JPH07120258A - Distance detection device using in-vehicle camera - Google Patents

Abstract

(57) [Summary] [Purpose] Capture with one camera instead of a stereo camera
When detecting the distance of the point on the captured image from the vehicle
The turtle that changes with respect to the road surface due to pitching, etc.
The height and angle of the la
Detect without using a sensor and use this detection result
And accurately detect the distance. [Composition] Drawn to the road surface of a motorway or highway
Use a broken-line object with a known distance between
As a rule, the coordinate values on the image of three or more end points are β ₁~ Β
_nIs calculated by the image processing device 11, and the calculated coordinate value and the known end
From the distance between points and the focal length of the camera to the least squares method, etc.
Height of the CCD camera 8 in the height and angle calculation device 12
Calculate H and angle θ or tan θ and use the calculated values
The distance Y of the arbitrary object by the distance calculation device 13
It is calculated from the upper coordinate value β.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance detecting device using a vehicle-mounted camera, and more particularly, to an actual image from a vehicle at a point on the image by processing an image captured by one camera instead of a stereoscopic camera. When detecting the distance,
The height and angle of the camera that changes with respect to the road surface due to vehicle pitching, etc. are corrected and detected without using an external sensor such as a vehicle height sensor or an inclination sensor to improve the accuracy of distance detection. Is.

[0002]

2. Description of the Related Art In order to reduce the driving operation of an automobile, a constant speed traveling device has been put to practical use and an inter-vehicle distance control device has been developed.

The "constant speed traveling device" is an "automatic
It is also known as "speed control" or "cruise control." In a car equipped with this device,
When you press the set switch, the vehicle will travel at the set vehicle speed even if you release your foot from the accelerator pedal. The set vehicle speed can be changed by operating the control switch. When the driver operates the brake, the clutch, or shifts the gear, this function is canceled.

In order to ensure the safety when the above-mentioned constant speed traveling device is used, there are some which are added with the following functions. That is, the distance to the preceding vehicle is detected by an image captured by an in-vehicle camera by image processing or detected by a laser radar or the like, and when abnormally approaching the preceding vehicle, an alarm is issued to call attention to the driver. Alternatively, the gear shift stage is downshifted from the 4th speed (overdrive) to the 3rd speed, and deceleration is performed by overdriving off to operate the engine brake.

On the other hand, in the case of an automobile equipped with the "inter-vehicle distance control device", when the set switch is pushed, the target inter-vehicle distance is calculated from the vehicle speed of the own vehicle at that time, and the inter-vehicle distance with the preceding vehicle is detected to detect the preceding vehicle. The engine output and the brake are controlled so that the vehicle-to-vehicle distance between and becomes the target vehicle-to-vehicle distance, and the vehicle travels following the preceding vehicle. In this case, the inter-vehicle distance to the preceding vehicle is detected by performing image processing on the image captured by the vehicle-mounted camera or by using a laser radar or the like.

As a distance detecting method using an on-vehicle camera, a stereoscopic camera method and a single camera method are known.

In the stereoscopic camera method, distance detection is performed as follows. As shown in FIG. 6, the stereoscopic camera 1 is one in which two cameras, for example, CCD cameras 2 and 3 are arranged in a body 4 at a distance L in the lateral direction,
Mounted horizontally on the vehicle. These left and right cameras 2,
From 3, three images are obtained as shown in FIGS. 7 (a) and 7 (b). An image 6L, which is the same as the vehicle image 6R surrounded by the window 5 in the right image, is present in the left image at a position slightly laterally displaced. Therefore, the position of the most matched image is obtained by shifting the right side automobile image 6R surrounded by the window 5 by one pixel in the search range 7 of the left side image. At this time, as shown in FIG. 8, the focal lengths of the left and right cameras 2 and 3 are f, the distance between the optical axes of the left and right cameras 2 and 3 is L, the pixel pitch of the CCD is P, and the left and right vehicle images are aligned. Assuming that the number of pixels shifted up to is n, the distance (inter-vehicle distance) R to the preceding vehicle can be calculated by the following equation (1) according to the principle of triangulation.

## EQU00001 ## R = (f.L) / (n.P) ... Equation (1)

However, the stereoscopic camera is expensive,
In addition, the system configuration is complicated and the cost is high.

On the other hand, in the single camera method, distance detection is performed as follows. As shown in FIG. 9, one camera, for example, a CCD camera 8 has a height H with respect to the road surface 9,
The vehicle 10 is installed at an angle θ. From the CCD camera 8, one image is obtained as shown in FIG. Therefore, the image coordinate system is set to an ij orthogonal coordinate system (i coordinate is a horizontal position, j is a vertical position) as shown in FIG. 10, and the j coordinate value of the automobile image 6 is β and the focal length of the camera 8 is If f, the actual distance Y to the preceding car is
Can be calculated by

[Formula 2] Y = H (β · tan θ + f) / (f · tan θ−β) Equation (2)

The above-described single camera method requires only one camera, is cheaper than the stereoscopic camera method, and has a simple system configuration. However, the calculation of the equation (2) is performed with the height H and the angle θ of the CCD camera 8 being fixed values. Therefore, when the vehicle height or the posture of the vehicle 10 changes due to pitching or the like, the actual height H and the angle θ of the CCD camera 8 with respect to the road surface 9 change, which causes an error in distance detection.

As a method of eliminating the influence of the change of the height H and the angle θ of the CCD camera 8 with respect to the road surface 9,
Techniques disclosed in JP-A-1-273746, JP-A-3-118611, etc. are known.

In Japanese Patent Laid-Open No. 1-273746, a pitch sensor of a vehicle is detected by an inclination sensor using a G sensor or the like,
By correcting the operation timing of the electronic shutter of the camera according to the detection result, an image in a state where the vehicle is not tilted is obtained. However, the cost becomes higher because the tilt sensor is required. In Japanese Patent Laid-Open No. 3-118611, a pitch sensor of a vehicle is detected by an inclination sensor using a gyro or the like,
An image in which the pitching of the vehicle is canceled is obtained by converting the pitch angle into the number of rasters and changing the raster position at the start of image capturing. However, also in this case, the cost becomes high because the tilt sensor is required. In addition, the vehicle height may be detected by the vehicle height sensor and the height value of the camera may be corrected according to the detection result. However, in this case as well, the vehicle sensor is required, which increases the cost.

[0013]

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, it is an object of the present invention to process an image captured by a single camera rather than a stereoscopic camera so that the actual point of the image from the vehicle can be reduced. When detecting the distance, the height and angle of the camera that changes with respect to the road surface due to the pitching of the vehicle, etc. are corrected and detected by image processing without using an external sensor such as a vehicle height sensor or a tilt sensor,
An object of the present invention is to provide a device capable of accurately detecting a distance by using the detection result.

[0014]

A distance detecting device using an on-vehicle camera of the present invention for achieving the above object uses one camera mounted on a vehicle, and the height and angle of the camera with respect to a road surface and An apparatus for detecting an actual distance from a vehicle to a point on the image based on a focal length and a coordinate value on the image. The distance detection error is minimized by using the means for obtaining the coordinate values on the image for the endpoints more than that, the obtained coordinate values on the image for each endpoint, the known distance between the endpoints, and the focal length of the camera. And means for obtaining the height and angle of the camera with respect to the road surface.

[0015]

A white line having a length of 8 m is drawn every 20 m as a central broken line on the road surface of a motorway or an expressway. Therefore, the distance between the end points of the central broken line is a known value of 8 m and 12 m. In the present invention, the height and angle of the camera are calibrated by using a broken object such as the central broken line for pointing. That is, when a coordinate value on an image of a certain end point is obtained for a broken line-shaped object whose distance between the end points is known, such as the central broken line, this coordinate value is the height and angle of the camera with respect to the road surface and the focal length of the camera. And the actual distance of this endpoint from the vehicle. In this case, the focal length of the camera is known, but
The actual distance of the end point from the vehicle is naturally unknown, and the height and angle of the camera with respect to the road surface are also unknown because they change due to the pitching of the vehicle as described above. Therefore, if the coordinate values on the image for three or more end points are obtained, the actual height and angle of the camera with respect to the road surface can be obtained because the actual distance between the end points is known. However, since there is an error in the distance between the end points or an error in the coordinate value on the image, the height and angle that minimize the distance detection error are obtained by the least square method or the like. By using the height and angle of the camera with respect to the road surface obtained in this way, the accuracy when detecting the distance from the vehicle of the point on the image by image processing of the image captured by one camera instead of the stereoscopic camera Is improved. Further, since the height and angle of the camera with respect to the road surface can be obtained as a part of the image processing for distance detection, an external sensor such as a vehicle height sensor or a tilt sensor is unnecessary. Furthermore, when installing a camera in a vehicle, even if there are errors in height and angle, these can be absorbed, which contributes to ease of installation work.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a vehicle travel control system to which a distance detection device using an in-vehicle camera according to an embodiment is applied. 2 shows the processing flow, FIG. 3 shows the image captured by the camera and the coordinate values of the end points on the image, and FIG. 4 shows the white center broken line on the road and the method of recognizing the end points.

In FIG. 1, the distance detecting device has one CC.
It comprises a D camera 8, an image processing device 11, a height and angle calculation device 12, and a distance calculation device 13. The height and angle calculation device 12 and the distance calculation device 13 are one functional unit in the travel control device 14 for controlling the inter-vehicle distance or for driving at a constant speed. Reference numeral 9 indicates a road surface.

The CCD camera 8 is mounted on the vehicle 10 as shown in FIG. When a vehicle is driving on an expressway or a motorway, there is a central broken line that draws a white line 8 m long every 20 m, so
The CCD camera 8 can photograph this central broken line. The image processing device 11 takes in an image as shown in FIG. 3 by inputting a video signal from the CCD camera 8. In this image, 15 is the white line image of the central broken line. Further, 16 is an image of a continuous line on the road side, and 17 is a horizon. The image processing apparatus 11 recognizes the central broken line by performing image processing on the captured image, and sets the j coordinate value of the end point of each white line image 15 in the i-j image coordinate system of FIG. ₁ , β ₂ ... β _n (n ≧ 3),
It is given to the height and angle calculation device 12. However, the i coordinate is the lateral direction of the vehicle, and the j coordinate is the longitudinal coordinate of the vehicle.

The recognition of the central broken line is performed as follows, for example. That is, as shown in FIG. 4, the brightness of pixels is checked along four horizontal lines W1 to W4, bright points are selected as white line candidates, and upper candidate points and lower candidate points are interpolated. The connected line segment is extracted as a white line. Then, the lightness of the pixel is checked along this line segment and its extension, and the point changed from a dark point to a bright point or from a bright point to a dark point is defined as the end point of the white line.

In the height and angle calculation device 12, the distance between the end points and the focal length of the camera are set as known values, and these values and the j coordinate value of each end point given from the image processing device 11 are set. Using, for example, the least squares method,
Height H of the camera to the road surface that minimizes the distance detection error
And the angle θ.

Next, an example of calculating the height H and the angle θ will be explained.
Reveal In the example shown in FIG. 3, the k-th end point from the front
j coordinate value β_kActual distance d of (k = 1 to n, n ≧ 3)_k
Is the distance of the first end point d₀Assuming that_k= D
₀+ Δ_kBecomes Δ_kIs known and the end point spacing or white line
Based on a length of 8 m and a white line period of 20 m, Δ when k is an odd number_k
= 20 (k-1) m, Δ when k is an even number_k= [20
(K-1) -8] m. Note that Δ₁= 0. one
Hand, using the camera height H and angle θ and the focal length f
J coordinate value β of the kth end point from the front_kThe distance corresponding to
If calculated, its value Y_kIs given by the following equation (3)
It

[Number 3] _{Y k = H (β k ·} tan θ + f) / (f · tan θ-β k) ··· (3)

When the above equation (3) is modified, the following equation (4) is obtained.
It Also, the calculated value Y_kAnd the actual distance d ₀+ Δ_kIs it
J coordinate value β_kSince it is a function of
Corresponding to.

[Number 4] _{Y k (f · tan θ-} β k) -H (β k · tan θ + f) = 0 ··· formula (4)

[Formula 5] (Y _k , β _k ) = (d ₀ + Δ _k , β _k ) ... Formula (5)

Further, in order to accurately correspond to the above equation (5), considering the following equation (6) as the error evaluation value ε _k , for example, the sum Σε from ε ₁ ² to ε _n ² with n ≧ 3. _The unknowns H, θ (or tan θ) and d ₀ may be calculated so that _k ² becomes the minimum, and by this, the height H and angle tan θ of the camera at that time, and the end point at the front end are calculated. The distance d ₀ is obtained.

## EQU6 ## ε _k = (d ₀ + Δ _k ) (f · tan θ−β _k ) −H (β _k · tan θ + f) (6)

Therefore, the height and angle calculating apparatus 1 of this embodiment
2 calculates the camera height H and the angles tan θ and d ₀ by the following calculation formula (7) using the error evaluation value ε _k of the previous formula (6).

[Equation 7] ∂ (Σε _k ² ) / ∂H = 0 ∂ (Σε _k ² ) / ∂ (tan θ) = 0 ∂ (Σε _k ² ) / ∂d ₀ = 0

The distance calculation device 13 calculates the height H of the CCD camera 8 relative to the road surface 9 calculated as described above, the angle θ, or
Using tan θ, the distance Y of the arbitrary object is calculated from the j coordinate value β on the image and the focal length f of the CCD camera 8 by the above equation (2). In this case, H, θ, or tan θ correctly reflects the change due to the pitching of the vehicle, so that the distance of an arbitrary object can be correctly detected even if the vehicle has pitching or the like. Therefore, by using the correct height H and the angle tan θ of the CCD camera 8 calculated by the height and angle calculation device 12, the end point of each white line 15 of the central broken line on the image of the rotation circuit 18 as shown in FIG. Since the distance between the end points or the distance deviates from the actual value by detecting the distance, the radius of curvature of the turning circuit 18 can be accurately calculated from the deviation amount. By using the calculated value of the radius of curvature, control is performed such that the traveling control device 14 warns the driver of deceleration and steering necessary when the vehicle enters the turning circuit, or automatically performs a correction operation. Is possible.

[0026]

According to the present invention, a broken line-shaped object having a known interval between end points, such as a central broken line drawn on the road surface of a motorway or a highway, is used as an object to indicate on an image of three or more end points. Calculate the coordinate values, detect the height and angle of the camera by the least-squares method, etc. from the calculated coordinate values and the distance between the known end points and the focal length of the camera, and detect the distance using the detected height and angle. I do. Therefore, even if the height and angle of the camera change due to vehicle pitching or the like, accurate distance detection can be performed using one camera without using an external sensor such as a vehicle height sensor or an inclination sensor.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a vehicle travel control system to which a distance detection device using an in-vehicle camera according to an embodiment of the present invention is applied.

FIG. 2 is a diagram showing a processing flow.

FIG. 3 is a diagram showing coordinate values on an image captured by a camera and an image of an end point.

FIG. 4 is a diagram showing a method of recognizing a white central broken line on a road and its end points.

FIG. 5 is a diagram showing an image of a rotating circuit.

FIG. 6 is a diagram showing a stereoscopic camera.

FIG. 7 is a diagram showing a distance detection method of a stereoscopic camera method.

FIG. 8 is a diagram showing the principle of triangulation with a stereoscopic camera.

FIG. 9 is a diagram showing the height and angle of a camera in the single camera method.

FIG. 10 is a diagram showing a distance detection method of a single camera method.

[Explanation of symbols]

8 CCD camera 9 Road surface 10 Vehicle 11 Image processing device 12 Height and angle calculation device 13 Distance calculation device 14 Travel control device 15 White line image 16 Roadside line image 17 Horizon line 18 Rotation circuit image H Camera height θ Camera angle β ₁ , Β ₂ , β ₃ , β ₄ j-coordinate value of the end point d ₀ Distance of the first end point

Claims (1)

[Claims] 1. Using one camera mounted on a vehicle, the height and angle of the camera with respect to the road surface, the focal length of the camera, and the coordinate values on the image are used to determine the actual point on the image from the vehicle. In a device for detecting a distance, a means for obtaining coordinate values on an image for three or more endpoints of a dashed line-shaped object having a known distance between the endpoints formed on the traveling path of the vehicle, and an image for each endpoint obtained An in-vehicle device having means for determining a height and an angle of a camera with respect to a road surface that minimizes a distance detection error by using the above coordinate values, a known distance between end points, and a focal length of the camera. Distance detection device using a camera.