JP4451179B2 - Lane position detection system - Google Patents

Description

  The image obtained by imaging the road surface with the in-vehicle camera is converted into a bird's-eye view image, the luminance of the bird's-eye view image is integrated in parallel with the vehicle traveling direction, and the luminance profile in the direction perpendicular to the traveling direction is obtained to determine the position of the white line. The present invention relates to a lane position detection system for detection.

  2. Description of the Related Art Conventionally, a method is known in which a camera is installed facing forward or backward in the traveling direction of a vehicle, and a camera image captured using a viewpoint conversion technique is converted into a bird's-eye view image (for example, Patent Document 1, Patent) Further, there has been proposed a lane marker position detection device that detects the position of a white line (lane marker) on the road surface from the converted overhead image (see Japanese Patent Application No. 2002-246859). And Japanese Patent Application No. 2003-146535).

  FIG. 7 is a block diagram showing a schematic configuration of the above-described lane marker position detection apparatus. The lane marker position detection device 1 includes a camera 2, a bird's-eye view image conversion device 3, a white line detection / deviation warning device 4, and a monitor 5. FIG. 8 is an image taken by a camera (rear camera) 2 installed at the rear of the vehicle. The image photographed by the camera 2 is changed to an overhead image by the overhead image conversion device 3 as shown in FIG.

  The white line detection / departure alarm device 4 includes a microcomputer 6, a work memory 7, an encoder 8, a buffer memory 9, and an alarm device 10. The microcomputer 6 integrates the overhead image converted by the overhead image conversion device 3 for each pixel using the work memory 7 and graphs the integrated luminance for each pixel in the horizontal direction. A luminance profile of the image is generated (step S1 in FIG. 10). FIG. 9B shows an ideal luminance profile of the overhead view image shown in FIG. Signs, white lines, etc. written in white on the road surface show high intensity (luminance value), so the peak corresponding to the white line from the intensity value (brightness level), its position, peak width, etc. is the luminance profile. (Step S2 in FIG. 10). When the overhead image is output to the monitor 5, the image signal of the overhead image is converted into a composite signal or the like by the encoder 8 and output to the monitor. Note that the warning device 10 issues a warning such as a buzzer to the driver when it is determined that the vehicle is not traveling along (along) the white line based on the comparison between the vehicle position and the white line position (step of FIG. 10). 3). A buffer memory 9 installed between the overhead image conversion device 3 and the microcomputer 6 is a memory for synchronizing both.

As described above, if the brightness profile generated by the microcomputer 6 is detected as an ideal value, the graphs shown in FIGS. 9B and 11A are obtained, but are generated realistically. The luminance profile is a graph composed of continuous curves as shown in FIG. 11B under the influence of noise and the like. For this reason, the microcomputer 6 performs lane detection after performing processing for emphasizing the signal portion related to the white line as shown in FIG. 11C by performing filter processing using a high-pass filter or the like on the luminance profile. .
JP-A-3-99952 JP-A-9-171348 Japanese Patent Laid-Open No. 2001-114048 JP 2001-116567 A

However, since the road environment is diverse and there are many feature points other than the white line on the road surface, a portion other than the white line may appear as a peak intensity in the generated luminance profile. Also, depending on the situation, this peak intensity may appear prominently, and if there is no difference in the intensity ratio with the white line, there is a risk of erroneously recognizing the lane. In particular, if the road surface condition changes due to changes in weather or time zone, it is highly likely that it will be misrecognized, so it is difficult to handle all road surface conditions using a single filter process. There was a problem.

  The present invention has been made in view of the above-described problems, and it is an object of the present invention to provide a lane position detection system capable of automatically performing optimal white line detection processing according to various road conditions and road environments. And

The invention according to claim 1 converts an image obtained by imaging a road surface with an in-vehicle camera into a bird's-eye view image, integrates the luminance of the bird's-eye view image in parallel with the vehicle traveling direction, and luminance in a direction perpendicular to the traveling direction. In the lane position detection system for obtaining a profile and detecting the position of a white line by applying a filter process to the brightness profile , a plurality of filters having different frequency characteristics are prepared as filters used for the filter process, and the one brightness profile On the other hand, the present invention is a lane position detection system that compares the peak intensities between a plurality of luminance profiles obtained by performing filter processing using each of the plurality of filters, and determines a white line position. And
The invention according to claim 2 is the lane position detection system of claim 1, using a plurality of high-pass filter for one of the brightness profile, among a plurality of the luminance profile that has been subjected to the filtering process Are compared, the portion where the difference in peak intensity shows a certain level or more is deleted as an erroneous signal.

The invention according to claim 3 is the lane position detection system according to claim 1, wherein the filter used for the filter processing is a differential filter and a high-pass filter, and the luminance profile is subjected to filter processing using the differential filter. the partial double peak appears is determined as a candidate of the white line position in, and wherein the luminance profile subjected to filtering, over there narrow down further the white line position by using the high-pass filter.

According to the lane position detection system according to the present invention, the filtering process is performed using a plurality of filters to compare the peak intensities of the luminance profiles, so that the detection accuracy of white line detection can be improved.

  Hereinafter, a lane position detection system according to the present invention will be described with reference to the drawings. The lane position detection system according to the present invention is characterized in that white line detection accuracy is enhanced by using a plurality of information. As a method of improving the white line detection accuracy in this way, (1) a method of judging road conditions with reference to results detected by sensors installed in vehicles and operating conditions of electrical equipment, and (2) a plurality of methods Two types of methods are used: a method of selecting an appropriate filter process or a result while evaluating the difference in the results by parallelizing the above processes. These two types of methods will be described using a principle description and a plurality of representative examples. However, since there are a wide variety of actual road conditions and road environments, the processing method of the present invention is not limited to the examples. It is not limited to what is shown.

(1) Method for Determining Road Conditions Based on Detection Results of Sensors and the like and Operational Conditions of Electrical Equipment FIG. 1 is a block diagram showing a lane position detection system according to the present invention. The lane position detection system 20 includes a camera 21, an overhead view generation unit 22, a profile generation unit 23, a lane detection unit 24, an alarm unit 25, and an environment determination unit 26. Detection results of various sensors 27 installed in the vehicle, operating conditions of the electrical equipment, and the like are transmitted to the environment determination unit 26. Specifically, the environment determination unit 26 includes a vehicle speed pulse sensor, a gear switch, a wiper switch, a light sensor (light sensor for automatically turning on and off the headlight), a headlight, a direction indicator switch, a rudder angle sensor, and a navigation system (road information). (Map information), location information, date / time information, acceleration sensors, etc., to receive information such as road surface conditions (ambient brightness, wet / dry conditions, etc.), road environment information (highways, general roads, (Number of lanes / road width), vehicle running status, driving lane identification, road curve / straight line status, presence / absence of lane change, etc.

  The environment determination unit 26 transmits a determination result such as a road surface condition to the overhead view generation unit 22, the profile generation unit 23, the lane detection unit 24, and the like. Based on the received determination result, the profile generation unit 23 performs processing for selecting a region for generating a brightness profile in the overhead image (focused region control processing) and selection / adjustment of a filter for filter processing applied to the luminance profile. One or more luminance profiles are generated.

FIG. 2A is a bird's-eye view showing the rear road surface condition of a vehicle traveling at high speed in rainy weather. In such an environment in rainy weather, compared to that in fine weather,
Features 1. A spear-like water splash is generated by the rear wheel, and a pseudo white line 30 is generated.

    Feature 2. Since the illuminance at the outer periphery decreases due to rain (low illuminance), background noise increases relatively in the overhead image.

  It has the characteristics In particular, the feature 1 is an important problem because the possibility that the splash is erroneously recognized as a pseudo white line is increased when the luminance profile is generated as shown in FIG.

  For this reason, the environment determination part 26 determines whether the surroundings are rainy using a wiper switch and a speed sensor. In particular, since the wiper switch is set in a stepwise manner from an intermittent operation state to a continuous operation state depending on rain conditions, it is possible to determine the strength of rain. For example, in a situation where the water splashes on the road surface, it is necessary to accumulate water on the road surface. Therefore, it can be estimated that the water spray can occur when the wiper is switched to the continuous operation state.

  In addition, if the vehicle does not travel at a certain speed or longer, a long splash mark does not remain on the road surface. Therefore, the environment determination unit 26 performs the splash handling process by determining the traveling speed information together with the continuous operation state of the wiper. It is determined whether or not to do so.

  When the two conditions of the wiper operating condition and the vehicle traveling speed information are satisfied, the environment determining unit 26 determines that the road condition is in an environment where splashing can occur, and performs processing corresponding to the splashing for the profile generating unit 23. Give instructions to do so.

  When it is determined that the environment can be splashed, the profile generation unit 23 first changes the cutoff frequency of the high-pass filter (HPF) for filtering the luminance profile. For example, a white line-shaped locus 30 due to splashing is shown with a blurred edge in the overhead image compared to the actual white line 31. Moreover, since the splash spreads out of the tire, the apparent width in the overhead view image becomes wider than the white line. Since the splash peak value contains more low-frequency components than the white line peak value, the signal strength due to splashing is selected by setting the cutoff frequency of the high-pass filter higher than usual, as shown in FIG. Decrease. This cut-off frequency is determined in advance by experiments or the like. Since the change in the cut-off frequency weakens the signal intensity, it is desirable that the lower one is used when the weather is fine when there is no such problem of spraying.

  As described above, the lane detection unit 24 performs the white line position detection process after the rain condition specific filtering process is performed. The white line detection process in the lane detection unit 24 also performs the determination process dedicated to the rain condition. Since the pseudo white line 30 due to splashing has a characteristic that occurs at the position of the rear wheel, erroneous detection can be reduced by performing processing using the characteristic.

  For example, since the splash spreads outside the tire, the apparent width in the overhead view image is wider than the white line, and a width difference tends to appear between the peak width of the splash and the peak width of the white line. For this reason, by evaluating the error of the peak width more heavily, it is possible to increase the determination accuracy between the splash and the white line 31, and to reduce erroneous detection. Further, by setting the weight of the signal at the wheel position 33 to be relatively light at the detected peak position, it is possible to reduce false detection of a pseudo white line of splashing from the tire.

  Furthermore, by changing the filter processing (filter processing related to the time axis, time filter) based on the time axis for changes in the luminance profile determined over time (temporal), it may also be due to rainy weather, etc. When it is considered that background noise is likely to be mixed in a bird's-eye view image due to a decrease in peripheral illuminance (low illuminance), a filter with a cut-off frequency shifted to the low-circumference side in a temporal low-pass filter (LPF) By switching, it is possible to reduce noise and improve the stability of detection intensity. In addition, it is not limited only to the structure which performs all three elements of the change process in a filter part (spatial filter), the process change in a determination part, and the process change in a time filter part, depending on road conditions etc. In some cases, it is possible to detect the lane with sufficient accuracy by selectively performing one of the processes. Accordingly, the lane detection processing is not limited to the above-described one, and it is possible to improve the reliability comprehensively by specifying road conditions and the like with various sensors and selecting the optimum filter characteristics.

  In order to improve the reliability of the lane detection, not only the filter characteristics are controlled as shown in [Embodiment 1], but also an overhead view of the overhead view image for performing the lane detection by controlling the overhead view generation unit 22. A method of controlling the pattern or image processing area is also effective. Such image processing includes two types of methods: a method of changing the scale of the overhead pattern itself, and a method of processing only a specific scanning line region of the image. The method of changing the scale of the overhead view pattern is realized by the processing in the overhead view generation unit 22, and the method of processing only a specific scanning line region is realized by the processing in the profile generation unit 23. Each is an effective method for coarse adjustment and fine adjustment of an overhead image.

  For example, it is desirable to appropriately switch the bird's-eye view image used for lane detection depending on whether the road on which the vehicle is traveling is a straight road or a curve. When the vehicle is traveling in a straight line, it is possible to detect the peak of the white line 31 with high accuracy by creating a luminance profile using a wide image area from the front end to the rear end of the overhead image as much as possible. In addition, the peak due to noise can be reduced compared to the white line peak. Further, the difference from the peak of the pseudo white line (white wave line) 30 such as splashing can be clarified, and the signal intensity of the white line 31 can be stably secured. On the other hand, when traveling on a curve as shown in FIG. 3A, in order to ensure the detection accuracy of the lane position, a vehicle foreground portion (side closer to the vehicle) 35 that can be approximated to a straight road. It is desirable to use the bird's-eye view image for lane detection processing. The detection of the curve is determined using information such as the sensor 27 described above, for example, navigation information from the car navigation system, steering angle information of the steering wheel by the steering angle sensor, or a difference in rotational speeds of the left and right vehicle speed sensors. When the environment determination unit 26 determines that the vehicle is traveling on a curve, the profile generation unit 23 changes the range of the overhead view image from the entire range of the overhead view image to the foreground range 35 based on the signal from the environment determination unit 26. To generate a profile. At this time, which one of the two methods described above is to be adopted is appropriately selected in consideration of hardware restrictions and the like. FIG. 3B shows a luminance profile generated for the entire range of the overhead image, and FIG. 3C shows a luminance profile generated only for the foreground range 35 of the overhead image. As apparent from FIGS. 3B and 3C, in the luminance profile using only the foreground range 35, the peak intensity of the white line portion in the far view range 36 (the portion indicated by the chain line in FIG. 3C). Is not included, the peak width is narrowed, and the detection accuracy of the lane position is improved.

  FIG. 4 is a bird's-eye view image showing the rear road surface condition of a vehicle traveling at high speed at night. As shown in FIG. 4, the light of the light does not reach far away at night, so when performing the lane detection process based on the brightness of the white line 31, the range in which the white line detection process can be performed effectively is the light of the license plate Is a region close to the vehicle (processing region 1 in FIG. 4) that is a range in which the road surface can be irradiated.

The environment determination unit 26 determines whether or not the traveling time is nighttime by detecting whether or not the lamps are turned on or by receiving time information from the car navigation system navigation. When the environment determination unit 26 determines that it is nighttime, the profile generation unit extracts only the range of the processing area 1 in FIG. 4 and creates a luminance profile using only this range. By generating the luminance profile using only the processing region 1, it is possible to improve the reliability of the luminance profile and improve the white line detection accuracy. When this specific method is used, two types of methods can be used as in [Example 2].
(2) A method of selecting an appropriate filter process or result while parallelizing a plurality of processes and evaluating the difference between the results.

  Next, a method for parallelizing a plurality of processes (independent determination by parallel filter processing) will be described.

  When the information of the various sensors 27 described above cannot be obtained sufficiently, several filter processes adapted to specific conditions are operated to generate a plurality of profiles. Thereafter, the white line detection accuracy is increased by making a comprehensive or selective determination using each profile. This method is classified into the following two methods.

  Method 1 A method of performing white line detection after comparing luminance profiles and eliminating erroneous signals (Example 4).

Method 2 A method in which white lines are detected for each luminance profile and judged by comparison (Example 5)
Hereinafter, the two methods described above will be described. In the following description, the description will be made using an example in which two filters are used together for the sake of convenience. However, in many cases, it is desirable to make a determination using three or more filters under a fail-safe idea. The number varies depending on the situation, and is not limited to two.

  When the pseudo white line due to the spider-like spray described in (1) is displayed on the road surface, the cutoff frequency is determined for the edge blurring portion expressed as the characteristics of the spray, and the filter processing is performed. As in 2 (c), the peak intensity generated in the luminance profile due to the splash can be reduced or enhanced. Therefore, when comparing the luminance profiles subjected to a plurality of filter processes, it can be determined that the portion with a different peak intensity state is more likely to be a portion other than the white line 31 (for example, a sprayed portion). For this reason, it is possible to reduce false detection of lane detection by applying two filter processes at the same time and ignoring signals whose peak intensity difference is greater than a certain level or reducing the weighting. Become.

  FIG. 5A is a bird's-eye view image showing roads in which the color of the road surface is different due to repair or the like.

  As shown in FIG. 5A, when there is a wide range of dark areas (repair surface 40) and bright areas (road surface 41), the intensity profile intensity changes in the vicinity of the boundary 42 like a step function. Since a high frequency component is included, there is a problem that signal strength is likely to remain even if filtering is performed, and erroneous recognition is likely to occur (FIG. 5B).

  In order to avoid such a problem, an inflection point is detected by using a differential filter together to determine whether the value of the peak of the luminance profile is the white line 31 or the boundary 42 of the light and dark area. When the filtering process using the differential filter is performed, as shown in FIG. 5C, there is one change point at the boundary 42 portion of the light and dark region, so there is one peak, but it is as bright as the white line 31. Double peaks appear in areas where the area is constant. Therefore, by applying a filtering process using a differential filter, a position where a double peak occurs in the luminance profile is set as a candidate for the position of the white line 31, and other places are determined to be positions other than the position of the white line 31 and ignored. Or by reducing the weighting of the evaluation function, the detection error can be reduced.

  In principle, it is possible to determine the position of the white line using only the differential filter from the beginning. However, the differential filter emphasizes the peaks if the noise is abruptly changing even with low-intensity noise, so the number of peaks tends to increase, and the amount of calculation increases. There is also sex. Therefore, the two processes of the filter process using the high-pass filter as shown in FIG. 5B and the filter process using the differential filter as shown in FIG. It is effective to suppress misrecognition by the effect. Further, it is possible to reduce the overall filter processing by extracting the region of interest first with one filter and locally applying the other filter processing to only that region. That is, the combined use of the filter processing can be expected to produce a synergistic effect of two aspects of improving the white line recognition rate and reducing the load.

  Further, in the road situation in which the boundary 42 appears due to the dark area and the bright area, not only the boundary is caused by the repair surface and the normal road surface as shown in FIG. 5A, but also a part of the road is shaded. Thus, the present invention can be similarly applied to a case where a boundary between a dark region and a bright region appears due to comparison with a portion exposed to another day.

  In order to create a brightness profile and detect white lines, it is desirable to perform brightness integration using a bird's-eye view of a wide range from the far side of the vehicle to the side of the vehicle as much as possible to obtain the peak intensity. Thus, it is possible to stably detect the white line. However, if too far away information is used, as shown in [Example 2], it is difficult to detect an accurate white line position when the vehicle is traveling on a curve, and the vehicle has approached abnormally. There is a problem that erroneous detection is likely to occur when a vehicle is present.

  Therefore, for example, as shown in FIG. 3, it is possible to independently detect whether the road is a curve by dividing the bird's-eye view image for each region and processing the near view and the distant view independently.

Specific processing procedures are exemplified as follows: A brightness profile is generated using the entire range (full screen) of the overhead image, and the white line position (position 1) is estimated.
2. A luminance profile is generated using the foreground area of the overhead image, and the white line position (position 2) is estimated from the vicinity of position 1.
3. A luminance profile is generated using the perspective view area of the overhead image, and the white line position (position 3) is estimated from the vicinity of position 1.
4). 4. If the error between position 1 and position 2 is less than the allowable value, that position is recognized as a white line position. When the position 3 is shifted with respect to the position 2, it is determined as a curve.
6). When position 3 is significantly different from position 2, it is determined that an abnormal situation (such as an approaching vehicle) is present.
It becomes. By passing through this step, it is possible to automatically detect a curve run or the like and improve the accuracy and reliability of white line detection.

  FIG. 6A is a bird's-eye view image showing a normal white line and a white line that has become difficult to see due to damage or dirt. If the white line to be detected in white line detection is severely damaged due to road construction or aging deterioration, and it is difficult to see the white line, the profile intensity will be lower than the normal white line 45 even if a brightness profile is created. Since it is not possible to obtain an appropriate peak intensity, there is a risk of erroneous detection of white line detection.

  Originally, the filter process has the property of weakening the absolute value of the signal strength, so the filter process is performed in accordance with the normal white line 45 (for example, the filter process using a bandpass filter. The filter used at this time is the filter 1. )), There are cases where a weak signal cannot be effectively separated as shown in FIG. On the other hand, when a filtering process (for example, a filtering process using a high-pass filter; the filter used at this time is a filter 2) adapted to a weak signal is applied to a luminance profile of normal intensity, it is shown in FIG. As such, there is a problem that the background noise is picked up and the processing tends to be complicated.

To cope with such a situation, when two or more types of filters with different intensity ranges that can detect white lines are used together, signal detection determination is performed in order from the filter corresponding to the strong intensity, and the signal cannot be detected The filter used for white line detection is selected by referring to the filter processing results of lower strength in order. In the example of FIG.
1. Usually, the position of the white line is detected by filter processing using the filter 1 (FIG. 6B).

2. When the white line undetected state continues for a certain time, the white line position is detected by filter processing using the filter 2 (FIG. 6C).
It becomes. Since the filter 2 has a pseudo peak as described above, the processing load of the filter processing becomes heavy, and the number of times that processing can be performed per unit time is reduced. However, compared with the undetected state using the filter 1, white line detection is significantly performed. Accuracy can be improved. Further, since the reliability of the peak intensity detected by the filter 1 is considered to be high, the reliability is improved by searching for the position of the white line 46 that is difficult to see by trusting the peak intensity. Can be achieved. As an example of the filter configuration as described above, a high-pass filter (HPF) or a band-pass filter (BPF) whose cutoff frequency band and filter order are adjusted is used.

  The lane position detection system according to the present invention has been described above with reference to the drawings. However, the lane position detection system according to the present invention is not limited to the above-described one, and is designed within a range that can be considered by those skilled in the art. Changes and improvements are also included in the lane position detection system according to the present invention.

It is the block diagram which showed the lane position detection system which concerns on this invention. (A) is the bird's-eye view image showing the road surface condition of the vehicle traveling at high speed in rainy weather, (b) shows the luminance profile of the bird's-eye view image of (a), and (c) is shown in (b). In comparison, a luminance profile in which the cutoff frequency of the high-pass filter is set higher is shown. (A) is a bird's-eye view image showing a road surface condition of a vehicle traveling at a high speed on a curve, and (b) shows a luminance profile generated using the entire region of the bird's-eye view image of (a). c) shows a luminance profile generated using the near view area of the overhead image of (a). It is the bird's-eye view image which showed the road surface condition of the vehicle which is driving at high speed at night. (A) is a bird's-eye view image showing roads with different road surface colors due to repairs, etc., (b) shows a luminance profile that has been filtered by a high-pass filter, and (c) shows a differential filter. The luminance profile which performed the filter process is shown. (A) is a bird's-eye view image showing a normal white line and a white line that has become difficult to see due to scratches or dirt, and (b) shows a luminance profile that has been subjected to filter processing by a bandpass filter. ) Shows a luminance profile that has been filtered by a high-pass filter. It is the block diagram which showed the conventional lane position detection apparatus. It is the image image | photographed with the camera (rear camera) installed in the vehicle back. (A) is an overhead image of the image shown in FIG. 8, and (b) is a luminance profile. It is the flowchart which showed the lane position detection process in the conventional lane position detection apparatus. (A) shows an ideal luminance profile generated from a bird's-eye view image, (b) shows an actual luminance profile, and (c) shows a filtering process using a high-pass filter on the luminance profile shown in (b). The brightness | luminance profile which gave is shown.

Explanation of symbols

20 lane position detection system 21 camera 22 overhead view generation unit 23 profile generation unit 24 lane detection unit 25 alarm unit 26 environment determination unit 27 sensor

Claims (3)

An image obtained by imaging the road surface with the in-vehicle camera is converted into a bird's-eye view image, and the luminance profile of the bird's-eye view image is integrated in parallel with the vehicle traveling direction to obtain a luminance profile in a direction perpendicular to the traveling direction. In the lane position detection system that detects the position of the white line by applying filter processing,
A plurality of filters having different frequency characteristics are prepared as filters used for the filter processing, and a plurality of luminance profiles obtained by applying filter processing using each of the plurality of filters to the one luminance profile A lane position detection system characterized in that the white line position is determined by comparing peak intensities between the two. Using a plurality of high-pass filter, the portion indicated with respect to one of the brightness profile, when comparing among a plurality of the luminance profile that has been subjected to the filtering process, the difference is above a certain magnitude of the peak intensity The lane position detection system according to claim 1, wherein the lane position detection system is deleted as an erroneous signal. The filter used for the filter processing is a differential filter and a high-pass filter, a portion where a double peak appears in a luminance profile subjected to filter processing using the differential filter is determined as a candidate for a white line position, and the high-pass filter is The vehicle position detection system according to claim 1, wherein the position of the white line is further narrowed down from the brightness profile subjected to the filtering process.

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