Patent Publication Number: US-2021163036-A1

Title: Image processing device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of U.S. patent application Ser. No. 16/201,159, filed on Nov. 27, 2018, which is a continuation application of U.S. patent application Ser. No. 15/527,931, filed on May 18, 2017, now U.S. Pat. No. 10,166,998, issued on Jan. 1, 2019, which is a national stage application of PCT Application No. PCT/JP2015/005730, filed on Nov. 17, 2015, which is based on Japanese Patent Applications No. 2014-243429, filed on Dec. 1, 2014, and No. 2015-200537, filed on Oct. 8, 2015, the disclosures of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an image processing device that generates a display image used for display in a head-up display device. 
     BACKGROUND ART 
     In recent years, there have been developed vehicles equipped with driving assistance devices such as a lane departure warning device (LDW device) and a lane keeping assist device (LKA device). Each of these devices captures an image of a traveling road using a camera and extracts a lane marking for travel from the captured image to acquire positional information of the lane marking. Then, when it is determined that a traveling vehicle has departed from the lane marking or the possibility of departure is high on the basis of the acquired positional information, the determination is notified to a driver for warning or a steering force is applied. 
     In a display device described in Patent Literature 1, when the above device is in a normally operable active state, the active state of the driving assistance device is notified to a driver by displaying a pattern that is suggestive of the active state on the display device. Further, there is a case unable to detect the lane marking such as when there is no lane marking on the traveling road, when the lane marking partially peels off, or when there is a foreign substance such as sand on the lane marking. In such a case, a driver is made to recognize that the driving assistance device is not in an active state by not displaying the pattern. 
     However, merely displaying the pattern in the above manner is not sufficient for intuitive recognition of an active state of the LDW device or the LKA device. 
     PRIOR ART LITERATURES 
     Patent Literature 
     Patent Literature 1: JP-2004-533080-A 
     SUMMARY OF INVENTION 
     It is an object of the present disclosure to provide an image processing device that makes it easy for a driver to intuitively recognize a state of a driving assistance device that operates by detecting the position of a lane marking. 
     According to an aspect of the present disclosure, an image processing device that generates a display image and is applied to a driving assistance system, which includes: a driving assistance device that detects a relative position of a lane marking arranged on a traveling road with respect to a vehicle and assists a driving of the vehicle based on a detected positional information; 
     and a head-up display device that projects a display image on a projection area arranged on the vehicle to visually recognize a virtual image of the display image, the image processing device includes: an acquisition device that acquires the positional information; and a generation device that generates the display image including a predetermined display element. The generation device generates the display image to visually recognize the display element at a position associated with the positional information acquired by the acquisition device and to visually recognize the display element as a shape inclined toward the vehicle from the lane marking. 
     According to the above image processing device, the display element is visually recognized at the position associated with the positional information of the lane marking detected by the driving assistance device. Thus, the position of the display element changes in conjunction with a change of the positional information. That is, when the relative position of the lane marking with respect to the vehicle fluctuates in the vehicle width direction while the vehicle travels, the display element can be displayed as if the display element also fluctuated in the vehicle width direction in response to the fluctuation of the relative position. Further, the above invention displays the display element by the head-up display device. Thus, the display element (virtual image) is visually recognized as being superimposed on the traveling road (real image) which is visually recognized in front of a windshield. Therefore, since the display element which is visually recognized in a superimposed manner changes its position in conjunction with the positional information in this manner, it becomes easy for a driver to intuitively recognize that the driving assistance device is in an active state. 
     Further, according to the above image processing device, the display element is visually recognized as the shape that is inclined toward the vehicle from the lane marking. Thus, the inclination of the display element makes it easy for a viewer to visualize an image of the vehicle guided or restricted to the inside of the lane marking. Therefore, it becomes easy for a driver to intuitively recognize that the driving assistance device is in an active state such that driving of the vehicle is assisted on the basis of the positional information of the lane marking. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a sectional view illustrating a vehicle-mounted position of a head-up display device which is provided in a driving assistance system to which an image processing device is applied in a first embodiment of the present disclosure; 
         FIG. 2  is a diagram illustrating the relationship between a background that is within sight from the interior side of a windshield and a position where a display image is visually recognized in the first embodiment; 
         FIG. 3  is a block diagram illustrating the driving assistance system and the image processing device according to the first embodiment; 
         FIG. 4  is a diagram illustrating visual recognition positions of display elements (virtual images) with respect to lane markings (real images) in the first embodiment; 
         FIG. 5  is a diagram illustrating visual recognition positions of display elements (virtual images) with respect to lane markings (real images) in a second embodiment of the present disclosure; 
         FIG. 6  is a diagram illustrating visual recognition positions of display elements (virtual images) with respect to lane markings (real images) in a third embodiment of the present disclosure; 
         FIG. 7  is a diagram illustrating visual recognition positions of display elements (virtual images) with respect to lane markings (real images) in a fourth embodiment of the present disclosure; 
         FIG. 8  is a diagram illustrating visual recognition positions of display elements (virtual images) with respect to lane markings (real images) in a fifth embodiment of the present disclosure; 
         FIG. 9  is a diagram illustrating visual recognition positions of display elements (virtual images) with respect to lane markings (real images) in a sixth embodiment of the present disclosure; 
         FIG. 10  is a diagram illustrating the shapes of display elements when the recognition rate of lane markings is high in an eighth embodiment of the present disclosure; 
         FIG. 11  is a diagram illustrating the shapes of display elements when the recognition rate of the lane markings is low in the eighth embodiment; 
         FIG. 12  is a diagram illustrating the shapes of display elements when the recognition rate of lane markings is high in a ninth embodiment of the present disclosure; 
         FIG. 13  is a diagram illustrating the shapes of display elements when the recognition rate of the lane markings is low in the ninth embodiment; 
         FIG. 14  is a diagram illustrating the number of display elements when the recognition rate of lane markings is high in a tenth embodiment of the present disclosure; 
         FIG. 15  is a diagram illustrating the number of display elements when the recognition rate of the lane markings is low in the tenth embodiment; 
         FIG. 16  is a diagram illustrating the shapes of display elements when driving assistance is in standby in an enabled state in an eleventh embodiment of the present disclosure; 
         FIG. 17  is a diagram describing an automatic offset function by the driving assistance system in a twelfth embodiment of the present disclosure; 
         FIG. 18  is a diagram describing an automatic cornering function by the driving assistance system in the twelfth embodiment: 
         FIG. 19  is a diagram illustrating the shapes of display elements in the traveling condition of  FIG. 17 ; 
         FIG. 20  is an imaginary diagram of the cross-sectional shapes of the display elements taken along dot-dash lines A, C in  FIG. 19 ; 
         FIG. 21  is an imaginary diagram of the cross-sectional shapes of the display elements taken along a dot-dash line B 1  in  FIG. 19 ; 
         FIG. 22  is a diagram illustrating the shapes of display elements in the traveling condition of  FIG. 18 ; 
         FIG. 23  is an imaginary diagram of the cross-sectional shapes of the display elements taken along a dot-dash line B 2  in  FIG. 22 ; 
         FIG. 24  is a diagram illustrating the shapes of display elements in the traveling condition of  FIG. 17  in a thirteenth embodiment of the present disclosure; 
         FIG. 25  is an imaginary diagram of the cross-sectional shapes of the display elements taken along a dot-dash line B 10  in  FIG. 24 ; 
         FIG. 26  is a diagram illustrating the shapes of display elements in the traveling condition of  FIG. 18 ; and 
         FIG. 27  is an imaginary diagram of the cross-sectional shapes of the display elements taken along a dot-dash line B 20  in  FIG. 26 . 
     
    
    
     EMBODIMENTS FOR CARRYING OUT INVENTION 
     Hereinbelow, a plurality of embodiments for carrying out the disclosure will be described with reference to the drawings. In each of the embodiments, a part corresponding to an item described in the preceding embodiment is denoted by the same reference sign as the already described item, and repetitive description may be omitted. In each of the embodiments, when only a part of a configuration is described, the other preceding embodiments can be referred to and applied to the other part of the configuration. 
     First Embodiment 
     As illustrated in  FIG. 1 , a display device  20  and a head-up display device (HUD  30 ) are attached to an instrument panel  11  which is installed in a cabin of a vehicle  10 . The display device  20  includes a liquid crystal panel  21  which is housed in a case  22 . The display device  20  is disposed in front of a driver of the vehicle  10  (refer to  FIG. 2 ). The liquid crystal panel  21  displays various warning indications and a vehicle speed. 
     The HUD  30  includes a liquid crystal panel  31  and a reflecting mirror  32  which are housed in a case  33 . The HUD  30  is disposed below a windshield  12  which is located in front of the driver. Light of a display image emitted from the liquid crystal panel  31  is reflected by the reflecting mirror  32 . Reflected light reflected by the reflecting mirror  32  is projected on a projection area  12   p  which is formed in the vehicle  10 . The projection area  12   p  is formed by a reflecting sheet  12   a  which is attached to the interior side of the windshield  12 . Accordingly, a virtual image of the display image is visually recognized by the driver of the vehicle  10 . Specifically, the virtual image is visually recognized at the front side of the vehicle  10  (outside the cabin) with respect to the windshield  12 . 
       FIG. 2  illustrates the positional relationship between scenery that is within sight in front of the vehicle  10  through the windshield  12  and a virtual image formed by the HUD  30  at an angle of an eye point of the driver. An example of  FIG. 2  shows a condition in which the vehicle  10  is traveling on an expressway with three lanes. Specifically, the vehicle  10  is traveling on the central one of the three lanes in a traveling road R. Another vehicle V is within sight on the front of the left lane. Further, the traveling road R is provided with a plurality of lane markings R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9  which demarcate the three lanes. The lane markings R 1 , R 2 , R 3 , R 8 , R 9  demarcate the center lane and the right lane and are formed at regular intervals with a predetermined pitch in a traveling direction. The lane markings R 4 , R 5 , R 6 , R 7 , R 8  demarcate the center lane and the left lane and are formed at regular intervals with a predetermined pitch in the traveling direction. 
     A display image (virtual image) formed by the HUD  30  includes a vehicle speed display element Ms which indicates the vehicle speed and predetermined display elements M 1 , M 2 , M 3 , M 4 , M 5 , M 6  (described below). The display elements M 1  to M 6  are located above the vehicle speed display element Ms and visually recognized in a view field region above a hood (not illustrated) of the vehicle  10 . In addition to the vehicle speed display element Ms, concrete examples of the display element included in the display image include an indication display of a traveling direction of the vehicle  10  by a navigation device and various warning displays. 
     An electronic control unit (ECU  40 ) illustrated in  FIG. 3  is mounted on the vehicle  10  and constitutes a display system together with the display device  20  and the HUD  30 . The ECU  40  controls operations of the display device  20  and the HUD  30 . For example, the ECU  40  acquires vehicle speed information through a local area network in the vehicle, and performs control on the basis of the acquired vehicle speed information so that the display device  20  and the HUD  30  display a vehicle speed. The ECU  40  is provided with a memory such as a ROM or a RAM, a CPU, an I/O, and a bus which connects these members. Some or all of functions executed by the ECU  40  may be configured as hardware by one or more ICs. 
     An in-vehicle camera  13  which captures an image of the face of the driver is attached to the instrument panel  11 . The ECU  40  analyzes a face image of the driver captured by the in-vehicle camera  13  and calculates an eyeball position (eye point position) of the driver. Then, a projection position of the display image is adjusted according to the eye point position obtained by the analysis so that a virtual image is visually recognized at a desired position. 
     For example, the projection position of the vehicle speed display element Ms is adjusted so that the vehicle speed display element Ms is not superimposed on the steering wheel. Further, the projection positions of the display elements M 1  to M 6  are adjusted so that the display elements M 1  to M 6  are visually recognized as being superimposed on the lane markings R 1  to R 6 . Note that an initial eye point position (initial position) may be analyzed before the driver sits on the driver&#39;s seat and starts driving, and the initial position may be continuously used during travel. Alternatively, the eye point position may be periodically analyzed and updated during travel. 
     A front camera  50  which captures an image of the front side and an electronic control unit (ECU  60 ) which functions as a lane keeping assist device are mounted on the vehicle  10 . For example, in a traveling condition of  FIG. 2 , among the lane markings R 1  to R 9  which are formed on the traveling road R, the camera  50  captures an image of the lane markings R 1  to R 8  which are located in front of the vehicle. 
     The ECU  60  analyzes an image captured by the front camera  50  and calculates relative positions of the lane markings R 1  to R 6  with respect to the vehicle  10  and calculates the shapes and sizes of the lane markings R 1  to R 6 . In the example of  FIG. 2 , the relative positions of the pair of lane markings R 1  to 
     R 3  and R 4  to R 6  are detected by the ECU  60 , and the ECU  60  executes driving assistance control (described below) on the basis of positional information indicating the relative positions. For example, it is determined, on the basis of the calculated positional information, whether the vehicle  10  has departed from the center lane against the intension of the driver or whether the possibility of departure is a predetermined possibility or more. When it is determined that the vehicle  10  has departed or the possibility of departure is high, the ECU  60  controls the operation of a steering device (not illustrate) so as to apply a steering force in the direction of preventing the departure. 
     For example, when a speed of reducing a relative distance with respect to one of the pair of lane markings R 1  to R 3  and R 4  to R 6 , specifically, with respect to the lane marking R 1  to R 3  is a predetermined speed or more in a condition in which a direction indicator is not operated, it is determined that the possibility of departure from the lane marking R 1  to R 3  is high. Then, a steering force toward the other lane marking R 4  to R 6  is applied. Accordingly, when the vehicle  10  is about to depart to the right lane in the middle of traveling on the central line, a steering force is applied in the direction of pulling the vehicle  10  back to the center lane. 
     The ECU  60  when executing such control corresponds to a “driving assistance device” which detects the relative positions of the lane markings R 1  to R 6  with respect to the vehicle  10  and assists driving of the vehicle  10  on the basis of the detected positional information. The positional information calculated by the ECU  60  is transmitted to the ECU  40  through the local area network in the vehicle. The ECU  40  generates the display image described above on the basis of the acquired positional information. 
     The ECU  40  when functioning to acquire positional information from the driving assistance device corresponds to an acquisition device  41 . The ECU  40  when functioning to generate a display image corresponds to a generation device  42 . The ECU  40  transmits data of the generated display image to the liquid crystal panel  31  of the HUD  30  to control light of the display image emitted from the liquid crystal panel  31 . That is, the ECU  40  corresponds to an “image processing device” which is applied to a driving assistance system provided with the HUD  30  and the ECU  60  and generates the display image. 
     Next, the predetermined display elements M 1  to M 6  included in the display image will be described in detail with reference to  FIG. 4 . 
       FIG. 4  represents a view from an eye point position which is analyzed in an image of the in-vehicle camera  13 . Thus, for example, when the traveling road R on the front side is viewed while moving the eye point position rightward without changing a display image illustrated in  FIG. 4 , the display elements M 1  to M 6  are visually recognized as being shifted to the left side with respect to the lane markings R 1  to R 6 . The generation device  42  generates the display image in such a manner that the display elements M 1  to M 6  and the lane markings R 1  to R 6  are visually recognized in a positional relationship illustrated in  FIG. 4  when the front side of the vehicle is viewed from the analyzed eye point position. 
     That is, the display elements M 1  to M 6  are visually recognized as shapes inclined toward the vehicle  10  from the lane markings R 1  to R 6  in a direction (right-left direction) that is perpendicular to an extending direction of the lane markings R 1  to R 6  (front-rear direction) and horizontal. In other words, the display elements M 1  to M 6  are visually recognized as inclined planes whose height in the up-down direction is reduced toward the center of the lane from the lane markings R 1  to R 6 . 
     Typically, each of the lane markings R 1  to R 6  has a rectangular shape whose longitudinal direction is aligned with the traveling direction, and each of the display elements M 1  to M 6  also has a rectangular shape whose longitudinal direction is aligned with the traveling direction correspondingly. Hereinbelow, the positional relationship between the lane marking R 4  and the display element M 4  will be described in detail. Note that the same applies to the positional relationship between the other lane markings R 1  to R 3 , R 5 , R 6  and the other display elements M 1  to M 3 , M 5 , M 6 , and description thereof will be omitted. Further,  FIG. 4  represents a view in an ideal state in which there is no deviation in detection of the eye point position and detection of the lane markings R 1  to R 6 . However, in practice, there is a deviation between these detected positions and actual positions. Thus, the display elements M 1  to M 6  are viewed at positions shifted from the positions illustrated in  FIG. 4 . 
     A visible outline of the lane marking R 4  at the side (the inner side) corresponding to the lane on which the vehicle  10  is traveling (an inner visible outline R 4   a ) and a visible outline of the display element M 4  at the inner side (an inner visible outline M 4   a ) are located at the same position. That is, the two inner visible outlines R 4   a,  M 4   a  are located at the same position in the right-left direction. The two inner visible outlines R 4   a,  M 4   a  have the same length. The two inner visible outlines R 4   a,  M 4   a  are parallel to each other. 
     A visible outline of the lane marking R 4  at the outer side (an outer visible outline R 4   b ) and a visible outline of the lane marking M 4  at the outer side (an outer visible outline M 4   b ) are located at different positions in the right-left direction. Specifically, the outer visible outline M 4   b  of the display element M 4  is located inside the outer visible outline R 4   b  of the lane marking R 4 . The two outer visible outlines R 4   b,  M 4   b  have the same length. The two outer visible outlines R 4   b,  M 4   b  are parallel to each other. 
     A visible outline of the lane marking R 1  at the near side (a near side visible outline R 4   c ) and the lower end of the inner visible outline M 4   a  of the display element M 4  are located at the same position in the up-down direction. A visible outline of the lane marking R 4  at the far side (a far side visible outline R 4   d ) and the upper end of the inner visible outline M 4   a  of the display element M 4  are located at the same position in the up-down direction. 
     A visible outline of the display element M 4  at the lower side (a lower visible outline M 4   c ) is not parallel to the near side visible outline R 4   c  of the lane marking R 4 . The outer end of the lower visible outline M 4   c  of the display element M 4  is located above the inner end thereof. Thus, the lower visible outline M 4   c  is visually recognized as a line that is inclined downward toward the inner side. 
     A visible outline of the display element M 4  at the upper side (an upper visible outline M 4   d ) is not parallel to the far side visible outline R 4   d  of the lane marking R 4 . The outer end of the upper visible outline M 4   d  of the display element M 4  is located above the inner end thereof. Thus, the upper visible outline M 4   d  is visually recognized as a line that is inclined downward toward the inner side. 
     In this manner, the inner visible outline M 4   a  and the outer visible outline M 4   b  of the display element M 4  are visually recognized as lines that are parallel to the lane marking R 4 . On the other hand, the lower visible outline M 4   c  and the upper visible outline M 4   d  of the display element M 4  are visually recognized as inclined lines. Thus, the entire display element M 4  is visually recognized as an inclined plane that is inclined downward toward the inner side. Note that a part (the half or more) of the display element M 4  is visually recognized as being superimposed on the lane marking R 4 . 
     Further, the display element M 4  is visually recognized as the inclined plane with the inner visible outline M 4   a  of the display element M 4  aligned with the inner visible outline R 4   a  of the lane marking R 4 . Thus, a virtual three-dimensional object RM 4  which includes the display element M 4  as a first virtual plane and the lane marking R 4  as a second virtual plane is visually recognized. That is, the display element M 4  which is a virtual image and the lane marking R 4  which is a real image are integrated so as to be visually recognized as one virtual three-dimensional object RM 4  by an optical illusion. The second virtual plane is visually recognized as the bottom face of the virtual three-dimensional object RM 4  which is placed on the traveling road R, and the first virtual plane is visually recognized as an inclined plane projecting upward from the traveling road R by an optical illusion. 
     In the example of  FIG. 4 , the plurality of lane markings R 1  to R 6  are formed at a predetermined pitch in the traveling direction of the traveling road R. Correspondingly, the plurality of display elements M 1  to M 6  are also visually recognized as being arranged at the predetermined pitch in the traveling direction. Further, the pair of lane markings R 1  to R 3  and R 4  to R 6  are located on the right and left sides of the vehicle  10 . Correspondingly, the plurality of display elements M 1  to M 6  are also visually recognized on the right and left sides of the vehicle  10 . 
     As the vehicle  10  travels, a background including the traveling road R which is within sight at the exterior side of the windshield  12  is visually recognized as if the background flew from the front side of the vehicle  10  toward the rear side thereof. That is, lane markings that are located at positions indicated by R 3 , R 6  in  FIG. 4  at a first point approach the vehicle  10  in such a manner that the lane markings move to positions of R 2 , R 5  at a second point thereafter and then move to positions of R 1 , R 4  at a third point thereafter. Further, display positions of the plurality of display elements M 1  to M 6  are also changed corresponding to such a relative position change of the lane markings R 1  to R 6 . Further, the display elements M 1  to M 6  are displayed in a manner to be gradually enlarged as time passes. The enlarging speed is equal to an approaching speed of the lane markings R 1  to R 6 . Thus, the display elements M 1  to M 6  are visually recognized as if the display elements M 1  to M 6  approached the driver together with the lane markings R 1  to R 6  as the lane markings R 1  to R 6  approach the vehicle  10 . Further, the display elements M 1  to M 6  are visually recognized as if the display elements M 1  to M 6  approached the driver with the same speed as the lane markings R 1  to R 6 . 
     An inner region surrounded by the visible outlines M 4   a,  M 4   b,  M 4   c,  M 4   d  of each of the display elements M 1  to M 6  is displayed in a predetermined color. 
     In the example of  FIG. 4 , each of the visible outlines M 4   a,  M 4   b,  M 4   c,  M 4   d  (contours) and the inner region are displayed in different colors. 
     As described above, according to the present embodiment, the acquisition device  41  which acquires positional information of the lane markings R 1  to R 6  and the generation device  42  which generates the display image including the predetermined display elements M 1  to M 6  are provided. The generation device  42  generates the display image in such a manner that the display elements M 1  to M 6  are visually recognized at positions associated with the acquired positional information and visually recognized as shapes inclined toward the vehicle from the lane markings R 1  to R 6 . 
     According to this configuration, the display elements M 1  to M 6  are visually recognized at the positions associated with the positional information of the lane markings R 1  to R 6  detected by the ECU  60  which functions as the driving assistance device. Thus, the positions of the display elements M 1  to M 6  change in conjunction with a change of the positional information. Further, the display elements M 1  to M 6  are displayed by the HUD  30 . Thus, the display elements M 1  to M 6  (virtual images) are visually recognized as being superimposed on the traveling road R (real image) which is visually recognized in front of the windshield  12 . Therefore, since the positions of the display elements M 1  to M 6  which are visually recognized in a superimposed manner change in conjunction with the positional information in this manner, it becomes easy for the driver to intuitively recognize that the driving assistance device is in an active state. 
     Further, according to the present embodiment, the display elements M 1  to M 6  are visually recognized as shapes inclined toward the vehicle  10  from the lane markings R 1  to R 6 . Thus, the inclination of the display elements M 1  to M 6  makes it easy for a viewer to visualize an image of the vehicle  10  guided or restricted to the inside of the lane markings R 1  to R 6 . Therefore, it becomes easy for the driver to intuitively recognize that the driving assistance device is in an active state. 
     The active state is a standby state that, when the ECU  60  normally detects the lane markings R 1  to R 6  and departure or a high possibility of departure is determined, enables application of a steering force in the direction of preventing the departure. An inactive state is a state unable to detect the lane markings R 1  to R 6  such as when the lane markings R 1  to R 6  are not present on the traveling road R, when the lane markings R 1  to R 6  partially peel off, or when there is a foreign substance such as sand on the lane markings R 1  to R 6 . 
     Further, in the present embodiment, the generation device  42  generates the display image in such a manner that the display elements M 1  to M 6  are visually recognized as approaching the driver as the lane markings R 1  to R 6  approach the vehicle  10  along with the travel of the vehicle  10 . This facilitates a natural view of the display elements M 1  to M 6  (virtual images) blending into the traveling road R (real image) which is visually recognized in front of the windshield  12 . Thus, it is possible to reduce the possibility of the driver feeling uncomfortable with the display elements M 1  to M 6  displayed at positions that overlap the traveling road R. 
     Further, in the present embodiment, the generation device  42  generates the display image in such a manner that each of the display elements M 1  to M 6  (virtual images) is visually recognized as the first virtual plane, each of the lane markings R 1  to R 6  (real images) is visually recognized as the second virtual plane, and the virtual three-dimensional objects RM 1  to RM 6  each of which includes the first virtual plane and the second virtual plane are visually recognized. Thus, the virtual three-dimensional objects RM 1  to RM 6  are visually recognized as shapes inclined toward the vehicle  10  from the lane markings R 1  to R 6 . This enables facilitation of the effect of making it easy for the driver to intuitively recognize operation contents of the driving assistance device. 
     Further, in the present embodiment, the generation device  42  generates the display image in such a manner that the display elements M 1  to M 6  are visually recognized as being superimposed on the lane markings R 1  to R 6 . Thus, in the background including the traveling road R which is within sight at the exterior side of the windshield  12 , a range in which the display elements M 1  to M 6  are superimposed on a part other than the lane markings R 1  to R 6  (the other background part) can be reduced. Thus, it is possible to prevent the other background part from becoming hard to see by the display elements M 1  to M 6  and to improve the visibility with respect to the other background part. 
     Further, in the present embodiment, when the plurality of lane markings R 1  to R 6  are formed at a predetermined pitch in the traveling direction of the traveling road R, the generation device  42  generates the display image in such a manner that the plurality of display elements M 1  to M 6  are visually recognized as being arranged at the predetermined pitch in the traveling direction. Thus, it is possible to reduce the range in which the display elements M 1  to M 6  are superimposed on the other background part and to improve the visibility with respect to the other background part. 
     Further, in the present embodiment, when the driving assistance device detects the pair of lane markings R 1  to R 3  and R 4  to R 6  which are located on the right and left sides of the vehicle  10 , the generation device  42  generates the display image in such a manner that the display elements M 1  to M 3  are visually recognized with respect to the lane marking R 1  to R 3  and the display elements M 4  to M 6  are visually recognized with respect to the lane marking R 4  to R 6 . Accordingly, the inclination of the display elements M 1  to M 3  and M 4  to M 6  makes it easy for a viewer to visualize an image of the vehicle  10  guided or restricted from both the right and left sides of the vehicle  10 . Thus, it is possible to facilitate the above effect of making it easy to intuitively recognize the active state of the driving assistance device. 
     Second Embodiment 
     In the first embodiment, the display image is generated in such a manner that the length of the inner visible outline R 4   a  of the lane marking R 4  and the length of the inner visible outline M 4   a  of the display element M 4  are visually recognized as being equal to each other. On the other hand, in the present embodiment illustrated in  FIG. 5 , a display image is generated in such a manner that the length of the inner visible outline M 4   a  of the display element 
     M 4  is visually recognized as being shorter than the length of the inner visible outline R 4   a  of the lane marking R 4 . 
     Specifically, the lower end of the inner visible outline M 4   a  of the display element M 4  is visually recognized above the near side visible outline R 4   c  of the lane marking R 4 . Further, the upper end of the inner visible outline M 4   a  of the display element M 4  is visually recognized below the far side visible outline R 4   d  of the lane marking R 4 . 
     According to this configuration, eve when there is a little deviation in detection of the eye point position and detection of the lane markings R 1  to R 6 , the deviation does not change a view in which the inner visible outline M 4   a  is present between the near side visible outline R 4   c  and the far side visible outline R 4   d.  Thus, a change in the view caused by a detection deviation is less likely to occur, and the robustness of the view with respect to a detection deviation can be improved. 
     Third Embodiment 
     In the first embodiment, the position of the inner visible outline R 4   a  of the lane marking R 4  is aligned with the position of the inner visible outline M 4   a  of the display element M 4  in the direction (right-left direction) perpendicular to the traveling direction. On the other hand, in the present embodiment illustrated in  FIG. 6 , a display image is generated in such a manner that the inner visible outline M 4   a  of the display element M 4  is visually recognized on the inner side relative to the inner visible outline R 4   a  of the lane marking R 4  in the right-left direction. 
     Further, in the first embodiment, the display image is generated in such a manner that the outer visible outline M 4   b  of the display element M 4  is visually recognized on the inner side relative to the outer visible outline R 4   b  of the lane marking R 4  in the right-left direction. On the other hand, in the present embodiment illustrated in  FIG. 6 , the display image is generated in such a manner that the outer visible outline M 4   b  of the display element M 4  is visually recognized on the outer side relative to the outer visible outline R 4   b  of the lane marking R 4  in the right-left direction. 
     As described above, according to the present embodiment, the length in the right-left direction of the display element M 4  is visually recognized as being longer than the length in the right-left direction of the lane marking R 4 , and the display element M 4  is visually recognized as being superimposed across the lane marking R 4  in the right-left direction. Thus, even when there is a little deviation in detection of the eye point position and detection of the lane markings R 1  to R 6 , the deviation does not change the view. Thus, a change in the view caused by a detection deviation is less likely to occur, and the robustness of the view with respect to a detection deviation can be improved. Further, since the display element M 4  is visually recognized as being superimposed across the lane marking R 4  in the right-left direction, it becomes easy for a driver to recognize that the display element M 4  is displayed in association with the position of the lane marking R 4 . 
     Fourth Embodiment 
     In the first embodiment, the second virtual plane of the virtual three-dimensional object RM 4  is visually recognized as the bottom face of the virtual three-dimensional object RM 4  which is placed on the traveling road R, and the first virtual plane of the virtual three-dimensional object RM 4  is visually recognized as an inclined plane projecting upward from the traveling road R by an optical illusion. On the other hand, in the present embodiment illustrated in  FIG. 7 , the second virtual plane of the virtual three-dimensional object RM 4  is visually recognized as the bottom face of the virtual three-dimensional object RM 4  which is placed on the traveling road R, and the first virtual plane of the virtual three-dimensional object RM 4  is visually recognized as an inclined plane recessed downward from the traveling road R by an optical illusion. 
     Specifically, the inner visible outline R 4   a  of the lane marking R 4  and the outer visible outline M 4   b  of the display element M 4  are located at the same position in the right-left direction. The inner visible outline R 4   a  and the outer visible outline M 4   b  have the same length and are parallel to each other. The inner visible outline M 4   a  and the outer visible outline M 4   b  of the display element M 4  are visually recognized as lines that are parallel to the lane marking R 4 . On the other hand, the lower visible outline M 4   c  and the upper visible outline M 4   d  of the display element M 4  are visually recognized as inclined lines. Thus, the entire display element M 4  is visually recognized as an inclined plane that is inclined downward toward the inner side. 
     Fifth Embodiment 
     In the fourth embodiment, the inner visible outline R 4   a  of the lane marking R 4  and the outer visible outline M 4   b  of the display element M 4  are located at the same position in the right-left direction. On the other hand, in the present embodiment illustrated in  FIG. 8 , the outer visible outline M 4   b  of the display element M 4  is visually recognized on the inner side relative to the inner visible outline R 4   a  of the lane marking R 4  in the right-left direction. That is, the display element M 4  and the lane marking R 4  are visually recognized with a gap CL present between the inner visible outline R 4   a  and the outer visible outline M 4   b  so that the display element M 4  and the lane marking R 4  are not superimposed on each other. Note that it is desired that the display elements M 1  to M 6  be visually recognized as being located in a region between the vehicle  10  and the lane marking R 4 . 
     Sixth Embodiment 
     In the fourth embodiment, when the plurality of lane markings R 1  to R 3 , R 4  to R 6  are formed in the traveling direction, as many display elements M 1  to M 3 , M 4  to M 6  as the lane markings R 1  to R 3 , R 4  to R 6  are displayed so as to be visually recognized. On the other hand, in the present embodiment illustrated in  FIG. 9 , a display element M 10  which extends in the traveling direction is displayed so as to be visually recognized with respect to the plurality of lane markings R 1  to R 3  which are arranged in the traveling direction, and a display element M 40  which extends in the traveling direction is displayed so as to be visually recognized with respect to the plurality of lane markings R 4  to R 6  which are arranged in the traveling direction. 
     According to this configuration, even when there is a deviation in the traveling direction in detection of the eye point position and detection of the lane markings R 1  to R 6 , the deviation hardly changes a view of the positions of the display elements M 10 , M 40  with respect to the lane markings R 1  to R 6 . Thus, a change in the view caused by a detection deviation is less likely to occur, and the robustness of the view with respect to a detection deviation can be improved. 
     Seventh Embodiment 
     In each of the above embodiments, the display positions of the display elements M 1  to M 6  are changed in response to the approach of the lane markings R 1  to R 6  to the vehicle  10  along with the travel of the vehicle. Thus, as the lane markings R 1  to R 6  approach the vehicle  10 , the display positions of the display elements M 1  to M 6  in the traveling direction are changed so that the display elements M 1  to M 6  are visually recognized as if the display elements M 1  to M 6  approached a driver. On the other hand, in the present embodiment, the display positions in the traveling direction are displayed in a fixed manner. However, the display positions are changed according to the positions of the lane markings R 1  to R 6  in the right-left direction. 
     In short, in the present embodiment, the generation device  42  generates a display image in such a manner that, even when the lane markings R 1  to R 6  approach the vehicle  10  as the vehicle  10  travels, a distance between a driver of the vehicle  10  and the display elements M 1  to M 6  is visually recognized as being kept constant. Accordingly, the display elements M 1  to M 6  do not move up and down. Thus, it is possible to reduce the possibility of the driver feeling uncomfortable with movement of the display elements M 1  to M 6 . 
     Eighth Embodiment 
     As described above in the first embodiment, the driving assistance device may fall into an inactive state. For example, the inactive state is a state unable to detect the lane markings R 1  to R 6  such as when the lane markings R 1  to R 6  are not present on the traveling road R, when the lane markings R 1  to R 6  partially peel off, or when there is a foreign substance such as sand on the lane markings R 1  to R 6 . On the other hand, even in an active state which is able to detect the lane markings R 1  to R 6 , the accuracy of detection may be deteriorated due to a degree of peeling off of the lane markings R 1  to R 6  or a degree of the foreign substance. 
     In the present embodiment, in an active state, the shape of each of the display elements M 10 , M 40  is varied according to the detection accuracy of the lane markings R 1  to R 6 . Specifically, the ECU  40  or the ECU  60  calculates a numerical value to be an index of the detection accuracy as a recognition rate. The generation device  42  generates a display image in such a manner that a virtual three-dimensional object having a steeper inclination angle of the display elements M 10 , M 40  is visually recognized as the calculated recognition rate becomes higher. The virtual three-dimensional object is visually recognized with virtual band-shaped objects formed of the two display elements M 10 , M 40  arranged side by side on the right and left sides by an optical illusion. 
     For example, the display elements M 10 , M 40  are displayed in a mode of  FIG. 10  when the recognition rate is equal to or more than a threshold and displayed in a mode of  FIG. 11  when the recognition rate is less than the threshold. These display elements M 10 , M 40  are the combination of  FIG. 9  and  FIG. 4 . That is, similarly to  FIG. 9 , each of the display elements M 10 , M 40  has a band shape extending in the traveling direction. Further, similarly to  FIG. 4 , each of the display elements M 10 , M 40  has a shape that is visually recognized as an inclined plane extending upward from the traveling road R by an optical illusion. 
     Further, each of the display elements M 10 , M 40  has a shape that is inclined in the direction of reducing the up-down direction height toward the vehicle  10  from the lane markings R 1  to R 6 , and has a larger inclination angle θ as the calculated recognition rate becomes higher. In other words, the visible outline of each of the display elements M 10 , M 40  forms a flat quadrangle. The inclination angle θ of the lower short side of the quadrangle (the lower visible outline M 40 C, M 10 C) with respect to the horizontal direction is made larger as the recognition rate becomes higher. Note that the inclination angle of each of the display elements M 10 , M 40  is constant regardless of the recognition rate. 
     As described above, according to the present embodiment, the shape of each of the display elements M 10 , M 40  is varied according to the detection accuracy of the lane markings R 1  to R 6 . This makes it easy to intuitively recognize the detection accuracy with which the driving assistance device is operating. 
     A steeper inclination angle θ gives a user a stronger impression that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1  to R 6 . In the present embodiment focusing on this point, the inclination angle θ of each of the display elements M 10 , M 40  is made steeper as the detection accuracy becomes higher. Thus, the detection accuracy of the lane markings R 1  to R 6  by the driving assistance device, that is, the probability that the driving assistance device functions to apply a steering force in the direction of preventing departure is represented by a difference in the inclination angle θ of each of the display elements M 10 , M 40 . This makes it easy to intuitively recognize the probability. 
     Ninth Embodiment 
     In the eighth embodiment, the inclination angle θ of each of the display elements M 10 , M 40  is made steeper as the detection accuracy becomes higher. On the other hand, in the present embodiment, the up-down direction height of each of the display elements M 10 , M 40  is made higher as the detection accuracy becomes higher. Specifically, when the recognition rate is equal to or more than a threshold, the up-down direction height of each of the display elements M 10 , M 40  is increased as illustrated in  FIG. 12 . That is, the length in the short side of each of the display elements M 10 , M 40  having a quadrangular shape is increased. On the other hand, when the recognition rate is lower than the threshold, the up-down direction height of each of the display elements M 10 , M 40  is reduced as illustrated in  FIG. 13 . 
     Further, each of the display elements M 10 , M 40  has a shape that is inclined in the direction of reducing the up-down direction height toward the vehicle  10  from the lane markings R 1  to R 6  and has a band shape extending in the traveling direction. The up-down direction height H of the band shape is set to be larger as the calculated recognition rate becomes higher. In other words, the length of each of the lower visible outlines M 40 C, M 10 C is made longer as the recognition rate becomes higher. Note that the inclination angle of each of the display elements M 10 , M 40  is set constant regardless of the recognition rate. 
     A higher height of each of the display elements M 10 , M 40  gives a user a stronger impression that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1  to R 6 . In the present embodiment focusing on this point, the up-down direction height of each of the display elements M 10 , M 40  is made higher as the detection accuracy becomes higher. Thus, the probability that the driving assistance device functions to apply a steering force in the direction of preventing departure is represented by a difference in the height of each of the display elements M 10 , M 40 . This makes it easy to intuitively recognize the probability. 
     Tenth Embodiment 
     In the ninth embodiment, each of the display elements M 10 , M 40  has a band shape extending in the traveling direction. On the other hand, in the present embodiment, similarly to the first embodiment, a plurality of display elements M 1 , M 2 , M 3 , M 3   a,  M 3   b,  M 4 , M 5 , M 6 , M 6   a,  M 6   b  are arranged side by side in the traveling direction. Further, an interval between the display elements M 1  to M 6   b  in the traveling direction is made shorter as the detection accuracy becomes higher. In other words, the number of display elements M 1  to M 6   b  is increased as the detection accuracy becomes higher. Specifically, when the recognition rate is equal to or more than a threshold, the interval is made shorter as illustrated in  FIG. 14  to increase the number of display elements M 1  to M 6   b.  On the other hand, when the recognition rate is lower than the threshold, the interval is made longer as illustrated in  FIG. 15  to reduce the number of display elements M 1  to M 6 . 
     A shorter interval between the display elements M 1  to M 6   b,  that is, a larger number of display elements M 1  to M 6   b  gives a user a stronger impression that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1  to R 6 . In the present embodiment focusing on this point, the interval between the display elements M 1  to M 6   b  is made shorter to increase the number of display elements M 1  to M 6   b  as the detection accuracy becomes higher. Thus, the probability that the driving assistance device functions to apply a steering force in the direction of preventing departure is represented by a difference in the interval between the display elements M 1  to M 6   b  and the number of display elements M 1  to M 6   b.  This makes it easy to intuitively recognize the probability. 
     Eleventh Embodiment 
     As described above in the first embodiment, a state unable to execute driving assistance due to circumstances such that the driving assistance device cannot detect the lane markings R 1  to R 6  is called an inactive state. Further, even in an active state in which the lane markings R 1  to R 6  are detected and driving assistance is executable, the driving assistance may be put on standby without starting the driving assistance when a user does not allow the start of the driving assistance. In the present embodiment, the shape of each of the display elements M 10 , M 40  is varied between such a standby time and the above execution time when the driving assistance is executed. The execution time corresponds to the standby state described in the first embodiment. 
     For example, during the execution time of the driving assistance device, as illustrated in  FIGS. 10 to 13 , the display elements M 10 , M 40  are displayed so as to be visually recognized as being inclined. On the other hand, during the standby time, as illustrated in  FIG. 16 , the display elements M 10 , M 40  are displayed so as to be visually recognized as not being inclined with an inclination angle θ of zero. In other words, the lower visible outlines M 40 C, M 10 C are made horizontal. Further, when the driving assistance device is in the inactive state, the display elements M 10 , M 40  are deleted so as not to be displayed. 
     As described above, according to the present embodiment, the shape of each of the display elements M 10 , M 40  is varied between the standby time and the execution time of the driving assistance device. This makes it easy to intuitively recognize whether the driving assistance device is in either the standby state or the execution state. 
     A steeper inclination angle θ or a higher up-down direction height of the display elements M 10 , M 40  gives a user a stronger impression that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1  to R 6 . In the present embodiment focusing on this point, the shape of each of the display elements M 10 , M 40  is varied in such a manner that a virtual three-dimensional object with a steeper inclination angle θ or a higher up-down direction height of the display elements M 10 , M 40  is visually recognized at the execution time than at the standby time. Specifically, during the standby time, the inclination angle θ is made zero to make the up-down direction height zero. Thus, it is possible to improve intuitive recognizability to recognize whether the current state is the standby state or the execution state. 
     Twelfth Embodiment 
     As described above, the ECU  60  illustrated in  FIG. 3  functions as the lane keeping assist device. That is, it is determined whether the vehicle  10  has departed from a part of the traveling road R between the lane markings R 1  to R 6  against the intension of a driver or whether the possibility of departure is high. Then, when an affirmative determination is made, the ECU  60  controls the operation of the steering device so as to apply a steering force in the direction of preventing the departure. 
     Further, in the present embodiment, the ECU  60  has an automatic offset function illustrated in  FIG. 17  and an automatic cornering function illustrated in  FIG. 18 . The automatic offset function automatically controls a traveling position in the vehicle width direction of the vehicle  10  so as to be temporarily changed from the current position within a range where the vehicle  10  does not depart from a part of the traveling road R between the pair of lane markings R 1 , R 4 . A control target includes the steering device, a brake device, and a travel drive output device. Concrete examples of the travel drive output device include an internal combustion engine and an electric motor. 
     The automatic offset function automatically and temporarily changes the traveling position, in a traveling section where an external object present outside the vehicle  10  and the vehicle  10  travel side by side, in the direction of expanding a distance in the vehicle width direction between the external object and the vehicle  10 . In the example of  FIG. 17 , the external object is a vehicle  10 A which travels in the same direction as the vehicle  10  on a lane adjacent to a lane where the vehicle  10  travels. In addition to the vehicle  10 A, concrete examples of the external object include a pedestrian and a signboard for traffic control which accompanies road works. 
     When the vehicle  10  travels along a curve, the automatic cornering function automatically and temporarily changes the traveling position in the direction of reducing a curve traveling radius within the range where the vehicle  10  does not depart from the part between the pair of lane markings R 1 , R 4 . In the example of  FIG. 18 , the traveling position in the vehicle width direction of the vehicle  10  is changed rightward during a period when the vehicle  10  travels rightward along a curve and changed leftward during a period when the vehicle  10  travels leftward along a curve. Accordingly, the curve traveling radius during curve traveling is reduced to reduce a centrifugal force acting on the vehicle  10  by the curve traveling. 
     In the following description, a current position in the vehicle width direction inside each pair of the lane markings R 1  to R 6  before operating the automatic offset function or the automatic cornering function is referred to as a reference position PA. In the traveling section of the vehicle  10 , a section where the vehicle  10  is going to travel at the reference position PA is referred to as a reference traveling section W 1 . A section where the vehicle  10  is going to travel at a position that is temporarily changed from the reference position PA, that is, an offset position PB 1  is referred to as a changed traveling section W 3 . A traveling section where the vehicle  10  moves from the reference position PA to the offset position PB 1  is referred to as a transient traveling section W 2 . A section where the vehicle  10  is going to return to the reference position PA by finishing the operation of the automatic offset function or the automatic cornering function is also referred to as the reference traveling section W 1 . 
     The display element M 10  includes reference display parts M 10 A, M 10 C and a change display part M 10 B 1  described below. The display element M 40  includes reference display parts M 40 A, M 40 C and a changed display part M 40 B 1 . The reference display parts M 10 A, M 40 A, M 10 C, M 40 C are visually recognized at positions associated with the reference traveling section W 1 . The changed display parts M 10 B 1 , M 40 B 1 , M 10 B 2 , M 40 B 2  are visually recognized at positions associated with the changed traveling section W 3 , W 31 , W 32 . 
     In the condition of  FIG. 17  in which the automatic offset function operates, in the lane markings R 1 , R 4  which are respectively located on the right and left sides of the vehicle  10 , the lane marking R 4  which is located at the side where the external object is present with respect to the vehicle  10  is referred to as an object side lane marking R 4 , and the lane marking R 1  which is located at the opposite side thereof is referred to as a counter object side lane marking R 1 . In the reference display parts M 10 A, M 40 A, M 10 C, M 40 C, the reference display parts M 40 A, M 40 C which are visually recognized at positions associated with the object side lane marking R 4  are referred to as object side reference display parts M 40 A, M 40 C. The reference display parts M 10 A, M 10 C which are visually recognized at positions associated with the counter object side lane marking R 1  are referred to as counter objet side reference display parts M 10 A, M 10 C. In the changed display parts M 10 B 1 , M 40 B 1 , the changed display part M 40 B 1  which is visually recognized at a position associated with the object side lane marking R 4  is referred to as an object side changed display part M 40 B 1 , and the changed display part M 10 B 1  which is visually recognized at a position associated with the counter object side lane marking R 1  is referred to as a counter object side changed display part  40 C. 
     The generation device  42  generates an image in such a manner that each of the reference display parts M 10 A, M 40 A, M 10 C, M 40 C and each of the changed display parts M 10 B 1 , M 40 B 1  are visually recognized as virtual three-dimensional objects having different shapes. Specifically, the image is generated in such a manner that, in the reference display parts M 10 A, M 40 A, M 10 C, M 40 C, an inclination angle θ of the objet side reference display parts M 40 A, M 40 C and an inclination angle θ of the counter objet side reference display parts M 10 A, M 10 C are visually recognized as being equal to each other. Further, the image is generated in such a manner that, in the changed display parts M 10 B 1 , M 40 B 1 , an inclination angle θ of the object side changed display part M 40 B 1  and an inclination angle θ of the counter object side changed display part M 10 B 1  are visually recognized as being different from each other. 
     In the condition of  FIG. 18  in which the automatic cornering function operates, in the lane markings R 1 , R 4  which are respectively located on the right and left sides of the vehicle  10 , a lane marking that is located at the side where the curve traveling radius is large with respect to the vehicle  10  is referred to as an outer lane marking, and a lane marking that is located at the opposite side thereof is referred to as an inner lane marking. In the reference display parts M 10 A, M 40 A, M 10 C, M 40 C, the reference display parts M 40 A, M 40 C which are visually recognized at positions associated with the outer lane marking are referred to as outer reference display parts M 40 A, M 40 C. The reference display parts M 10 A, M 10 C which are visually recognized at positions associated with the inner lane marking are referred to as inner reference display parts M 10 A, M 10 C. In the changed display parts M 10 B 1 , M 40 B 1 , M 10 B 2 , M 40 B 2 , the changed display parts M 40 B 1 , M 10 B 2  which are visually recognized at positions associated with the outer lane marking are referred to as outer changed display parts M 40 B 1 , M 10 B 2 . The changed display parts M 10 B 1 , M 40 B 2  which are visually recognized at positions associated with the inner lane marking are referred to as inner changed display parts M 10 B 1 , M 40 B 2 . 
     The generation device  42  generates the image in such a manner that each of the reference display parts M 10 A, M 40 A, M 10 C, M 40 C and each of the changed display parts M 10 B 1 , M 40 B 1 , M 10 B 2 , M 40 B 2  are visually recognized as virtual three-dimensional objects having different shapes. Specifically, the image is generated in such a manner that, in the reference display parts M 10 A, M 40 A, M 10 C, M 40 C, an inclination angle θ of the outer reference display parts M 40 A, M 40 C and an inclination angle θ of the inner reference display parts M 10 A, M 10 C are visually recognized as being equal to each other. Further, the image is generated in such a manner that, in the changed display parts M 10 B 1 , M 40 B 1 , an inclination angle θ of the outer changed display parts M 40 B 1 , M 10 B 2  and an inclination angle θ of the inner changed display part M 10 B 1 , M 40 B 2  are visually recognized as being different from each other. 
     First, a concrete example of display according to the automatic offset function will be described. 
     For example, when the automatic offset function is operated as illustrated in  FIG. 17 , the shapes of the display elements M 10 , M 40  are set as illustrated in  FIG. 19 . In the condition illustrated in  FIG. 17 , the traveling position in the vehicle width direction of the vehicle  10  is changed from the reference position PA to the offset position PB 1  during a period when the vehicle  10  passes the vehicle  10 A. After the vehicle  10  passes the vehicle  10 A, the traveling position is then changed from the offset position PB 1  to the current position PA. 
     Further, the reference display parts M 10 A, M 40 A, M 10 C, M 40 C are visually recognized as if the inclination angle θ of the object side reference display parts M 40 A, M 40 C and the inclination angle θ of the counter object side reference display parts M 10 A, M 10 C were equal to each other. As a result, as illustrated in  FIG. 20 , the object side reference display part M 40 A, M 40 C and the counter object side reference display part M 10 A, M 10 C are visually recognized as if the object side reference display part M 40 A, M 40 C and the counter object side reference display part M 10 A, M 10 C were three-dimensional objects that are inclined with the same inclination angle θ by an optical illusion. 
     On the other hand, the changed display parts M 10 B 1 , M 40 B 1  are visually recognized as if the inclination angle θ of the object side changed display part M 40 B 1  were larger than the inclination angle θ of the counter object side changed display part M 10 B 1 . As a result, as illustrated in  FIG. 21 , the object side changed display part M 40 B 1  and the counter object side changed display part M 10 B 1  are visually recognized as if the object side changed display part M 40 B 1  and the counter object side changed display part M 10 B 1  were three-dimensional objects that are inclined with different inclination angles θ by an optical illusion. Specifically, the object side changed display part M 40 B 1  is visually recognized as if object side changed display part M 40 B 1  were a three-dimensional object that exists with a steeper inclination angle than the counter object side changed display part M 10 B 1  by an optical illusion. 
     In the example of  FIG. 17 , the reference position PA is a central part between the object side lane marking R 4  and the counter object side lane marking R 1 . The offset positon PB 1  is a position that is more distant from the object side lane marking than the reference position PA is. 
     Next, a concrete example of display according to the automatic cornering function will be described. 
     For example, when the automatic cornering function is operated as illustrated in  FIG. 18 , the shapes of the display elements M 10 , M 40  are set as illustrated in  FIG. 22 . In the condition illustrated in  FIG. 18 , the traveling position in the vehicle width direction of the vehicle  10  is changed from the reference position PA to a right position (the offset position PB 1 ) when the vehicle  10  travels rightward along a curve and changed from the reference position PA to a left position (an offset position PB 2 ) when the vehicle  10  travels leftward along a curve. 
     Further, the reference display parts M 10 A, M 40 A, M 10 C, M 40 C are visually recognized as if the inclination angle θ of the outer reference display parts M 40 A, M 40 C and the inclination angle θ of the inner reference display parts M 10 A, M 10 C were equal to each other, and, as a result, visually recognized as illustrated in  FIG. 20  by an optical illusion. 
     On the other hand, the changed display parts M 10 B 1 , M 40 B 1  associated with the changed traveling section W 31  where the vehicle  10  travels along the right curve are visually recognized as if the inclination angle θ of the outer changed display part M 40 B 1  were larger than the inclination angle θ of the inner changed display part M 10 B 1 , and, as a result, visually recognized as illustrated in  FIG. 21  by an optical illusion. Specifically, the outer changed display part M 40 B 1  is visually recognized as if the outer changed display part M 40 B 1  were a three-dimensional object that exists with a steeper inclination angle than the inner changed display part M 10 B 1  by an optical illusion. 
     Further, the changed display parts M 10 B 2 , M 40 B 2  associated with the changed traveling section W 32  where the vehicle  10  travels along the left curve are visually recognized as if the inclination angle θ of the outer changed display part M 10 B 2  were larger than the inclination angle θ of the inner changed display part M 40 B 2 , and, as a result, visually recognized as illustrated in  FIG. 23  by an optical illusion. Specifically, the outer changed display part M 10 B 2  is visually recognized as if the outer changed display part M 10 B 2  were a three-dimensional object that exists with a steeper inclination angle than the inner changed display part M 40 B 2  by an optical illusion. 
     As described above, according to the present embodiment, the generation device  42  generates the display image in such a manner that each of the reference display parts M 10 A, M 10 C, M 40 A, M 40 C and each of the changed display parts M 10 B 1 , M 40 B 1  are visually recognized as virtual three-dimensional objects having different shapes. 
     According to this configuration, when the automatic offset function or the automatic cornering function is operated to automatically change the traveling position from the current position (reference position PA) to the offset position PB 1 , PB 2 , the reference display part and the changed display part can be visually recognized as different shapes prior to the change. Further, the reference display part is visually recognized at a position associated with the reference traveling section W 1 , and the changed display part is visually recognized at a position associated with the changed traveling section W 3 , W 31 , W 32 . This makes it easy for a user who makes such a visual recognition to intuitively grasp that automatic control is performed so as to change the traveling position in the changed traveling section W 3 , W 31 , W 32 . Thus, prior to automatically offset-moving the traveling position by the automatic offset function or the automatic cornering function, it is possible to allow a user to intuitively grasp that the automatic control is going to be performed. 
     Further, in the present embodiment, when the traveling position is automatically offset-moved by the automatic offset function, the generation device  42  generates the display image in such a manner that the object side changed display part M 40 B 1  and the object side reference display part M 40 A are visually recognized as virtual three-dimensional objects having different shapes. 
     According to this configuration, one of the pair of right and left display parts, the one being located at the side where the external object is present, is changed. That is, the object side reference display part M 40 A associated with the reference traveling section W 1  and the object side changed display part M 40 B 1  associated with the changed traveling section W 3  can be visually recognized as different shapes. This makes it easy for a user who makes such a visual recognition to intuitively grasp whether the external object is present on either the right or left side, that is, whether the offset movement is performed to either the right or left side. Thus, prior to automatically offset-moving the traveling position by the automatic offset function, it is possible to allow a user to intuitively grasp that the offset movement is going to be performed. 
     A steeper inclination angle θ of the display elements M 10 , M 40  gives a user a stronger impression that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1 , R 4 . In the present embodiment focusing on this point, the generation device  42  generates the display image in such a manner that the object side changed display part M 40 B 1  is visually recognized as a virtual three-dimensional object with a steeper inclination angle than the object side reference display part M 40 A. Thus, prior to automatically offset-moving the traveling position by the automatic offset function, it is possible to allow a user to intuitively grasp a direction of the offset movement, that is, a direction separating from the external object. 
     Further, in the present embodiment, the generation device  42  generates the display image in such a manner that the counter object side changed display part M 10 B 1  and the counter object side reference display part M 10 A are visually recognized as virtual three-dimensional objects having different shapes. That is, making the shapes of display parts different from each other between the reference traveling section W 1  and the changed traveling section W 3 , W 31 , W 32  is also applied to the counter object side display parts in addition to the object side display parts. Thus, it is possible to facilitate the above effect of allowing a user to intuitively grasp that the traveling position is going to be automatically offset-moved. 
     Further, in the present embodiment, the generation device  42  generates the display image in such a manner that the counter object side changed display part M 10 B 1  is visually recognized as a virtual three-dimensional object with a gentler inclination angle than the inclination angle of the counter object side reference display part M 10 A. Thus, at the counter object side, an impression given to a user that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1 , R 4  at a changed position becomes weak. Thus, prior to automatically offset-moving the traveling position by the automatic offset function, it is possible to facilitate allowing a user to intuitively grasp a direction of the offset movement, that is, a direction separating from the external object. 
     Further, in the present embodiment, when the traveling position is automatically moved by the automatic cornering function, the generation device  42  generates the display image in such a manner that the outer changed display part M 40 B 1  and the outer reference display part M 40 A are visually recognized as virtual three-dimensional objects having different shapes. 
     Accordingly, one of the pair of right and left display parts, the one being located at the side having a larger curve traveling radius, is changed. That is, the outer reference display part M 40 A associated with the reference traveling section W 1  and the outer changed display part M 40 B 1  associated with the changed traveling section W 31  can be visually recognized as different shapes. This makes it easy for a user who makes such a visual recognition to intuitively grasp whether the traveling position is moved to either the right or left side. Thus, prior to automatically moving the traveling position by the automatic cornering function, it is possible to allow a user to intuitively grasp the movement. 
     A steeper inclination angle θ of the display elements M 10 , M 40  gives a user a stronger impression that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1 , R 4 . In the present embodiment focusing on this point, the generation device  42  generates the display image in such a manner that the outer changed display part M 40 B 1  is visually recognized as a virtual three-dimensional object with a steeper inclination angle than the outer reference display part M 40 A. Thus, prior to automatically moving the traveling position by the automatic cornering function, it is possible to allow a user to intuitively grasp a direction of the movement. 
     Further, in the present embodiment, the generation device  42  generates the display image in such a manner that the inner changed display part M 10 B 1  and the inner reference display part M 10 A are visually recognized as virtual three-dimensional objects having different shapes. That is, making the shapes of display parts different from each other between the reference traveling section W 1  and the changed traveling section W 3 , W 31 , W 32  is also applied to the inner display parts in addition to the outer display parts. Thus, it is possible to facilitate the above effect of allowing a user to intuitively grasp that the traveling position is going to be automatically moved. 
     Further, in the present embodiment, the generation device  42  generates the display image in such a manner that the inner changed display part M 10 B 1  is visually recognized as a virtual three-dimensional object with a gentler inclination angle than the inclination angle of the inner reference display part M 10 A. Thus, at the inner side, an impression given to a user that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1 , R 4  at a changed position becomes weak. Thus, prior to automatically moving the traveling position by the automatic cornering function, it is possible to facilitate allowing a user to intuitively grasp a direction of the movement. 
     Thirteenth Embodiment 
     In the twelfth embodiment, the display part associated with the reference traveling section W 1  and the display part associated with the changed traveling section W 3  are visually recognized as having different inclination angles θ. On the other hand, in the present embodiment, the display part associated with the reference traveling section W 1  and the display part associated with the changed traveling section W 3  are visually recognized as having different up-down direction heights. 
     Specifically, when the automatic offset function is operated as illustrated in  FIG. 17 , the shapes of the display elements M 10 , M 40  are set as illustrated in  FIG. 24 . 
     The reference display parts M 10 A, M 40 A, M 10 C, M 40 C are visually recognized as if the up-down direction height of the object side reference display parts M 40 A, M 40 C were equal to the up-down direction height of the counter object side reference display parts M 10 A, M 10 C. As a result, as illustrated in  FIG. 20 , in the objet side reference display parts M 40 A, M 40 C and the counter object side reference display parts M 10 A, M 10 C, the display parts are visually recognized as if the object side display part and the counter object side display part were three-dimensional objects having the same up-down direction height by an optical illusion. 
     On the other hand, the changed display parts M 10 B 1 , M 40 B 1  are visually recognized as if the up-down direction height of the object side changed display part M 40 B 1  were larger than the up-down direction height of the counter object side changed display part M 10 B 1 . As a result, as illustrated in  FIG. 25 , the display parts are visually recognized as if the object side display part were a three-dimensional object having a higher up-down direction height H than the counter object side display part by an optical illusion. Note that the inclination angle θ is set to be equal between the object side and the counter object side at both the reference position and the changed position. 
     Next, a concrete example of display according to the automatic cornering function will be described. For example, when the automatic cornering function is operated as illustrated in  FIG. 18 , the shapes of the display elements M 10 , M 40  are set as illustrated in  FIG. 26 . 
     The reference display parts M 10 A, M 40 A, M 10 C, M 40 C are visually recognized as if the up-down direction height H of the outer reference display parts M 40 A, M 40 C were equal to the up-down direction height of the inner reference display parts M 10 A, M 10 C, and, as a result, visually recognized as illustrated in  FIG. 20  by an optical illusion. 
     On the other hand, the changed display parts M 10 B 1 , M 40 B 1  associated with the changed traveling section W 31  where the vehicle  10  travels along the right curve are visually recognized as if the up-down direction height H of the outer changed display part M 40 B 1  at the outer side of curve traveling were larger than the up-down direction height H of the inner changed display part M 10 B 1  at the inner side of curve traveling, and, as a result, visually recognized as illustrated in  FIG. 25  by an optical illusion. 
     Further, the changed display parts M 10 B 2 , M 40 B 2  associated with the changed traveling section W 32  where the vehicle  10  travels along the left curve are visually recognized as if the up-down direction height H of the outer changed display part M 10 B 2  at the outer side of curve traveling were larger than the up-down direction height H of the inner changed display part M 40 B 2  at the inner side of curve traveling, and, as a result, visually recognized as illustrated in  FIG. 27  by an optical illusion. 
     As described above, according to the present embodiment, similarly to the twelfth embodiment, each of the reference display parts M 10 A, M 10 C, M 40 A, M 40 C and each of the changed display parts M 10 B 1 , M 40 B 1  are visually recognized as virtual three-dimensional objects having different shapes. Further, the object side changed display part M 40 B 1  and the object side reference display part M 40 A are visually recognized as virtual three-dimensional objects having different shapes. Further, the outer changed display part M 40 B 1  and the outer reference display part M 40 A are visually recognized as virtual three-dimensional objects having different shapes. Thus, prior to automatically moving the traveling position by the automatic offset function or the automatic cornering function, it is possible to allow a user to intuitively grasp that the automatic control is going to be performed. 
     A higher up-down direction height H of the display elements M 10 , M 40  gives a user a stronger impression that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1 , R 4 . In the present embodiment focusing on this point, the generation device  42  generates the display image in such a manner that the object side changed display part M 40 B 1  is visually recognized as a virtual three-dimensional object with a higher up-down direction height H than the object side reference display part M 40 A. Thus, prior to automatically offset-moving the traveling position by the automatic offset function, it is possible to allow a user to intuitively grasp a direction of the offset movement, that is, a direction separating from the external object. Further, the generation device  42  generates the display image in such a manner that the outer changed display part M 40 B 1  is visually recognized as a virtual three-dimensional object with a higher up-down direction height H than the outer reference display part M 40 A. Thus, prior to automatically moving the traveling position by the automatic cornering function, it is possible to allow a user to intuitively grasp a direction of the movement. 
     Further, in the present embodiment, the generation device  42  generates the display image in such a manner that the counter object side changed display part M 10 B 1  is visually recognized as a virtual three-dimensional object with a lower up-down direction height H than the up-down direction height H of the counter object side reference display part M 10 A. Thus, at the counter object side, an impression given to a user that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1 , R 4  at a changed position becomes weak. Thus, prior to automatically offset-moving the traveling position by the automatic offset function, it is possible to facilitate allowing a user to intuitively grasp a direction of the offset movement, that is, a direction separating from the external object. Further, the generation device  42  generates the display image in such a manner that the inner changed display part M 10 B 1  is visually recognized as a virtual three-dimensional object with a lower up-down direction height H than the up-down direction height H of the inner reference display part M 10 A. Thus, at the inner side of curve traveling, an impression given to a user that the vehicle  10  is automatically controlled so as not to depart from the lane markings R 1 , R 4  at a changed position becomes weak. Thus, prior to automatically moving the traveling position by the automatic cornering function, it is possible to facilitate allowing a user to intuitively grasp a direction of the movement. 
     Other Embodiments 
     Although the preferred embodiments of the disclosure have been described above, the disclosure is not limited at all to the above embodiments and can be modified in various manners as exemplified below. Not only combinations of parts that are specifically and clearly stated that the combinations are possible in each of the embodiments, but also partial combinations of the embodiments are also possible even if not clearly stated unless otherwise the combinations constitute a hindrance. 
     The right and left display elements M 1  to M 6  may be displayed in different modes when the driving assistance device applies a steering force in the direction of preventing departure from the lane markings R 1  to R 6  to make it easy to intuitively recognize the contents of the operation of the driving assistance device. For example, when the vehicle  10  has departed from the left side lane markings R 4 , R 5 , R 6  of  FIG. 2  or when the possibility of departure is a predetermined possibility or more, the driving assistance device applies a steering force in the direction of moving the traveling direction of the vehicle  10  rightward. In this case, the left side display elements M 4 , M 5 , M 6  are caused to flash or a display color thereof is changed so that the left side display elements M 4 , M 5 , M 6  are more emphasized than the right side display elements M 1 , M 2 , M 3 . 
     Further, the degree of departure or the degree of the possibility of departure may be represented by the inclination angle of the display elements M 1  to M 6 . That is, the inclination angle may be made steeper as the amount of departure from the lane markings R 1  to R 6  becomes larger, or the possibility of departure becomes higher. 
     The driving assistance device (ECU  60 ) illustrated in  FIG. 3  assists driving by applying a steering force. When the vehicle  10  has departed from the lane markings R 1  to R 6  or when the possibility of departure is a predetermined possibility or more, an alarm sound or an alarm voice may be output from a speaker. 
     In the first embodiment, the display image is generated in such a manner that, corresponding to the lane markings R 1  to R 6  arranged at a predetermined pitch in the traveling direction of the traveling road R, the plurality of display elements M 1  to M 6  are also visually recognized as being arranged at the predetermined pitch in the traveling direction. Alternatively, the display image may be generated in such a manner that the display elements M 1  to M 6  are visually recognized at a pitch different from the pitch of the traveling road R. 
     When there is a pedestrian who has a predetermined degree of possibility of collision with the vehicle  10  or more, it is desired to prohibit the display of the display elements M 1  to M 6  to facilitate concentration of an attention to the pedestrian. Further, when the lane markings R 1  to R 6  are not detected, it is desired to prohibit the display of the display elements M 1  to M 6 . 
     The color of the display elements M 1  to M 6  may be changed according to the color of the lane markings R 1  to R 6  or the traveling road R detected by the front camera  50 . For example, the color of the display elements M 1  to M 6  may be changed to an inconspicuous color to reduce an uncomfortable feeling with the display elements M 1  to M 6 . 
     In each of the above embodiments, the inner region surrounded by the visible outlines M 4   a,  M 4   b,  M 4   c,  M 4   d  of each of the display elements M 1  to M 6  is displayed in a predetermined color, and each of the visible outlines M 4   a,  M 4   b , M 4   c,  M 4   d  (contours) and the inner region are displayed in different colors. Alternatively, each of the visible outlines M 4   a,  M 4   b,  M 4   c,  M 4   d  and the inner region may be displayed in the same color. In other words, the display of the visible outlines M 4   a,  M 4   b,  M 4   c,  M 4   d  may be deleted so as to display only the inner region. The transmittance of the display color of the inner region may be set to be low enough to make a superimposed part between the traveling road R and the display elements M 1  to M 6  visually unrecognizable or may be set to be high enough to make the superimposed part visually recognizable. 
     In the twelfth and thirteenth embodiments, the display image is generated in such a manner that the counter object side reference display part M 10 A and the counter object side changed display part M 10 B 1  are visually recognized as virtual three-dimensional objects having different shapes. Alternatively, the display image may be generated in such a manner that the counter object side reference display part M 10 A and the counter object side changed display part M 10 B 1  are visually recognized as virtual three-dimensional objects having the same shape. That is, the counter object side changed display part M 10 B 1  may not be visually recognized as having a gentle inclination angle θ or having a low up-down direction height H. Similarly, the display image may be generated in such a manner that the inner reference display part M 10 A and the inner changed display part M 10 B 1  are visually recognized as virtual three-dimensional objects having the same shape. 
     In the twelfth and thirteenth embodiments, the reference display part and the changed display part are visually recognized as having different inclination angles or different up-down direction heights. Alternatively, the reference display part and the changed display part may be visually recognized differently from each other by other modes. Further, the reference display part and the changed display part may be displayed in different colors. Further, the object side changed display part M 40 B 1  and the outer changed display part M 40 B 1  may be displayed in a color different from the color of the other display parts. 
     In the eighth to tenth embodiments, the display elements are visually recognized as having different inclination angles or different up-down direction heights according to the recognition rate. Alternatively, the shapes of the display elements may be made different from each other according to the recognition rate by other modes. Further, the colors of the display elements may be made different from each other according to the recognition rate. 
     In the example of  FIG. 1 , light of the display image emitted from the HUD  30  is projected on the reflecting sheet  12   a.  Alternatively, the reflecting sheet  12   a  may be omitted, and light of the display image may be directly projected on the windshield  12 . In such a mode, the windshield  12  forms the projection area  12   p.  Further, a light transmissive projection member which is a separate body from the windshield  12  may be disposed in front of the driver&#39;s seat, and light of the display image may be projected on the projection member. In such a mode, the face of the projection member facing the driver forms the projection area  12   p.  In the example illustrated in  FIG. 1 , the HUD  30  which emits light of the display image from the liquid crystal panel  31  is employed. Alternatively, an HUD that emits light of the display image by performing scanning with a laser beam instead of the liquid crystal panel  31  may be employed. 
     Means and/or a function of the ECU  40  (control device) can be provided by a software recorded in a substantial storage medium and a computer that executes the software, a software only, a hardware only, or a combination thereof. For example, when the control device is provided by a circuit as a hardware, the control device can be provided by a digital circuit including many logic circuits or an analog circuit. 
     While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. The present disclosure is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.