance is sufficiently large, the risk of collision may be low even if the relative speed is high. Conversely, when the inter-vehicle distance is small, the risk of collision may be high even if the relative speed is low. In this embodiment, by changing the threshold value for determining whether the following vehicle V2 is suddenly approaching based on the inter-vehicle distance, it is possible to determine whether a following vehicle V2 is suddenly approaching the host vehicle V1.

[0052] In this embodiment, in step S8, the output control unit 225 warns of danger by sound or image display when it is determined in step S4 by the sudden approach determination unit 224 that the following vehicle V2 is rapidly approaching. This makes it possible to notify the occupants of the host vehicle V1 of the presence of the rapidly approaching following vehicle V2 and to prompt the occupants to look at the display 13 to notify them of the danger.

[0053] [Modifications] The present invention is not limited to the above-described embodiment, and includes the following modifications within the scope of achieving the object of the present invention.

[0054] In the above embodiment, an example has been shown in which the output control unit 225 does not perform the first process or the second process when a rapidly approaching following vehicle V2 is not detected and the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 is equal to or greater than the first predetermined distance and less than the second predetermined distance. In contrast, the output control unit 225 may perform the second process when the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 is equal to or greater than the first predetermined distance.

[0055] [Variation 2] In the above embodiment, the output control unit 225 does not perform the first process or the second process when the following vehicle V2 is rapidly approaching, regardless of the inter-vehicle distance. However, this is not limiting. For example, when the following vehicle V2 is rapidly approaching, the output control unit 225 may display a display image cropped from an image captured by the camera 11 without adjusting the size of the image of the following vehicle if the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 is less than a first predetermined distance. In other words, when the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 is equal to or greater than the first predetermined distance, particularly equal to or greater than a second predetermined distance, the output control unit 225 may perform the second process to enlarge the image of the following vehicle V2. In this case, the display image may be generated so that the image of the following vehicle V2 is larger than when the mirror image of the following vehicle V2 is displayed in a rearview mirror. This emphasizes the rapidly approaching following vehicle V2, making it easier for the occupant to notice the rapidly approaching following vehicle V2.

[0056] [Modification 3] In the above embodiment, an example has been shown in which the display control device 1 includes the distance sensor 12, and the inter-vehicle distance detection unit 222 detects the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 using the distance sensor 12. In contrast, the display control device 1 may not be provided with the distance sensor 12, and the inter-vehicle distance detection unit 222 may calculate the inter-vehicle distance between the host vehicle V1 and the following vehicle V2 from an image captured by the camera 11. In this case, it is preferable to use a stereo camera as the camera 11.

[0057] In the above embodiment, the sudden approach determination unit 224 changes the threshold value for determining that a sudden approach has occurred depending on the inter-vehicle distance by referring to the mapping data. However, a preset fixed value may be used as the threshold value for determining that the following vehicle V2 is rapidly approaching, regardless of the inter-vehicle distance.

[0058] The threshold value may also be changed depending on the road on which the host vehicle V1 is traveling. For example, the threshold value may be changed according to the legal speed limit. In this case, mapping data for each legal speed limit is prepared. The sudden approach determination unit 224 receives satellite signals from a Global Navigation Satellite System (GNSS) to determine the current position, and reads information on the legal speed limit of the road corresponding to the current position from the map data stored in the storage unit 21. Then, by referring to the mapping data corresponding to the legal speed limit, the following vehicle V2 may be determined to be approaching suddenly based on the inter-vehicle distance and relative speed, as in the above embodiment.

[0059] 1...display control device, 11...camera, 12...distance sensor, 13...display, 14...speaker, 20...controller, 21...memory unit, 22...processor, 23...output unit, 221...acquisition unit, 222...inter-vehicle distance detection unit, 223...relative speed calculation unit, 224...rapid approach determination unit, 225...output control unit, V1...own vehicle, V2...following vehicle

Claims

1. A display control method in which a computer displays an image captured by a camera that captures images behind a vehicle on a display installed inside the vehicle, wherein the computer carries out the following steps: an inter-vehicle distance detection step of detecting the inter-vehicle distance between the vehicle and a following vehicle traveling behind the vehicle; a relative speed calculation step of calculating the relative speed between the vehicle and the following vehicle; a rapid approach determination step of determining whether the following vehicle is rapidly approaching the vehicle based on the inter-vehicle distance and the relative speed; and a display control step of displaying the captured image on the display, wherein in the display control step, if it is determined that the following vehicle is rapidly approaching, the size of the following vehicle included in the captured image is displayed on the display without adjustment, and if it is determined that the following vehicle is not rapidly approaching, the size of the following vehicle included in the captured image is adjusted based on the inter-vehicle distance and displayed on the display.

2. The display control method according to claim 1, wherein the sudden approach determination step determines whether the following vehicle is suddenly approaching the vehicle using mapping data that indicates the relationship between the relative speed, the inter-vehicle distance, and whether the following vehicle is suddenly approaching the vehicle.

3. The display control method according to claim 1, further comprising the step of: issuing a warning of danger by audio or image display when it is determined in the sudden approach determination step that the following vehicle is rapidly approaching.

4. A display control device comprising: a camera that captures an image of the area behind a vehicle and obtains the captured image; a display provided inside the vehicle and that displays the captured image; an inter-vehicle distance detection unit that detects the distance between the vehicle and a following vehicle traveling behind the vehicle; a relative speed calculation unit that calculates the relative speed between the vehicle and the following vehicle; a sudden approach determination unit that detects a sudden approach of the following vehicle to the vehicle based on the inter-vehicle distance and the relative speed; and an output control unit that displays the captured image on the display, wherein the output control unit, if it detects a sudden approach of the following vehicle, displays the size of the following vehicle included in the captured image on the display without adjusting it, and if it does not detect a sudden approach of the following vehicle, adjusts the size of the following vehicle included in the captured image based on the inter-vehicle distance and displays it on the display.

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