JP2707427B2 - Road area snow detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road area snow detecting apparatus for detecting snow on a road surface, for example, for displaying snow information on a road information display.

[0002]

2. Description of the Related Art Conventionally, as a method of detecting the state of a road surface, infrared light having a different wavelength is projected on the road surface, and a reflected light component reflected from the road surface is detected to detect a snowy state, a frozen state, and a dry state of the road surface. A method of determining the state has been used.

[0003]

As described above, the conventional method using infrared rays has a problem that the detection range is a spot-like narrow range and thus lacks generality.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to detect a snow-covered state and a dry or frozen state of a road surface accurately by detecting a wide area. A snow detection device is to be provided.

[0005]

SUMMARY OF THE INVENTION A road area snow detecting apparatus according to the present invention achieves the above-mentioned object. The apparatus includes an image pickup means for photographing a road surface, and a digital signal output from the image pickup means. , A Fourier transform unit for performing a Fourier transform on a digital signal recorded by the frame memory, and a memory for recording a power spectrum image in a frequency space obtained by the transform by the Fourier transform unit And a filter unit for extracting a power spectrum at a fundamental frequency in the power spectrum image, and when the value of the power spectrum extracted by the filter unit is larger than a set threshold, snowfall, and when the value is small, dry or dry. A determination unit that outputs a frozen state.

The determination unit may calculate the characteristics of the distribution of the frequency components in the power spectrum image from the variance, and determine the drying and freezing based on a magnitude comparison between the variance and a threshold.

[0007]

The road image data photographed by the image pickup means is converted into a digital signal by an analog-to-digital converter and recorded in a frame memory. The Fourier transform unit performs a Fourier transform on the luminance data recorded in the frame memory and outputs a power spectrum image.

[0008] The filter unit extracts a power spectrum component at a fundamental frequency from the power spectrum image output from the Fourier transform unit. When the value of the power spectrum output from the filter unit is larger than the set value, the determination unit determines that it is in the snowy state, and when it is smaller, it is in the dry or frozen state and outputs it.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is an operation flowchart of the embodiment. In FIG. 1, 1
Reference numeral 1 denotes a television camera for photographing a road surface; 12, an analog-to-digital converter (AD) for converting an image signal from the television camera into a digital signal; 13, a frame memory for recording an original image from the AD converter 12; Is a Fourier transform unit for Fourier transforming the image signal from the frame memory 13, 15 is a memory for recording a power spectrum image obtained by performing Fourier transform in the Fourier transform unit,
16 is a filter unit for extracting a power spectrum component at a fundamental frequency (center) from the power spectrum image, 17 is a determination unit for comparing the characteristic value extracted by the filter unit 16 with a preset threshold, 18 Is an output unit that outputs the determination result from the determination unit 17, 19 is an interface (I / O), and 20 is a processor (CPU) that performs the processing shown in the flowchart of FIG.

Next, the operation of the first embodiment will be described with reference to the operation flowchart of FIG.
An analog signal of a road surface image captured by the television camera 11 (FIG. 3 (A) is a dry road surface, (B) is a frozen road surface, and (C) is a snowy road surface) is converted by the AD converter 12 into a digital signal.
This digital signal is recorded in the frame memory 13.

In processing S2, the digital signal of the frame memory 13 is subjected to Fourier transform in the Fourier transform unit 14, and the digital signal of the Fourier transformed image is recorded in the memory 15. That is, FIG. 3 (A), (B), (C)
Are Fourier-transformed by the Fourier transform unit 14, power spectrum images in the frequency space shown in FIGS. 4A, 4B, and 4C are obtained.

That is, in the dry state shown in FIG. 3A, there are patterns such as pebbles contained in the asphalt on the road surface, and the image output by the Fourier transform is as shown in FIG. In the frozen state of FIG. 3B, pebbles and the like are hidden by ice, and the image output by Fourier transform is shown in FIG.
(B), and furthermore, it becomes white in the snow-covered state of FIG. 3 (C).
(C).

FIG. 5 shows the intensity of a power spectrum output by Fourier transform in a dry state (solid line), a frozen state (fine chain line) and a snow-covered state (large chain line). FIG. 6 is an enlarged view of a circle of FIG.
From this drawing, it shows a large value in the snow-covered state compared to the dry and frozen states.

In step S3, the power spectrum component at the fundamental frequency in the power spectrum image obtained by the Fourier transform by the Fourier transform unit 14 is filtered by the filter unit 1.
Extract at 6.

That is, the feature value is larger than the threshold value and
If it is determined to be ES (process S4), a signal indicating that it is in a snow-covered state (process S6) is output, and if it is determined to be NO, a signal indicating that it is in a frozen or dry state (process S7) is output.

Next, since the characteristic value of the dry road surface and the characteristic value of the frozen road surface are very close to the characteristic value of the snow-covered road surface, the two are discriminated using another method. Therefore, the discrimination between the drying and the frozen road surface can be performed by calculating the characteristics of the distribution of the frequency components in the power spectrum image from the variance σ ² or the standard deviation σ in the determination unit 17.

That is, in order to obtain the variance σ ² in the determination unit 17, from FIG.

(Equation 1) Is obtained by performing the following operation. Also, the variance σ ^2, which is a parameter for determining the variation, can be obtained as the standard deviation σ, which is the square root of the variance.

As described above, the characteristic value is obtained from the variance σ ² , the standard deviation σ, and the average of the distance from the fundamental frequency according to the equation (2). in so difference is large, setting the threshold appropriately dry the be reliably determined freezing, thus, after determining that drying and freezing for the the snow, and dried by a determination by the dispersion sigma ² freeze And the snow, freezing, and drying conditions can be accurately determined.

(Equation 2)

[0019]

As described above, according to the present invention, a power spectrum image is obtained by performing Fourier transform on luminance data obtained by photographing a road surface, and a power spectrum component at a fundamental frequency in the power spectrum image is extracted. Then, the power spectrum value is determined to be a snowy state, a dry state, and a frozen state depending on whether or not the value of the power spectrum is greater than a set value, so that the road surface state is accurately detected and output. This has the effect of, for example,

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a road surface freezing detection device of the present invention.

FIG. 2 is an operation flowchart of the embodiment.

FIG. 3 is a halftone image displayed on a display in a road surface state.

FIG. 4 is a halftone image in which a power spectrum obtained by Fourier transforming the above image is displayed on a display.

FIG. 5 is a diagram showing a power spectrum.

FIG. 6 is a partially enlarged view of the above.

FIG. 7 shows real space coordinates for calculating the average of the variance, the standard deviation, and the distance from the center of the fundamental frequency from the luminance data of the power spectrum image of FIG.

FIG. 8 is a diagram showing a variance value calculated from the luminance data of the power spectrum image of FIG. 4;

[Explanation of symbols]

 Reference Signs List 11 TV camera 12 Analog-to-digital converter (AD) 13 Frame memory 14 Fourier transform unit 16 Filter unit 17 Judgment unit 18 Output unit

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-77946 (JP, A) JP-A-57-77945 (JP, A) JP-A-59-126230 (JP, A)

Claims (2)

(57) [Claims] 1. An image pickup means for photographing a road surface, a frame memory for converting an image output from the image pickup means into a digital signal and recording the digital signal, and a Fourier transform unit for performing a Fourier transform on the digital signal recorded in the frame memory. A memory for recording a power spectrum image on a frequency space obtained by conversion by the Fourier transform unit, a filter unit for extracting a power spectrum at a fundamental frequency in the power spectrum image, and a filter extracted by the filter unit. A road area snow detection device comprising: a determination unit that outputs a snowfall when the value of the power spectrum is larger than a set threshold, and outputs a dry or frozen state when the value is small. 2. The method according to claim 1, wherein the determination unit calculates a characteristic of a distribution of the frequency component in the power spectrum image from a variance, and determines a dry state and a frozen state based on a magnitude comparison between the variance value and a threshold value. The road area snow detection device according to claim 1, wherein