Patent Publication Number: US-2023135043-A1

Title: Rearward Image Displaying Device and Rearward Image Displaying Method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C.§119 to Japanese Patent Application No. 2021-177105 filed on Oct. 29, 2021. The content of the application is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a rearward image displaying device and rearward image displaying method. 
     Description of the Related Art 
     Conventionally technologies for displaying an image to the rear of the vehicle have been disclosed. 
     The vehicle rearward displaying device set forth in Patent Document 1 comprises: a camera for imaging to the rear of a vehicle; a display processing portion for displaying the rearward vehicle image that was captured by the camera; an incline detecting portion for detecting a change in incline in the front/rear direction of the vehicle; and an imaging range switching portion for switching, in the vertical direction, the imaging range that corresponds to a range displayed by the display processing portion while traveling over a prescribed range after detecting a change in the incline, and then returning the imaging range to the original imaging range after there has ceased to be a change in incline. 
     Prior Art Document 
     Patent Document 
     [Patent Document 1] Japanese Unexamined Patent Application Publication 2018-150010 
     However, with the technology set forth in Patent Document 1, the imaging range is switched in accordance with a change in incline in the front/rear direction of the vehicle, so there have been cases wherein it has been difficult to identify visually what type of vehicle is traveling to the rear of the vehicle. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a rearward image displaying device and rearward image displaying method wherein visual identification of the type of vehicle that is traveling to the rear of the vehicle is easy. 
     In order to achieve the object set forth above, the rearward image displaying device according to the present invention comprises: an imaging portion configured to generate a captured image by imaging, through a camera, to the rear of a vehicle; a first generating portion configured to generate a first rearward image by extracting an image from a region of a portion of the captured image; an incline detecting portion configured to detect an incline angle of the vehicle; a second generating portion configured to generate a second rearward image, which is different from the first rearward image, by extracting an image from a region of another portion of the captured image depending on the incline angle; and a display controlling portion configured to display the first rearward image and the second rearward image on a display. 
     In order to achieve the object set forth above, the rearward image displaying method according to the present invention includes: an imaging step for generating a captured image by imaging, through a camera, to the rear of a vehicle; a first generating step for generating a first rearward image by extracting an image from a region of a portion of the captured image; an incline detecting step for detecting an incline angle of the vehicle; a second generating step for generating a second rearward image, which is different from the first rearward image, by extracting an image from a region of another portion of the captured image depending on the incline angle; and a display controlling step for displaying the first rearward image and the second rearward image on a display. 
     Effects of the Invention 
     In the present invention, a first rearward image that is generated by extracting an image from a region that is part of a captured image and a second rearward image is generated by extracting an image from a region that is another part of the captured image are displayed on a display, enabling easy visual identification of what type of vehicle is traveling to the rear of the vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram depicting an example of a structure for a rearward image displaying system and rearward image displaying device. 
         FIG.  2    is a diagram depicting an example of a reference rearward image, a top rearward image, and a bottom rearward image. 
         FIG.  3    is a diagram depicting an example of a displayed image in a first state. 
         FIG.  4    is a diagram depicting an example of a displayed image in a second state. 
         FIG.  5    is a diagram depicting an example of a displayed image in a third state. 
         FIG.  6    is a diagram depicting an example of a displayed image in a fourth state. 
         FIG.  7    is a flowchart showing an example of processing in a rearward image displaying device. 
         FIG.  8    is a flowchart showing an example of processing in a rearward image displaying device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment according to the present invention will be explained below referencing the drawings. 
     The structure of a rearward image displaying system  100  and a rearward image displaying device  1  will be explained first, referencing  FIG.  1   .  FIG.  1    is a diagram depicting an example of the structure of a rearward image displaying system  100  and of a rearward image displaying device  1 . 
     As illustrated in  FIG.  1   , the rearward image displaying system  100  comprises a rearward image displaying device  1 , a camera  21 , an incline sensor  22 , a distance measuring sensor  23 , an operating portion  24 , and a displaying portion  25 . The rearward image displaying system  100  is mounted in a vehicle V 1 . The vehicle V 1  will be explained in reference to  FIG.  2   . 
     A camera  21  follows an instruction from the rearward image displaying device  1  to capture an image to the rear of the vehicle V 1 , to generate a captured image PA. The camera  21  comprises an image sensor such as a CCD (Charge-Coupled Device), CMOS (Complementary Metal-Oxide-Semiconductor), or the like, and a data processing circuit for generating the captured image PA from the image sensor. 
     The imaging range corresponding to the captured image PA of the camera  21  is wider than the corresponding imaging range of the rearward image that is to be displayed on a display  251 . The rearward image is, for example, a first rearward image P 1 . In other words, an imaging viewing angle AVA that indicates an imaging range corresponding to the captured image PA is larger than a reference viewing angle AVT that indicates the imaging range of the first rearward image P 1 . 
     The first rearward image P 1 , the imaging viewing angle AVA, and the reference viewing angle AVT will be explained in reference to  FIG.  2   . 
     The incline sensor  22  detects an incline angle AN of the vehicle V 1 . The incline angle AN is at an angle between the front/rear direction of the vehicle V 1 , or the direction of travel D1, and the horizontal direction DH. The incline sensor  22  comprises a sensor such as an acceleration sensor, a gyro sensor, or the like, and a data processing circuit for generating the incline angle AN from the sensor. 
     The direction of travel D1, the horizontal direction DH, and the incline angle AN will be explained in reference to  FIG.  2   . 
     The distance measuring sensor  23  is, for example, a LiDAR (Light Detection and Ranging) equipped on the vehicle V 1 , and uses an electromagnetic signal to detect the distance LD to another vehicle V 2  that is traveling to the rear of the vehicle V 1 . 
     Although in the present embodiment the explanation will be for a case wherein the distance measuring sensor  23  is a LiDAR, there is no limitation thereto. The distance measuring sensor  23  may instead use, for example, a radar or a sonar sensor. 
     The operating portion  24  comprises keys, switches, or the like, and receives operations from a user who is riding in the vehicle V 1 . The user may be, for example, the driver. The operating portion  24  outputs, to the rearward image displaying device  1 , an operating signal in accordance with the operations it has received. The operations received by the operating portion  24  include, for example, an operation for displaying the first rearward image P 1  on the display  251  as a main image PM, an operation for displaying on the display  251  a second rearward image P 2  as the main image PM, and the like. The second rearward image P 2  and the main image PM will be explained in reference to  FIG.  2   . 
     The displaying portion  25  comprises a display  251 , and displays various images on the display  251 . A liquid crystal display, an organic EL display, or the like, is used for the display  251 . 
     The displaying portion  25  displays the first rearward image P 1 , the second rearward image P 2 , and the like, on the display  251 . 
     The rearward image displaying device  1  is a computer comprising a processor  11 , such as a CPU (Central Processing Unit) or MPU (Micro-Processing Unit), or the like, and a memory  12 , such as a ROM (Read-Only Memory) or RAM (Random Access Memory), or the like. The rearward image displaying device  1  comprises, in addition to these devices, a storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive), or the like, an interface circuit for connecting sensors, peripheral devices, and the like, and an onboard network communication circuit for communicating with other onboard devices. In the rearward image displaying device  1 , a variety of functional structures is achieved through a processor  11  executing a control program  121  that is stored in the memory  12 . 
     The rearward image displaying device  1  is structured, for example, from an ECU (Electronic Control Unit). 
     Although in the present embodiment the explanation is for a case wherein the rearward image displaying device  1  is structured from an ECU, there is no limitation thereto. The rearward image displaying device  1  should be a computer comprising a processor  11  and a memory  12 . For example, the rearward image displaying device  1  may be structured from a personal computer, or structured from a tablet terminal. 
     The rearward image displaying device  1  comprises an imaging portion  111 , a first generating portion  112 , an incline detecting portion  113 , a second generating portion  114 , a distance detecting portion  115 , a display controlling portion  116 , an image storing portion  122 , and an incline storing portion  123 . Specifically, the processor  11  functions as the imaging portion  111 , the first generating portion  112 , the incline detecting portion  113 , the second generating portion  114 , the distance detecting portion  115 , and the display controlling portion  116  through executing a control program  121  that is stored in the memory  12 . Additionally, through the processor  11  executing a control program  121  that is stored in the memory  12 , the memory  12  is caused to function as the image storing portion  122  and the incline storing portion  123 . 
     The image storing portion  122  stores the captured image PA. The captured image PA is acquired from the camera  21  by the imaging portion  111  and stored in the image storing portion  122 . The captured image PA is read out by the first generating portion  112  and the second generating portion  114 . 
     The incline storing portion  123  stores the incline angle AN. The incline angle AN is acquired from the incline sensor  22  by the incline detecting portion  113  and stored in the incline storing portion  123 . The incline angle AN is read out by the second generating portion  114 . 
     The imaging portion  111  captures an image to the rear of the vehicle V 1  through a camera  21 , to generate to the captured image PA. Specifically, the imaging portion  111  acquires the captured image PA by imaging using the camera  21 . Additionally, the imaging portion  111  causes the captured image PA to be stored in the image storing portion  122 . 
     The first generating portion  112  generates the first rearward image P 1  by extracting an image from a region that is part of the captured image PA. The first rearward image P 1  may be, for example, a reference rearward image PT. The reference rearward image PT is an image extracted from a region of the center portion of the captured image PA. 
     The reference rearward image PT will be explained further in reference to  FIG.  2   . 
     The incline detecting portion  113  detects the incline angle AN of the vehicle V 1 . Specifically, the incline detecting portion  113  acquires the incline angle AN detected by the incline sensor  22 . The incline detecting portion  113  stores the incline angle AN in the incline storing portion  123 . 
     The second generating portion  114  extracts an image from a region that is another portion of the captured image PA, based on the incline angle AN, to generate a second rearward image P 2  that is different from the first rearward image P 1 . The second rearward image P 2  includes a top rearward image PU and a bottom rearward image PD. The top rearward image PU is an image to the upper rear of the vehicle V 1 , within image PA. The bottom rearward image PD is an image to the bottom rear of the vehicle V 1 , within the captured image PA. 
     The top rearward image PU and the bottom rearward image PD will be explained further in reference to  FIG.  2   . 
     Specifically, depending on a state evaluated by the display controlling portion  116 , the second generating portion  114  generates the top rearward image PU or the bottom rearward image PD as the second rearward image P 2 . The state evaluated by the display controlling portion  116  is a first state ST 1  through a fourth state ST 4 . 
     The relationship between the first state ST 1  through the fourth state ST 4  and the image generated by the second generating portion  114  will be explained in reference to  FIG.  2    through  FIG.  6   . 
     The distance detecting portion  115  detects a distance LD between the vehicle V 1  and another vehicle V 2  that is traveling to the rear of the vehicle V 1 . Specifically, the distance detecting portion  115  acquires the distance LD from the distance measuring sensor  23 . 
     The display controlling portion  116  displays the first rearward image P 1  and the second rearward image P 2  on the display  251 . 
     Specifically, the display controlling portion  116  displays a main image PM that is displayed in a first region AR 1  of the display region AR of the display  251 , and a sub-image PS that is displayed in a second region AR 2 , which is narrower than the first region AR 1 , in the display region AR. Moreover, the display controlling portion  116  displays one of these images, the first rearward image P 1  or the second rearward image P 2 , as the main image PM, and displays the other of these images, the first rearward image P 1  or the second rearward image P 2 , as the sub-image PS. 
     The first region AR 1  and the second region AR 2  will be explained further in reference to  FIG.  3    through  FIG.  6   . 
     For example, the display controlling portion  116  displays the first rearward image P 1  as the main image PM in the first region AR 1  within the display region AR of the display  251 , and displays the second rearward image P 2  as the sub-image PS in the second region AR 2  within the display region AR of the display  251 . Additionally, the display controlling portion  116  may display the second rearward image P 2  as the main image PM in the first region AR 1  within the display region AR of the display  251 , and may display the first rearward image P 1  as the sub-image PS in the second region AR 2  within the display region AR of the display  251 . 
     Furthermore, for example, the display controlling portion  116  may display the main image PM in the entirety of the display region AR of the display  251 . A region that does not include an image of a vehicle in the main image PM is set for the second region AR 2 . The sub-image PS is displayed in the second region AR 2 . 
     Additionally, in response to a change in the incline angle AN over time, for example, the display controlling portion  116  may determine which image, of the first rearward image P 1  and the second rearward image P 2 , is to be displayed as the main image PM in the first region AR 1 . 
     In response to a change of the incline angle AN over time, for example, the display controlling portion  116  may evaluate whether the vehicle V 1  is in a first state ST 1 , a second state ST 2 , a third state ST 3 , or a fourth state ST 4 . 
     The first state ST 1  is a state wherein the vehicle V 1  has entered onto an upwardly inclined road RU from a first road R 1  that is substantially level. The second state ST 2  is a state wherein the vehicle V 1  has entered into a second road R 2  that is substantially level from an upwardly inclined road RU. The third state ST 3  is a state wherein the vehicle V 1  has entered into a downwardly inclined road RD from a second road R 2  that is substantially level. The fourth state ST 4  is a state wherein the vehicle V 1  has entered into a third road R 3  that is substantially level from the downwardly inclined road RD. 
     The first state ST 1  through fourth state ST 4  will be explained further in reference to  FIG.  3    through  FIG.  6   . 
     Additionally, if the distance LD detected by the distance detecting portion  115  is less than a threshold value LS, the display controlling portion  116  does not display the second rearward image P 2  on the display  251 . The threshold value LS may be, for example, 10 m. In this case, the display controlling portion  116  displays the first rearward image P 1  alone in the entirety of the display region AR of the display  251 . 
     Note that the threshold value LS may instead be set depending on the speed of travel of the vehicle V 1 . For example, preferably the threshold value LS is longer at faster travel speeds of the vehicle V 1 . Additionally, the threshold value LS may be set in accordance with the change in the incline angle AN over time, for example. 
     Preferably the threshold value LS is shorter the greater the change in the incline angle AN over time. 
     While in the present embodiment, the explanation is for a case wherein the display controlling portion  116  determines which image, of the first rearward image P 1  and the second rearward image P 2 , to display in the first region AR 1  as the main image PM depending on the change in the incline angle AN over time, there is no limitation thereto. For example, the display controlling portion  116  may determine instead which image, of the first rearward image P 1  and the second rearward image P 2 , to display the first region AR 1  as the main image PM in response to an operation by the user on the operating portion  24 . 
     While, in the present embodiment, the explanation is for a case wherein the display controlling portion  116  displays a main image PM that is displayed in the first region AR 1  within the display region AR of the display  251  and a sub-image PS that is displayed in a second region AR 2 , which is narrower than the first region AR 1 , within the display region AR, there is no limitation thereto. The display controlling portion  116  should instead display the first rearward image P 1  and the second rearward image P 2  on the display  251 . 
     The display controlling portion  116  may, for example, divide the display region AR of the display  251  into two equal parts, and display the first rearward image P 1  in one of the display regions and display the second rearward image P 2  in the other display region. The display controlling portion  116  may instead, for example, divide the display region AR of the display  251  into two equal parts, a right display region and a left display region, and display the first rearward image P 1  in the right display region and the second rearward image P 2  in the left display region. 
       FIG.  2    will be referenced next to explain the reference rearward image PT, the top rearward image PU, and the bottom rearward image PD.  FIG.  2    is a diagram depicting an example of the reference rearward image PT, the top rearward image PU, and the bottom rearward image PD. 
       FIG.  2    depicts a side view  301  that shows an example of the change in the incline angle AN of the road traveled by the vehicle V 1  and an image diagram  400  that shows an example of the captured image PA that is captured by the camera  21 . 
     The side view  301  shows the vehicle V 1  that is traveling in the travel direction D1, and the vehicle V 2  that is traveling in the travel direction D2, to the rear of the vehicle V 1 . The vehicle V 1  has entered into an upwardly inclined road RU from a first road R 1  that is substantially level. That is, the side view  301  shows that the vehicle V 1  is in the first state ST 1 . The upwardly inclined road RU is positioned connecting between a substantially level first road R 1  and a substantially level second road R 2 . The incline angle AN of the vehicle V 1  is the angle formed between the travel direction D1 of the vehicle V 1  and the horizontal direction DH. 
     The incline angle AN is detected by the incline sensor  22 . 
     The distance LD is the distance between the vehicle V 1  and the vehicle V 2 . The distance LD is detected by the distance measuring sensor  23 . 
     The vehicle V 2  corresponds to an example of “another vehicle.” 
     The camera  21  is disposed on the rear of the vehicle V 1 . The imaging viewing AVA indicated by the dotted lines shows the imaging range of the camera  21  in the vertical direction. 
     The imaging viewing AVA may be, for example, 90°. The reference viewing angle AVT, indicated by the dash-dot lines, shows the imaging range, in the vertical direction, of the camera  21  corresponding to a reference rearward angle PT. A top viewing angle AVU, indicated by the dotted lines, indicates the imaging range, in the vertical direction, of the camera  21  corresponding to the top rearward image PU. The bottom viewing angle AVD, indicated by the dotted lines, indicates the imaging range, in the vertical direction, of the camera  21 , corresponding to the bottom rearward image PD. The reference viewing angle AVT, the top viewing angle AVU, and the bottom viewing angle AVD may each be, for example, 45°. 
     The captured image PA is shown in the image diagram  400 . The captured image PA includes a vehicle image PV 2  and a vehicle image PV 3 . The vehicle image PV 2  is an image of the vehicle V 2 . The vehicle image PV 3  is an image of a vehicle V 3 . The vehicle V 3  is traveling in a lane that is opposite of the lane traveled by the vehicle V 1  and the vehicle V 2 . 
     The rectangular imaging viewing angle AVA of the solid lines, the rectangular reference viewing angle AVT of the dash-dot lines, the rectangular top viewing angle AVU of the dotted lines, and the rectangular bottom viewing angle AVD of the dotted lines are shown in the image diagram  400 . 
     The top viewing angle AVU is disposed at an upper portion of the imaging viewing angle AVA. The reference viewing angle AVT is disposed in a center portion, in the vertical direction, of the imaging viewing angle AVA. The bottom viewing angle AVD is disposed in a lower portion of the imaging viewing angle AVA. Additionally, the top viewing angle AVU, the reference viewing angle AVT, and the bottom viewing angle AVD are each arranged in a crosswise-direction center portion of the imaging viewing angle AVA. 
     The captured image PA of the camera  21  is an image within the imaging viewing angle AVA shown in the image diagram  400 . In the image diagram  400 , the reference viewing angle AVT shows the imaging range of the reference rearward image PT, the top viewing angle AVU shows the imaging range of the top rearward image PU, and the bottom viewing angle AVD shows the imaging range of the bottom rearward image PD. 
     The first generating portion  112  extracts the reference rearward image PT from the region in the vertical-direction center portion of the captured image PA that corresponds to the reference viewing angle AVT to generate the reference rearward image PT as the first rearward image P 1 . 
     The second generating portion  114  extracts the top rearward image PU from a region of the upper portion of the captured image PA that corresponds to the top viewing angle AVU to generate the top rearward image PU as the second rearward image P 2 . The second generating portion  114  extracts the bottom rearward image PD from a region in the lower portion of the captured image PA that corresponds to the bottom viewing angle AVD, to generate the bottom rearward image PD as the second rearward image P 2 . 
     The region in the center portion of the captured image PA that corresponds to the reference viewing angle AVT corresponds to an example of a “region of a portion.” 
     The region of the upper portion of the captured image PA that corresponds to the top viewing angle AVU and the region of the lower portion of the captured image PA that corresponds to the bottom viewing angle AVD each corresponds to examples of a “region of another portion.” 
     The displayed image that is displayed in the display  251  will be explained next in reference to  FIG.  3    through  FIG.  6   . In the present embodiment a case wherein a rear view display that is wider than it is tall will be explained as the display  251 . 
       FIG.  3    is a diagram depicting an example of a displayed image in the first state ST 1 . Examples of a conventional side view  310  and an image diagram  510  are shown at the top in  FIG.  3   . 
     As shown in the side view  310 , the reference rearward image PT is generated by extracting the reference rearward image PT from a region of the center portion that corresponds to the reference viewing angle AVT in the imaging range that corresponds to the captured image PA of the camera  21 . 
     Additionally, as shown in the image diagram  510 , the reference rearward image PT is displayed in the entirety of the display region AR of the display  251 . The reference rearward image PT includes the vehicle image PV 2  and the vehicle image PV 3 . A mark MV indicates the vehicle image PV 2 . As depicted in the image diagram  510 , a lower portion of the vehicle image PV 2  is displayed in the display  251 . 
     Examples of a side view  311  and an image diagram  511  according to the present embodiment are shown at the bottom in  FIG.  3   . 
     As shown in the side view  311 , the first generating portion  112  generates a reference rearward image PT as the first rearward image P 1  by extracting the reference rearward image PT from a region of the center portion that corresponds to the reference viewing angle AVT in the imaging range that corresponds to the captured image PA of the camera  21 . The second generating portion  114  generates the top rearward image PU, as the second rearward image P 2 , by extracting the top rearward image PU from a region of the upper portion that corresponds to the top viewing angle AVU of the imaging range that corresponds to the captured image PA of the camera  21 . 
     Additionally, as shown in the image diagram  511 , the display controlling portion  116  sets the first region AR 1  and the second region AR 2  in the display region AR of the display  251 . In the present embodiment, the second region AR 2  is disposed at the upper right corner of the display region AR. The first region AR 1  is wider than the second region AR 2 , and is the region that is not the second region AR 2  in the display region AR. 
     The display controlling portion  116  displays the top rearward image PU as the main image PM in the first region AR 1  and displays the reference rearward image PT as the sub-image PS in the second region AR 2 . 
     If, for example, the top rearward image PU is displayed in the entirety of the display region AR of the display  251  as the main image PM, the second region AR 2  may be set to a region, in the top rearward image PU, that does not include an image of a vehicle. 
     The entirety of the vehicle image PV 2  is displayed in the top rearward image PU that is displayed in the first region AR 1  of the image diagram  511 . Additionally, the top direction imaging mark MU is displayed in the first region AR 1  of the image diagram  511 . The top direction imaging mark MU indicates that the top rearward image PU is displayed in the first region AR 1 . A second image display mark MP 2  is a heavy line that is positioned around the periphery of the first region AR 1 . The second image display mark MP 2  indicates that the second rearward image P 2  is displayed in the first region AR 1 . 
     As depicted in the image diagram  511 , the entirety of the vehicle image PV 2  is displayed in the top rearward image PU that is displayed in the first region AR 1 , thus enabling easy visual identification, by the user, of the type of vehicle V 2  that is traveling to the rear of the vehicle V 1 . 
       FIG.  4    is a diagram depicting an example of a displayed image in the second state ST 2 . Examples of a conventional side view  320  and an image diagram  520  are shown at the top in  FIG.  4   . 
     A vehicle V 1  and a vehicle V 2  that is traveling in the travel direction D2 to the rear of the vehicle V 1  are shown in the side view  320 . The vehicle V 1  has entered from an upwardly inclined road RU into a second road R 2  that is substantially level. That is, the side view  320  shows that the vehicle V 1  is in the second state ST 2 . 
     As shown in the side view  320 , the reference rearward image PT is generated by extracting the reference rearward image PT from a region of the center portion that corresponds to the reference viewing angle AVT in the imaging range that corresponds to the captured image PA of the camera  21 . 
     Additionally, as shown in the image diagram  520 , the reference rearward image PT is displayed in the entirety of the display region AR of the display  251 . The reference rearward image PT includes the vehicle image PV 2  and the vehicle image PV 3 . A mark MV indicates the vehicle image PV 2 . As depicted in the image diagram  520 , an upper portion of the vehicle image PV 2  is displayed in the display  251 . 
     Examples of a side view  321  and an image diagram  521  according to the present embodiment are shown at the bottom in  FIG.  4   . 
     As shown in the side view  321 , the first generating portion  112  generates a reference rearward image PT as the first rearward image P 1  by extracting the reference rearward image PT from a region of the center portion that corresponds to the reference viewing angle AVT in the imaging range that corresponds to the captured image PA of the camera  21 . The second generating portion  114  generates the bottom rearward image PD, as the second rearward image P 2 , by extracting the bottom rearward image PD from a region of the lower portion that corresponds to the bottom viewing angle AVD of the imaging range that corresponds to the captured image PA of the camera  21 . 
     Additionally, as shown in the image diagram  521 , the display controlling portion  116  sets the first region AR 1  and the second region AR 2  in the display region AR of the display  251 . 
     The display controlling portion  116  displays the reference rearward image PT as the main image PM in the first region AR 1  and displays the bottom rearward image PD as the sub-image PS in the second region AR 2 . 
     If, for example, the reference rearward image PT is displayed in the entirety of the display region AR of the display  251  as the main image PM, the second region AR 2  may be set to a region, in the reference rearward image PT, that does not include an image of a vehicle. 
     The entirety of the vehicle image PV 2  is displayed in the bottom rearward image PD that is displayed in second region AR 2  of the image diagram  521 . Additionally, the bottom direction imaging mark MD is displayed in the second region AR 2  of the image diagram  521 . The bottom direction imaging mark MD indicates that the bottom rearward image PD is displayed in the second region AR 2 . A second image display mark MP 2  is a heavy line that is positioned around the periphery of the second region AR 2 . The second image display mark MP 2  indicates that the second rearward image P 2  is displayed in the second region AR 2 . 
     As depicted in the image diagram  521 , the entirety of the vehicle image PV 2  is displayed in the bottom rearward image PD that is displayed in the second region AR 2 , thus enabling easy visual identification, by the user, of the type of vehicle V 2  that is traveling to the rear of the vehicle V 1 . 
       FIG.  5    is a diagram depicting an example of a displayed image in the third state ST 3 . Examples of a conventional side view  330  and an image diagram  530  are shown at the top in  FIG.  5   . 
     A vehicle V 1  and a vehicle V 2  that is traveling in the travel direction D2 to the rear of the vehicle V 1  are shown in the side view  330 . The vehicle V 1  has entered into a downwardly inclined road RD from a second road R 2  that is substantially level. That is, the side view  330  shows that the vehicle V 1  is in the third state ST 3 . 
     As shown in the side view  330 , the reference rearward image PT is generated by extracting the reference rearward image PT from a region of the center portion that corresponds to the reference viewing angle AVT in the imaging range that corresponds to the captured image PA of the camera  21 . 
     Additionally, as shown in the image diagram  530 , the reference rearward image PT is displayed on the display  251 . The reference rearward image PT includes the vehicle image PV 2  and the vehicle image PV 3 . A mark MV indicates the vehicle image PV 2 . As depicted in the image diagram  530 , an upper portion of the vehicle image PV 2  is displayed in the display  251 . 
     Examples of a side view  331  and an image diagram  531  according to the present embodiment are shown at the bottom in  FIG.  5   . 
     As shown in the side view  331 , the first generating portion  112  generates a reference rearward image PT as the first rearward image P 1  by extracting the reference rearward image PT from a region of the center portion that corresponds to the reference viewing angle AVT in the imaging range that corresponds to the captured image PA of the camera  21 . The second generating portion  114  generates the bottom rearward image PD, as the second rearward image P 2 , by extracting the bottom rearward image PD from a region of the lower portion that corresponds to the bottom viewing angle AVD of the imaging range that corresponds to the captured image PA of the camera  21 . 
     Additionally, as shown in the image diagram  531 , the display controlling portion  116  sets the first region AR 1  and the second region AR 2  in the display region AR of the display  251 . 
     The display controlling portion  116  displays the reference rearward image PT as the main image PM in the first region AR 1  and displays the bottom rearward image PD as the sub-image PS in the second region AR 2 . 
     If, for example, the reference rearward image PT is displayed in the entirety of the display region AR of the display  251  as the main image PM, the second region AR 2  may be set to a region, in the reference rearward image PT, that does not include an image of a vehicle. 
     The entirety of the vehicle image PV 2  is displayed in the bottom rearward image PD that is displayed in second region AR 2  of the image diagram  531 . Additionally, the bottom direction imaging mark MD is displayed in the second region AR 2  of the image diagram  531 . The bottom direction imaging mark MD indicates that the bottom rearward image PD is displayed in the second region AR 2 . A second image display mark MP 2  is a heavy line that is positioned around the periphery of the second region AR 2 . The second image display mark MP 2  indicates that the second rearward image P 2  is displayed in the second region AR 2 . 
     As depicted in the image diagram  531 , the entirety of the vehicle image PV 2  is displayed in the bottom rearward image PD that is displayed in the second region AR 2 , thus enabling easy visual identification, by the user, of the type of vehicle V 2  that is traveling to the rear of the vehicle V 1 . 
       FIG.  6    is a diagram depicting an example of a displayed image in the fourth state ST 4 . Examples of a conventional side view  340  and an image diagram  540  are shown at the top in  FIG.  6   . 
     A vehicle V 1  and a vehicle V 2  that is traveling in the travel direction D2 to the rear of the vehicle V 1  are shown in the side view  340 . The vehicle V 1  has entered from a downwardly inclined road RD into a third road R 3  that is substantially level. That is, the side view  340  shows that the vehicle V 1  is in the fourth state ST 4 . 
     As shown in the side view  340 , the reference rearward image PT is generated by extracting the reference rearward image PT from a region of the center portion that corresponds to the reference viewing angle AVT in the imaging range that corresponds to the captured image PA of the camera  21 . 
     Additionally, as shown in the image diagram  540 , the reference rearward image PT is displayed on the display  251  as the first rearward image P 1 . The reference rearward image PT includes the vehicle image PV 2  and the vehicle image PV 3 . A mark MV indicates the vehicle image PV 2 . As depicted in the image diagram  540 , a lower portion of the vehicle image PV 2  is displayed in the display  251 . 
     Examples of a side view  341  and an image diagram  541  according to the present embodiment are shown at the bottom in  FIG.  6   . 
     As shown in the side view  341 , the first generating portion  112  generates a reference rearward image PT as the first rearward image P 1  by extracting the reference rearward image PT from a region of the center portion that corresponds to the reference viewing angle AVT in the imaging range that corresponds to the captured image PA of the camera  21 . The second generating portion  114  generates the top rearward image PU, as the second rearward image P 2 , by extracting the top rearward image PU from a region of the upper portion that corresponds to the top viewing angle AVU of the imaging range that corresponds to the captured image PA of the camera  21 . 
     Additionally, as shown in the image diagram  541 , the display controlling portion  116  sets the first region AR 1  and the second region AR 2  in the display region AR of the display  251 . 
     The display controlling portion  116  displays the top rearward image PU as the main image PM in the first region AR 1  and displays the reference rearward image PT as the sub-image PS in the second region AR 2 . 
     If, for example, the top rearward image PU is displayed in the entirety of the display region AR of the display  251  as the main image PM, the second region AR 2  may be set to a region, in the top rearward image PU, that does not include an image of a vehicle. 
     The entirety of the vehicle image PV 2  is displayed in the top rearward image PU that is displayed in the first region AR 1  of the image diagram  541 . Additionally, the top direction imaging mark MU is displayed in the first region AR 1  of the image diagram  541 . The top direction imaging mark MU indicates that the top rearward image PU is displayed in the first region AR 1 . A second image display mark MP 2  is a heavy line that is positioned around the periphery of the first region AR 1 . The second image display mark MP 2  indicates that the second rearward image P 2  is displayed in the first region AR 1 . 
     As depicted in the image diagram  541 , the entirety of the vehicle image PV 2  is displayed in the top rearward image PU that is displayed in the first region AR 1 , thus enabling easy visual identification, by the user, of the type of vehicle V 2  that is traveling to the rear of the vehicle V 1 . 
     As explained in reference to  FIG.  3    through  FIG.  6   , a first rearward image P 1  and a second rearward image P 2  that is different from the first rearward image P 1  are displayed on the display  251 , enabling easy visual identification by the user of the type of vehicle V 2  that is traveling to the rear of the vehicle V 1 . 
     While in  FIG.  3    through  FIG.  6    the explanation was for a case wherein the second region AR 2  was disposed at the upper right corner of the display region AR of the display  251 , there is no limitation thereto. When the main image PM is displayed in the entirety of the display region AR of the display  251 , preferably the second region AR 2  is a region in the main image PM that does not include an image of a vehicle. This is so that the image of the vehicle in the main image PM will not be hidden by the sub-image PS through displaying the sub-image PS in the second region AR 2 . This enables an improvement in the visibility of the main image PM. 
       FIG.  7    and  FIG.  8    will be referenced next to explain the processing in the rearward image displaying device  1 .  FIG.  7    and  FIG.  8    are flowcharts showing an example of the processing in the rearward image displaying device  1 . 
     First, as illustrated in  FIG.  7   , in Step S 101  the imaging portion  111  generates the captured image PA by capturing an image, through the camera  21 , to the rear of the vehicle V 1 . 
     Next, in Step S 103 , the first generating portion  112  generates a first rearward image P 1  by extracting an image from a region of a portion of the captured image PA. The first rearward image P 1  may be, for example, the reference rearward image PT. 
     Next, in Step S 105 , the incline detecting portion  113  detects the incline angle AN of the vehicle V 1 . 
     Following this, in Step S 107 , the distance detecting portion  115  detects the distance LD between the vehicle V 1  and another vehicle V 2  that is traveling to the rear of the vehicle V 1 . 
     Next, in Step S 109 , the display controlling portion  116  evaluates whether or not the distance LD is greater than a threshold value LS. 
     If the display controlling portion  116  evaluates that the distance LD is not greater than the threshold value LS (Step S 109 : NO), processing advances to Step S 111 . 
     In Step S 111 , the display controlling portion  116  displays the first rearward image P 1 , that is, the reference rearward image PT, in the entirety of the display region AR of the display  251 . Processing then returns to Step S 101 . 
     If the display controlling portion  116  evaluates that the distance LD is greater than the threshold value LS (Step S 109 : YES), processing advances to Step S 113  of  FIG.  8   . 
     Given this, in Step S 113  of  FIG.  8    the display controlling portion  116  evaluates whether or not the vehicle V 1  is in the first state ST 1 , depending on the change in the incline angle AN over time. The first state ST 1  is a state wherein the vehicle V 1  has entered onto an upwardly inclined road RU from a first road R 1  that is substantially level. 
     If the display controlling portion  116  evaluates that the vehicle V 1  is not in the first state ST 1  (Step S 113 : NO), processing advances to Step S 121 . If the display controlling portion  116  evaluates that the vehicle V 1  is in the first state ST 1  (Step S 113 : YES), processing advances to Step S 115 . 
     Given this, in Step S 115 , the second generating portion  114  generates the top rearward image PU by extracting the top rearward image PU from the captured image PA as the second rearward image P 2 . 
     Next, in Step S 117 , the display controlling portion  116  sets the second rearward image P 2  as the main image PM. 
     Following this, in Step S 119 , the display controlling portion  116  combines the first rearward image P 1 , as the sub-image PS, with the main image PM. That is, the display controlling portion  116  generates a displayed image by combining the main image PM and the sub-image PS, with the top rearward image PU, which is the second rearward image P 2 , as the main image PM, and the first rearward image P 1  as the sub-image PS. Following this, the display controlling portion  116  displays the generated displayed image on the display  251 . Processing then returns to Step S 101  of  FIG.  7   . 
     If NO in Step S 113 , that is, if the display controlling portion  116  has evaluated that the vehicle V 1  is not in the first state ST 1 , then, in Step S 121 , the display controlling portion  116  evaluates whether or not the vehicle V 1  is in the second state ST 2 , depending on the change in the incline angle AN over time. The second state ST 2  is a state wherein a second road R 2  that is substantially level has been entered from an upwardly inclined road RU. 
     If the display controlling portion  116  evaluates that the vehicle V 1  is not in the second state ST 2  (Step S 121 : NO), processing advances to Step S 129 . If the display controlling portion  116  evaluates that the vehicle V 1  is in the second state ST 2  (Step S 121 : YES), processing advances to Step S 123 . 
     Given this, in Step S 123 , the second generating portion  114  generates the bottom rearward image PD by extracting the bottom rearward image PD from the captured image PA as the second rearward image P 2 . 
     Next, in Step S 125 , the display controlling portion  116  sets the first rearward image P 1  as the main image PM. 
     Following this, in Step S 127 , the display controlling portion  116  combines the second rearward image P 2 , as the sub-image PS, with the main image PM. That is, the display controlling portion  116  generates a displayed image by combining the main image PM and the sub-image PS, with the first rearward image P 1  as the main image PM, and the bottom rearward image PD, which is the second rearward image P 2 , as the sub-image PS. Following this, the display controlling portion  116  displays the generated displayed image on the display  251 . Processing then returns to Step S 101  of  FIG.  7   . 
     If NO in Step S 121 , that is, if the display controlling portion  116  has evaluated that the vehicle V 1  is not in the second state ST 2 , then, in Step S 129 , the display controlling portion  116  evaluates whether or not the vehicle V 1  is in the third state ST 3 , depending on the change in the incline angle AN over time. The third state ST 3  is a state wherein a downwardly inclined road RD has been entered from a second road R 2  that is substantially level. 
     If the display controlling portion  116  evaluates that the vehicle V 1  is not in the third state ST 3  (Step S 129 : NO), processing advances to Step S 137 . If the display controlling portion  116  evaluates that the vehicle V 1  is in the third state ST 3  (Step S 129 : YES), processing advances to Step S 131 . 
     Given this, in Step S 131 , the second generating portion  114  generates the bottom rearward image PD by extracting the bottom rearward image PD from the captured image PA as the second rearward image P 2 . 
     Next, in Step S 133 , the display controlling portion  116  sets the first rearward image P 1  as the main image PM. 
     Following this, in Step S 135 , the display controlling portion  116  combines the second rearward image P 2 , as the sub-image PS, with the main image PM. That is, the display controlling portion  116  generates a displayed image by combining the main image PM and the sub-image PS, with the first rearward image P 1  as the main image PM, and the bottom rearward image PD, which is the second rearward image P 2 , as the sub-image PS. Following this, the display controlling portion  116  displays the generated displayed image on the display  251 . Processing then returns to Step S 101  of  FIG.  7   . 
     If NO in Step S 129 , that is, if the display controlling portion  116  has evaluated that the vehicle V 1  is not in the third state ST 3 , then, in Step S 137 , the display controlling portion  116  evaluates whether or not the vehicle V 1  is in the fourth state ST 4 , depending on the change in the incline angle AN over time. The fourth state ST 4  is a state wherein a third road R 3  that is substantially level is entered from the downwardly inclined road RD. 
     If the display controlling portion  116  evaluates that the vehicle V 1  is not in the fourth state ST 4  (Step S 137 : NO), processing advances to Step S 145 . 
     In Step S 145 , the display controlling portion  116  displays the first rearward image P 1  in the entirety of the display region AR of the display  251 . Processing then returns to Step S 101 . 
     If the display controlling portion  116  evaluates that the vehicle V 1  is in the fourth state ST 4  (Step S 137 : YES), processing advances to Step S 139 . 
     Given this, in Step S 139 , the second generating portion  114  generates the top rearward image PU by extracting the top rearward image PU from the captured image PA as the second rearward image P 2 . 
     Next, in Step S 141 , the display controlling portion  116  sets the second rearward image P 2  as the main image PM. 
     Following this, in Step S 143 , the display controlling portion  116  combines the first rearward image P 1 , as the sub-image PS, with the main image PM. That is, the display controlling portion  116  generates a displayed image by combining the main image PM and the sub-image PS, with the top rearward image PU, which is the second rearward image P 2 , as the main image PM, and the first rearward image P 1  as the sub-image PS. Following this, the display controlling portion  116  displays the generated displayed image on the display  251 . Processing then returns to Step S 101  of  FIG.  7   . 
     Step S 101  corresponds to an example of an “imaging step.” Step S 103  corresponds to an example of a “first generating step.” Step S 105  corresponds to an example of an “incline detecting step.” 
     Step S 115 , Step S 123 , Step S 131 , and Step S 139  correspond to examples of a “second generating step.” 
     Moreover, Step S 119 , Step S 127 , Step S 135 , and Step S 143  correspond to examples of a “display controlling step.” 
     As explained in reference to  FIG.  7    and  FIG.  8   , the display controlling portion  116  evaluates whether or not the vehicle V 1  is in a first state ST 1 , a second state ST 2 , a third state ST 3 , or a fourth state ST 4 , depending on the change over time in the incline angle AN. Given this, the second generating portion  114  generates a top rearward image PU or a bottom rearward image PD as the second rearward image P 2 , depending on the state evaluated by the display controlling portion  116 . The display controlling portion  116  displays the first rearward image P 1  and the second rearward image P 2  on the display  251 . 
     Through this, the top rearward image PU or the bottom rearward image PD is generated as the second rearward image P 2 , depending on the state evaluated by the display controlling portion  116 , enabling the top rearward image PU or the bottom rearward image PD to be generated and displayed appropriately as the second rearward image P 2 . This enables easy visual identification of what type of vehicle V 2  is traveling to the rear of the vehicle V 1 . 
     As explained above in reference to  FIG.  1    through  FIG.  8   , the rearward image displaying device  1  according to the present embodiment comprises: an imaging portion  111  for generating a captured image PA by imaging, through a camera  21 , to the rear of the vehicle V 1 ; a first generating portion  112  for generating a first rearward image P 1  by extracting an image from a region of a portion of the captured image PA; an incline detecting portion  113  for detecting an incline angle AN of the vehicle V 1 ; a second generating portion for generating a second rearward image P 2 , which is different from the first rearward image P 1 , by extracting an image of a region of another portion of the captured image PA depending on the incline angle AN; and a display controlling portion  116  for displaying the first rearward image P 1  and the second rearward image P 2  on the display  251 . 
     That is, a first rearward image P 1  is generated by extracting an image from a region of a portion of the captured image PA, and a second rearward image P 2  that is different from the first rearward image P 1  is generated through extracting an image from another portion of the captured image PA, depending on the incline angle AN. Given this, the first rearward image P 1  and the second rearward image P 2  are displayed on the display  251 . 
     As a result, the second rearward image P 2  is generated by extracting an image from a region of another portion of the captured image PA depending on the incline angle AN, enabling the second rearward image P 2  to be generated through extraction from a suitable region of the captured image PA. Additionally, because the first rearward image P 1  and the second rearward image P 2  are displayed on the display  251 , this enables easy visual identification of what type of vehicle V 2  is traveling to the rear of the vehicle V 1 . 
     Additionally, a distance detecting portion  115  is provided for detecting a distance LD between the vehicle V 1  and another vehicle V 2  that is traveling to the rear of the vehicle V 1 , and the display controlling portion  116  does not display the second rearward image P 2  on the display  251  if the distance LD is below a threshold value LS. 
     In other words, if the distance LD is below the threshold value LS, the first rearward image P 1  will be displayed alone in the entirety of the display region AR of the display  251 . The threshold value LS may be set, for example, so that the vehicle image PV 2  will be included in the first rearward image P 1  if the distance LD is less than the threshold value LS. Consequently, because the vehicle image PV 2  is included in the first rearward image P 1  and the first rearward image P 1  alone is displayed in the entirety of the display region AR of the display  251 , this enables easy visual identification of what type of vehicle V 2  is traveling to the rear of the vehicle V 1 . 
     Additionally, the display controlling portion  116  displays a main image PM that is displayed in a first region AR 1  within the display region AR of the display  251 , and a sub-image PS that is displayed in a second region AR 2 , which is narrower than the first region AR 1 , in the display region AR, displaying one of the images, the first rearward image P 1  or the second rearward image P 2 , as the main image PM and the other of the images, the first rearward image P 1  or the second rearward image P 2 , as the sub-image PS. 
     That is, one of the images, the first rearward image P 1  or the second rearward image P 2 , is displayed as the main image PM, and the other of the images, the first rearward image P 1  or the second rearward image P 2 , is displayed as the sub-image PS. Determining the main image PM and the sub-image PS appropriately enables easy visual identification what type of vehicle V 2  is traveling to the rear of the vehicle V 1 . 
     Moreover, the display controlling portion  116  displays the main image PM in the entirety of the display region AR of the display  251  and sets, as the second region AR 2 , a region wherein no image of a vehicle is included in the main image PM, and displays the sub-image PS in the second region. 
     Thus a region wherein no image of a vehicle is included in the main image PM is set as the second region AR 2 , enabling the second region AR 2  to be set appropriately. 
     Additionally, the rearward image displaying method according to the present embodiment includes: an imaging step for generating a captured image PA by imaging, through a camera  21 , to the rear of the vehicle V 1 ; a first generating step for generating a first rearward image P 1  by extracting an image from a region of a portion of the captured image PA; an incline detecting step for detecting an incline angle AN of the vehicle V 1 ; a second generating step for generating a second rearward image P 2 , which is different from the first rearward image P 1 , by extracting an image from a region of another portion of the captured image PA, depending on the incline angle AN; and a display controlling step for displaying the first rearward image P 1  and the second rearward image P 2  on a display  251 . 
     Thus the method according to the present embodiment has the same effects in operation as the rearward image displaying device  1  according to the present embodiment. 
     The embodiment set forth above is no more than an illustration of one form of the present invention, and the present invention may be modified and applied appropriately in a range that does not deviate from the spirit and intent thereof. 
     For example, for ease in understanding the present invention,  FIG.  1    is a diagram wherein the structural elements are shown partitioned into the main processing details, and the structural elements may be partitioned into more structural elements depending on the processing details. Moreover, the partitioning may be such that more processes are carried out by a single structural element. 
     Moreover, the processes in any of the structural elements may be executed in a single hardware or executed by a plurality of hardware. Moreover, the processes of each structural elements may be achieved by a single program, or by a plurality of programs. 
     Additionally, in  FIG.  1    the rearward image displaying device  1  may be provided integrated with the incline sensor  22 , the operating portion  24 , and/or the displaying portion  50 . 
     In addition, while in the present embodiment the display controlling portion  116  evaluated whether or not the vehicle V 1  was in any of the first state ST 1  through the fourth state ST 4  depending on a change in the incline angle AN over time, there is no limitation thereto. Instead the second generating portion  114  may generate the top rearward image PU or the bottom rearward image PD as the second rearward image P 2  depending on the incline angle AN. 
     Moreover, when the obstacle displaying method according to the present invention is achieved using a computer, the structure may be in the form of a recording medium whereon a control program  121  to be executed by a computer is recorded, or a transmitting medium for transmitting the control program  121 . 
     The recording medium may use a magnetic or optical recording medium, or a semiconductor memory device. Specifically, it may be a fixed recording medium or a portable recording medium such as a flexible disk, an HDD, a CD-ROM (Compact Disk Read-Only Memory), a DVD, a Blu-ray® disc, a magnetooptical disc, a flash memory, a card-type recording medium, or the like. Moreover, the recording medium may be a RAM, a ROM, or a non-volatile storage device, such as an HDD, provided by the rearward image displaying device  1 . 
     Additionally, the rearward image displaying device  1  may download the control program  121  from a server device that is connected communicatively through a network to the rearward image displaying device  1 . 
     Moreover, the processing unit in the flowcharts shown in  FIG.  7    and  FIG.  8    are partitioned depending on the main processing details thereof to facilitate easy understanding of the processes of the rearward image displaying device  1 , for example, but the present invention is not limited by the names and ways in which the processing units are divided. The processes of the rearward image displaying device  1  may be divided into more processing units depending on the process details. Moreover, the processes of the rearward image displaying device  1  may instead be divided so as to include more processes in a single processing unit. 
     EXPLANATIONS OF REFERENCE SYMBOLS 
     
         
           100 : Rearward Image Displaying System 
           1 : Rearward Image Displaying Device 
           11 : Processor 
           111 : Imaging Portion 
           112 : First Generating Portion 
           113 : Incline Detecting Portion 
           114 : Second Generating Portion 
           115 : Distance Detecting Portion 
           116 : Display Controlling Portion 
           12 : Memory 
           121 : Control Program 
           122 : Image Storing Portion 
           123 : Incline Storing Portion 
           21 : Camera 
           22 : Incline Sensor 
           23 : Distance Measuring Sensor 
           24 : Operating Portion 
           25 : Displaying Portion 
           251 : Display 
         AN: Incline Angle 
         AR 1 : First Region 
         AR 2 : Second Region 
         AVA Imaging Viewing Angle 
         MD: Bottom Direction Imaging Mark 
         MU: Top Direction Imaging Mark 
         P 1 : First Rearward Image 
         P 2 : Second Rearward Image 
         PA: Captured Image 
         PM: Main Image 
         PS: Sub-Image 
         V 1 , V 2 , V3: Vehicles