JP3296055B2 - Distance detection device using in-vehicle camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance detecting apparatus using an on-vehicle camera, and more particularly, to processing an image captured by a single camera, not a stereoscopic camera, so that a point on the image is actually detected from a vehicle. When detecting distance,
The accuracy of distance detection is improved by correcting and detecting the height and angle of the camera, which changes with respect to the road surface due to the pitching of the vehicle, without using external sensors such as a vehicle height sensor and tilt sensor. It 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.

[0003] The "constant speed traveling device"
It is also called "speed control" or "cruise control." In vehicles equipped with this device,
When the set switch is pressed, the vehicle keeps running at the set vehicle speed even when the accelerator pedal is released. The set vehicle speed can be changed by operating the control switch. This function is canceled when the driver steps on the brake, depresses the clutch, shifts the gear, or the like.

[0004] In order to ensure safety when the above-mentioned constant-speed traveling device is used, some devices have the following additional functions. That is, the distance from the preceding vehicle is detected by processing the image captured by the on-board camera or detected by a laser radar, etc., and when approaching the preceding vehicle abnormally, a warning is issued to alert the driver to attention. Alternatively, the gear shift stage is downshifted from fourth speed (overdrive) to third speed, and the speed is reduced by overdrive-off for operating the engine brake.

On the other hand, in an automobile equipped with an "inter-vehicle distance control device", when a set switch is pressed, a 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. It controls the engine output and the brake so that the inter-vehicle distance between the vehicle and the vehicle becomes the target inter-vehicle distance, and tracks the preceding vehicle to travel. In this case, the distance between the vehicle and the preceding vehicle is detected by performing image processing on an image captured by an on-vehicle camera, or by using a laser radar or the like.

As a distance detection method using a vehicle-mounted camera, a stereo vision 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 has two cameras, for example, CCD cameras 2 and 3 arranged in a body 4 at an interval L in the horizontal direction.
Mounted horizontally on the vehicle. These left and right cameras 2,
From FIG. 3, two images are obtained as shown in FIGS. 7 (a) and 7 (b). Then, the same image 6L as the car image 6R surrounded by the window 5 in the right image exists at a position slightly shifted in the horizontal direction in the left image. Thus, the position of the most matching image is determined while shifting the right-side car image 6R surrounded by the window 5 by one pixel within the search range 7 of the left-side image. At this time, as shown in FIG. 8, the focal length of each of the left and right cameras 2 and 3 is 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 match. 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) based on the principle of triangulation.

R = (f · L) / (n · P) Equation (1)

[0008] However, stereo vision cameras are expensive,
Further, the system configuration is complicated and the cost increases.

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,
Installed on the vehicle 10 at an angle θ. One image is obtained from the CCD camera 8 as shown in FIG. Therefore, the image coordinate system is an ij orthogonal coordinate system (i-coordinate is a horizontal position, j is a vertical position) as shown in FIG. 10, the j-coordinate value of the car image 6 is β, and the focal length of the camera 8 is Assuming that f, the actual distance Y to the preceding vehicle is given by the following equation (2).
Can be calculated by

Y = H (β · tan θ + f) / (f · tan θ−β) Expression (2)

The single camera method described above requires only one camera, is less expensive than the stereoscopic camera method, and has a simple system configuration. However, the calculation of Expression (2) has been performed with the height H and the angle θ of the CCD camera 8 fixed. Therefore, when the vehicle height or attitude 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, and an error occurs in distance detection.

As a method of removing the influence of the change of the height H and the angle θ of the CCD camera 8 on the road surface 9,
The techniques disclosed in Japanese Patent Application Laid-Open Nos. 1-273746 and 3-118611 are known.

In JP-A-1-273746, a pitch angle 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 which the vehicle is not tilted is obtained. However, the cost increases because the tilt sensor is required. In JP-A-3-118611, a pitch angle of a vehicle is detected by a tilt sensor using a gyro or the like,
By converting the pitch angle into the number of rasters and changing the raster position at which image capture is started, an image in which pitching of the vehicle is canceled is obtained. However, also in this case, the cost increases because the tilt sensor is required. In addition, the vehicle height may be detected by a vehicle height sensor, and the height value of the camera may be corrected according to the detection result. However, in this case, the cost is increased because the vehicle sensor is required.

[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 instead of a stereoscopic camera so that a point on the image is actually obtained from a vehicle. When detecting the distance, the height and angle of the camera, which changes with respect to the road surface due to the pitching of the vehicle, are detected and corrected 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 detecting a distance with high accuracy by utilizing the detection result.

[0014]

A distance detecting apparatus using a vehicle-mounted camera according to the present invention, which achieves the above object, uses one camera mounted on a vehicle, and measures the height and angle of the camera with respect to a road surface and the camera. In a device for detecting an actual distance of a point on an image from a vehicle from a focal length and a coordinate value on an image, three dashed objects having a known interval between end points formed on a traveling path of the vehicle. Or a means for obtaining coordinate values on the image for the endpoints greater than or equal to each other, a distance detection error is minimized by using the determined coordinate values on the image for each endpoint, a known interval between the endpoints, and the focal length of the camera. Means for calculating 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 a highway, so that 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 using a dashed object such as the center dashed line as an object. That is, when a coordinate value on an image of a certain end point is obtained for a dashed object whose interval between the end points is known, such as a center broken line, the 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,
The actual distance of the end point from the vehicle is, of course, 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. Thus, 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 interval 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 in detecting the distance of the point on the image from the vehicle 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 part of image processing for distance detection, external sensors such as a vehicle height sensor and a tilt sensor are not required. Furthermore, when a camera is installed in a vehicle, even if there is an error in height and angle, this can be absorbed, which contributes to simplification of installation work.

[0016]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a traveling control system of an automobile to which a distance detection device using a vehicle-mounted camera according to an embodiment is applied. 2 shows a processing flow, FIG. 3 shows an image captured by a camera and coordinate values of an end point on the image, and FIG. 4 shows a white center broken line on a road and a method of recognizing the end point.

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 distance between vehicles or traveling 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 running on a highway or a motorway, there is a central dashed line with a white line of 8m length drawn every 20m on the road.
The CCD camera 8 can photograph the center broken line. The image processing device 11 captures an image as shown in FIG. 3 by inputting a video signal from the CCD camera 8. In this image, reference numeral 15 is a white line image with a broken center line. 16 is an image of a continuous line on the roadside, and 17 is a horizon. The image processing apparatus 11 performs image processing on the captured image, recognizes the center broken line, and sequentially determines three or more j coordinate values of the end point of each white line image 15 in the ij image coordinate system of FIG. ₁ , β ₂ ... β _n (n ≧ 3)
It is given to the height and angle calculation device 12. Here, the i coordinate is the coordinate in the lateral direction of the vehicle, and the j coordinate is the coordinate in the front and rear direction of the vehicle.

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

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

Next, an example of calculation processing of the height H and the angle θ will be described.
I will tell. In the example shown in FIG. 3, the k-th end point from the front is
j coordinate value β_k(K = 1 to n, n ≧ 3) actual distance d_k
Is the distance of the first endpoint to d₀Assuming that d_k= D
₀+ Δ_kBecomes Δ_kIs known, and the end point interval or white line
From the length 8m and the white line cycle 20m, if k is an odd number, Δ_k
= 20 (k-1) m, when k is an even number, Δ_k= [20
(K-1) -8] m. Note that Δ₁= 0. one
Using the camera height H, angle θ and focal length f
J-coordinate value β of k-th end point from the front_kMeasure the distance corresponding to
If it is calculated, its value Y_kIs given by the following equation (3)
You.

Y _k = H (β _k · tan θ + f) / (f · tan θ−β _k ) Equation (3)

When the above equation (3) is modified, the following equation (4) is obtained.
You. 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

Y _k (f · tan θ−β _k ) −H (β _k · tan θ + f) = 0 Equation (4)

(Y _k , β _k ) = (d ₀ + Δ _k , β _k ) Equation (5)

Further, in the Equation (5) to correspond precisely, the sum of considering for example the following equation as the evaluation value epsilon _k error (6), from epsilon ₁ ² to epsilon _n ² as n ≧ 3 Σε _The unknowns H, θ (or tan θ) and d ₀ may be calculated so that _k ² is minimized, whereby the height H and angle tan θ of the camera at that time, and the end point at the forefront distance d ₀ of is obtained.

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

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

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

The distance calculating device 13 calculates the height H, the angle θ or the height H of the CCD camera 8 with respect to the road surface 9 calculated as described above.
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, since H, θ or tan θ correctly reflects changes due to the pitching of the vehicle, the distance of any object can be correctly detected even if the vehicle is pitched. Therefore, using the correct height H and angle tan θ of the CCD camera 8 calculated by the height and angle calculator 12, the end point of each white line 15 of the center broken line on the image of the circuit 18 as shown in FIG. By detecting the distance, the interval or distance between the end points deviates from the actual value, so that the radius of curvature of the circuit 18 can be accurately calculated from the deviation amount. By using the calculated value of the radius of curvature, the driving control device 14 warns the driver about deceleration, steering, and the like necessary when the vehicle enters the lane, or performs control such as automatically performing a correction operation. Is possible.

[0026]

According to the present invention, a dashed object having a known interval between endpoints, such as a center dashed line drawn on the road surface of a motorway or an expressway, is used as a pointing object to display three or more endpoints on an image. The coordinate values are obtained, the height and angle of the camera are detected by the least square method or the like from the obtained coordinate values, the distance between the known end points, and the focal length of the camera, and the distance is detected using the detected height and angle. I do. Therefore, even if the height and angle of the camera change due to the pitching of the vehicle 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 the drawings]

FIG. 1 is a diagram showing a configuration of a traveling control system of an automobile to which a distance detection device using an on-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 an image captured by a camera and coordinate values on an image of an end point.

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

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

FIG. 6 is a diagram showing a stereo vision camera.

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

FIG. 8 is a diagram showing the principle of triangulation by 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 using the single camera method.

[Explanation of symbols]

Reference Signs List 8 CCD camera 9 Road surface 10 Vehicle 11 Image processing device 12 Height and angle calculation device 13 Distance calculation device 14 Traveling control device 15 White line image 16 Roadside line image 17 Horizon 18 Circuit 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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-15605 (JP, A) JP-A-5-23298 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01C 3/06 B60R 21/00

Claims (1)

(57) [Claims] 1. Using a 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 of the point on the image from the vehicle. An apparatus for detecting a distance, comprising: means for obtaining coordinate values on an image of three or more end points of a dashed object having a known interval between end points formed on a traveling path of a vehicle; and an image of each obtained end point. Means for obtaining a height and an angle of a camera with respect to a road surface with a minimum distance detection error by using the above coordinate values, the known distance between end points, and the focal length of the camera. A distance detection device using a camera.