Lane detection apparatus and lane detection method

A lane detection apparatus that detects a lane along which a vehicle travels includes: a side detection portion that detects a side lane division existing on a side of the vehicle; a front detection portion that detects a front lane division existing in front of the vehicle; a traveling speed detection portion that detects a traveling speed of the vehicle; a position correction portion that corrects a position of the front lane division based on a time lag of imaging timing between the side vehicle onboard camera and the front vehicle onboard camera, and the traveling speed; a checkup portion that compares a position of the side lane division and a corrected position of the front lane division; and an output portion that outputs the position of the side lane division as a detection result.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is based on Japanese Patent Application No. 2014-151052 filed on Jul. 24, 2014, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a technology detecting a travelling lane on the basis of analysis of an image captured by a vehicle onboard camera.

BACKGROUND ART

A road for a traveling vehicle is divided by a white line or other types of marks into multiple lanes. A vehicle is required to travel within a lane. A vehicle is equipped with an vehicle onboard camera for detecting a lane division (such as a white line, a curbstone, and a center divider) beforehand based on a front image captured by the vehicle onboard camera to give a warning to a driver when the vehicle is to deviate from the lane against intension of the driver.

When a vehicle travels along a lane, a lane division (such as a white line) which is detected on a front of the vehicle passes through the side of the vehicle. Accordingly, there is proposed a technology which analyzes a side image captured from a vehicle to detect a white line or the like existing on the side of the vehicle, instead of detecting a white line or the like based on a front image (Patent Literature 1). Since the white line or the like existing on the side of the vehicle is located close to the vehicle, it is supposed that the white line or the like is detectable with higher positional accuracy in comparison with the white line or the like existing in front of the vehicle.

The inventor of the present application has found the following. The technology for detecting a white line or the like based on analysis of a side image captured from a vehicle may erroneously detect a white line or the like. In this case, it may be difficult to secure sufficient reliability.

An image conventionally used for detecting a white line or the like is a relatively far image in the traveling direction (a front direction) of the vehicle, and the detected white line or the like is located far away from the vehicle. By contrast, a white line or the like contained in a side image is located close to the vehicle. The position of the white line or the like contained in the front image does not widely shift within the image even during high-speed traveling of the vehicle. However, the position of the white line or the like in the side image may shift widely and rapidly. Accordingly, the white line or the like contained in the side image may become difficult to track during traveling of the vehicle. Moreover, a situation that a shadow of the vehicle, a connection of the road surface or the like appears in the side image in parallel with the white line or the like may occur. In this case, tracking of the white line or the like may be difficult, and distinction between the white line or the like and the objects other than the white line or the like may also become difficult. During detection of the white line or the like from the side image, the white line or the like may be lost sight, an object other than the white line may be erroneously detected, and it may be difficult to secure sufficient reliability.

PRIOR ART LITERATURE

Patent Literature

Patent Literature 1: JP 2010-79573 A

SUMMARY OF INVENTION

It is an object of the present disclosure to provide a technology enabling to detect a lane division with high reliability based on a side image captured from a vehicle.

According to one aspect of the present disclosure, a lane detection apparatus mounted on a vehicle including a plurality of vehicle onboard cameras and detecting a lane along which the vehicle travels, based on analysis of images captured by the plurality of vehicle onboard cameras, is provided. The lane detection apparatus includes: a side detection portion that detects a side lane division existing on a side of the vehicle, based on an image captured by a side vehicle onboard camera imaging an area around the side of the vehicle; a front detection portion that detects a front lane division existing in front of the vehicle, based on an image captured by a front vehicle onboard camera imaging an area around the front of the vehicle; a traveling speed detection portion that detects a traveling speed of the vehicle; a position correction portion that corrects a position of the front lane division based on a time lag of imaging timing between the side vehicle onboard camera and the front vehicle onboard camera, and the traveling speed; a checkup portion that compares a position of the side lane division and a corrected position of the front lane division; and an output portion that outputs the position of the side lane division as a detection result when the position of the side lane division and the corrected position of the front lane division are matched with each other.

According to another aspect of the present disclosure, a lane detection method that detects a lane along which a vehicle travels, based on analysis of images captured by a plurality of vehicle onboard cameras, is provided. The lane detection method includes: a side detection step that detects a side lane division existing on a side of the vehicle, based on an image captured by a side vehicle onboard camera imaging an area around the side of the vehicle; a front detection step that detects a front lane division existing in front of the vehicle, based on an image captured by a front vehicle onboard camera imaging an area around the front of the vehicle; a traveling speed detection step that detects a traveling speed of the vehicle; a position correction step that corrects a position of the front lane division based on a time lag of imaging timing between the side vehicle onboard camera and the front vehicle onboard camera, and the traveling speed; a checkup step that comparing a position of the side lane division and a corrected position of the front lane division; and an output step that outputs the position of the side lane division as a detection result when the position of the side lane division and the corrected position of the front lane division are matched with each other.

According to the lane detection apparatus and the lane detection method of the present disclosure, a lane division is detectable with high reliability based on a side image captured from a vehicle.

DESCRIPTION OF EMBODIMENTS

FIG. 1illustrates a vehicle1equipped with a lane detection apparatus100. As illustrated inFIG. 1, the vehicle1includes a left side camera10L which images an area (a surround of the left side) around the left side from the vehicle1, and a right side camera10R which images an area (a surround of the right side) around the right side, a front camera11F which images an area (a surround of the front) around the front from the vehicle1, a rear camera11B which images an area (a surround of the rear) around the rear, and a vehicle speed sensor14which detects a traveling speed of the vehicle1, in addition to the lane detection apparatus100.

In the present embodiment, the left side camera10L and the right side camera10R correspond to a side vehicle onboard camera. The front camera11F corresponds to a front vehicle onboard camera. The rear camera11B corresponds to a rear vehicle onboard camera.

Images captured by the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B, and an output from the vehicle speed sensor14are input to the lane detection apparatus100to detect a lane by a method described below. The lane detection apparatus100outputs information on the detected lane to a vehicle control apparatus200.

The vehicle control apparatus200gives a warning to a driver, or assists the driver to operate a steering wheel in a direction for maintaining the vehicle within the lane, for example, when the vehicle control apparatus200determines based on the received information that the driver is to deviate from the lane against the intention of the driver.

FIG. 2schematically illustrates an internal configuration of the lane detection apparatus100of the present embodiment. As illustrated inFIG. 2, the lane detection apparatus100of the present embodiment includes a side detection portion101, a front detection portion102, a rear detection portion103, a traveling speed detection portion104, a front correction portion105, a rear correction portion106, a time lag acquisition portion107, a time lag memory portion108, a checkup portion109, and an output portion110.

Incidentally, these ten “portions” in this context are only abstractions provided in the interior of the lane detection apparatus100, and classified in view of functions of the lane detection apparatus100for analyzing images captured by the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B during detection of a lane. It should not be understood that the lane detection apparatus100is physically sectioned into ten portions. Accordingly, these “portions” may be realized as a computer program executed by a CPU, an electronic circuit including an LSI and a memory, or a combination of these program and electronic circuit.

The side detection portion101acquires an image of the left side of the vehicle1from the left side camera10L, and an image of the right side of the vehicle1from the right side camera10R. The side detection portion101analyzes the captured image of the left side of the vehicle1to detect a lane division such as a white line or the like (hereinafter referred to as a lane division) existing on the left side of the vehicle1. The side detection portion101analyzes the captured image of the right side of the vehicle1to detect a lane division existing on the right side of the vehicle1.

The lane division detected on the left side or the right side of the vehicle1corresponds to a side lane division of the present disclosure.

The front detection portion102acquires an image of the front of the vehicle1from the front camera11F, and analyzes the acquired image to detect a lane division existing in front of the vehicle1.

The rear detection portion103acquires an image of the rear of the vehicle1from the rear camera11B, and analyzes the acquired image to detect a lane division existing in the rear of the vehicle1.

The lane division detected in front of the vehicle1corresponds to a front lane division. The lane division detected in the rear of the vehicle1corresponds to a rear lane division.

The time lag acquisition portion107acquires information on time lags of imaging timing between the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B at a start of the respective cameras. The acquired information on the time lags is stored in the time lag memory portion108.

The traveling speed detection portion104acquires, from the vehicle speed sensor14, a traveling speed of the vehicle1at the time of imaging by the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B. To be precise, each of the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B captures an image at different timing. However, based on consideration that the traveling speed of the vehicle1does not greatly changes during the time lags of imaging timing between the cameras, the traveling speed detection portion104acquires the traveling speed at the imaging timing of any one of the cameras from the vehicle speed sensor14.

The front correction portion105corrects the position of the lane division (such as white line) detected by the front detection portion102while considering the time lag of imaging timing of the front camera11F from imaging timing of the left side camera10L, or considering the time lag of imaging timing of the front camera11F from imaging timing of the right side camera10R.

For correcting the time lag of imaging timing of the front camera11F from imaging timing the left side camera10L, information on the time lag between the left side camera10L and the front camera11F is read from the time lag memory portion108, and corrected in consideration of the traveling speed detected by the traveling speed detection portion104. For correcting the time lag of imaging timing of the front camera11F from imaging timing the right side camera10R, information on the time lag between the right side camera10R and the front camera11F is read from the time lag memory portion108, and corrected in consideration of the traveling speed detected by the traveling speed detection portion104.

The rear correction portion106corrects the position of the lane division detected by the rear detection portion103while considering the time lag of imaging timing of the rear camera11B from imaging timing of the left side camera10L, or considering the time lag of imaging timing of the rear camera11B from imaging timing the right side camera10R.

For correcting the time lag of imaging timing of the rear camera11B from imaging timing the left side camera10L, information on the time lag between the left side camera10L and the rear camera11B is read from the time lag memory portion108, and corrected in consideration of the traveling speed detected by the traveling speed detection portion104. For correcting the time lag of imaging timing of the rear camera11B from imaging timing the right side camera10R, information on the time lag between the right side camera10R and the rear camera11B is read from the time lag memory portion108, and corrected in consideration of the traveling speed detected by the traveling speed detection portion104.

The front correction portion105and the rear correction portion106of the present embodiment correspond to a position correction portion.

The checkup portion109compares the position of the lane division detected by the side detection portion101, the position of the lane division corrected by the front correction portion105, and the position of the lane division corrected by the rear correction portion106, so that the checkup portion109determines whether these positions of the lane divisions are matched with each other.

When it is determined that the positions of the lane divisions are alignment each other, the position of the lane division detected by the side detection portion101is output to the vehicle control apparatus200as a lane detection result.

(Basic Principle to Detect Side Lane Division of Vehicle1)

FIG. 3illustrates an example of the vehicle equipped with the foregoing lane detection apparatus100in a state of traveling along a lane divided by lane divisions (the white lines2in this example). Each of the front camera11F, the rear camera11B, the left side camera10L, and the right side camera10R includes a wide-angle lens such as a so-called fish-eye lens. The front camera11F images an area around the front of the vehicle1, while the rear camera11B images an area around the rear of the vehicle1. Similarly, the left side camera10L images an area around the left side of the vehicle1, while the right side camera10R images an area around the right side of the vehicle1.

Accordingly, the white lines2on the front, rear, left side, and right side of the vehicle1are detectable based on analysis of images captured by the four vehicle onboard cameras.

FIG. 4Aillustrates an example of an image captured by the left side camera10L.FIG. 4Billustrates an example of an image captured by the front camera11F.FIG. 4Cillustrates an example of an image captured by the rear camera11B.FIGS. 4A to 4Cillustrate a comparison between the position of the lane division (the white line2) detected by the left side camera10L, and the positions of the lane divisions (the white line2) detected by the front camera11F and the rear camera11B.

A front part of the white line2captured by the left side camera10L is also contained in the image captured by the front camera11F, while a rear part of the same white line2captured by the left side camera10L is also contained in the image captured by the rear camera11B. It is assumed in this condition that the positions detected from the respective images captured by the left side camera10L, the front camera11F, and the rear camera11B as positions of the white lines2with respect to the vehicle1are matched with each other within a tolerance. The same is applicable to the images of the right side camera10R, the front camera11F, and the rear camera11B.

It is therefore confirmable whether the detection result of the white line2detected on the side of the vehicle1based on the images captured by the left side camera10L and the right side camera10R is valid by referring to the detection result of the white line2obtained based on the image captured by the front camera11F or the rear camera11B.

More specifically, it is supposed that the distance between the vehicle1and the left white line2is detected as a distance L1based on the image captured by the left side camera10L as illustrated inFIG. 4A. Also, it is supposed that the distance between the vehicle1and the left white line2is detected as a distance Lf by the front camera11F (refer toFIG. 4B), and as a distance Lb by the rear camera11B (refer toFIG. 4C).

In this case, when the distance Lf detected by the front camera11F or the distance Lb detected by the rear camera11B agrees with the distance L1detected by the left side camera10L within a tolerance, it is determined that the white line2on the left side of the vehicle1has been correctly detected. The same is applicable to the white line2on the right side of the vehicle1.

Accordingly, the lane detection apparatus100of the present embodiment illustrated inFIG. 2is capable of detecting the white line2with sufficient reliability based on the images captured by the left side camera10L and the right side camera10R, while avoiding false detection.

Discussed above has been an ideal situation on the assumption that the four vehicle onboard cameras (the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B) capture images at the same timing (or with a slight time lag recognized as substantially equivalent timing). However, the four vehicle onboard cameras do not necessarily capture image at the same timing. In addition, the vehicle1continues traveling while the four vehicle onboard cameras are capturing images.

Accordingly, in an actual situation, the positions at which the four vehicle onboard cameras (the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B) capture images are slightly different as indicated by broken lines inFIG. 3.

When the vehicle1travels at a relatively low speed, or travels along the lane, images substantially equivalent to the images illustrated inFIGS. 4A to 4Care captured by the vehicle onboard cameras located at positions slightly different as indicated by the broken lines inFIG. 3. In this case, the foregoing description is applicable even when imaging timing is different for each of the vehicle onboard cameras. Accordingly, the white line2is detectable with sufficient reliability based on the images captured by the left side camera10L and the right side camera10R.

However, when the vehicle1changes the lane during high-speed traveling, for example, an influence may be produced by different imaging timing for each of the vehicle onboard cameras.

FIG. 5illustrates an example of differences in the position of imaging between the vehicle onboard cameras produced when the vehicle1changes the lane during high-speed traveling.

For example, it is supposed that the four vehicle onboard cameras (the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B) mounted on the vehicle1capture images in the order of the front camera11F, the rear camera11B, the left side camera10L, and the right side camera10R, for example. InFIG. 5, the position of the vehicle1at the time of imaging by the front camera11F is indicated by a solid line, while each of the positions of the vehicle1at the time of imaging by the rear camera11B, the left side camera10L, and the right side camera10R after imaging by the front camera11F is indicated by a fine broken line.

FIG. 6Aillustrates an image captured by the front camera11F (an image captured at the position of the vehicle1indicated by the solid line inFIG. 5), whileFIG. 6Billustrates an image captured by the left side camera10L.FIG. 6AandFIG. 6Billustrate a difficulty which may be caused when imaging timing is different for each of the vehicle onboard cameras at the time of a lane change in a high-speed traveling condition. When the vehicle1travels obliquely toward the white line2at a high speed as described with reference toFIG. 5, the vehicle1comes considerably close to the white line2during a period from the time of imaging by the front camera11F to the time of imaging by the left side camera10L. In this case, the position of the white line2located on the left side of the vehicle1and detected based on the image captured by the front camera11F is not matched with the position of the corresponding white line2detected based on the image captured by the left side camera10L. InFIG. 6AandFIG. 6B, the distance between the vehicle1and the white line2is indicated as a distance measured in the left direction from the head of the vehicle1. InFIG. 6B, the left white line2detected inFIG. 6Ais indicated by a fine broken line.

Accordingly, it may become difficult to confirm whether the detection result of the white line2on the side of the vehicle1is valid based on the detection result of the white line2obtained in front of or in the rear of the vehicle1when the vehicle1changes the lane during high-speed traveling as illustrated inFIG. 5.

For overcoming this difficulty, the lane detection apparatus100of the present embodiment confirms validity of the detection result of the white line2on the side of the vehicle1in the following manner to detect the lane with sufficient reliability even at the time of a lane change in the high-speed traveling condition of the vehicle1.

FIG. 7andFIG. 8are flowcharts of a lane detection process performed by the lane detection apparatus100of the present embodiment.

As illustrated in the figures, the lane detection apparatus100initially starts the four vehicle onboard cameras (the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B) in response to a start of the lane detection process. Thereafter, the lane detection apparatus100acquires time lags of imaging timing between the respective vehicle onboard cameras (S100). More specifically, each of the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B captures an image in a fixed imaging cycle after the start, and outputs the captured image to the lane detection apparatus100. In this case, a uniform imaging cycle is set for the respective vehicle onboard cameras. However, the respective vehicle onboard cameras are not necessarily started at completely identical timing. Accordingly, each of the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B continuously produces a phase difference determined at the start between each other during cyclical imaging.

FIG. 9illustrates a state of imaging by the left side camera10L, the front camera11F, the rear camera11B, and the right side camera10R in the same imaging cycle while producing a fixed phase difference between each other.

The lane detection apparatus100of the present embodiment acquires a time lag Tlf of imaging timing of the front camera11F from imaging timing of the left side camera10L, and a time lag Tlb of imaging timing of the rear camera11B from imaging timing of the left side camera10L after the start of the four vehicle onboard cameras in response to the start of the lane detection process illustrated inFIG. 7. In addition, the lane detection apparatus100acquires a time lag Trf of imaging timing of the front camera11F from imaging timing of the right side camera10R, and a time lag Trb of imaging timing of the rear camera11B from imaging timing of the right side camera10R. Furthermore, the lane detection apparatus100acquires a time lag Tbf of imaging timing of the front camera11F from imaging timing of the rear camera11B. The respective time lags thus acquired are stored in the time lag memory portion108illustrated inFIG. 2.

Subsequently, the lane detection apparatus100acquires an image of an area around the left side of the vehicle1from the left side camera10L, an image of an area around the right side of the vehicle1from the right side camera10R, an image of an area around the front of the vehicle1from the front camera11F, and an image of an area around the rear of the vehicle1from the rear camera11B (S101).

The lane detection apparatus100analyzes the image captured by the left side camera10L to detect the lane division (white line2in this example) on the left side of the vehicle1(S102), and analyzes the image captured by the right side camera10R to detect the lane division (the white line2) on the right side of the vehicle1(S103).

Similarly, the lane detection apparatus100detects the lane division (the white line2) in front of the vehicle1based on the image captured by the front camera11F (S104), and detects the lane division (the white line2) in the rear of the vehicle1based on the image captured by the rear camera11B (S105).

Each ofFIG. 10AandFIG. 10Billustrates a state of detection of the white line2in front of the vehicle1based on the image captured by the front camera11F. As illustrated inFIG. 10AandFIG. 10B, the position of the white line2is detected as an equation expressing a line in an X-Y coordinate system with an origin located at the position of the vehicle1.

Each ofFIG. 10CandFIG. 10Dillustrates a state of detection of the white line2in the rear of the vehicle1based on the image captured by the rear camera11B. Each ofFIG. 10EandFIG. 10Fillustrates a state of detection of the white line2on the left side of the vehicle1based on the image captured by the left side camera10L. Each ofFIG. 10GandFIG. 10Hillustrates a state of detection of the white line2on the right side of the vehicle1based on the image captured by the right side camera10R. Each of the white lines2illustrated in these figures is detected as an equation expressing a line in the X-Y coordinate system.

After detection of the white line2, the lane detection apparatus100determines whether the lane division (the white line2in this example) has been detected in each of the front and the rear of the vehicle1(S106inFIG. 7). In general, the white line2or other types of lane divisions are detectable in each of the front and rear of the vehicle1during traveling of the vehicle1along the lane. Accordingly, it is estimated that any abnormal condition has occurred when no lane division is detected in each of the front and rear of the vehicle1.

When no lane division is detected in each of the front and rear of the vehicle1(S106: no), notification about the abnormal condition is issued with an alarm sound output from a not-shown speaker, or lighting of a not-shown lamp (S110).

When a lane division is detected in each of the front and rear of the vehicle1(S106: yes), the traveling speed of the vehicle1is acquired from the vehicle speed sensor14(S107). The traveling speed may be acquired at the time of acquisition of the images from the vehicle onboard cameras in S101.

After acquisition of the vehicle speed, the lane detection apparatus100determines whether the lane division (the white line2in this example) has been detected on each of the left side and the right side of the vehicle1(S108).

When it is determined that the lane division has been detected on each of the left side and the right side of the vehicle1(S108: yes), the time lag Tlf of imaging timing of the front camera11F from imaging timing of the left side camera10L (refer toFIG. 9), and the time lag Tlb of imaging timing of the rear camera11B from imaging timing of the left side camera10L (refer toFIG. 9) are acquired (S109). These time lags have been acquired beforehand in S100and have been stored in the time lag memory portion108(refer toFIG. 2) at the start of the lane detection process.

Thereafter, the position of the lane division (the white line2) detected in each of the front and the rear of the vehicle1is corrected (S111inFIG. 8) based on the traveling speed of the vehicle1acquired in S107, and the time lags acquired in S109.

Each ofFIG. 11AandFIG. 11Billustrates correction of the position of the lane division (the white line2) detected in front of the vehicle1. The position of the lane division (the white line2) detected in front of the vehicle1is acquired at timing earlier than the timing of detection of the position of the lane division (the white line2) on the left side of the vehicle1by the time lag Tlf. During the period of this time lag, the vehicle1moves in a direction to come closer to the white line2by a distance (traveling speed V)×(time lag Tlf). Accordingly, the position of the lane division (the white line2) in front of the vehicle1illustrated inFIG. 11Ais shifted in the direction opposite to the traveling direction of the vehicle1by the distance (traveling speed V)×(time lag Tlf) to correct the position to a position illustrated inFIG. 11B.

The position of the lane division (the white line2) detected in the rear of the vehicle1is corrected in a similar manner. More specifically, the position of the lane division (the white line2) detected in the rear of the vehicle1is acquired at earlier timing than the timing of detection of the position of the lane division (the white line2) on the left side of the vehicle1by the time lag Tlb. Accordingly, the position of the lane division (the white line2) in the rear of the vehicle1is shifted in the traveling direction of the vehicle1by a distance (traveling speed V)×(time lag Tlb).

Subsequently, the lane detection apparatus100determines whether the position of the lane division (the white line2) detected on the left side of the vehicle1is matched with the corrected position of the lane division (the white line2) in each of the front and the rear of the vehicle1(S112inFIG. 8).

As described with reference toFIGS. 10A to 10H, each of the position of the lane division (the white line2) on the left side of the vehicle1and the positions of the lane divisions (white lines2) in front of and in the rear of the vehicle1is detected as an equation expressing a line in the X-Y coordinate system. Furthermore, the position of the lane division (the white line2) in each of the front and the rear of the vehicle1is corrected such that the corresponding line is shifted in the X direction in the X-Y coordinate system. Accordingly, these lines are only compared in the X-Y coordinate system to determine whether the respective lines are matched (i.e., matched within tolerance).

When it is determined that the detected positions of the lane divisions (white lines2) are matched at three points on the left side, in front, and in the rear of the vehicle1(S112: yes), this condition of alignment is recognized as a state that the lane division (the white line2) on the left side has been correctly detected. Subsequently, similar operation is initiated for the lane division (the white line2) on the right side.

When it is determined that the detected positions of the lane divisions (white lines2) are not matched at three points on the left side, in front, and in the rear of the vehicle1(S112: no), this condition of non-alignment is considered most likely to come from false detection of the lane division (the white line2) on the left side. Accordingly, the position of the lane division (the white line2) on the left side is switched to a position estimated based on the position of the lane division (the white line2) on the left side of the vehicle1detected in a previous process (S113).

According to the present embodiment, the position of the lane division (the white line2) detected on the left side of the vehicle1is compared with the position of the lane division (the white line2) detected in front of the vehicle1, and further with the position of the lane division (the white line2) detected in the rear of the vehicle1. In a more simplified method, however, alignment may be confirmed by a comparison between the position of the lane division (the white line2) on the left side of the vehicle1and the position of the lane division (the white line2) either in front of or in the rear of the vehicle1. In this case, a processing load imposed on the lane detection apparatus100decreases.

However, when the position of the lane division (the white line2) on the left side of the vehicle1is compared with both the positions of the lane divisions (white lines2) in front of and in the rear of the vehicle1as in the present embodiment, false detection is securely eliminated by double checking.

When the process for the lane division (the white line2) on the left side is completed in the foregoing manner, a similar process is initiated for the lane division (the white line2) on the right side. More specifically, the time lag Trf of imaging timing of the front camera11F from imaging timing of the right side camera10R (refer toFIG. 9), and the time lag Trb of imaging timing of the rear camera11B from imaging timing of the right side camera10R (refer toFIG. 9) are acquired (S114)

After acquisition of the time lags, each of the positions of the lane divisions (white lines2) detected in front of and in the rear of the vehicle1is corrected (S115). For correction, the position of the lane division (the white line2) detected in front of the vehicle1is shifted in the direction opposite to the traveling direction of the vehicle1by a distance of (a traveling speed V)×(a time lag Trf). On the other hand, the position of the lane division (the white line2) detected in the rear of the vehicle1is shifted in the traveling direction of the vehicle1by the distance of (the traveling speed V)×(the time lag Trb) for correction.

After the correction, it is determined whether the position of the lane division (the white line2) detected on the right side of the vehicle1is matched with the positions of the corrected lane divisions (the white lines2) in front of and in the rear of the vehicle1(S116). The position of the lane division (the white line2) detected on the right side of the vehicle1is detected as an equation expressing a line in the X-Y coordinate system, similarly to the position of the lane division (the white line2) detected on the left side. Accordingly, alignment of the positions of the lane divisions (the white lines2) on the right side, in front, and in the rear of the vehicle1is easily confirmable.

When it is determined that the respective positions of the lane divisions (white lines2) are not matched (S116: no), this non-alignment is considered most likely to come from false detection of the lane division (the white line2) on the right side. Accordingly, the position of the lane division (the white line2) on the right side is switched to a position estimated based on the lane division (the white line2) on the right side detected in a previous process (S117).

When it is determined that the positions of the lane divisions (white lines2) are matched on the right side, in front, and in the rear of the vehicle1(S116: yes), this condition of alignment is recognized as a state that that the lane division (the white line2) on the right side has been correctly detected. Accordingly, the process for switching the position to a position estimated from the previous detection result (S117) is skipped.

Incidentally, alignment of the position of the lane division (the white line2) detected on the right side of the vehicle1may be determined only by a comparison with the position of the lane division (the white line2) either in front of or in the rear of the vehicle1.

Thereafter, the position of the lane division (the white line2) on the left side and the position of the lane division (the white line2) on the right side both detected by the foregoing process are output to the vehicle control apparatus200as a lane detection result (S118).

After the output, it is determined whether to end lane detection (S119). When ending of lane detection is not desired (S119: no), the flow returns to S101inFIG. 7to again acquire images from the four vehicle onboard cameras (the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B), and starts a series of the foregoing steps.

Discussed above is the process performed when the lane division (the white line2) in each of the front and the rear of the vehicle1is detected (S106: yes inFIG. 7) and when the lane division (the white line2) is detected on each of the left side and the light side of the vehicle1(S108: yes).

When no lane division (the white line2) is detected on each of the left side and the right side (S108: no) of the vehicle1in the state that the lane division (the white line2) has been detected in each of the front and the rear of the vehicle1(S106: yes), this condition is recognized as a situation that the vehicle1crosses the lane division (the white line2) as illustrated inFIG. 12.

In this case, the lane detection apparatus100initiates a lane division estimation process (S200) described below.

As described with reference toFIGS. 10A to 10H, the one lane division (the white line2) on the left side of the vehicle1and the one lane division (the white line2) on the right side of the vehicle1, i.e., the two lane divisions (white lines2) in total are detected in each of the images captured by the front camera11F and the rear camera11B in the normal condition (situation in which the vehicle1does not cross the white line2). In this case, the inside position of each of the two detected lane divisions (white lines2) is determined as the position of the lane division (the white line2) in S104and105inFIG. 7(refer toFIG. 10A,FIG. 10B,FIG. 10C, andFIG. 10D).

However, when the vehicle1crosses the lane division (the white line2) as in an example illustrated inFIG. 12, only the one lane division (the white line2) is detected in each of the images captured by the front camera11F and the rear camera11B. In this case, the position of the center line of the detected lane division (the white line2) is determined as the position of the lane division (the white line2). More specifically, the position of the center line of the lane division (the white line2) in the image captured by the front camera11F is determined as the position of the lane division (the white line2) in S104inFIG. 7as in an example illustrated inFIG. 13AandFIG. 13B. On the other hand, the position of the center line of the lane division (the white line2) in the image captured by the rear camera11B is determined as the position of the lane division (the white line2) in S105inFIG. 7as in an example illustrated inFIG. 13CandFIG. 13D.

FIG. 14is a flowchart showing the lane division estimation process.

As illustrated inFIG. 14, the time lag Tbf of imaging timing of the front camera11F from imaging timing of the rear camera11B is initially acquired in the lane division estimation process (S201).

As described with reference toFIG. 9, the time lag Tbf has been acquired at the start of the lane detection process illustrated inFIG. 7andFIG. 8, and has been stored in the time lag memory portion108beforehand.

After acquisition of the time lag, the position of the lane division (the white line2) detected in front of the vehicle1is corrected based on the traveling speed detected in S107inFIG. 7, and the time lag Tbf (S202). More specifically, the position of the lane division (the white line2) detected in front of the vehicle1is shifted in the direction opposite to the traveling direction of the vehicle1by a distance (traveling speed V)×(time lag Tbf) as in an example illustrated inFIG. 15AandFIG. 15B. This shift corrects the position of the lane division (the white line2) as in the example illustrated inFIG. 15Ato a position of the lane division (the white line2) as in the example illustrated inFIG. 15B.

After the correction, it is determined whether the corrected position of the lane division (the white line2) in the front area is matched with the position of the lane division (the white line2) in the rear area (whether these positions are matched within tolerance) (S203).

When alignment is confirmed (S203: yes), the position of the lane division (the white line2) under a lower surface of the vehicle1is estimated based on the position of the lane division (the white line2) detected in the rear of the vehicle1and the corrected position of the lane division (the white line2) in front of the vehicle1(S204). The process in S204corresponds to a lane division estimation section. More specifically, each of the position of the lane division (the white line2) in the rear of the vehicle1and the corrected position of the lane division (the white line2) in front of the vehicle1is expressed as a line in the X-Y coordinate system. Therefore, an intermediate line between these lines is easily obtainable. The position of the lane division (the white line2) under the lower surface of the vehicle1is estimated based on the intermediate line thus obtained.FIG. 16illustrates an example of estimation of the position of the lane division (the white line2) achieved by the foregoing method.

According to the present embodiment described herein, the front camera11F captures an image at earlier timing than imaging timing of the rear camera11B (refer toFIG. 9). However, when the front camera11F captures an image after the imaging by the rear camera11B, the time lag Tbf becomes a negative value. In this case, the shift direction of the lane division (the white line2) in front of the vehicle1becomes the opposite direction. Therefore, the position of the lane division (the white line2) in front of the vehicle1is shifted in the traveling direction of the vehicle1by a distance of (the traveling speed V)×(the time lag Tbf).

According to the present embodiment described herein, the lane division (the white line2) to be corrected is the lane division (the white line2) in front of the vehicle1detected based on the image captured by the front camera11F. However, the lane division to be corrected is not limited to the lane division (the white line2) contained in the image of the front camera11F, but may be the lane division (the white line2) contained in the image captured earlier by either the front camera11F or the rear camera11B. For example, when the front camera11F captures an image at earlier timing than imaging timing of the rear camera11B, the lane division (the white line2) in front of the vehicle1(based on the image captured by the front camera11F) is shifted in the direction opposite to the traveling direction of the vehicle1. However, when the front camera11F captures an image after imaging by the rear camera11B, the lane division (the white line2) in the rear of the vehicle1(based on the image of the rear camera11B) may be shifted in the traveling direction of the vehicle1.

In this case, the position of the lane division (the white line2) is estimated with reference to the image captured at the latest imaging timing corresponding to either the imaging timing of the front camera11F or the imaging timing of the rear camera11B. Accordingly, accuracy of estimation increases.

After estimation of the position of the lane division (the white line2) under the lower surface of the vehicle1by the foregoing method (S204inFIG. 14), the estimated position of the lane division (the white line2) is output to the vehicle control apparatus200(S205). After the output is completed, the lane division estimation process inFIG. 14ends. Then, the flow returns to the lane detection process inFIG. 7andFIG. 8.

However, when it is determined in S203inFIG. 14that the corrected position of the lane division (the white line2) in the front area is not matched with the position of the lane division (the white line2) in the rear area (S203: no), a notification about a condition that the lane division (the white line2) under the lower surface of the vehicle1cannot be estimated is output to the vehicle control apparatus200(S206). After the output is completed, the lane division estimation process inFIG. 14ends. Then, the flow returns to the lane detection process inFIG. 7andFIG. 8.

After the flow returns from the lane estimation process (S200), it is determined whether to end detection of the lane in the lane detection process illustrated inFIG. 7(S119inFIG. 8).

When ending of lane detection is not desired (S119: no), the flow returns to S101inFIG. 7to again acquire images from the four vehicle onboard cameras (the left side camera10L, the right side camera10R, the front camera11F, and the rear camera11B), and starts a series of the foregoing steps. When ending of lane detection is desired (S119: yes), the lane detection process illustrated inFIG. 7andFIG. 8ends.

As described above, the lane detection apparatus100of the present embodiment is capable of confirming whether the position of the lane division (the white line2) detected on each of the left side and the right side of the vehicle1is valid based on the position of the lane division (the white line2) detected in front of or in the rear of the vehicle1. When the vehicle1changes the lane during high-speed traveling, the position of the lane division (the white line2) detected in front or in the rear of the vehicle1is corrected. Validity of the position of the lane division (the white line2) detected on each of the left side and the right side is confirmable based on this correction. Accordingly, the position of the lane division (the white line2) is detectable with sufficient reliability from the images captured by the left side camera10L and the right side camera10R.

There are provided a lane detection apparatus and a lane detection method in various modes according to the present disclosure. For example, according to a lane detection apparatus and a lane detection method in a mode of the present disclosure, a side lane division existing on the side of a vehicle is detected based on an image captured by a side vehicle onboard camera imaging an area around the side of the vehicle. In addition, a front lane division existing in front of the vehicle is detected based on an image captured by a front vehicle onboard camera imaging an area around the front of the vehicle. The position of the front lane division is corrected based on a time lag of imaging timing between the side vehicle onboard camera and the front vehicle onboard camera, and a traveling speed. A comparison is made between the corrected position of the front lane division and the position of the side vehicle division. When both the positions are matched with each other, the detection result of the position of the side lane division is output as a lane detection result.

Even in case of detection of the side lane division based on an image of the side of the vehicle, false detection does not occur. Accordingly, the lane division is detectable with high reliability based on the side image captured from the vehicle. Moreover, the corrected position of the front lane division is compared with the position of the side lane division. In this case, false detection of the side lane division is avoidable even during high-speed traveling of the vehicle. Accordingly, the lane division is detectable with high reliability.

A lane detection apparatus according to an example of the present disclosure detects a lane along which a vehicle travels, based on analysis of images captured by multiple vehicle onboard cameras. The lane detection apparatus includes: a side detection portion that detects a side lane division existing on the side of the vehicle, based on an image captured by a side vehicle onboard camera imaging an area around the side of the vehicle; a front detection portion that detects a front lane division existing in front of the vehicle, based on an image captured by a front vehicle onboard camera imaging an area around the front of the vehicle; a checkup portion that compares the position of the side lane division and the position of the front lane division; and an output portion that outputs the position of the side lane division as a detection result when the position of the side lane division and the position of the corrected front lane division are matched with each other.

While various embodiments, configurations, and aspects of the lane detection apparatus and the lane detection method according to the present disclosure have been exemplified, the embodiments, configurations, and aspects of the present disclosure are not limited to those described above. For example, embodiments, configurations, and aspects obtained from an appropriate combination of technical elements disclosed in different embodiments, configurations, and aspects are also included within the scope of the embodiments, configurations, and aspects of the present disclosure.