JPH02161337A - Road surface state detecting device - Google Patents

Abstract

PURPOSE:To extremely simplify the maintenance/inspection work by a concise device by extracting a vertical polarization image and a horizontal polarization image from in a reflected light from a road surface in the vicinity of a specific angle, and deciding a road surface state, based on a variation of density information in each image. CONSTITUTION:To a TV camera 11 installed toward a road surface 1 at an angle of about 53 deg., an image of an object to be monitored is inputted. In this state, when a linear polarizer 12 is set to a vertical polarization position, a video signal of a vertical polarization image is outputted from the TV camera 11, passes through an LPF 13 and an A/D converter 14 and sent to image memories 15, 16. When an input of one screen of the vertical polarization image to the image memory 15 is ended, a control part 22 sets a sampling timer 23, rotates the polarizer 12 by a time-up signal l and sets a plane of polarization to a horizontal polarization position. Thereafter, a video signal of a horizontal polarization image is outputted from the camera 11, brought to A/D conversion 14, digital density data (a) of multi-gradation is selected and stored in the image memory 16, and digital density data of the memories 15, 16 are brought to logarithmic calculation 17, 18, brought to difference conversion 19 and outputted to a microcomputer 21.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a road surface condition detection device for detecting the dry state and wet (wet, frozen, etc.) state of a road surface.

[Conventional technology]

As this type of road condition detection device,
There is one described in Publication No. 896.

This conventional device uses a pattern matching method to determine the road surface condition, and as shown in FIG. A patterned target 55 is laid with three types of reflectors arranged at predetermined intervals: a road surface section 52, a bright section 53 that is brighter than the road surface section 52, and a dark section 54 that is darker than the road surface section 52. 25
6, the reflected light is adjusted to a constant light intensity by an automatic light intensity device 57, and then photographed by an imaging device 58 such as an ITV camera and converted into a video signal. 12 prepared in advance in 59
Compare with reference patterns corresponding to each road surface condition such as dry, rainy, frozen, snowy, etc. as shown in Figures 1) to (e),
The road surface condition is detected based on whether the patterns match or not.

[Problem to be solved by the invention]

However, in the case of the above-mentioned conventional device, in order to actually judge the road surface condition, it is necessary to lay out the target 55 for pattern recognition on the road surface in advance, which makes the installation work complicated, and the tire Detection accuracy deteriorates over time due to dirt, discoloration, and decolorization of the target due to contact with other objects, and maintenance and inspection work after installation must be performed frequently. Furthermore, there is also the problem that unevenness is likely to be formed on the target surface due to the running of the vehicle, and the reflected light pattern changes, making it impossible to obtain pattern recognition results according to theory.

Furthermore, the conventional device described above determines the dry and wet conditions of the entire road surface from spot information on the road surface in the target area, but if the target area is different from other road surface areas other than the target area. The road surface condition, for example, if water that has accumulated on the hood of a vehicle has fallen into the target area, or if water has accumulated in the ruts of a car that have formed in the target area, the road surface as a whole is dry. There has been a problem in that it is not possible to accurately grasp the condition of the entire road surface, which has a wide area, such as sometimes determining that the road surface is wet even though the road surface is wet.

The present invention was developed in view of the above circumstances, and focuses on the fact that the polarization state of road surface reflected light changes depending on the road surface condition. It is an object of the present invention to provide a road surface condition detection device capable of determining conditions over a wide area.

[Means to solve the problem]

In order to achieve the above object, the present invention, as shown in the principle in FIG. Polarizing element 3 whose polarization plane can be varied vertically and horizontally
, a polarization angle control means 4 for variably controlling the polarization plane of the polarization element in vertical and horizontal directions, and an image storage means 5 for storing at least two or more images with different polarization angles output from the road surface imaging means; The image forming apparatus includes road surface condition determining means 6 for determining whether the road surface is dry or wet based on changes in brightness and darkness between images having different polarization angles.

[For production]

Before explaining the operation of the road surface condition detection device of the present invention, the refraction and reflection of light and polarization, which are the basis of the road surface condition determination process of the present invention, will be described.

Generally, the plane of vibration of light in natural light is random, but in order to make it easier to understand, in the following we will use vertically polarized light (S
polarized light) and horizontally polarized light (P
Only two types of light (polarized light) are picked up.

Now, in FIG. 3(a), 11. If I, , If is the light intensity of the incident light 9 reflected light and refracted light, and M, , M, , M is the area of the incident light 9 the area of the reflected light 9 M, then the incident light I and the reflected light are I1. Each energy W of the refracted light rr,
W,, W, can be expressed by the following equation.

Further, the energy reflectance R of the substance A on which light is incident is defined as the following equation.

Here, when the energy reflectances Rp and Rs of horizontally polarized light (P polarized light) and vertically polarized light (S polarized light) are calculated for an arbitrary incident angle φ from Fresnel's formula, the following equations are obtained.

Note that φ and T represent the incident angle of 2M shown in FIG. 3(b).

From this equation (3), when (φ+γ) becomes π/2, R
The denominator of P, tan” (φ+γ), becomes infinite, so the energy reflectance RP of horizontally polarized light (P polarized light) is 0.
becomes. That is, when (φ+γ) is π/2, all the horizontally polarized light components are transmitted, and the reflected light reflected from the substance A is only the vertically polarized (S-polarized) component. Expressing this in the formula, π φ+γ= ・−・−−−−
...--(4). From 5nell's law, the refractive index n in Fig. 3('b).

The relationship with n2 is n-thickness sin φ = tanr ・------(
5) n! If the relationship of equation (5) holds true, all horizontally polarized light components will pass through material A, and the reflected light from material A will be only vertically polarized light.

Figures 4 and 5 show the energy reflectance R1°R3 of water and ice.
As is clear from this figure, which shows a measurement example of It can be seen that there is a difference. On the other hand, on a rough surface such as asphalt that constitutes a road surface, light is diffusely reflected almost all over the surface, so there is almost no difference in the level of reflected light between the horizontally polarized light component and the vertically polarized light component on a dry road surface.

Therefore, by detecting changes in the vertical and horizontal polarization components of the reflected light near 53°, it is possible to distinguish between a dry state and a wet state of the road surface.

The road surface condition detection device of the present invention is constructed based on the above conclusion, and the road surface imaging means 2 picks up only light rays in the vicinity of 53° in the reflected light from the road surface 1. At this time,
The polarization angle of the polarization element 3 disposed in front of the road surface imaging means 2 is alternately switched between the horizontal direction and the vertical direction at constant time intervals of about 10 milliseconds to several seconds by the polarization angle control means 4.

Therefore, horizontally polarized images and vertically polarized images of the road surface 1 are alternately input to the road surface imaging means 2, and each image is converted by the road surface imaging means 2 into a video signal that provides contrast density.

The image storage means 5 stores the horizontal polarization image and the vertical polarization image outputted from the road surface imaging means 2 as image data, and sends the image data to the road surface condition determination means 6. Then, the road surface condition determining means 6 determines whether the road surface is dry or wet based on the density data of the horizontally polarized image and the vertically polarized image.
Determine whether the device is wet, frozen, etc.).

Fig. 6 shows an example of a vertically polarized light (S polarized light) image and a horizontally polarized light (P polarized light) image when the road surface is dry when the road surface imaging means 2 is installed near 53 degrees, and Fig. 7 shows an example of a captured image when the road surface is wet. An example of capturing a vertically polarized light (S polarized light) image and a horizontally polarized light (P polarized light) image is shown below.

When the road surface is dry as shown in Fig. 6(a) and (b), the road surface 1
As mentioned above, can be considered as an almost entire surface diffuse reflector, so even if the polarization plane of the polarizing element 3 placed in front of the road surface imaging means 2 is changed to vertical or horizontal directions as shown in (a) and (b), , there is almost no change in brightness or darkness between the two images.For this reason, for example, if you subtract the density values at the same pixel position between the images in (a) and (b), the subtracted image will have a density value of The image will be zero. Furthermore, if the density values at the same pixel positions are divided, the resulting divided image will be a uniform image with a density value of approximately 1.

On the other hand, when the road surface is wet as shown in Fig. 7(a) and (b),
(The vertical polarization image in Figure 81 has almost no difference from the dry image in Figure 6 Ta), but there are areas where water is present (wet, frozen, etc.)
In this case, all horizontally polarized light (P-polarized light) components are transmitted, absorbed and reflected by the asphalt surface below. Therefore, most of the reflected light from the road surface is vertically polarized (S-polarized) component, and (b) In the horizontally polarized image in figure 1, the contrast density value in the area where moisture exists, indicated by hatching in the figure, is small (as an image) becomes dark).

For this reason, for example, by calculating the difference in density values between the same pixel positions in the images shown in FIGS. 3(a) and 3(b), it is possible to accurately extract only the portion where moisture is present.

As mentioned above, when the road surface is dry and when the road surface is wet, 53
Since the vertically polarized image and the horizontally polarized image in the vicinity are significantly different from each other, the road surface condition can be accurately detected from the photographed image by comparing the density changes between these images using the road surface condition determining means 6.

In the case of the present invention, any light source that illuminates the road surface can be used as detection light as long as it is near 53 degrees, so there is no need to use specific light as the illumination light source that illuminates the road surface. Therefore, the reflected light component of natural light Because it can be used directly, it is easy to obtain image data of the entire road surface, and as a result, it is possible to determine the extent of the road surface condition, such as whether the entire road surface is wet or only a part of it is wet. This makes it possible to make accurate judgments.

As the road surface imaging means 2, it goes without saying that a well-known imaging device such as an ITV camera (image pickup tube, CCD, etc.) may be used.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 8 is an example of a road surface condition detection device according to the present invention,
In the figure, 11 is a television camera such as an ITV camera as a road surface imaging means, 12 is a linear polarizer placed in front of the television camera 11, 13 is a low-pass filter, 14 is an A/D converter, and 15.16 is an input image. 17 and 18 are logarithmic calculators, 19 are difference calculators, 20 are output memories that store calculation results, and 21 are microprocessors that perform road surface condition determination processing. , 22 is a control unit that performs variable control of the polarization angle of the linear polarizer 12 and sampling control for capturing image data, and 23 is a sampling timer.

The television camera 11, for example, as shown in FIG.
Road surface 1 is located on the side of the road where the road surface condition should be monitored.
It is installed at an angle of approximately φ=53° toward the In addition, if detection at night is also considered, the night illumination light 24
It is more desirable to install it near etc.

Next, the operation of the embodiment having the above configuration will be explained.

Images of the road surface to be monitored as shown in FIGS. 6 and 7 are input to the television camera 11, which is installed at an angle of approximately 53 degrees toward the road surface 1.

The control unit 22 outputs the polarization angle control signal g, and the linear polarizer 1
2 is rotated to the vertical polarization position, and in synchronization with this, the image capture signal m is output to the A/D converter I4.

When the linear polarizer 12 is set to the vertical polarization position, a video signal of a vertically polarized image as shown in FIG. 6(a) or FIG. 7(a) is output from the television camera II, and this video signal is passed through a low-pass filter. 13 to the A/D converter 14. Then, the A/D converter 14 samples the video signal of this vertically polarized image, converts it into multi-gradation digital density data a, and sends it to the image memory 15.16.

Note that the low-pass filter 13 is inserted for the purpose of removing high-frequency noise components. - In general, noise generated from amplifiers inside imaging equipment such as television cameras exists almost uniformly from high frequency components to low frequency components, so by removing this high frequency component with the low-pass filter 13, random noise In addition to reducing components, this also prevents aliasing noise from occurring during sampling.

Next, the control unit 22 outputs an image memory selection signal,
One of the two image memories I5 is selected, and digital density data for one screen of the vertically polarized image is stored in the image memory 15.

When the capture of one screen worth of digital density data of a vertically polarized image into the image memory 15 is completed, the control unit 22 outputs a timer start signal k, and the sampling timer 23 is set with a time-up time of several tens of milliseconds to several seconds. Start. Then, the sampling timer 23 times up after a certain period of time has elapsed, and outputs a time-up signal l to the control section 22.

After receiving the time-up signal E, the control unit 22 outputs the polarization angle control signal g again, rotates the linear polarizer 12 to change its polarization plane from the vertical polarization position to the horizontal polarization position, and further synchronizes with this. , the image capture signal m is sent to the A/D converter 14
Output to.

When the linear polarizer 12 is set to the horizontal polarization position, the television camera 11 outputs a video signal of a horizontally polarized image as shown in FIG. The signal is sent to converter 14. And A
The /D converter 14 samples the video signal of this horizontally polarized image and converts it into multi-gradation digital density data a.
Send to image memory 15°16.

Next, the control unit 22 outputs an image memory selection signal C to select the image memory 16, and stores one screen worth of digital density data of the horizontal polarization image in the image memory 16.

When the digital density data for one screen of the vertically polarized image and the horizontally polarized image has been captured in the above manner, the digital density data stored in the image memory 15.16 is subjected to logarithmic calculation by the logarithm calculator 17.18. Thereafter, it is sent to the difference calculator 19 via data buses d and e.

The difference calculator 19 calculates the difference for each corresponding pixel of the vertically polarized image and the horizontally polarized image sent from the logarithm calculators 17 and 18, and outputs the logarithmic difference calculation value f to the memory 2.
Output to 0 and store. In this way, the digital density data of the two images are once logarithmically converted by the logarithm calculators 17 and 18, and then the difference calculation is performed by the difference calculator 19.
This means that the calculation process is equivalent to division, that is, the same calculation as calculating the density ratio for each corresponding pixel of the vertically polarized image and the horizontally polarized image.

When the logarithmic difference calculation is completed for the IN plane of the vertically polarized image and the horizontally polarized image, the difference calculator 19 outputs a calculation end signal to the microprocessor 21.

When the microprocessor 21 receives the calculation end signal, it reads the logarithmic difference calculation data from the output memory 20 via the data bus i, and executes the following road surface condition determination process based on the logarithmic difference calculation value. . When this road surface condition determination process is completed, the microprocessor 21 outputs a process end signal j to the control unit 22,
The state of the control unit 22 is returned to the initial state, and the above-described processes are repeated again.

FIG. 10 is a flowchart of the road surface condition determination processing performed by the microprocessor 21 described above.

When the microprocessor 21 receives the computation end signal from the difference calculator 19, it specifies the detection area of the road surface in which the road surface condition determination process is to be performed (step [1]), and selects from the output memory 20 information that exists within the specified area. The logarithmic difference calculation value for each pixel is read out, and these values are added (step [2]).

As mentioned above, when the road surface is dry (Fig. 6 (a)
)(b)) There is no significant difference in the density value between the vertically polarized image and the horizontally polarized image, so the step [
2] is a small value.

On the other hand, when the road surface is wet due to rain, etc. or frozen and moist (Fig. 7(a)(b)'), there is a large difference in the density value between the vertically polarized image and the horizontally polarized image. This occurs, and the added value in step [2] becomes a large value.

The magnitude of the above added value is determined using a predetermined threshold in step [3], and if it is larger than the set threshold, it is determined that the road surface is in a wet state.
4]), and when it is smaller than the threshold value, it is determined that the road surface is in a dry state (step [5]).

As described above, the dry state and wet state of the road surface can be stably detected based on changes in the density data of the vertically polarized light image and the horizontally polarized light image.

Although the presence of moisture on the road surface is the same between a slightly damp road surface and a state where puddles form, there is a big difference in the reflection level between the two, and it is simply a matter of the light intensity of total reflected light. Although it is difficult to accurately determine the road surface condition by simply comparing the levels, it is possible to know the relative behavior of each polarization component by taking the ratio of the vertical polarization image and the horizontal polarization image as in the above example. This makes it possible to uniquely determine the road surface condition.

Furthermore, in the above embodiment, the relative ratio of the difference between the vertically polarized image and the horizontally polarized image is determined by capturing the vertically polarized image and the horizontally polarized image at a short time interval of several tens of milliseconds to several seconds. It is not affected by changes in brightness and can stably capture data.

In addition, although the above-described embodiment shows an example in which a video signal consisting of an analog signal is converted into a digital signal and each processing is performed digitally, similar processing can also be performed analogously. In this case, for example, the video signals of the horizontally polarized image and the vertically polarized image output by the television camera 11 are respectively recorded in an analog signal format, and then the difference between the two signals is determined by reproducing them in synchronization. may be integrated by an integrating circuit or the like, and the magnitude of the integrated value may be determined by a threshold value.Furthermore, in order to designate a road surface condition determination area, the video signal may be gated in synchronization with the designated area.

〔Effect of the invention〕

As is clear from the above description, when using the road surface condition detection device of the present invention, reflected light from the road surface at an angle of about 53° is utilized, and a vertically polarized image and a horizontally polarized image are extracted from the reflected light. The density information is obtained and the road surface condition is determined based on the change in density information in each image, which eliminates the need for a dedicated target and specific irradiation light source for pattern recognition as in conventional devices. This has the advantage that the device can be constructed in a more compact manner, and its installation, maintenance, and inspection operations are also extremely simple.

Furthermore, in the road surface condition detection device of the present invention, 53°
Since reflected light in the vicinity can be used as detection light regardless of whether it is natural light or illumination light, reflected light in the vicinity of 53° emitted from the entire surface of the road surface to be detected can be used as image information, making it possible to use conventional equipment as image information. This eliminates the need to determine the condition of the entire road surface based on spot-like partial reflected light information from a target placed on a part of the road surface, making it possible to accurately determine the dry or wet condition of the road surface based on the area. It has this excellent effect.

[Brief explanation of the drawing]

Fig. 1 is an illustration of the principle of the present invention, Fig. 2 is an illustration of horizontal polarization and vertical polarization, Fig. 3 is an illustration of refraction and reflection of light, Fig. 4 is a measurement diagram of water reflectance, and Fig. 5 Figure 6 shows an example of an image taken when the road surface is dry; Figure 7 shows an example of an image taken when the road surface is wet; and Figure 8 shows an example of the image taken when the road surface is wet. Figure 9 is a diagram showing an example of installing a television camera, Figure 10 is a flowchart of road surface condition determination processing, Figure 11 is a diagram showing a conventional example, and Figure 12 is a diagram showing a conventional example. It is an explanatory diagram of a detection principle. DESCRIPTION OF SYMBOLS 1... Road surface, 2... Road surface imaging means, 3... Polarization element, 4... Polarization angle control means, 5... Image storage means,
6... Road surface condition determination means, N... Road surface normal. (a) Vertical polarization plane image (b)
Horizontal polarization plane image taken when the road surface is dry Figure 6

Claims (1)

[Scope of Claims] Road surface imaging means disposed at an angle of approximately 53° with respect to the road surface normal; a polarizing element disposed in front of the road surface imaging means and capable of varying the plane of polarization in vertical and horizontal directions; polarization angle control means for variably controlling the polarization plane of the polarization element in vertical and horizontal directions; image storage means for storing at least two or more images output from the road surface imaging means with different polarization angles; A road surface condition detection device comprising a road surface condition determining means for determining whether a road surface is dry or wet based on changes in brightness and darkness between different images.