JPH07104159B2 - Absolute distance detection method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inter-vehicle distance detection method for detecting a distance to a preceding vehicle, and more particularly to an absolute distance from the preceding vehicle using two image pickup devices. The present invention relates to an absolute inter-vehicle distance detection method that measures an actual inter-vehicle distance in real time, displays the inter-vehicle distance, and issues an alarm when an abnormal approach occurs.

[Conventional technology]

As a distance detection method for detecting the distance to an object, a method using ultrasonic waves or laser light is conventionally known. These are devices that project ultrasonic waves or laser light to capture reflected waves from an object, and thereby measure the absolute distance from the observation point to the object without contact.

[Problems to be solved by the invention]

However, the distance detection method using ultrasonic waves or laser light has the following various problems.

． What can be measured by these methods is basically the distance from the observation point to the reflection point on the object.Therefore, when measuring the distance to the preceding vehicle that is running, the vehicle body shakes and the relative position changes. Therefore, it is difficult to measure the distance reliably.

． When the object is a long distance, it is necessary to increase the output of ultrasonic waves or laser light, which causes a cost or space problem.

． In the case of ultrasonic waves, the beam width cannot be narrowed so much that it is difficult to measure long distances. Laser light can have a sharp directivity, but there is a problem that it is dangerous if the beam enters the human eye.

[Means for solving problems]

Therefore, in the present invention, a horizontal component is extracted by performing an image pickup device for picking up an image of a moving object and a spatial differentiation process for obtaining a change value of vertical brightness with respect to an image of the object by the image pickup device. The horizontal component extracting means, the binarizing means for binarizing the horizontal component, and the two points where the horizontal histogram value of the binarized image exceeds the threshold value m. At least two sets of means for detecting the significant width in the horizontal direction by determining the significant width in the vertical direction and determining the widest width in which the histogram value in the vertical direction in the vertical significant region is not less than the average value Meaningful width detection means is provided.

Moreover, the distance to the object is obtained and displayed based on the coordinates of the corresponding points of the two sets of images determined by the significant widths in the horizontal direction and the vertical direction when the respective image pickup devices are provided separately. Adopting a configuration in which a means for generating an alarm by detecting that the distance is equal to or less than a predetermined value is provided,
We are trying to achieve the purpose by this.

[Action]

An object is imaged using two imaging devices, and the imaged images are subjected to image processing to extract the object. The coordinates of the corresponding points in both the extracted images are obtained, the distance b and the focal length f of both imaging devices are known, and a computer performs a calculation based on a predetermined calculation formula based on the principle of triangulation to determine the object Find the absolute distance of and display this on the distance meter. At this time, it is also possible to set a constant threshold value and generate an output when the inter-vehicle distance z becomes equal to or less than the threshold value to issue an alarm of abnormal approach.

Example of Invention

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, image pickup devices 1 and 2 are for picking up an image of an object, especially a preceding vehicle, and can be, for example, an ITV camera using a camera tube or a CCD camera using a CCD element. The image pickup devices 1 and 2 are installed at positions that do not hinder the driving of the vehicle 3 and at appropriate positions where a sufficient forward field of view can be secured, with a slight distance between the image pickup devices 1 and 2. The image pickup devices 1 and 2 may be installed horizontally apart from each other, but in the following description, it is assumed that they are installed vertically.

The image signals of the imaging devices 1 and 2 are analog digital (A / D)
After being converted from an analog signal to a digital signal in the converter 4, it is input to the processing device 5. The processing device 5 has a memory 6. The digitized image signal from the A / D converter 4 is stored in the memory 6 at every predetermined image capturing time. The processing device 5 further includes a computer 7, and the imaging devices 1 and 1 stored in the memory 6
The distance to the preceding vehicle is sequentially calculated from the image data of 2 according to the principle of triangulation and displayed on the inter-vehicle distance meter 8. At this time, the computer 7 determines whether the distance to the preceding vehicle is increasing or decreasing from the comparison of the distance measurement values at each time, and displays “approaching” or “separating”. Can also be performed, for example, by displaying signs of + and-. Further, the computer 7 compares the obtained distance with the preceding vehicle with a preset threshold value, and when the threshold value is less than or equal to the threshold value, displays "abnormal approach",
Alternatively, control such as sounding a buzzer to give an alarm can be performed.

The algorithm of the process for detecting the inter-vehicle distance in the computer 7 will be described below. 2 (a) and (b),
The image data of the image pickup devices 1 and 2 installed above and below, respectively, is shown as an example, and “p′q′r ′” separated by a broken line.
The range "s'" indicates the range in which the vehicle image 11 exists. A'and B'indicate ordinate positions on the screen corresponding to the upper and lower ends of the image 11, and C'and D'indicate abscissa positions on the screen corresponding to the left and right ends.

In the present invention, the method of triangulation is applied to the information on this screen to calculate the absolute inter-vehicle distance from the preceding vehicle in real time. The method of the present invention utilizes the fact that the image of the rear view of the vehicle has a horizontal edge component when the vehicle is straight ahead to speed up the processing, and observes a certain point on the vehicle body of the preceding vehicle to measure the distance. Unlike the conventional technique for measuring, the preceding vehicle is grasped and processed as a certain area on the screen, so that a reliable measurement result can be obtained.

FIG. 3 is a flowchart showing the flow of processing in the computer 7. In the figure, each step indicated by S indicates processing of image data of the image pickup apparatus 1, and each step indicated by S ′ indicates processing of image data of the image pickup apparatus 2.

Hereinafter, this will be described step by step.

． Detection of horizontal component (steps S1 and S'1) Vertical spatial differentiation processing is performed on the image data from the image pickup devices 1 and 2 shown in FIGS. Find a differential image that represents the horizontal component.

.2 binarization (steps S2, S'2) The differential pixel (hereinafter simply referred to as "pixel") of each point in the image obtained above is set to "0" by a certain threshold value n.
(White) ”and“ 1 (black) ”are binarized to remove noise. For example, when each pixel value <n; each pixel value is set to "0 (white)".

When each pixel value ≧ n; each pixel value is set to “1 (black)”.

FIGS. 4 (a) and 4 (b) show images obtained by binarizing the image data shown in FIGS. 2 (a) and 2 (b) after detecting the horizontal component.

.A, B determination (steps S3, S'3) For each image as shown in FIGS. 4 (a) and 4 (b) obtained above, the value of each pixel (0
Alternatively, 1) is integrated to create a horizontal histogram as shown in FIGS. 5A and 5B, and a certain threshold value m is applied to this histogram so that the histogram exceeds the threshold value m. Find the points at the top and bottom, and call them A and B, respectively. Then, as shown in FIGS. 6 (a) and 6 (b), the vertical processing area is defined with A and B as upper and lower limits, respectively.

.C, D determination (steps S4, S'4) For each processing area shown in FIGS. 6 (a) and 6 (b) defined above, the value (0 or 1) of each pixel is vertically integrated. Then, a histogram in the vertical direction as shown in FIGS. 7 (a) and (b) is created, the average value is obtained, and the widest range satisfying the histogram value ≧ average value is obtained, and the points at both ends are obtained. And C and D respectively. Since C and D are determined by obtaining the average value in this way, even if there is noise as indicated by a in the histogram in the vertical direction, it will not be detected.

FIGS. 8 (a) and 8 (b) show an extracted image of a vehicle, which is sized by A, B and C, D determined in this way, and is shown by being surrounded by a broken line. Range `` pqr
"s" corresponds to the range of the image data shown in FIGS. 2 (a) and 2 (b).

． Calculation of Inter-Vehicle Distance In FIG. 1, the lower imaging device 2 is at a height H from the ground, the upper imaging device 1 is at a height b from the imaging device 2, and the lenses of both imaging devices have the same focus. It has a distance f and its optical axis is parallel and parallel to the ground.

As shown in FIG. 9, a coordinate system with the lens center of the image pickup device 2 as the origin, the height direction as the Y axis, the traveling direction of the vehicle as the Z axis, and the direction orthogonal to these as the X axis is considered. Car P
Let (x, y, z) be the coordinates of the image pU of P on the image plane of the upper imaging device 1 (φU, ηU), and the image pD of P on the image plane of the lower imaging device 2 The coordinates are (φD, η
D). Here, pU and pD respectively correspond to the vertex p of the extracted image “pqrs” of the image pickup devices 1 and 2 in FIG.

4 of the image "pqrs" shown in FIGS. 8 (a) and 8 (b)
The two vertices p, q, r, s correspond to each other, and in the distance detection method of the present invention, the absolute inter-vehicle distance may be calculated for any of the vertices. In a truck-type vehicle, the loading platform is projected, so that it is preferable to perform this at the vertex p or q. In the following, the inter-vehicle distance is calculated for the point p.

The following relationship exists between the coordinates (φD, ηD) of the image pD of the lower imaging device 2 and the coordinates (x, y, z) of the point P.

φD = f · (x / z) ··· ηD = f · (y / z) ··· Next, the correspondence between the point P viewed from the position (0, b, 0) of the upper imaging device 1 and the image is obtained. Now relative coordinates (x ', y', z ')
Shall be defined as follows.

x ′ = xy ′ = y−b z ′ = z If rewritten by relative coordinates (x ′, y ′, z ′), the coordinates of the upper imaging device 1 will be (0,0,0), and the point P The coordinates are (x ', y', z '), and the coordinates of the image pU are as follows.

φU = f · (x ′ / z ′) = f · (x / z) = φD …… ηU = f · (y ′ / z ′) = f · (y−b) / z …… Therefore The coordinates (x, y, z) are calculated as follows.

x = b · φD / (ηD−ηU) …… y = b · ηD / (ηD−ηU) …… z = b · f / (ηD−ηU) …… From the formula, f · y = ηD · zy = ΗD · z / f, substituting this into the equation yields ηU = f · [(ηD · z / f) −b] / z, from which the vehicle distance z can be calculated as follows.

z = b · f / (ηD−ηU) ... Since b and f are constants in the formula, the computer 7
Can know the coordinates ηU and ηD on the image planes of both the upper and lower image pickup devices and perform the calculation according to the formula to obtain the inter-vehicle distance.

When the absolute inter-vehicle distance is obtained in this way, the display is performed on the inter-vehicle distance meter 8. The display may be performed in an analog manner using an indicator or the like, or may be performed digitally using a liquid crystal element or the like.

Further, with respect to the inter-vehicle distance, a certain threshold value d can be set, and the computer 7 compares the inter-vehicle distance z with the threshold value d to generate an output signal when the inter-vehicle distance: z <d, As a result, the driver can be warned of the abnormal approach by, for example, sounding a buzzer.

As described above, according to the present embodiment, the absolute value of the inter-vehicle distance from the preceding vehicle can be measured and displayed in real time, and at the same time an alarm is issued to alert the driver when an abnormal approach occurs. This is extremely effective in preventing traffic accidents.

〔The invention's effect〕

Since the present invention is configured and functions as described above, according to this, since the significant width detecting means operates as described above,
The noise can be removed well. As a result, the inter-vehicle distance can be satisfactorily measured even in an environment where it is very difficult to perform the inter-vehicle distance between relatively moving objects in one moving body in terms of image processing. Moreover, since the image processing is performed by utilizing the fact that the rear view of the front vehicle has many horizontal edge components, the excellent noise removal and the extraction processing of the front vehicle can be performed very quickly. Therefore, the structure is simple and the processing is high-speed, and because the processing that makes use of the characteristics of the rear view is used, the accuracy of noise removal is also good, and therefore the accuracy of the inter-vehicle distance detection is also good. . Also, the first
Also, the same processing may be performed on the image from the second imaging device, and the configuration of the absolute inter-vehicle distance detection method becomes simple. In this way, it is possible to accurately calculate the inter-vehicle distance and detect abnormal approach by effectively extracting only the vehicle portion for which the noise is effectively removed and the inter-vehicle distance is calculated. An excellent absolute vehicle distance detection method can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention, FIG. 2 is a diagram illustrating image data in an image pickup apparatus, and FIG.
FIG. 4 is a flowchart showing the flow of processing in the computer. FIG. 4 is a diagram showing an image obtained by binarizing after detecting a horizontal component. FIG. 5 is a diagram showing a horizontal histogram. FIG. 6 is a vertical process. FIG. 7 is a diagram showing a region, FIG. 7 is a diagram showing a vertical histogram, FIG. 8 is a diagram showing an extracted image of a vehicle, and FIG. 9 is a diagram showing a coordinate system. 1,2 ... Imaging device, 3 ... Vehicle, 4 ... Analog-to-digital (A / D) converter, 5 ... Processing device, 6 ... Memory,
7 ... Computer, 8 ... Vehicle distance meter.

Claims (1)

[Claims] 1. An image pickup apparatus for picking up an image of a moving object, and a horizontal component is extracted by performing a spatial differentiation process for obtaining a change value of vertical brightness for an image of the object by the image pickup apparatus. The horizontal direction component extraction means, the binarization means for binarizing the horizontal direction component, and the two points at which the histogram value in the horizontal direction of this binarized image exceeds the threshold value m At least two sets of means for detecting the significant width in the horizontal direction by determining the significant width in the vertical direction and obtaining the widest width in which the histogram value in the vertical direction in the vertical significant region is not less than the average value A significant width detecting means is provided, and the distance to the object is obtained and displayed based on the coordinates of the corresponding points of the two sets of images determined by the significant width in the horizontal direction when the respective imaging devices are provided apart from each other. With An absolute inter-vehicle distance detection method characterized by being equipped with means for detecting that the distance has fallen below a predetermined value and issuing an alarm.